40 odd years ago, some big (really big) variable speed DC motors I
installed, came with a rather ridiculously precise spec., suggesting it
needed to run at some silly full speed figure like 548rpm +/- 1 RPM.
Checking with head office and the designer, they confirmed it had to be
exactly so.

All we had at the time were mechanical tachometers, not very precise
and no way to connect apart from to the side of a large coupling, so I
set about designing something digital and entirely electronic, using an
IR head. Work it did, very well and quite precise. It cost the company
around £30 for the parts for me to build it, in my spare time. That was
left with the company when I moved on.

A couple of weeks ago, working on the tractor mowers governor system,
that specified a tick over speed and a full engine speed. I had no
obvious way to measure its speed, so I began thinking shall I build, or
just see what is for sale ready to use. Laser, ready to use, with
guaranteed precision, in a nice protective carry case all for £7.03 and
delivery within one month - no contest ;o)

Yes, I could have measured the ignition pulse period on my 'scope, or
on my Marconi counter timer, but where is the fun in that when compared
to a new toy?

In message , Harry Bloomfield
writes
40 odd years ago, some big (really big) variable speed DC motors I
installed, came with a rather ridiculously precise spec., suggesting it
needed to run at some silly full speed figure like 548rpm +/- 1 RPM.
Checking with head office and the designer, they confirmed it had to be
exactly so.

All we had at the time were mechanical tachometers, not very precise
and no way to connect apart from to the side of a large coupling, so I
set about designing something digital and entirely electronic, using an
IR head. Work it did, very well and quite precise. It cost the company
around £30 for the parts for me to build it, in my spare time. That was
left with the company when I moved on.

A couple of weeks ago, working on the tractor mowers governor system,
that specified a tick over speed and a full engine speed. I had no
obvious way to measure its speed, so I began thinking shall I build, or
just see what is for sale ready to use. Laser, ready to use, with
guaranteed precision, in a nice protective carry case all for £7.03 and
delivery within one month - no contest ;o)

Yes, I could have measured the ignition pulse period on my 'scope, or
on my Marconi counter timer, but where is the fun in that when compared
to a new toy?

You have to wonder who determines these specifications..

As a sprog apprentice, I was sent out to an American air force
installation near London to supervise test runs on a DC motor generator
set.

The spec. called for the set to take over the load (comms of some sort)
within 10mS! of the mains supply failing.

Needless to say 10mS could not be achieved. Simple reactance
calculations of the motor field winding would have shown this.

The cure was a thumping great flywheel.....
--
Tim Lamb

In article ,
Tim Lamb wrote:
In message , Harry Bloomfield
writes
40 odd years ago, some big (really big) variable speed DC motors I
installed, came with a rather ridiculously precise spec., suggesting it
needed to run at some silly full speed figure like 548rpm +/- 1 RPM.
Checking with head office and the designer, they confirmed it had to be
exactly so.

All we had at the time were mechanical tachometers, not very precise
and no way to connect apart from to the side of a large coupling, so I
set about designing something digital and entirely electronic, using an
IR head. Work it did, very well and quite precise. It cost the company
around £30 for the parts for me to build it, in my spare time. That was
left with the company when I moved on.

A couple of weeks ago, working on the tractor mowers governor system,
that specified a tick over speed and a full engine speed. I had no
obvious way to measure its speed, so I began thinking shall I build, or
just see what is for sale ready to use. Laser, ready to use, with
guaranteed precision, in a nice protective carry case all for £7.03 and
delivery within one month - no contest ;o)

Yes, I could have measured the ignition pulse period on my 'scope, or
on my Marconi counter timer, but where is the fun in that when compared
to a new toy?

You have to wonder who determines these specifications..

As a sprog apprentice, I was sent out to an American air force
installation near London to supervise test runs on a DC motor generator
set.

The spec. called for the set to take over the load (comms of some sort)
within 10mS! of the mains supply failing.

Needless to say 10mS could not be achieved. Simple reactance
calculations of the motor field winding would have shown this.

The cure was a thumping great flywheel.....

That's what was used in a telephone exchange I visited in the 1950s.

--
from KT24 in Surrey, England

charles presented the following explanation :
You have to wonder who determines these specifications..

As a sprog apprentice, I was sent out to an American air force
installation near London to supervise test runs on a DC motor generator
set.

The spec. called for the set to take over the load (comms of some sort)
within 10mS! of the mains supply failing.

Needless to say 10mS could not be achieved. Simple reactance
calculations of the motor field winding would have shown this.

The cure was a thumping great flywheel.....

That's what was used in a telephone exchange I visited in the 1950s.

This was three motors, driving three big pump sets, pumping from a
reservoir, all remotely monitored and controlled by telemetry from the
other side of a city.

I did a similar thing with a new fangled device called a hall effect sensor
and a magnet glued to the spindle grin.

Not very imaginative and in those days simple pulse counters were el
cheapo.
Brian

--
----- -
This newsgroup posting comes to you directly from...
The Sofa of Brian Gaff...

Blind user, so no pictures please!
"Harry Bloomfield" wrote in message
news
40 odd years ago, some big (really big) variable speed DC motors I
installed, came with a rather ridiculously precise spec., suggesting it
needed to run at some silly full speed figure like 548rpm +/- 1 RPM.
Checking with head office and the designer, they confirmed it had to be
exactly so.

All we had at the time were mechanical tachometers, not very precise and
no way to connect apart from to the side of a large coupling, so I set
about designing something digital and entirely electronic, using an IR
head. Work it did, very well and quite precise. It cost the company around
£30 for the parts for me to build it, in my spare time. That was left with
the company when I moved on.

A couple of weeks ago, working on the tractor mowers governor system, that
specified a tick over speed and a full engine speed. I had no obvious way
to measure its speed, so I began thinking shall I build, or just see what
is for sale ready to use. Laser, ready to use, with guaranteed precision,
in a nice protective carry case all for £7.03 and delivery within one
month - no contest ;o)

Yes, I could have measured the ignition pulse period on my 'scope, or on
my Marconi counter timer, but where is the fun in that when compared to a
new toy?

"Tim Lamb" wrote in message
...

In message , Harry Bloomfield
writes
40 odd years ago, some big (really big) variable speed DC motors I
installed, came with a rather ridiculously precise spec., suggesting it
needed to run at some silly full speed figure like 548rpm +/- 1 RPM.
Checking with head office and the designer, they confirmed it had to be
exactly so.

All we had at the time were mechanical tachometers, not very precise and
no way to connect apart from to the side of a large coupling, so I set
about designing something digital and entirely electronic, using an IR
head. Work it did, very well and quite precise. It cost the company around
£30 for the parts for me to build it, in my spare time. That was left with
the company when I moved on.

A couple of weeks ago, working on the tractor mowers governor system, that
specified a tick over speed and a full engine speed. I had no obvious way
to measure its speed, so I began thinking shall I build, or just see what
is for sale ready to use. Laser, ready to use, with guaranteed precision,
in a nice protective carry case all for £7.03 and delivery within one
month - no contest ;o)

Yes, I could have measured the ignition pulse period on my 'scope, or on
my Marconi counter timer, but where is the fun in that when compared to a
new toy?

You have to wonder who determines these specifications..

As a sprog apprentice, I was sent out to an American air force installation
near London to supervise test runs on a DC motor generator set.

The spec. called for the set to take over the load (comms of some sort)
within 10mS! of the mains supply failing.

Needless to say 10mS could not be achieved. Simple reactance calculations
of the motor field winding would have shown this.

The cure was a thumping great flywheel.....

Back in the early 1970's I worked on the control computer (Ferranti Argus
500 with Argus 400 i/o) for Wiggins Teape's No 5 paper mill in Dartford.
Under the raised control room was a motor generator set with a similar
thumping great flywheel, to buy time for change over in the event of a power
cut.

I had engineers who refused to visit the place as the girls on the paper
cutting line were definitely not 'PC' and were known to literally remove
visiting engineers trousers Talk about sexual harassment - it wasn't only
the paper making process that made for a hot and steamy atmosphere !

Andrew

On 17/08/2017 10:43, Andrew Mawson wrote:

Back in the early 1970's I worked on the control computer (Ferranti
Argus 500 with Argus 400 i/o) for Wiggins Teape's No 5 paper mill in
Dartford. Under the raised control room was a motor generator set with a
similar thumping great flywheel, to buy time for change over in the
event of a power cut.

I had engineers who refused to visit the place as the girls on the paper
cutting line were definitely not 'PC' and were known to literally remove
visiting engineers trousers Talk about sexual harassment - it wasn't
only the paper making process that made for a hot and steamy atmosphere !

Andrew



Several members of my family worked there in the 70s, apparently the
work's outings were legendary

Of course it's all gone and turned into housing now.

Lee explained on 17/08/2017 :
Several members of my family worked there in the 70s, apparently the work's
outings were legendary

Of course it's all gone and turned into housing now.

What was really appreciated by me, was the fact that all of that work I
did back then, will still be there and very much still in full use.

Brian Gaff formulated the question :
I did a similar thing with a new fangled device called a hall effect sensor
and a magnet glued to the spindle grin.

Not very imaginative and in those days simple pulse counters were el
cheapo.

From what I remember, I used a proper crystal controlled counter timer
circuit, interfaced to an LED display and a combined IR transmitter /
receiver module. With the latter bolted on a bit of broom rod, so the
shaft could be reached. It focused over just a few inches, so had to be
close.

Shaft was polished with a bit of emery, then a bit of black tape added
to create the pulse.

In message , Harry Bloomfield
writes
Lee explained on 17/08/2017 :
Several members of my family worked there in the 70s, apparently the
work's outings were legendary

Of course it's all gone and turned into housing now.

What was really appreciated by me, was the fact that all of that work I
did back then, will still be there and very much still in full use.

Well the Clywedog reservoir dam is still standing. Now you have
reminded me, I wonder how the Germanium transistors fitted in the
control gear are holding up!

--
Tim Lamb