I've just finally bitten the bullet and installed a Honeywell CM67
Programmable Room Stat in my hallway. I bought the version with Optimum
Start capability - which purports to decide for itself when to switch on the
heating in order to achieve the target temperature by the programmed start
time.

This seems to be working, but I'm curious to know what algorithm it uses in
order to decide when to turn on the heating. The literature doesn't make
this clear, so I wonder whether any of you actually know?

Several possibilities present themselves to me:
* it could assume a fixed (factory set) rate of rise of temperature, and
apply this to the current temperature in order to work out long long it will
take to get to the target temperature
* it could depend on one of the parameters - such as Proportional Band
Width - which can be set in the Installer Set-up Mode
* if it's *really* clever, it could calibrate itself by observing the actual
rate of temperature rise when the heating is on, and then apply this to its
future predictions

Does anyone out there know what it actually does?
--
Cheers,
Set Square
______
Please reply to newsgroup. Reply address is Black Hole!

On Sun, 8 Feb 2004 12:09:44 -0000, "Set Square"
wrote:

I've just finally bitten the bullet and installed a Honeywell CM67
Programmable Room Stat in my hallway. I bought the version with Optimum
Start capability - which purports to decide for itself when to switch on the
heating in order to achieve the target temperature by the programmed start
time.

This seems to be working, but I'm curious to know what algorithm it uses in
order to decide when to turn on the heating. The literature doesn't make
this clear, so I wonder whether any of you actually know?

Several possibilities present themselves to me:
* it could assume a fixed (factory set) rate of rise of temperature, and
apply this to the current temperature in order to work out long long it will
take to get to the target temperature
* it could depend on one of the parameters - such as Proportional Band
Width - which can be set in the Installer Set-up Mode
* if it's *really* clever, it could calibrate itself by observing the actual
rate of temperature rise when the heating is on, and then apply this to its
future predictions

Does anyone out there know what it actually does?



http://content.honeywell.com/uk/homes/files/pag113.pdf

http://tinyurl.com/2yc23


If you look at Adaptive Intelligent Recovery, it is basically doing
what you describe in your third point - i.e. if you turn that feature
on, the controller measures the rate of rise of temperature and uses
it to calculate the next heating period's start time also accounting
for the starting temperature. This is a relatively simple
controller, so it appears that it only does this session by session.
A really intelligent controller would store the temperature points by
time over more days because the rate of change of temperature is not
absolutely linear, although it is to a first approximation. Hence
the method used is a lot better than doing nothing at all.
All of that has to do with optimised starting.

The proportional band has to do with the behaviour of the controller
(it is a proportional plus integral controller)

Proportional control is that the heat contribution over a period of
time is adjusted to match the heat loss and maintain the temperature
accurately. There are controllers that will do this in a genuinely
analogue way by modulating the boiler output to match the requirement.

However, many boilers can only be controlled in an on/off fashion aand
indeed this is also true of most zone valves if you were using that as
a means of control. In order to control this type of device, the
controller does so by using time proportions. A simple example
might be that if you want 50% of the average output, the boiler is
turned on for 5 minutes and off for 5 minutes. For 80%, it would be
on for 8 and off for 2.

The CM67 does this but allows some additional settings.

- There is an cycle rate setting of 3,6,9,12 cycles per hour. If the
entity being controlled can react quickly without any disadvantages
(e.g. if you were controlling electric heating), then you could set 12
cycles per hour. At the other extreme, devices that show
inefficiency or might have other problems if cycled too frequently
would be run at three cycles per hour. In between you have typical
gas heating, which is run at 6 cycles/hour i.e. cycles last ten
minutes. So the behaviour would be as in my example above.
Note that the minimum on time is set to 1 minute, which in effect will
be 10%.


- Proportional bandwidth is the temperature range about the set point
where proportional control operates. Within this range, the
controller operates in this cycling mode. Below it, the output will
always be on and above it will always be off.

Adjustment for this will depend on the heating system and thermal
inertia of the house. Ideally what you want to have happen, is that
when starting from cold, if the current temperature is below the
proportional lower limit, then the optimisation should time operation
to fire the boiler at 100%. However, as the temperature rises into
the proportional band, the cycling control should begin to take
effect. If possible, you want to avoid the temperature overshooting
above the proportional band because a) you use more energy than needed
and b) the temperature may tend to oscillate for a long time before
settling. This is most likely to happen in well insulated properties
with oversized heating. It is really a trade off between achieving
the set point quickly and not overshooting.
On this controller, you can vary the proportional bandwidth to help
with that, in that it will enter cycling operation earlier on the rise
and begin backing off the average heat output of the system.

The proportional bandwidth may be taken into account in the optimised
start. That's not clear.

The best thing to do is to check the temperature rise behaviour by
recording temperature readings (say) every ten minutes during start up
for a few days. Plot a graph if you like.
You can then experiment with proportional bandwidth if needed.




..andy

To email, substitute .nospam with .gl

Set Square wrote on 08/02/2004 :-
This seems to be working, but I'm curious to know what algorithm it uses in
order to decide when to turn on the heating. The literature doesn't make
this clear, so I wonder whether any of you actually know?

20 years ago I designed one of these controllers and the next stage in
its development was to include the facility which you mention. The
whole idea was well ahead of the market at that time, so I was
struggling on new ground.

I got as far as working out a rough algorithm. It went something
like...

Starting with a basic programmed in setting, then incrementing or
decrementing preheat time value, based on whether it attained the
temperature before or after the set time. Which equates roughly with
your last suggested method.

It was all very experimental. There was a theory going around, that in
order to achieve this function, that an outside temperature sensor
would be needed to enable the calculation to be done satisfactorily. I
wonder if your unit includes an outdoor temperature sensor?

--
Regards,
Harry (M1BYT)...

Remove the 'NOSPAM' in my email address to reply.

Free Amateur Radio Courses:-
http://www.ukradioamateur.org

On Sun, 08 Feb 2004 13:26:54 GMT, Harry Bloomfield
wrote:

Set Square wrote on 08/02/2004 :-
This seems to be working, but I'm curious to know what algorithm it uses in
order to decide when to turn on the heating. The literature doesn't make
this clear, so I wonder whether any of you actually know?

20 years ago I designed one of these controllers and the next stage in
its development was to include the facility which you mention. The
whole idea was well ahead of the market at that time, so I was
struggling on new ground.

I got as far as working out a rough algorithm. It went something
like...

Starting with a basic programmed in setting, then incrementing or
decrementing preheat time value, based on whether it attained the
temperature before or after the set time. Which equates roughly with
your last suggested method.

It was all very experimental. There was a theory going around, that in
order to achieve this function, that an outside temperature sensor
would be needed to enable the calculation to be done satisfactorily. I
wonder if your unit includes an outdoor temperature sensor?

I've done some work on this as well. Working purely on an internal
reading and time, you can make a first approximation assumption that
heat loss and thermal inertia effects are linear with time. That is
roughly true and better than doing nothing. It becomes better if the
controller can gather data and average over several heating sessions.

The CM67 type of controller doesn't use outside temperature sensing
but some of the sophisticated boiler controllers have outside sensors.

On mine, there is an outside sensor which goes on a north facing wall
out of the sun and gives the boiler a temperature signal based on
resistance. There is an inside controller which senses temperature
and hooks up to the boiler with a pulse width modulated digital code,
in effect providing an analogue temperature value.

It is possible to set the proportional bandwidth and the relative
sensitivities to each of these terms, with data being accumulated over
several days. The boiler output is then linearly modulated from 3kW
to full power by controlling the fan speed (influences gas input rate)
and pump power level. The slope and end points of the boiler
temperature vs the environment temperatures can be varied as well.

The controller behaviour can be logged to a PC so I can look at the
temperatures and power levels over a period of time.

I've tried running with the outside sensing turned off and it does
make some difference, although principally when there are fast moving
changes in outside temperature.




..andy

To email, substitute .nospam with .gl

"Harry Bloomfield" wrote in message
. uk...
Set Square wrote on 08/02/2004 :-
This seems to be working, but I'm curious to know what algorithm it uses
in
order to decide when to turn on the heating. The literature doesn't make
this clear, so I wonder whether any of you actually know?

20 years ago I designed one of these controllers and the next stage in
its development was to include the facility which you mention. The
whole idea was well ahead of the market at that time, so I was
struggling on new ground.

Self adaptive optimum start, and optimum stop, controllers have been around
on the commercial field for over 20 years. Microprocessor based too.

I got as far as working out a rough algorithm. It went something
like...

Starting with a basic programmed in setting, then incrementing or
decrementing preheat time value, based on whether it attained the
temperature before or after the set time. Which equates roughly with
your last suggested method.

It was all very experimental. There was a theory going around, that in
order to achieve this function, that an outside temperature sensor
would be needed to enable the calculation to be done satisfactorily. I
wonder if your unit includes an outdoor temperature sensor?

It is far better with an outside temperature sensor, But using just one
inside temp sensor, a decent optimised start performance can be achieved.

The DCD controller has a number of user set time zones during the day. Each
one is optimised on and off (I believe). The CM67 is only optimised on, in
the morning period, so I believe. Subsequently the DCD controller saves a
lot on energy.

In an earlier contribution to this discussion,
Andy Hall wrote:



http://content.honeywell.com/uk/homes/files/pag113.pdf

http://tinyurl.com/2yc23


If you look at Adaptive Intelligent Recovery, it is basically doing
what you describe in your third point - i.e. if you turn that feature
on, the controller measures the rate of rise of temperature and uses
it to calculate the next heating period's start time also accounting
for the starting temperature. This is a relatively simple
controller, so it appears that it only does this session by session.
A really intelligent controller would store the temperature points by
time over more days because the rate of change of temperature is not
absolutely linear, although it is to a first approximation. Hence
the method used is a lot better than doing nothing at all.
All of that has to do with optimised starting.

The proportional band has to do with the behaviour of the controller
(it is a proportional plus integral controller)

Proportional control is that the heat contribution over a period of
time is adjusted to match the heat loss and maintain the temperature
accurately. There are controllers that will do this in a genuinely
analogue way by modulating the boiler output to match the requirement.

However, many boilers can only be controlled in an on/off fashion aand
indeed this is also true of most zone valves if you were using that as
a means of control. In order to control this type of device, the
controller does so by using time proportions. A simple example
might be that if you want 50% of the average output, the boiler is
turned on for 5 minutes and off for 5 minutes. For 80%, it would be
on for 8 and off for 2.

The CM67 does this but allows some additional settings.

- There is an cycle rate setting of 3,6,9,12 cycles per hour. If the
entity being controlled can react quickly without any disadvantages
(e.g. if you were controlling electric heating), then you could set 12
cycles per hour. At the other extreme, devices that show
inefficiency or might have other problems if cycled too frequently
would be run at three cycles per hour. In between you have typical
gas heating, which is run at 6 cycles/hour i.e. cycles last ten
minutes. So the behaviour would be as in my example above.
Note that the minimum on time is set to 1 minute, which in effect will
be 10%.


- Proportional bandwidth is the temperature range about the set point
where proportional control operates. Within this range, the
controller operates in this cycling mode. Below it, the output will
always be on and above it will always be off.

Adjustment for this will depend on the heating system and thermal
inertia of the house. Ideally what you want to have happen, is that
when starting from cold, if the current temperature is below the
proportional lower limit, then the optimisation should time operation
to fire the boiler at 100%. However, as the temperature rises into
the proportional band, the cycling control should begin to take
effect. If possible, you want to avoid the temperature overshooting
above the proportional band because a) you use more energy than needed
and b) the temperature may tend to oscillate for a long time before
settling. This is most likely to happen in well insulated properties
with oversized heating. It is really a trade off between achieving
the set point quickly and not overshooting.
On this controller, you can vary the proportional bandwidth to help
with that, in that it will enter cycling operation earlier on the rise
and begin backing off the average heat output of the system.

The proportional bandwidth may be taken into account in the optimised
start. That's not clear.

The best thing to do is to check the temperature rise behaviour by
recording temperature readings (say) every ten minutes during start up
for a few days. Plot a graph if you like.
You can then experiment with proportional bandwidth if needed.




.andy

To email, substitute .nospam with .gl


Many thanks for your very full asnwer, Andy - and for the links. My CM67 is
the hard-wired rather than RF model, and the leaflet which came with it is
slightly different. The "Adaptive Intelligent Recovery" section in the RF
model leaflet does say fairly explicitly that it uses the start-up
performance this time around to decide what to do next time. My leaflet is a
lot less explicit. Its equivalent paragraph is entitled "Optimisation
(Variable Start Time)" and says:
"The Programmable Thermostat will delay the start time to the last possible
moment, so that the desired temperature is reached by the start of the
program (sic) period. Simply set the times at which you would like to be
warm and the Programmable Thermostat will switch on when required up to a
maximum of 3 hours early."

I assume that the hard-wired version works in the same way as the RF version
in this respect, but it seems strange that they use different words to
describe it.

As you say, it appears that it bases its temperature rise rate value on what
happened at the most recent startup period - rather than averaging it over a
number of periods.

Thankyou for explaining cycles per hour too. Presumably with the default 10
minute cycle (6 per hour) once it has done its thing within the current
cycle, it won't turn the boiler on again until the start of the next 10
minute cycle even if the house has cooled rapidly in the meantime because
(say) some fool has opened all the doors and windows? Presumably also, the
minimum ON time only applies once it has decided to turn the boiler on. That
is, it never runs the boiler for less than a minute. However, it may - and
often does - decide not to run it at all within a particular cycle - e.g.
when the actual temp is way above the target temp, as in over-night
conditions.
--
Cheers,
Set Square
______
Please reply to newsgroup. Reply address is Black Hole!

In an earlier contribution to this discussion,
IMM wrote:


The CM67 is only
optimised on, in the morning period, so I believe.

This does not stack up with my experience! My CM67 is programmed to provide
a lunchtime boost of 21 degC from 12:30 to 13:30 having been set back to 18
degC for the morning period. The boiler usually fires up just before 12 in
order to achieve the target temperature by 12:30. If you monitor the target
temperature on the stat, it changes this from 18 to 21 at the point when it
decides to fire up, rather than at the programmed time.
--
Cheers,
Set Square
______
Please reply to newsgroup. Reply address is Black Hole!

On Sun, 8 Feb 2004 15:22:09 -0000, "Set Square"
wrote:




Many thanks for your very full asnwer, Andy - and for the links. My CM67 is
the hard-wired rather than RF model, and the leaflet which came with it is
slightly different.

I think that if you poke around on the sites a little, you will find
the CM61 or CM67. There are possibly a few differences in the RF
version to save battery power, but functionally from when I looked
them they are basically the same as the wired one.

The "Adaptive Intelligent Recovery" section in the RF
model leaflet does say fairly explicitly that it uses the start-up
performance this time around to decide what to do next time. My leaflet is a
lot less explicit. Its equivalent paragraph is entitled "Optimisation
(Variable Start Time)" and says:
"The Programmable Thermostat will delay the start time to the last possible
moment, so that the desired temperature is reached by the start of the
program (sic) period. Simply set the times at which you would like to be
warm and the Programmable Thermostat will switch on when required up to a
maximum of 3 hours early."


It is a bit vague isn't it. Probably written by a technical author
who didn't understand the product.

I assume that the hard-wired version works in the same way as the RF version
in this respect, but it seems strange that they use different words to
describe it.

As you say, it appears that it bases its temperature rise rate value on what
happened at the most recent startup period - rather than averaging it over a
number of periods.

Thankyou for explaining cycles per hour too. Presumably with the default 10
minute cycle (6 per hour) once it has done its thing within the current
cycle, it won't turn the boiler on again until the start of the next 10
minute cycle even if the house has cooled rapidly in the meantime because
(say) some fool has opened all the doors and windows?

That would be true unless the temperature has fallen so rapidly that
you reach the edge of the proportional band. At that point, the
controller will go to 100% on. Obviously this is another factor that
you could trade in deciding on the bandwidth setting. If the sudden
loss of heat situation happens a lot, then setting the bandwidth
narrower might be in order.


Presumably also, the
minimum ON time only applies once it has decided to turn the boiler on. That
is, it never runs the boiler for less than a minute.

If you set it to the 10 minute cycle, yes. Depending on the nature
of the house and system, setting a longer cycle might be worth doing -
e.g. if it's an older (say cast iron) boiler and not overpowered for
the house.

However, it may - and
often does - decide not to run it at all within a particular cycle - e.g.
when the actual temp is way above the target temp, as in over-night
conditions.

Correct. But that is where you have gone outside the proportional
band anyway. On the way down, as you come into the band, the boiler
would begin firing as soon as 10% heat or more is demanded.

Another factor that I should have mentioned is the boiler thermostat.
If the boiler is oversized or the heat is not being disposed of
quickly enough, that will come into play and have an impact on the
system. You would notice this if the boiler has a tendency to short
cycle without the controller in operation. Ideally, when starting
from cold, the boiler thermostat shouldn't come into play until you
are getting towards the set point if at all.




..andy

To email, substitute .nospam with .gl

"Set Square" wrote in message
...
In an earlier contribution to this discussion,
IMM wrote:


The CM67 is only
optimised on, in the morning period, so I believe.

This does not stack up with my experience! My CM67 is programmed to
provide
a lunchtime boost of 21 degC from 12:30 to 13:30 having been set back to
18
degC for the morning period. The boiler usually fires up just before 12 in
order to achieve the target temperature by 12:30. If you monitor the
target
temperature on the stat, it changes this from 18 to 21 at the point when
it
decides to fire up, rather than at the programmed time.


As some will remember, with the groups useful advice I fitted a CM67RF to
my existing system a few weeks back. It's transformed the level of control
and refinement compared to before (a TRV only system) but if like me you are
new to these types of stat it does take a bit of mind set change to get the
best out of programming the device e.g. one error I made was to set the
target temp time too early because I was thinking along the lines of giving
the house a chance to warm up before getting up. The CM67 started the system
up in the middle of the night. A bit of tweaking sorted that.out.

I've not changed the factory settings but like most tuning (bikes, cars, IT
systems etc.) I'm going along the path of changing one user setting at a
time and checking the results over the next or so. I may move on the factory
settings but I doubt it.

Jules

"JH" wrote in message
...

"Set Square" wrote in message
...
In an earlier contribution to this discussion,
IMM wrote:


The CM67 is only
optimised on, in the morning period, so I believe.

This does not stack up with my experience! My CM67 is programmed to
provide
a lunchtime boost of 21 degC from 12:30 to 13:30 having been set back to
18
degC for the morning period. The boiler usually fires up just before 12
in
order to achieve the target temperature by 12:30. If you monitor the
target
temperature on the stat, it changes this from 18 to 21 at the point when
it
decides to fire up, rather than at the programmed time.


As some will remember, with the groups useful advice I fitted a CM67RF to
my existing system a few weeks back. It's transformed the level of control
and refinement compared to before (a TRV only system) but if like me you
are
new to these types of stat it does take a bit of mind set change to get
the
best out of programming the device e.g. one error I made was to set the
target temp time too early because I was thinking along the lines of
giving
the house a chance to warm up before getting up. The CM67 started the
system
up in the middle of the night. A bit of tweaking sorted that.out.

I've not changed the factory settings but like most tuning (bikes, cars,
IT
systems etc.) I'm going along the path of changing one user setting at a
time and checking the results over the next or so. I may move on the
factory
settings but I doubt it.

Jules

And I fitted one just after Jules (after tapping you lot up for info). It
has totally transformed our house. It feels comfortable ALL the time now!

In an earlier contribution to this discussion,
Andy Hall wrote:

On Sun, 8 Feb 2004 15:22:09 -0000, "Set Square"
wrote:


Thankyou for explaining cycles per hour too. Presumably with the
default 10 minute cycle (6 per hour) once it has done its thing
within the current cycle, it won't turn the boiler on again until
the start of the next 10 minute cycle even if the house has cooled
rapidly in the meantime because (say) some fool has opened all the
doors and windows?

That would be true unless the temperature has fallen so rapidly that
you reach the edge of the proportional band. At that point, the
controller will go to 100% on. Obviously this is another factor that
you could trade in deciding on the bandwidth setting. If the sudden
loss of heat situation happens a lot, then setting the bandwidth
narrower might be in order.

Ah, now I understand the proportional band width a bit better - I had
previously assumed that it had something to do with the gain - but it is
actually the temperature band within which the controller exercises what
might be called "time division proportionality". Outside that band it is
either fully on or fully off (if I'm right). I presume that there isn't any
user control over the gain applied to either the proportional or integral
feedback? [I must admit that, having only worked in the past on analog
controllers for mechanical systems, I'm not too clear on how the principles
apply to something which has only an on/off output].



Presumably also, the
minimum ON time only applies once it has decided to turn the boiler
on. That is, it never runs the boiler for less than a minute.

If you set it to the 10 minute cycle, yes. Depending on the nature
of the house and system, setting a longer cycle might be worth doing -
e.g. if it's an older (say cast iron) boiler and not overpowered for
the house.

My house *is* well insulated, and the boiler is at least adequate. It is a
10-year-old Baxi Solo 70/4 PF - which *does* have a cast iron heat
exchanger, albeit of fairly low water holding capacity such that pump
over-run is required. Could you please explain in slightly more detail what
the likely effect would be of setting the cycles per hour to (say) 3 rather
than 6. Should I also increase the minimum ON time to more than one minute?
[For example, for oil boilers the leaflet says to set to 3 cycles/hr and 4
minutes min ON time].


Another factor that I should have mentioned is the boiler thermostat.
If the boiler is oversized or the heat is not being disposed of
quickly enough, that will come into play and have an impact on the
system. You would notice this if the boiler has a tendency to short
cycle without the controller in operation. Ideally, when starting
from cold, the boiler thermostat shouldn't come into play until you
are getting towards the set point if at all.


The boiler is on permanently when the system starts up from cold. When it
gets hot, but the room stat set point is not yet reached, the boiler *does*
cycle on its own stat - but I've always regarded this as normal. Do you
regard it as a problem?

One more point, while I think about it. One of the features on the CM67 is
something called "pump exercise" which purports to run the pump for 15
seconds each day. This is presumably to stop it seizing up if not used
during the summer. I can't quite figure out how this is supposed to work
since, on most systems the boiler and pump are either connected in parallel,
or the pump is controlled by the boiler to provide over-run. Either way, you
can't have the pump on without the boiler also being on - unless, I suppose,
you turn the boiler stat down to zero. Is this what you're supposed to do?
[This is of purely academic interest in my case because the boiler and pump
run all year for DHW anyway].

Thanks for sharing your expertise - it is very educational!
--
Cheers,
Set Square
______
Please reply to newsgroup. Reply address is Black Hole!

I've just installed a Honeywell CM67(RF) and I've been trying to figure out
how it is operating
so the information in this thread has been useful to me.
The boiler I have is a Vaillant Turbomax Plus.
Once the house is up to the set temperature everything is fine, but it does
seem to take a long
time to get there even in 'mild' weather, set to 19.5 Degrees C

The boiler has a temperature control on it - should I set this to max and
let the CM67 take over?

Does anyone know which has priority - the boiler's thermostat or the
external (CM67)

"Set Square" wrote in message
...
In an earlier contribution to this discussion,
Andy Hall wrote:

On Sun, 8 Feb 2004 15:22:09 -0000, "Set Square"
wrote:


Thankyou for explaining cycles per hour too. Presumably with the
default 10 minute cycle (6 per hour) once it has done its thing
within the current cycle, it won't turn the boiler on again until
the start of the next 10 minute cycle even if the house has cooled
rapidly in the meantime because (say) some fool has opened all the
doors and windows?

That would be true unless the temperature has fallen so rapidly that
you reach the edge of the proportional band. At that point, the
controller will go to 100% on. Obviously this is another factor that
you could trade in deciding on the bandwidth setting. If the sudden
loss of heat situation happens a lot, then setting the bandwidth
narrower might be in order.

Ah, now I understand the proportional band width a bit better - I had
previously assumed that it had something to do with the gain - but it is
actually the temperature band within which the controller exercises what
might be called "time division proportionality". Outside that band it is
either fully on or fully off (if I'm right). I presume that there isn't
any
user control over the gain applied to either the proportional or integral
feedback? [I must admit that, having only worked in the past on analog
controllers for mechanical systems, I'm not too clear on how the
principles
apply to something which has only an on/off output].



Presumably also, the
minimum ON time only applies once it has decided to turn the boiler
on. That is, it never runs the boiler for less than a minute.

If you set it to the 10 minute cycle, yes. Depending on the nature
of the house and system, setting a longer cycle might be worth doing -
e.g. if it's an older (say cast iron) boiler and not overpowered for
the house.

My house *is* well insulated, and the boiler is at least adequate. It is a
10-year-old Baxi Solo 70/4 PF - which *does* have a cast iron heat
exchanger, albeit of fairly low water holding capacity such that pump
over-run is required. Could you please explain in slightly more detail
what
the likely effect would be of setting the cycles per hour to (say) 3
rather
than 6. Should I also increase the minimum ON time to more than one
minute?
[For example, for oil boilers the leaflet says to set to 3 cycles/hr and 4
minutes min ON time].


Another factor that I should have mentioned is the boiler thermostat.
If the boiler is oversized or the heat is not being disposed of
quickly enough, that will come into play and have an impact on the
system. You would notice this if the boiler has a tendency to short
cycle without the controller in operation. Ideally, when starting
from cold, the boiler thermostat shouldn't come into play until you
are getting towards the set point if at all.


The boiler is on permanently when the system starts up from cold. When it
gets hot, but the room stat set point is not yet reached, the boiler
*does*
cycle on its own stat - but I've always regarded this as normal. Do you
regard it as a problem?

One more point, while I think about it. One of the features on the CM67 is
something called "pump exercise" which purports to run the pump for 15
seconds each day. This is presumably to stop it seizing up if not used
during the summer. I can't quite figure out how this is supposed to work
since, on most systems the boiler and pump are either connected in
parallel,
or the pump is controlled by the boiler to provide over-run. Either way,
you
can't have the pump on without the boiler also being on - unless, I
suppose,
you turn the boiler stat down to zero. Is this what you're supposed to do?
[This is of purely academic interest in my case because the boiler and
pump
run all year for DHW anyway].

Thanks for sharing your expertise - it is very educational!
--
Cheers,
Set Square
______
Please reply to newsgroup. Reply address is Black Hole!

On Sun, 8 Feb 2004 19:32:48 -0000, "Set Square"
wrote:

In an earlier contribution to this discussion,
Andy Hall wrote:

On Sun, 8 Feb 2004 15:22:09 -0000, "Set Square"
wrote:


Thankyou for explaining cycles per hour too. Presumably with the
default 10 minute cycle (6 per hour) once it has done its thing
within the current cycle, it won't turn the boiler on again until
the start of the next 10 minute cycle even if the house has cooled
rapidly in the meantime because (say) some fool has opened all the
doors and windows?

That would be true unless the temperature has fallen so rapidly that
you reach the edge of the proportional band. At that point, the
controller will go to 100% on. Obviously this is another factor that
you could trade in deciding on the bandwidth setting. If the sudden
loss of heat situation happens a lot, then setting the bandwidth
narrower might be in order.

Ah, now I understand the proportional band width a bit better - I had
previously assumed that it had something to do with the gain - but it is
actually the temperature band within which the controller exercises what
might be called "time division proportionality".

Bandwidth is a bad word to use but is the usual one. Normally it's
used in connection with radio and network engineering to mean
something completely different. The way you've described it for
this application is exactly right, though.

Outside that band it is
either fully on or fully off (if I'm right).

Yes. Also within the band, don't forget that there is the minimum
on-time which has an influence.


I presume that there isn't any
user control over the gain applied to either the proportional or integral
feedback?

Not directly. There will be several factors, including the house
behaviour which will affect behaviour.


[I must admit that, having only worked in the past on analog
controllers for mechanical systems, I'm not too clear on how the principles
apply to something which has only an on/off output].


If you want to think of it electronically, in the proportional range
it is roughly equivalent to a switch applying charge or discharging a
capacitor and being switched each way to set a fixed voltage. If you
were to take the voltage on the capacitor and filter it to remove the
short term variation, you will end up with more or less DC voltage
which increases and decreases according to required heat.

This is really all that is happening. The house has a much longer
time constant than the cycle rate of the controller and so there is a
smoothing effect.

The proportional switching is only there because most boilers don't
have an analogue input to control the power level.

This is a very common method of industrial temperature control where
the process and the heater have a long time constant.

To give you another example, I keep snakes in a large vivarium. The
particular species requires a relatively narrow temperature range and
high humidity. They also require a temperature gradient of a few
degrees along the length of the enclosure so that they can choose the
temperature that they would like.

For the heating, I have a special kind of ceramic heater surrounded
by a guard in the enclosure at one end, and a temperature sensor
(platinum resistance probe) in the centre. There is an industrial
temperature controller which drives the heater in proportional mode
through a solid state relay. The cycle time is ten seconds which is
fine for this arrangement.

The controller is really intended to acquire and maintain the setpoint
as quickly as possible and has autolearning modes to do this. Most of
the time, the temperature is held at 29.5 degrees. However, there is
a second control system for the humidity. This consists of a
humidity probe and controller for that, the output of which is used to
drive a pump. The pump delivers water from a reservoir to fine mist
sprayers in the enclosure, wetting the bark chips on the floor. The
humidity rises and the controller cuts off. Precise control is not
so critical so this controller is a simple on/off with a hysteresis of
5% of humidity.

However, one effect of the humidifier part running is to drop the
temperature. As the water evaporates, it requires its latent heat to
do so and there is a cooling effect. The thermal control adjusts and
brings the temperature back within a minute or so without
overshooting.

The snakes seem happy with the arrangement, which reminds me, I must
go and feed them.







Presumably also, the
minimum ON time only applies once it has decided to turn the boiler
on. That is, it never runs the boiler for less than a minute.

If you set it to the 10 minute cycle, yes. Depending on the nature
of the house and system, setting a longer cycle might be worth doing -
e.g. if it's an older (say cast iron) boiler and not overpowered for
the house.

My house *is* well insulated, and the boiler is at least adequate. It is a
10-year-old Baxi Solo 70/4 PF - which *does* have a cast iron heat
exchanger, albeit of fairly low water holding capacity such that pump
over-run is required. Could you please explain in slightly more detail what
the likely effect would be of setting the cycles per hour to (say) 3 rather
than 6. Should I also increase the minimum ON time to more than one minute?
[For example, for oil boilers the leaflet says to set to 3 cycles/hr and 4
minutes min ON time].


Another factor that I should have mentioned is the boiler thermostat.
If the boiler is oversized or the heat is not being disposed of
quickly enough, that will come into play and have an impact on the
system. You would notice this if the boiler has a tendency to short
cycle without the controller in operation. Ideally, when starting
from cold, the boiler thermostat shouldn't come into play until you
are getting towards the set point if at all.


The boiler is on permanently when the system starts up from cold. When it
gets hot, but the room stat set point is not yet reached, the boiler *does*
cycle on its own stat - but I've always regarded this as normal. Do you
regard it as a problem?

One more point, while I think about it. One of the features on the CM67 is
something called "pump exercise" which purports to run the pump for 15
seconds each day. This is presumably to stop it seizing up if not used
during the summer. I can't quite figure out how this is supposed to work
since, on most systems the boiler and pump are either connected in parallel,
or the pump is controlled by the boiler to provide over-run. Either way, you
can't have the pump on without the boiler also being on - unless, I suppose,
you turn the boiler stat down to zero. Is this what you're supposed to do?
[This is of purely academic interest in my case because the boiler and pump
run all year for DHW anyway].

Thanks for sharing your expertise - it is very educational!

..andy

To email, substitute .nospam with .gl

On Sun, 8 Feb 2004 20:36:51 -0000, "Frank McGuire"
wrote:

I've just installed a Honeywell CM67(RF) and I've been trying to figure out
how it is operating
so the information in this thread has been useful to me.
The boiler I have is a Vaillant Turbomax Plus.
Once the house is up to the set temperature everything is fine, but it does
seem to take a long
time to get there even in 'mild' weather, set to 19.5 Degrees C

The boiler has a temperature control on it - should I set this to max and
let the CM67 take over?

Yes you should. Keep an eye open for short cycling when the
controller is in the permanently on range. This would mean that you
are not getting heat away from the boiler fast enough, often because
pump setting is too low or radiators turned down too far.



Does anyone know which has priority - the boiler's thermostat or the
external (CM67)

The CM67 will give the boiler a demand for heat. The boiler will do
that until that goes away or the water temperature reaches the level
set by the boiler thermostat.

What you want to try to avoid is that the CM67 is creating a demand
for heat and the boiler is turning on and off on its own thermostat.
The system will still work, but you may get some inconsistent effects
with the controller depending on the heat actually required due to the
outside temperature. Ideally, you want if possible for the CM67 to
do the main control.



"Set Square" wrote in message
...
In an earlier contribution to this discussion,
Andy Hall wrote:

On Sun, 8 Feb 2004 15:22:09 -0000, "Set Square"
wrote:


Thankyou for explaining cycles per hour too. Presumably with the
default 10 minute cycle (6 per hour) once it has done its thing
within the current cycle, it won't turn the boiler on again until
the start of the next 10 minute cycle even if the house has cooled
rapidly in the meantime because (say) some fool has opened all the
doors and windows?

That would be true unless the temperature has fallen so rapidly that
you reach the edge of the proportional band. At that point, the
controller will go to 100% on. Obviously this is another factor that
you could trade in deciding on the bandwidth setting. If the sudden
loss of heat situation happens a lot, then setting the bandwidth
narrower might be in order.

Ah, now I understand the proportional band width a bit better - I had
previously assumed that it had something to do with the gain - but it is
actually the temperature band within which the controller exercises what
might be called "time division proportionality". Outside that band it is
either fully on or fully off (if I'm right). I presume that there isn't
any
user control over the gain applied to either the proportional or integral
feedback? [I must admit that, having only worked in the past on analog
controllers for mechanical systems, I'm not too clear on how the
principles
apply to something which has only an on/off output].



Presumably also, the
minimum ON time only applies once it has decided to turn the boiler
on. That is, it never runs the boiler for less than a minute.

If you set it to the 10 minute cycle, yes. Depending on the nature
of the house and system, setting a longer cycle might be worth doing -
e.g. if it's an older (say cast iron) boiler and not overpowered for
the house.

My house *is* well insulated, and the boiler is at least adequate. It is a
10-year-old Baxi Solo 70/4 PF - which *does* have a cast iron heat
exchanger, albeit of fairly low water holding capacity such that pump
over-run is required. Could you please explain in slightly more detail
what
the likely effect would be of setting the cycles per hour to (say) 3
rather
than 6. Should I also increase the minimum ON time to more than one
minute?
[For example, for oil boilers the leaflet says to set to 3 cycles/hr and 4
minutes min ON time].


Another factor that I should have mentioned is the boiler thermostat.
If the boiler is oversized or the heat is not being disposed of
quickly enough, that will come into play and have an impact on the
system. You would notice this if the boiler has a tendency to short
cycle without the controller in operation. Ideally, when starting
from cold, the boiler thermostat shouldn't come into play until you
are getting towards the set point if at all.


The boiler is on permanently when the system starts up from cold. When it
gets hot, but the room stat set point is not yet reached, the boiler
*does*
cycle on its own stat - but I've always regarded this as normal. Do you
regard it as a problem?

One more point, while I think about it. One of the features on the CM67 is
something called "pump exercise" which purports to run the pump for 15
seconds each day. This is presumably to stop it seizing up if not used
during the summer. I can't quite figure out how this is supposed to work
since, on most systems the boiler and pump are either connected in
parallel,
or the pump is controlled by the boiler to provide over-run. Either way,
you
can't have the pump on without the boiler also being on - unless, I
suppose,
you turn the boiler stat down to zero. Is this what you're supposed to do?
[This is of purely academic interest in my case because the boiler and
pump
run all year for DHW anyway].

Thanks for sharing your expertise - it is very educational!
--
Cheers,
Set Square
______
Please reply to newsgroup. Reply address is Black Hole!




..andy

To email, substitute .nospam with .gl

"Andy Hall" wrote in message
...

I keep snakes in a large vivarium.

My, oh my! It gets worse.

On Sun, 8 Feb 2004 21:31:17 -0000, "IMM" wrote:


"Andy Hall" wrote in message
.. .

I keep snakes in a large vivarium.

My, oh my! It gets worse.

Would you like to join them? I mentioned that they were due for
feeding. They are very affectionate and would be pleased to give
you a big hug.....


..andy

To email, substitute .nospam with .gl

"Mike Hibbert" wrote in message
...
As some will remember, with the groups useful advice I fitted a CM67RF to
my existing system a few weeks back. It's transformed the level of control
and refinement compared to before (a TRV only system) but if like me you
are
new to these types of stat it does take a bit of mind set change to get
the
best out of programming the device e.g. one error I made was to set the
target temp time too early because I was thinking along the lines of
giving
the house a chance to warm up before getting up. The CM67 started the
system
up in the middle of the night. A bit of tweaking sorted that.out.

I've not changed the factory settings but like most tuning (bikes, cars,
IT
systems etc.) I'm going along the path of changing one user setting at a
time and checking the results over the next or so. I may move on the
factory
settings but I doubt it.

Jules

And I fitted one just after Jules (after tapping you lot up for info). It
has totally transformed our house. It feels comfortable ALL the time now!

Are these things ever advertised? I only learnt about the existance of
programmer/thermostats where you can vary the temperature during the day from
earlier posts in this ng. I have always wanted such a device so when I learnt
that they existed I ordered one from plumbworld.

Installing and using the device has made me realise how slowly my house responds
to temperature changes. Maybe 1C /hour either up or down.

Michael Chare

"Andy Hall" wrote in message
...
On Sun, 8 Feb 2004 21:31:17 -0000, "IMM" wrote:


"Andy Hall" wrote in message
.. .

I keep snakes in a large vivarium.

My, oh my! It gets worse.

Would you like to join them? I mentioned that they were due for
feeding. They are very affectionate and would be pleased to give
you a big hug.....

What a weirdo!

"Andy Hall" wrote in message
news
On mine, there is an outside sensor which goes on a north facing wall
out of the sun and gives the boiler a temperature signal based on
resistance. There is an inside controller which senses temperature
and hooks up to the boiler with a pulse width modulated digital code,
in effect providing an analogue temperature value.

It is possible to set the proportional bandwidth and the relative
sensitivities to each of these terms, with data being accumulated over
several days. The boiler output is then linearly modulated from 3kW
to full power by controlling the fan speed (influences gas input rate)
and pump power level. The slope and end points of the boiler
temperature vs the environment temperatures can be varied as well.

The controller behaviour can be logged to a PC so I can look at the
temperatures and power levels over a period of time.

Is this a system sold with the boiler or something bought or developed
separately?

Just curious!


Michael Chare

On Sun, 8 Feb 2004 22:15:04 +0000 (UTC), "Michael Chare"
wrote:

"Andy Hall" wrote in message
news
On mine, there is an outside sensor which goes on a north facing wall
out of the sun and gives the boiler a temperature signal based on
resistance. There is an inside controller which senses temperature
and hooks up to the boiler with a pulse width modulated digital code,
in effect providing an analogue temperature value.

It is possible to set the proportional bandwidth and the relative
sensitivities to each of these terms, with data being accumulated over
several days. The boiler output is then linearly modulated from 3kW
to full power by controlling the fan speed (influences gas input rate)
and pump power level. The slope and end points of the boiler
temperature vs the environment temperatures can be varied as well.

The controller behaviour can be logged to a PC so I can look at the
temperatures and power levels over a period of time.

Is this a system sold with the boiler or something bought or developed
separately?



Integrated in as part of it.

http://www.man-heiztechnik.de/_html_...e/micromat.php


Just curious!


Michael Chare


..andy

To email, substitute .nospam with .gl

"Mike Hibbert" wrote in message
...
And I fitted one just after Jules (after tapping you lot up for info). It
has totally transformed our house. It feels comfortable ALL the time now!


Likewise. Plus work commitments means the house is empty for a few days
during the week ATM. Previously I'd frig around with the old timer to get
the house warm on my return but it didn't really do the job i.e. the air was
warm but the house still felt cold, much better now even without fine tuning
the programs or factory settings. I'll be interested to see in the gas bill
next time mind.

Thanks again to old CH hands in this group. Why on earth installers put the
Mickey Mouse stats or in my case none at all can only be put down to cost,
but for the sake of less than 90 quid it's false economy in my book.

Jules

"Andy Hall" wrote in message
...
On Sun, 8 Feb 2004 19:32:48 -0000, "Set Square"
wrote:

In an earlier contribution to this discussion,
Andy Hall wrote:

On Sun, 8 Feb 2004 15:22:09 -0000, "Set Square"
wrote:

Thankyou for explaining cycles per hour too. Presumably with the
default 10 minute cycle (6 per hour) once it has done its thing
within the current cycle, it won't turn the boiler on again until
the start of the next 10 minute cycle even if the house has cooled
rapidly in the meantime because (say) some fool has opened all the
doors and windows?

That would be true unless the temperature has fallen so rapidly that
you reach the edge of the proportional band. At that point, the
controller will go to 100% on. Obviously this is another factor that
you could trade in deciding on the bandwidth setting. If the sudden
loss of heat situation happens a lot, then setting the bandwidth
narrower might be in order.

Ah, now I understand the proportional band width a bit better - I had
previously assumed that it had something to do with the gain - but it is
actually the temperature band within which the controller exercises what
might be called "time division proportionality".

Proportional control has no time division. That would be PI control, which
the CM67 has. Most commercial controllers now tend to have PID control.

Full explanation.


PROPORTIONAL

Proportional control is a corrective action that is proportional to the
error. Remember that error is defined as the difference between the desired
value (setpoint) and the actual measured value (process variable).
Proportional control is referred to as either "gain" or "proportional band".
Proportional band is the percent of change in the controlled variable that
causes the controller output to move over 100% of its range. In other words,
a proportional band of 100% means that if the measured variable moves over
100% of its range, the controller output signal will move over 100% of its
range; or, if the measured variable moves 1% of its full range, then the
control output moves 1%. In general, as the proportional band percentage
gets smaller, the controller becomes more sensitive. It is possible to make
it so sensitive that a very small change in the process variable measurement
will result in very large controller output. For those who like to work in
gain instead of proportional band, the relationship between these terms is
simple: gain is the reciprocal of proportional band. If the proportional
band is 100%, then gain is 1/100%, or 1. If proportional band is 50%, then
gain is 1/50%, or 2.

A proportional-only controller cannot control most processes well because it
never reaches the desired setpoint. This offset, defined as the difference
between the desired setpoint and the actual process value that the
controller can achieve for the process, is due to the mathematical nature of
the proportional control mode. Because there is only one controller signal
output value associated with the particular process variable value the
controller is reading, the controller sticks to its rigid mathematical
association between input and output values. It cannot recognize that there
is a problem of not achieving the desired setpoint value with
proportional-only control. Increasing the controller gain will reduce, but
not eliminate, the offset, but too much gain will result in unstable control
that will oscillate endlessly above and below the desired setpoint.

INTEGRAL
Integral settings are defined in repeats per minute or minutes per repeat. A
setting of 10 repeats per minute will instruct the controller to repeat the
action 10 times each minute. In general, the more often the repeats, the
faster the offset will be eliminated. Integral control is a control mode
that acts only as long as an offset exists.


There are three basic modes of control:

1. Proportional - operates on off-set and never reaches setpoint
2. Integral - time.
4. Derivative - anticipation, measurting rate of change.

PID controllers, which incorporate all three, are generally better.
Certainly more flexible. In short, the PI of the CM67: proportional gets it
near the setpoint, but never reaches setpoint because it operates on
"offset". A proportional controler can sit there all day and not move and
the setpoint will not be reached. They need a prod. The Integral mode of
control operates on time and pulses the offset (the differnce bewteen the
setting the proportional mode has decided to stay on an the setpoint) up to
setpoint, giving high accuracy.

Be careful not to have the proportional band too tight as "hunting" will
occur, known is short cycling to you.

In a CM67, the control aspect that times the delayed start is separet from
the PI temperature control.

The time proportions of the CM67, are a crude way of keeping an on-off
boiler within the proportional band.

The CM67 can control an electric actuator. A better system would be a heat
bank, heated by a basic on-off control boiler (these are cheaper and have
simple more reliable basic controls. The CH flow and return pipes would
have a modulated 3-way valve, moved up and down by and electric actuator.
This can stop at any point in the travel. This way only PI control would be
used and guarantee much more accuracy of setpoint temperature control. As
many heat bank and thermal stores are recommended to be on 24/7, the boiler
can be controlled only by the heat bank and the CM67 moves the modulated
valve and switches on the pump when it calculates the start time.

Bandwidth is a bad word to use but is the usual one. Normally it's
used in connection with radio and network engineering to mean
something completely different.

It is not "bandwidth". It is "Proportional Band - width". The "width" is
the range of the band, e.g., 2C. That is the setpoint and 1C either side.

The way you've described it for
this application is exactly right, though.

Outside that band it is
either fully on or fully off (if I'm right).

Yes. Also within the band, don't forget that there is the minimum
on-time which has an influence.


I presume that there isn't any
user control over the gain applied to either the proportional or integral
feedback?

Not directly. There will be several factors, including the house
behaviour which will affect behaviour.


[I must admit that, having only worked in the past on analog
controllers for mechanical systems, I'm not too clear on how the
principles
apply to something which has only an on/off output].


If you want to think of it electronically, in the proportional range
it is roughly equivalent to a switch applying charge or discharging a
capacitor and being switched each way to set a fixed voltage. If you
were to take the voltage on the capacitor and filter it to remove the
short term variation, you will end up with more or less DC voltage
which increases and decreases according to required heat.

This is really all that is happening. The house has a much longer
time constant than the cycle rate of the controller and so there is a
smoothing effect.

The proportional switching is only there because most boilers don't
have an analogue input to control the power level.

This is a very common method of industrial temperature control where
the process and the heater have a long time constant.

snip crap about snakes, which should all be banned

"JH" wrote in message
...

"Mike Hibbert" wrote in message
...

And I fitted one just after Jules (after tapping you lot up for info).
It
has totally transformed our house. It feels comfortable ALL the time
now!

Likewise. Plus work commitments means the house is empty for a few days
during the week ATM. Previously I'd frig around with the old timer to get
the house warm on my return but it didn't really do the job i.e. the air
was
warm but the house still felt cold, much better now even without fine
tuning
the programs or factory settings. I'll be interested to see in the gas
bill
next time mind.

Thanks again to old CH hands in this group. Why on earth installers put
the
Mickey Mouse stats or in my case none at all can only be put down to cost,

And ignorance. Most installers know sweet nothing of control.

but for the sake of less than 90 quid it's false economy in my book.

On Sun, 8 Feb 2004 23:37:40 -0000, "IMM" wrote:


snip cut and pasted explanation

There are three basic modes of control:

1. Proportional - operates on off-set and never reaches setpoint
2. Integral - time.
4. Derivative - anticipation, measurting rate of change.

PID controllers, which incorporate all three, are generally better.
Certainly more flexible. In short, the PI of the CM67: proportional gets it
near the setpoint, but never reaches setpoint because it operates on
"offset". A proportional controler can sit there all day and not move and
the setpoint will not be reached. They need a prod. The Integral mode of
control operates on time and pulses the offset (the differnce bewteen the
setting the proportional mode has decided to stay on an the setpoint) up to
setpoint, giving high accuracy.

Be careful not to have the proportional band too tight as "hunting" will
occur, known is short cycling to you.

Hunting is hunting. It is not short cycling but movement around the
set point.


In a CM67, the control aspect that times the delayed start is separet from
the PI temperature control.

They could conceivably be related. the manufacturer doesn't say.


The time proportions of the CM67, are a crude way of keeping an on-off
boiler within the proportional band.

That was already covered.

The CM67 can control an electric actuator. A better system would be a heat
bank, heated by a basic on-off control boiler (these are cheaper and have
simple more reliable basic controls. The CH flow and return pipes would
have a modulated 3-way valve, moved up and down by and electric actuator.
This can stop at any point in the travel. This way only PI control would be
used and guarantee much more accuracy of setpoint temperature control. As
many heat bank and thermal stores are recommended to be on 24/7, the boiler
can be controlled only by the heat bank and the CM67 moves the modulated
valve and switches on the pump when it calculates the start time.

I think you are confusing the issue. From the control mathematics
perspective this is PI control exactly the same. All that this
achieves, although it will work is perhaps finer grain control of heat
delivery from the heatbank to the radiators. Of itself, the heatbank
is a red herring in this if the boiler is not part of the main control
loop.

I would also be surprised if a valve for this application would be
modulated with a ten minute or even 5 minute cycle time. but rather
that it would have some form of electronic control requiring a much
shorter cycle time -seconds or even sub second.
Can you suggest a make and model that would have the characteristics
to work with a controller like the CM6x which has a much longer time?



Bandwidth is a bad word to use but is the usual one. Normally it's
used in connection with radio and network engineering to mean
something completely different.

It is not "bandwidth". It is "Proportional Band - width". The "width" is
the range of the band, e.g., 2C. That is the setpoint and 1C either side.

Obviously, and that is explained in the data sheets. However it is
often written as a single word in controller data sheets.



snip crap about snakes, which should all be banned

Well.... they were around before you and will probably be afterwards.

This is a real life application using an industrial type of PID
controller and served as a reasonable explanation of some of the
principles.

I felt that it was a better illustration than simply cutting and
pasting material from a web site


..andy

To email, substitute .nospam with .gl

"Andy Hall" wrote in message
news
On Sun, 8 Feb 2004 23:37:40 -0000, "IMM" wrote:


snip cut and pasted explanation

There are three basic modes of control:

1. Proportional - operates on off-set and never reaches setpoint
2. Integral - time.
4. Derivative - anticipation, measurting rate of change.

PID controllers, which incorporate all three, are generally better.
Certainly more flexible. In short, the PI of the CM67: proportional gets
it
near the setpoint, but never reaches setpoint because it operates on
"offset". A proportional controler can sit there all day and not move
and
the setpoint will not be reached. They need a prod. The Integral mode
of
control operates on time and pulses the offset (the differnce bewteen the
setting the proportional mode has decided to stay on an the setpoint) up
to
setpoint, giving high accuracy.

Be careful not to have the proportional band too tight as "hunting" will
occur, known is short cycling to you.

Hunting is hunting. It is not short cycling but movement around the
set point.

It is a form of short cycling an easier for others to understand.

In a CM67, the control aspect that times the delayed start is separet
from
the PI temperature control.

They could conceivably be related. the manufacturer doesn't say.

Controlwise they have to be eparte. The user doesn't know this nor care.

The time proportions of the CM67, are a crude way of keeping an on-off
boiler within the proportional band.

That was already covered.

The CM67 can control an electric actuator. A better system would be a
heat
bank, heated by a basic on-off control boiler (these are cheaper and have
simple more reliable basic controls. The CH flow and return pipes would
have a modulated 3-way valve, moved up and down by and electric actuator.
This can stop at any point in the travel. This way only PI control would
be
used and guarantee much more accuracy of setpoint temperature control.
As
many heat bank and thermal stores are recommended to be on 24/7, the
boiler
can be controlled only by the heat bank and the CM67 moves the modulated
valve and switches on the pump when it calculates the start time.

I think you are confusing the issue.

Not at all.

From the control mathematics
perspective this is PI control exactly the same. All that this
achieves, although it will work is perhaps finer grain control of heat
delivery from the heatbank to the radiators. Of itself, the heatbank
is a red herring in this if the boiler is not part of the main control
loop.

Not so. The heat bank can sit there 24/7 keeping itself to its own setpoint
providing a nice constant heat source. Just a store of heat. The CM67 will
then just switch on the CH pump and modulate the CH actuator. Modulating a
3-way valve gives far more precise temperature control than switching in and
out a boiler.

Another way is that the thermal store can be switched on also by another
CM67. The desired time must be earlier than the time of the heating. This
is if you can replace the room temperature sensor with a water strap-on
cylinder sensor of course.

I would also be surprised if a valve for this application would be
modulated with a ten minute or even 5 minute cycle time. but rather
that it would have some form of electronic control requiring a much
shorter cycle time -seconds or even sub second.

All those cycle times in minutes would be redundant, as only PI control on
an actuator is required.

Can you suggest a make and model that would have the characteristics
to work with a controller like the CM6x which has a much longer time?

Bandwidth is a bad word to use but is the usual one. Normally it's
used in connection with radio and network engineering to mean
something completely different.

It is not "bandwidth". It is "Proportional Band - width". The "width"
is
the range of the band, e.g., 2C. That is the setpoint and 1C either
side.

Obviously, and that is explained in the data sheets. However it is
often written as a single word in controller data sheets.

snip crap about snakes, which should all be banned

Well.... they were around before you and will probably be afterwards.

Don't care They should not be allowed in the country. If a couple of those
get out and breed in the wild.

"Set Square" wrote in message
...
I've just finally bitten the bullet and installed a Honeywell CM67
Programmable Room Stat

Does anyone have any views on the relative merits of the Honeywell and ACL
Drayton programmable stats? Much of a muchness?

In article , Jh
wrote:
Thanks again to old CH hands in this group. Why on earth
installers put the Mickey Mouse stats or in my case none at all
can only be put down to cost, but for the sake of less than 90
quid it's false economy in my book.

Because people understand basic thermostats. I think the CM67 is a
brilliant piece of work (especially being able to use the party
button to kill the heating for a few hours if you go out) but you
need to understand the concept of time/temperature variations
rather than on/off and then how to override it when required.

It's not difficult but I put one in at my mum's place and she
really does not like. With a £10 stat when the rads went cold she
could just turn it up a bit more g. Expensive controls that
people cannot/will not master are a waste of money.

--
Tony Bryer SDA UK 'Software to build on' http://www.sda.co.uk
Free SEDBUK boiler database browser
http://www.sda.co.uk/qsedbuk.htm

"Kamel Norman" wrote in message
.com...
**** off, Harry, you useless goat penis.

Sore losers

--

Inside information? Never

Try Aunt Bessies foods, mmmmmmmmmmmmmmmm, yummy

On Mon, 9 Feb 2004 01:24:06 -0000, "IMM" wrote:


"Andy Hall" wrote in message
news
On Sun, 8 Feb 2004 23:37:40 -0000, "IMM" wrote:


snip cut and pasted explanation

There are three basic modes of control:

1. Proportional - operates on off-set and never reaches setpoint
2. Integral - time.
4. Derivative - anticipation, measurting rate of change.

PID controllers, which incorporate all three, are generally better.
Certainly more flexible. In short, the PI of the CM67: proportional gets
it
near the setpoint, but never reaches setpoint because it operates on
"offset". A proportional controler can sit there all day and not move
and
the setpoint will not be reached. They need a prod. The Integral mode
of
control operates on time and pulses the offset (the differnce bewteen the
setting the proportional mode has decided to stay on an the setpoint) up
to
setpoint, giving high accuracy.

Be careful not to have the proportional band too tight as "hunting" will
occur, known is short cycling to you.

Hunting is hunting. It is not short cycling but movement around the
set point.

It is a form of short cycling an easier for others to understand.

It's a totally different mechanism


In a CM67, the control aspect that times the delayed start is separet
from
the PI temperature control.

They could conceivably be related. the manufacturer doesn't say.

Controlwise they have to be eparte. The user doesn't know this nor care.

Not true. The piece controlling the optimised start could make very
good use of knowledge of the characteristics of the PI part. Whether
it does or not is a matter for the manufacturer.


The time proportions of the CM67, are a crude way of keeping an on-off
boiler within the proportional band.

That was already covered.

The CM67 can control an electric actuator. A better system would be a
heat
bank, heated by a basic on-off control boiler (these are cheaper and have
simple more reliable basic controls. The CH flow and return pipes would
have a modulated 3-way valve, moved up and down by and electric actuator.
This can stop at any point in the travel. This way only PI control would
be
used and guarantee much more accuracy of setpoint temperature control.
As
many heat bank and thermal stores are recommended to be on 24/7, the
boiler
can be controlled only by the heat bank and the CM67 moves the modulated
valve and switches on the pump when it calculates the start time.

I think you are confusing the issue.

Not at all.

You are because the heatbank is only a source of heat if designed to
be oversized by a reasonable amount so that the boiler behaviour goes
out of the equation.




From the control mathematics
perspective this is PI control exactly the same. All that this
achieves, although it will work is perhaps finer grain control of heat
delivery from the heatbank to the radiators. Of itself, the heatbank
is a red herring in this if the boiler is not part of the main control
loop.

Not so. The heat bank can sit there 24/7 keeping itself to its own setpoint
providing a nice constant heat source. Just a store of heat.

Exactly, but that's all.

The CM67 will
then just switch on the CH pump and modulate the CH actuator. Modulating a
3-way valve gives far more precise temperature control than switching in and
out a boiler.

I don't disagree with that notion but can you suggest a make and model
that can be modulated in a precise "analogue" way (i.e. part opened)
by a CM67 type of controller with a long cycle time?

There are certainly valves that can be modulated with a DC voltage (I
have some) and I could imagine pulse width modulated using a much
shorter cycle time - e.g. in the way that model control servos work.

If you can't suggest one that will work with the CM67 type of
controller, then the argument becomes a bit academic because either a
different type of controller is needed, which is not in the same price
bracket, or you would be talking about a standard motorised zone valve
and proportioned on/off control of it. That would be a bit better
than controlling a boiler on/off, although with a lightweight heat
exchange type, I don't think that the difference would be substantial.



Another way is that the thermal store can be switched on also by another
CM67. The desired time must be earlier than the time of the heating. This
is if you can replace the room temperature sensor with a water strap-on
cylinder sensor of course.

Yes of course, but this is adding extra complication. As you said, a
thermal store ought to be on 24/7 anyway.



I would also be surprised if a valve for this application would be
modulated with a ten minute or even 5 minute cycle time. but rather
that it would have some form of electronic control requiring a much
shorter cycle time -seconds or even sub second.

All those cycle times in minutes would be redundant, as only PI control on
an actuator is required.

The proportional pulse width output from the controller would be used,
but can you suggest a valve that will take this and use it to operate
the valve to arbitrary positions.





snip crap about snakes, which should all be banned

Well.... they were around before you and will probably be afterwards.

Don't care They should not be allowed in the country. If a couple of those
get out and breed in the wild.

Don't be silly. Clearly you know very little about herpetology.

First of all, the particular snakes in question (Brazilian Rainbow Boa
- Epichrates Cenchria Cenchria) range in the wild in the Brazilian
rainforest and their habitat is rapidly disappearing together with
their numbers in the wild. They do, however, breed and thrive
perfectly well in captivity, given the right conditions of temperature
and humidity (28 - 31 degrees and 70-80% humidity). In order for
them to breed, the conditions have to be right and there needs to be a
pattern of temperature drop and rise around the breeding time.
The UK climate simply won't create the conditions for them to breed in
the wild and they would be unlikely to live for very long in the wild
anyway. Considering the massive species loss in the rainforests,
anything that can be done to sustain them in captivity until their
natural habitat issues can be resolved is a positive step.


..andy

To email, substitute .nospam with .gl

The Lord alerted my mind to the presence of this EVIL article by Harry
Bloomfield, and I thusly replied:

Set Square wrote on 08/02/2004 :-
This seems to be working, but I'm curious to know what algorithm it
uses in order to decide when to turn on the heating. The literature
doesn't make this clear, so I wonder whether any of you actually know?

20 years ago I designed one of these controllers and the next stage in
its development was to include the facility which you mention. The
whole idea was well ahead of the market at that time, so I was
struggling on new ground.

I got as far as working out a rough algorithm. It went something
like...

You do like to sing your own praises, don't you?

--
The Reverend Parson Peter Parsnip
Smiting Sinful Usenet Users Since 1874

"A ******* shall not enter into the congregation of the Lord; even to his
tenth generation shall he not enter into the congregation of the Lord."
- Deuteronomy 23:2

"Andy Hall" wrote in message
...

snip cut and pasted explanation

There are three basic modes of control:

1. Proportional - operates on off-set and never reaches setpoint
2. Integral - time.
4. Derivative - anticipation, measurting rate of change.

PID controllers, which incorporate all three, are generally better.
Certainly more flexible. In short, the PI of the CM67: proportional
gets
it
near the setpoint, but never reaches setpoint because it operates on
"offset". A proportional controler can sit there all day and not move
and
the setpoint will not be reached. They need a prod. The Integral
mode
of
control operates on time and pulses the offset (the differnce bewteen
the
setting the proportional mode has decided to stay on an the setpoint)
up
to
setpoint, giving high accuracy.

Be careful not to have the proportional band too tight as "hunting"
will
occur, known is short cycling to you.

Hunting is hunting. It is not short cycling but movement around the
set point.

It is a form of short cycling an easier for others to understand.

It's a totally different mechanism

It constantly moves up and down in an on-off manner.

In a CM67, the control aspect that times the delayed start is separet
from
the PI temperature control.

They could conceivably be related. the manufacturer doesn't say.

Controlwise they have to be separte. The user doesn't know this nor
care.

Not true. The piece controlling the optimised start could make very
good use of knowledge of the characteristics of the PI part. Whether
it does or not is a matter for the manufacturer.

It could supply data to other control processes, but it is a separate
control process.

The time proportions of the CM67, are a crude way of keeping an on-off
boiler within the proportional band.

That was already covered.

The CM67 can control an electric actuator. A better system would be a
heat
bank, heated by a basic on-off control boiler (these are cheaper and
have
simple more reliable basic controls. The CH flow and return pipes
would
have a modulated 3-way valve, moved up and down by and electric
actuator.
This can stop at any point in the travel. This way only PI control
would
be
used and guarantee much more accuracy of setpoint temperature control.
As
many heat bank and thermal stores are recommended to be on 24/7, the
boiler
can be controlled only by the heat bank and the CM67 moves the
modulated
valve and switches on the pump when it calculates the start time.

I think you are confusing the issue.

Not at all.

You are because the heatbank is only a source
of heat if designed to be oversized by a reasonable
amount so that the boiler behaviour goes
out of the equation.

And, the modulating 3-way valve has finer accuracy to maintain a setpoint
temperature than switching on-off a boiler.

From the control mathematics
perspective this is PI control exactly the same. All that this
achieves, although it will work is perhaps finer grain control of heat
delivery from the heatbank to the radiators. Of itself, the heatbank
is a red herring in this if the boiler is not part of the main control
loop.

Not so. The heat bank can sit there 24/7 keeping itself to its own
setpoint
providing a nice constant heat source. Just a store of heat.

Exactly, but that's all.

See above.

The CM67 will
then just switch on the CH pump and modulate the CH actuator. Modulating
a
3-way valve gives far more precise temperature control than switching in
and
out a boiler.

I don't disagree with that notion
but can you suggest a make and model
that can be modulated in a precise "analogue"
way (i.e. part opened) by a CM67 type of
controller with a long cycle time?

The cycle times are not a part of the Integral aspect of the controller
AFAICS.

There are certainly valves that can be
modulated with a DC voltage (I
have some) and I could imagine pulse
width modulated using a much
shorter cycle time - e.g. in the way that
model control servos work.

There are 230v electric modulating valves available. Look in the CM67 pdf,
it has a diagram of one.

If you can't suggest one that will work with the CM67 type of
controller, then the argument becomes a bit academic because either a
different type of controller is needed, which is not in the same price
bracket, or you would be talking about a standard motorised zone valve
and proportioned on/off control of it. That would be a bit better
than controlling a boiler on/off, although with a lightweight heat
exchange type, I don't think that the difference would be substantial.

What I am on about is a "modulted" 3-port mixing valve, with an electric
actuator. I have a few here.

Another way is that the thermal store can be switched on also by another
CM67. The desired time must be earlier than the time of the heating.
This
is if you can replace the room temperature sensor with a water strap-on
cylinder sensor of course.

Yes of course, but this is adding extra complication. As you said, a
thermal store ought to be on 24/7 anyway.

It depends on how far you want to take it. A CM67 on a themal store will
learn how long it takes the boiler to heat it up, and bring it on at the
right time.

I would also be surprised if a valve for this application would be
modulated with a ten minute or even 5 minute cycle time. but rather
that it would have some form of electronic control requiring a much
shorter cycle time -seconds or even sub second.

All those cycle times in minutes would be redundant, as only PI control
on
an actuator is required.

The proportional pulse width output from the controller would be used,
but can you suggest a valve that will take this and use it to operate
the valve to arbitrary positions.

AFAIK, the cm67 when controlling the setpoint temperature, only applies PI
control modes. The cycle times appear to be an underlying control layer
which only allows the boiler and PI control on it at certain time periods.

snip crap about snakes, which should all be banned.
If Brazil is short of snakes then you should not be having one.

On Sun, 08 Feb 2004 13:26:54 GMT, Harry Bloomfield wrote:

Set Square wrote on 08/02/2004 :-
This seems to be working, but I'm curious to know what algorithm it uses in
order to decide when to turn on the heating. The literature doesn't make
this clear, so I wonder whether any of you actually know?

20 years ago I designed one of these controllers and the next stage in
its development was to include the facility which you mention.

Good, you must be nearly dead now then.

The
whole idea was well ahead of the market at that time, so I was
struggling on new ground.

Modesty, Harry.


I got as far as working out a rough algorithm. It went something
like...

Starting with a basic programmed in setting, then incrementing or
decrementing preheat time value, based on whether it attained the
temperature before or after the set time. Which equates roughly with
your last suggested method.

It was all very experimental. There was a theory going around, that in
order to achieve this function, that an outside temperature sensor
would be needed to enable the calculation to be done satisfactorily. I
wonder if your unit includes an outdoor temperature sensor?


Christ that was boring.

--
Phil Kyle - Usenet Legend.

http://philkyle2003.reachme.at/

"If Harry would just shut up half the
problems on this group would go away,
He brought the trolls here from
local.yorkshire in the first place!! " - wemfish

You are because the heatbank is only a source of heat if designed to
be oversized by a reasonable amount so that the boiler behaviour goes
out of the equation.


So what does a Suprima having a lockout wobbly have on all this then?...
--
Tony Sayer

On Mon, 9 Feb 2004 18:56:53 +0000, tony sayer
wrote:

You are because the heatbank is only a source of heat if designed to
be oversized by a reasonable amount so that the boiler behaviour goes
out of the equation.


So what does a Suprima having a lockout wobbly have on all this then?...


You'd need to ask Professor Stanley Unwin that question.

I'm pretty sure that he was IMM's english language teature.....








..andy

To email, substitute .nospam with .gl

In article , Andy Hall
writes
On Mon, 9 Feb 2004 18:56:53 +0000, tony sayer
wrote:

You are because the heatbank is only a source of heat if designed to
be oversized by a reasonable amount so that the boiler behaviour goes
out of the equation.


So what does a Suprima having a lockout wobbly have on all this then?...


You'd need to ask Professor Stanley Unwin that question.

I'm pretty sure that he was IMM's english language teature.....



Better get the glass out for the seance then, he threw off his mortal
coil a while ago.

Still, could you imagine the glass wizzing about with the
answer:-)).....
--
Tony Sayer

On Mon, 9 Feb 2004 20:02:48 +0000, tony sayer
wrote:

In article , Andy Hall
writes
On Mon, 9 Feb 2004 18:56:53 +0000, tony sayer
wrote:

You are because the heatbank is only a source of heat if designed to
be oversized by a reasonable amount so that the boiler behaviour goes
out of the equation.


So what does a Suprima having a lockout wobbly have on all this then?...


You'd need to ask Professor Stanley Unwin that question.

I'm pretty sure that he was IMM's english language teature.....



Better get the glass out for the seance then, he threw off his mortal
coil a while ago.

Still, could you imagine the glass wizzing about with the
answer:-)).....


Doesn't bear thinking about, does it?




..andy

To email, substitute .nospam with .gl

On Mon, 9 Feb 2004 16:59:17 -0000, "IMM" wrote:




Be careful not to have the proportional band too tight as "hunting"
will
occur, known is short cycling to you.

Hunting is hunting. It is not short cycling but movement around the
set point.

It is a form of short cycling an easier for others to understand.

It's a totally different mechanism

It constantly moves up and down in an on-off manner.

That's a good technical explanation....:-)



In a CM67, the control aspect that times the delayed start is separet
from
the PI temperature control.

They could conceivably be related. the manufacturer doesn't say.

Controlwise they have to be separte. The user doesn't know this nor
care.

Not true. The piece controlling the optimised start could make very
good use of knowledge of the characteristics of the PI part. Whether
it does or not is a matter for the manufacturer.

It could supply data to other control processes, but it is a separate
control process.

Of course.



The time proportions of the CM67, are a crude way of keeping an on-off
boiler within the proportional band.

That was already covered.

The CM67 can control an electric actuator. A better system would be a
heat
bank, heated by a basic on-off control boiler (these are cheaper and
have
simple more reliable basic controls. The CH flow and return pipes
would
have a modulated 3-way valve, moved up and down by and electric
actuator.
This can stop at any point in the travel. This way only PI control
would
be
used and guarantee much more accuracy of setpoint temperature control.
As
many heat bank and thermal stores are recommended to be on 24/7, the
boiler
can be controlled only by the heat bank and the CM67 moves the
modulated
valve and switches on the pump when it calculates the start time.

I think you are confusing the issue.

Not at all.

You are because the heatbank is only a source
of heat if designed to be oversized by a reasonable
amount so that the boiler behaviour goes
out of the equation.

And, the modulating 3-way valve has finer accuracy to maintain a setpoint
temperature than switching on-off a boiler.

Yes, except that I was referring to the heatbank.



From the control mathematics
perspective this is PI control exactly the same. All that this
achieves, although it will work is perhaps finer grain control of heat
delivery from the heatbank to the radiators. Of itself, the heatbank
is a red herring in this if the boiler is not part of the main control
loop.

Not so. The heat bank can sit there 24/7 keeping itself to its own
setpoint
providing a nice constant heat source. Just a store of heat.

Exactly, but that's all.

See above.

Glad to see that you clarified it.



The CM67 will
then just switch on the CH pump and modulate the CH actuator. Modulating
a
3-way valve gives far more precise temperature control than switching in
and
out a boiler.

I don't disagree with that notion
but can you suggest a make and model
that can be modulated in a precise "analogue"
way (i.e. part opened) by a CM67 type of
controller with a long cycle time?

The cycle times are not a part of the Integral aspect of the controller
AFAICS.

I am referring to the specific method of operating the control valve -
the signalling between the controller and the valve. The CM67
provides a pulse with a total width of anything from 5 to 20 minutes
depending on the what is configured on the setup. In order to
control the controlled device (boiler, motorised valve etc) it will be
on for between 1 minute and 100% of that time while operating in the
proportional band. On the fastest cycle time, that will equate to
a range between 60 and 300 seconds of on time per 300 second cycle.

What I have specifically asked you to provide is the make and model of
a valve which will operate in a modulated fashion given that type of
control signal.

Please reply to that specific point.

I would be surprised if such a thing exists. I know that there are
voltage controlled modulating valves ( I have some radiator valves
that can be controlled by 0-10v DC); and I could believe that there
are some that would modulate based on a pulse width with a much
shorter cycle time ( a second or less)




There are certainly valves that can be
modulated with a DC voltage (I
have some) and I could imagine pulse
width modulated using a much
shorter cycle time - e.g. in the way that
model control servos work.

There are 230v electric modulating valves available. Look in the CM67 pdf,
it has a diagram of one.

I just have. Presumably you are referring to the sheet I posted -
http://tinyurl.com/2yc23

It doesn't say anything about it being modulating.

There is a thermal actuator (diagram c) controlling a boiler. This
type of device is a thermally operated relay which controls the boiler
on and off, not modulating.

There is an electric actuator (diagram h) which is an electric
actuator. This is a motorised device to operate some kind of
mechanical entity such as a damper. It even shows the limit switches
which stop travel. This isn't a modulated device either.

Did you mean something different? Please provide the URL to the CM67
sheet that shows it if I have the wrong one.




If you can't suggest one that will work with the CM67 type of
controller, then the argument becomes a bit academic because either a
different type of controller is needed, which is not in the same price
bracket, or you would be talking about a standard motorised zone valve
and proportioned on/off control of it. That would be a bit better
than controlling a boiler on/off, although with a lightweight heat
exchange type, I don't think that the difference would be substantial.

What I am on about is a "modulted" 3-port mixing valve, with an electric
actuator. I have a few here.

I know. Please provide the make and model of them. I am simply
asking you to provide details of a *modulated* device which will work
with a CM67.




Another way is that the thermal store can be switched on also by another
CM67. The desired time must be earlier than the time of the heating.
This
is if you can replace the room temperature sensor with a water strap-on
cylinder sensor of course.

Yes of course, but this is adding extra complication. As you said, a
thermal store ought to be on 24/7 anyway.

It depends on how far you want to take it. A CM67 on a themal store will
learn how long it takes the boiler to heat it up, and bring it on at the
right time.

True.


I would also be surprised if a valve for this application would be
modulated with a ten minute or even 5 minute cycle time. but rather
that it would have some form of electronic control requiring a much
shorter cycle time -seconds or even sub second.

All those cycle times in minutes would be redundant, as only PI control
on
an actuator is required.

The proportional pulse width output from the controller would be used,
but can you suggest a valve that will take this and use it to operate
the valve to arbitrary positions.

AFAIK, the cm67 when controlling the setpoint temperature, only applies PI
control modes. The cycle times appear to be an underlying control layer
which only allows the boiler and PI control on it at certain time periods.

The cycle time is about choosing a control signal suitable for the
device being controlled e.g. boiler, zone valve, electric heater



snip crap about snakes, which should all be banned.
If Brazil is short of snakes then you should not be having one.

They didn't come from Brazil, they were captive bred in the UK.





..andy

To email, substitute .nospam with .gl

"Andy Hall" wrote in message
...
On Mon, 9 Feb 2004 16:59:17 -0000, "IMM" wrote:




Be careful not to have the proportional band too tight as "hunting"
will
occur, known is short cycling to you.

Hunting is hunting. It is not short cycling but movement around the
set point.

It is a form of short cycling an easier for others to understand.

It's a totally different mechanism

It constantly moves up and down in an on-off manner.

That's a good technical explanation....:-)

Good enough for you.

In a CM67, the control aspect that times the delayed start is
separet
from
the PI temperature control.

They could conceivably be related. the manufacturer doesn't say.

Controlwise they have to be separte. The user doesn't know this nor
care.

Not true. The piece controlling the optimised start could make very
good use of knowledge of the characteristics of the PI part. Whether
it does or not is a matter for the manufacturer.

It could supply data to other control processes, but it is a separate
control process.

Of course.

The time proportions of the CM67, are a crude way of keeping an
on-off
boiler within the proportional band.

That was already covered.

The CM67 can control an electric actuator. A better system would
be a
heat
bank, heated by a basic on-off control boiler (these are cheaper
and
have
simple more reliable basic controls. The CH flow and return pipes
would
have a modulated 3-way valve, moved up and down by and electric
actuator.
This can stop at any point in the travel. This way only PI control
would
be
used and guarantee much more accuracy of setpoint temperature
control.
As
many heat bank and thermal stores are recommended to be on 24/7,
the
boiler
can be controlled only by the heat bank and the CM67 moves the
modulated
valve and switches on the pump when it calculates the start time.

I think you are confusing the issue.

Not at all.

You are because the heatbank is only a source
of heat if designed to be oversized by a reasonable
amount so that the boiler behaviour goes
out of the equation.

And, the modulating 3-way valve has finer accuracy to maintain a setpoint
temperature than switching on-off a boiler.

Yes, except that I was referring to the heatbank.

The heat bank supplies the constant hot water for modulation purposes.

From the control mathematics
perspective this is PI control exactly the same. All that this
achieves, although it will work is perhaps finer grain control of
heat
delivery from the heatbank to the radiators. Of itself, the
heatbank
is a red herring in this if the boiler is not part of the main
control
loop.

Not so. The heat bank can sit there 24/7 keeping itself to its own
setpoint
providing a nice constant heat source. Just a store of heat.

Exactly, but that's all.

See above.

Glad to see that you clarified it.



The CM67 will
then just switch on the CH pump and modulate the CH actuator.
Modulating
a
3-way valve gives far more precise temperature control than switching
in
and
out a boiler.

I don't disagree with that notion
but can you suggest a make and model
that can be modulated in a precise "analogue"
way (i.e. part opened) by a CM67 type of
controller with a long cycle time?

The cycle times are not a part of the Integral aspect of the controller
AFAICS.

I am referring to the specific method of operating the control valve -
the signalling between the controller and the valve. The CM67
provides a pulse with a total width of anything from 5 to 20 minutes

A pulse? A signal going on and off continuously?

depending on the what is configured on the setup. In order to
control the controlled device (boiler, motorised valve etc) it will be
on for between 1 minute and 100% of that time while operating in the
proportional band. On the fastest cycle time, that will equate to
a range between 60 and 300 seconds of on time per 300 second cycle.

What I have specifically asked you to provide is the make and model of
a valve which will operate in a modulated fashion given that type of
control signal.

Please reply to that specific point.

The control signal is 230V.

I would be surprised if such a thing exists. I know that there are
voltage controlled modulating valves ( I have some radiator valves
that can be controlled by 0-10v DC); and I could believe that there
are some that would modulate based on a pulse width with a much
shorter cycle time ( a second or less)

There are certainly valves that can be
modulated with a DC voltage (I
have some) and I could imagine pulse
width modulated using a much
shorter cycle time - e.g. in the way that
model control servos work.

There are 230v electric modulating valves available. Look in the CM67
pdf,
it has a diagram of one.

I just have. Presumably you are referring to the sheet I posted -
http://tinyurl.com/2yc23

It doesn't say anything about it being modulating.

It does. A reversible motor. 230v on one terminal and it moves one way,
same the other way. Stop the singal and it stays where it is.

There is a thermal actuator (diagram c) controlling a boiler. This
type of device is a thermally operated relay which controls the boiler
on and off, not modulating.

There is an electric actuator (diagram h) which is an electric
actuator. This is a motorised device to operate some kind of
mechanical entity such as a damper. It even shows the limit switches
which stop travel. This isn't a modulated device either.

It appears to be.

Did you mean something different? Please provide the URL to the CM67
sheet that shows it if I have the wrong one.

If you can't suggest one that will work with the CM67 type of
controller, then the argument becomes a bit academic because either a
different type of controller is needed, which is not in the same price
bracket, or you would be talking about a standard motorised zone valve
and proportioned on/off control of it. That would be a bit better
than controlling a boiler on/off, although with a lightweight heat
exchange type, I don't think that the difference would be substantial.

What I am on about is a "modulted" 3-port mixing valve, with an electric
actuator. I have a few here.

I know. Please provide the make and model of them. I am simply
asking you to provide details of a *modulated* device which will work
with a CM67.

Any maker makes them. They are common.

Another way is that the thermal store can be switched on also by
another
CM67. The desired time must be earlier than the time of the heating.
This
is if you can replace the room temperature sensor with a water
strap-on
cylinder sensor of course.

Yes of course, but this is adding extra complication. As you said, a
thermal store ought to be on 24/7 anyway.

It depends on how far you want to take it. A CM67 on a themal store will
learn how long it takes the boiler to heat it up, and bring it on at the
right time.

True.

I would also be surprised if a valve for this application would be
modulated with a ten minute or even 5 minute cycle time. but rather
that it would have some form of electronic control requiring a much
shorter cycle time -seconds or even sub second.

All those cycle times in minutes would be redundant, as only PI
control
on
an actuator is required.

The proportional pulse width output from the controller would be used,
but can you suggest a valve that will take this and use it to operate
the valve to arbitrary positions.

AFAIK, the cm67 when controlling the setpoint temperature, only applies
PI
control modes. The cycle times appear to be an underlying control layer
which only allows the boiler and PI control on it at certain time
periods.

The cycle time is about choosing a control signal suitable for the
device being controlled e.g. boiler, zone valve, electric heater

AFAIK the CM67 can operate a 230v modulated valve. If that is not the case
(specs vague on this from wjat I have seen), then I think the Landis &
Staefa version can. If so, I would go for this controller not the CM67. I
tend to prefer Landis & Staefa controls anyhow. They are much more
reliable, better made, better user intefaces and generally cheaper too.

snip crap about snakes, which should all be banned.
If Brazil is short of snakes then you should not be having one.

They didn't come from Brazil, they were captive bred in the UK.

They should be sent back to the wild then.

"Andy Hall" wrote in message
...

You were on about individual radiator electronic control:

http://europe.hbc.honeywell.com/prod...cs/CMZONE.html

"IMM" wrote in message
...

AFAIK the CM67 can operate a 230v modulated valve. If that is not the
case
(specs vague on this from wjat I have seen), then I think the Landis &
Staefa version can. If so, I would go for this controller not the CM67.
I
tend to prefer Landis & Staefa controls anyhow. They are much more
reliable, better made, better user intefaces and generally cheaper too.

The Landis & Staefa RVP will give proportional control by driving a servo on
top of a mixing valve, measuring the flow, return, inside and outside
temperatures, deriving the setting from a pre learnt heating curve for your
house. Assuming your boiler already has a RVP the extra cost is about 200
quid for the valve and servo. With a rad based system I would recommend
fitting this type of control as the temperature swings are eliminated by
matching the heat input to the heat loss. But with UFH time constant you
would really gain much from these controls.