I have a car revcounter, and would like to know what the basic movement is
- like 1mA FSD or whatever. Any easy way to determine this?

--
*If God had wanted me to touch my toes, he would have put them on my knees

Dave Plowman London SW
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Dave Plowman (News) wrote:
I have a car revcounter, and would like to know what the basic movement is
- like 1mA FSD or whatever. Any easy way to determine this?


If its Smiths, 10mA was the Rule.

Try a 1.5v battery and a 150 ohm resistor. Should be about full scale.


Or a 5v supply and a 1k resistor. should be half scale.

"Dave Plowman (News)" wrote in message ...
I have a car revcounter, and would like to know what the basic movement is
- like 1mA FSD or whatever. Any easy way to determine this?

--
*If God had wanted me to touch my toes, he would have put them on my knees

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

You put a calibrated ammeter or multimeter on the appropriate range in series with
the movement and a potentiometer (say 5K Ohm) adjust the pot for FSD on the movement
under test and the calibrated meter gives the current.

I can't help but add I was surprised you asked this.

--
Graham.

%Profound_observation%

In article ,
Graham. wrote:
You put a calibrated ammeter or multimeter on the appropriate range in
series with the movement and a potentiometer (say 5K Ohm) adjust the pot
for FSD on the movement under test and the calibrated meter gives the
current.

I can't help but add I was surprised you asked this.

If it were say 50 micro amp, I'm not sure my DVM would measure this.

--
*My dog can lick anyone

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

Dave Plowman (News) wrote:
In article ,
Graham. wrote:
You put a calibrated ammeter or multimeter on the appropriate range in
series with the movement and a potentiometer (say 5K Ohm) adjust the pot
for FSD on the movement under test and the calibrated meter gives the
current.

I can't help but add I was surprised you asked this.

If it were say 50 micro amp, I'm not sure my DVM would measure this.

why would you take an expensive and fragile 50uA meter and put it in a car?

They are IIRC 10mA.

On Aug 10, 2:40*pm, "Dave Plowman (News)"
wrote:
I have a car revcounter, and would like to know what the basic movement is
- like 1mA FSD or whatever. Any easy way to determine this?

Take it out and look.

You could have an ammeter in there (Smiths were 10mA for a long time,
but I think they were more originally). You could also have an "air
core" gauge, which is two opposed fields (more stable needle position
against mechanical shocks and cancels supply voltage variations),
usually found on other gauges though. More recently it will be a
stepper. If it's fairly old post-war Smiths ('40s) it could even be a
synchro (fecking rare and valuable on the spares circuit, used in some
Bristols and Astons, AFAIR), from when they first started recycling
their aircraft instrument lines to go into cars.

Most of mine are stepper motors. If something breaks, it's easier to
rebuild a new mechanism into the old shell than it is to pay
watchmaker prices to get a Smiths mechanism repaired. This is also why
I have what's probably the only pre-war MG with an OBD-II diagnostic
connector.

In article
,
Andy Dingley wrote:
I have a car revcounter, and would like to know what the basic
movement is - like 1mA FSD or whatever. Any easy way to determine this?

Take it out and look.

It is a spare. I'm experimenting with different electronics.

You could have an ammeter in there (Smiths were 10mA for a long time,
but I think they were more originally). You could also have an "air
core" gauge, which is two opposed fields (more stable needle position
against mechanical shocks and cancels supply voltage variations),
usually found on other gauges though. More recently it will be a
stepper. If it's fairly old post-war Smiths ('40s) it could even be a
synchro (fecking rare and valuable on the spares circuit, used in some
Bristols and Astons, AFAIR), from when they first started recycling
their aircraft instrument lines to go into cars.

It's a moving coil type with a scale of approx 120 degrees. Late '70s. And
it's not 10 mA.

Most of mine are stepper motors. If something breaks, it's easier to
rebuild a new mechanism into the old shell than it is to pay
watchmaker prices to get a Smiths mechanism repaired. This is also why
I have what's probably the only pre-war MG with an OBD-II diagnostic
connector.

--
*Middle age is when it takes longer to rest than to get tired.

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

In article ,
The Natural Philosopher wrote:
Dave Plowman (News) wrote:
In article ,
Graham. wrote:
You put a calibrated ammeter or multimeter on the appropriate range
in series with the movement and a potentiometer (say 5K Ohm) adjust
the pot for FSD on the movement under test and the calibrated meter
gives the current.

I can't help but add I was surprised you asked this.

If it were say 50 micro amp, I'm not sure my DVM would measure this.

why would you take an expensive and fragile 50uA meter and put it in a
car?

They are IIRC 10mA.

It's not. The original electronic type may well have been.

--
*Money isn‘t everything, but it sure keeps the kids in touch

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

"Dave Plowman (News)" wrote in message
...
In article ,
Graham. wrote:
You put a calibrated ammeter or multimeter on the appropriate range in
series with the movement and a potentiometer (say 5K Ohm) adjust the pot
for FSD on the movement under test and the calibrated meter gives the
current.

I can't help but add I was surprised you asked this.

If it were say 50 micro amp, I'm not sure my DVM would measure this.

Well even a really cheap DVM will do 50 microamps if you put a suitable
resistor in series with the test item and put the DVM across the resistor
and use volts.

If it's fairly old post-war Smiths ('40s) it could even be a
synchro (fecking rare and valuable on the spares circuit, used in some
Bristols and Astons, AFAIR), from when they first started recycling
their aircraft instrument lines to go into cars.

Real motorbikes were still using these in the 50's and 60's. Could never
figure out how they worked, and never managed to fix a broken one.
Admittedly my smallest tool was a 1/4 Whitworth spanner.

On 10 Aug,
"Dave Plowman (News)" wrote:

In article ,
Graham. wrote:
You put a calibrated ammeter or multimeter on the appropriate range in
series with the movement and a potentiometer (say 5K Ohm) adjust the pot
for FSD on the movement under test and the calibrated meter gives the
current.

I can't help but add I was surprised you asked this.

If it were say 50 micro amp, I'm not sure my DVM would measure this.


I doubt 50microamp, not robust enough!

Stick a variable resistance[1] in series with the meter and 12volts, adjust
for FSD, measure value of resistor with mutleymeter and I=V/R

[1] If 50 microamps start with at least 270K.

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