|Posted on Monday, July 27, 2015 - 07:46 am: ||
I always wondered how the thermistors detected low fuel, so I thought about it and googled it.
Basically, the principal appears to be to try and "heat" the thermistor. If a thermistor is in an assembly covered in a liquid, it will be much harder to heat than if it is in an assembly out in the air.
So whatever ambient is, you can take a thermistor reading, pump a known quantity of heat (current over time) through it, then take another reading. That tells you how much the temperature has increased.
I would have to do some testing and thinking to figure out if the change in temperature would be constant over all ambient temperatures. The resistance change wouldn't be, thermistors are insanely nonlinear, but the temp change might be.
In other words, pump 5mA through a thermistor for 10 seconds and you will get a 2 degree rise in temperatures at 20 degrees ambient. Pump 5mA through a thermistor for 10 seconds and you will get a 2 degree rise in temperatures at 100 degrees ambient.
(Or even if not linear, perhaps the difference is low enough for a binary decision of "in liquid or not").
It would be fun to build one.
|Posted on Thursday, June 13, 2019 - 10:14 pm: ||
I connected my Motogadget low fuel LED light through relay trough the fuel pump thermistor to sense low fuel. It works very good. I do not know how it works in original instrument cluster tho.