Very good explanation, Captain. I agree that his should be a sticky.


Sent from my iPad using Tapatalk Pro

Wow, that's not at all how I thought it worked, but it's pretty damned clever.  I was assuming the sender unit's resistance was being used to actuate the gauge needle with electromagnets or some kind of friction clutch or something via a voltage divider.

Thanks again for the explanation - it's significantly better than anything I was able to find by just Googling around.  Again, it would be a shame if this knowledge stayed buried at the bottom of this not-so-interesting thread.

On 10/6/2020 at 4:49 AM, rcv said:

Again, it would be a shame if this knowledge stayed buried at the bottom of this not-so-interesting thread.

Agree!, I never took a look into them because i never ever had a problem with meters ever!.  Few pic's of those parts in this story would be also very nice..  

OK, I will convert this stuff to it's own thread when I get a few more minutes to make it read right. In the meantime.... I have more pics.

Here's a pic of one of the gauges. You can see the two different heating coils wrapped around two different "U" shaped bimetallic strips. Interesting to note that internets research indicates that "U" shape is part of the compensation as well. The concept is that the unheated side will compensate some for changes in ambient temperature. "They say" it doesn't get rid of all of the temperature based effects, but it helps some. Between that "U" shape and the compensation stage, the gauges seem to be really stable.

So this is an example of the compensated gauge with the two stages:

 

And here's a closer-upper pic of the compensation stage showing it's parts:

The switch opens and closes to keep the temperature of the compensation strip at a constant temperature (ave). If you put a Voltmeter on the sender unit, you'll see that it isn't a steady voltage, but is instead a square wave.