Hello Group
Help!
I am advised by manufacturer (Danfoss) that I should use 1.00mm2 two
solid copper core cable to connect their remote sensor to a TP7000M
prog roomstat and that the cabling must not be in close proximity to
any mains cabling.
The original cabling (1mm T&E, earth not connected) ran very close to
mains cabling. This caused wildly fluctuating temperature sensing (as
much as 5 degrees C on consecutive readings,which seem to be taken by
the controller at one minute intervals)
I have now re-routed the cabling to be , for the most part, 8-12
inches from any mains cable. I have used the 1mm T&E again. The
situation is considerably improved but I am still getting fluctuating
readings albeit more in the +- 1 degree C range. If I run a shortish
(about 1 metre) length of cable to the sensor absolutely nowhere near
any mains cabling the temperature readings are totally steady.
Since a reading even 0.5 degree below 'actual' temperature results in
a call for heat which then operates the zone valve and fires the Oil
boiler, the next reading may be at a heat higher than target and shuts
down everything, I can be left with the boiler running in bursts of
1 minute. I would like to avoid this if possible.
Any ideas on any appropriate cable to use - perhaps screened in some
way - or would some form of twisted pair help in any way? Is there any
1mm2 two core twisted pair available?
I'd like to resolve this before replacing
floorboards/redecorating.......
Many thanks for any input
Ian
Please reply to group - email address is not monitored
Ian

On Dec 1, 5:06 pm, Ian wrote:

Any ideas on any appropriate cable to use - perhaps screened in some
way - or would some form of twisted pair help in any way? Is there any
1mm2 two core twisted pair available?

Screened twisted pair. Connect the screen to earth at one end only,
this is usually at the controller. There's usually only mA of current
involved with sensors, I don't know why 1 mm2 is needed.

In article ,
Ian wrote:
Any ideas on any appropriate cable to use - perhaps screened in some
way - or would some form of twisted pair help in any way? Is there any
1mm2 two core twisted pair available?

I'm not sure why they specify 1mm except that it's the smallest TW&E
available. I can't see the resistance being a factor.

The very best cable for interference pick up rejection is star quad mic
cable. Might be difficult to get cut lengths, though.

But do you know what the cable carries? If only low voltage DC, it might
be possible to reduce the AC pickup by other means.

--
*A cubicle is just a padded cell without a door.

Dave Plowman London SW
To e-mail, change noise into sound.

On 1 Dec 2006 09:30:43 -0800, Aidan wrote:

Screened twisted pair. Connect the screen to earth at one end only,
this is usually at the controller. There's usually only mA of current
involved with sensors, I don't know why 1 mm2 is needed.

Smallest cable that has mains rated insulation? I suspect that even the
"low voltage" side of the device is not fully isolated from the mains
thus any external cabling needs to be mains rated.

Donno if you can get mains rated screened twisted pair. Machine control
maybe?

--
Cheers
Dave. pam is missing e-mail

In an earlier contribution to this discussion,
Dave Liquorice wrote:

On 1 Dec 2006 09:30:43 -0800, Aidan wrote:

Screened twisted pair. Connect the screen to earth at one end only,
this is usually at the controller. There's usually only mA of current
involved with sensors, I don't know why 1 mm2 is needed.

Smallest cable that has mains rated insulation? I suspect that even
the "low voltage" side of the device is not fully isolated from the
mains thus any external cabling needs to be mains rated.

Donno if you can get mains rated screened twisted pair. Machine
control maybe?


ISTR that you can use telephone cable to connect the remote sensor on a
Honeywell CM67. Presumably the battery powered logic in this stat is
completely isolated from the mains side of the switching relay.
--
Cheers,
Roger
______
Email address maintained for newsgroup use only, and not regularly
monitored.. Messages sent to it may not be read for several weeks.
PLEASE REPLY TO NEWSGROUP!

Dave Liquorice wrote:

On 1 Dec 2006 09:30:43 -0800, Aidan wrote:


Screened twisted pair. Connect the screen to earth at one end only,
this is usually at the controller. There's usually only mA of current
involved with sensors, I don't know why 1 mm2 is needed.


Smallest cable that has mains rated insulation? I suspect that even the
"low voltage" side of the device is not fully isolated from the mains
thus any external cabling needs to be mains rated.

Donno if you can get mains rated screened twisted pair. Machine control
maybe?

Failing that, you can buy braided tubular sleaving (designed for
military and industrial screening applications). You could earth that at
one end and run the T&E down the middle of it.

See RS part number 244-5203 for an example (there are a range of sizes)

--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

On Fri, 01 Dec 2006 17:38:00 +0000 (GMT), "Dave Plowman (News)"
wrote:


I'm not sure why they specify 1mm except that it's the smallest TW&E
available. I can't see the resistance being a factor.

The very best cable for interference pick up rejection is star quad mic
cable. Might be difficult to get cut lengths, though.

But do you know what the cable carries? If only low voltage DC, it might
be possible to reduce the AC pickup by other means.

I do not know what it carries but it is not mains.
Their installation instructions are silent on the matter. The advice
to use 1mm2 solid core - with a maximum length of 50m - was in
response to my question of wildly fluctuating readings . I guess it is
resistance related matter rather than anything else. I am only looking
at a length of about 8m.

I am minded to try some of this stuff
http://cpc.farnell.com/jsp/endecaSea...p?SKU=CBBR6416
since its relatively cheap but would be interested if anyone sees any
problem in so doing.

As I am sure is obvious to you guys, my knowledge of control system
cabling and its inherent difficulties is non existent!

Many thanks to all the respondents so far
Please reply to group - email address is not monitored
Ian

On Sat, 02 Dec 2006 14:49:19 +0000, Ian wrote:

I am minded to try some of this stuff
http://cpc.farnell.com/jsp/endecaSea...p?SKU=CBBR6416
since its relatively cheap but would be interested if anyone sees any
problem in so doing.

Foil screens aren't the best but worth a try I guess. I'd also get onto
the makers direct and find out why they specify 1mm T&E in case it is
down to insulation requirements.

--
Cheers
Dave. pam is missing e-mail

On Sat, 02 Dec 2006 22:21:59 +0000 (GMT), "Dave Liquorice"
wrote:

On Sat, 02 Dec 2006 14:49:19 +0000, Ian wrote:

I am minded to try some of this stuff
http://cpc.farnell.com/jsp/endecaSea...p?SKU=CBBR6416
since its relatively cheap but would be interested if anyone sees any
problem in so doing.

Foil screens aren't the best but worth a try I guess. I'd also get onto
the makers direct and find out why they specify 1mm T&E in case it is
down to insulation requirements.

Thanks Dave,
I'd come to the conclusion to talk to Danfoss again myself last night
whilst turning down the target temperature again!
I am sure your average heating installer doesn't do anything different
to what has been done so far...but then I guess the average user won't
be too bothered either. I'm beginning to wish I'd stayed with the old
anthracite boiler. You knew you were going to be too hot/cold with
that.
Please reply to group - email address is not monitored
Ian

Ian wrote:
Hello Group
Help!
I am advised by manufacturer (Danfoss) that I should use 1.00mm2 two
solid copper core cable to connect their remote sensor to a TP7000M
prog roomstat and that the cabling must not be in close proximity to
any mains cabling.
The original cabling (1mm T&E, earth not connected) ran very close to
mains cabling. This caused wildly fluctuating temperature sensing (as
much as 5 degrees C on consecutive readings,which seem to be taken by
the controller at one minute intervals)
I have now re-routed the cabling to be , for the most part, 8-12
inches from any mains cable. I have used the 1mm T&E again. The
situation is considerably improved but I am still getting fluctuating
readings albeit more in the +- 1 degree C range. If I run a shortish
(about 1 metre) length of cable to the sensor absolutely nowhere near
any mains cabling the temperature readings are totally steady.
Since a reading even 0.5 degree below 'actual' temperature results in
a call for heat which then operates the zone valve and fires the Oil
boiler, the next reading may be at a heat higher than target and shuts
down everything, I can be left with the boiler running in bursts of
1 minute. I would like to avoid this if possible.
Any ideas on any appropriate cable to use - perhaps screened in some
way - or would some form of twisted pair help in any way? Is there any
1mm2 two core twisted pair available?
I'd like to resolve this before replacing
floorboards/redecorating.......
Many thanks for any input
Ian
Please reply to group - email address is not monitored
Ian

Just a thought Ian, turning the problem around, do you have any dimmer
switches or any other thyristor/triac controlled devices connected to
your mains?

Some of these devices, if inadequately decoupled for RF, can put very
sharp spikes onto the mains. These spikes, being radio frequency (RF),
can easily couple into nearby wiring either capacitively or inductively.

If the controller is high impedance and, in turn is poorly decoupled,
the spikes could upset things.

In the old days of dial-up telephone connections to the internet, I was
scratching my head as to why my connection was slow and unreliable on
early winter mornings. My wife never had problems. Then it dawned on
us:- I would invariably put the main light on via the dimmer, but my
wife would always put on a standard lamp or two. In the evenings there
was no problem because she always had her way - lighting wise! We
switched the dimmer off and my problems disappeared. I had run the
telephone cable too close to the mains wiring and it was coupling into
the modem and causing havoc.

Maybe a red herring but just an idea worth checking.

HTH

Steve.