Peter
You have forgotten one thing, which will make a difference. The
voltage stabilizer. You will need to put that in the circuit to
get the proper readings.
This regulates the voltage to about 8 volts, if I remember correctly.
Because the circuit is just a resistor, and a heater, you can use a
pulsed regulator, i.e. 12 volts, then 0 volts. Depending on the input
voltage the pulse width changes. This is one method of regulating. The
other is using a transistor, and a Zeener diode, which is probably more
expensive.
The gadgets work like this. You have a heater coiled round a bi metalic
strip, this moves slightly as it heats up. This intern pushes the
needle
round the gauge. If it were to use a moving coil like most normal
meters,
it would jump all around the place when you went over any type of bump.
So a lower resistance at the sender, means more current flows through
the
circuit hence the heater gets hotter, and the needle moves into the hot.
A value of a couple of K is wrong for the sender, you can short it to
earth
but do it for a second, then off a second like that so you should have
it
about half on the gauge. Two person job unless you want to keep fit.
Those reading of 50 to 200 Ohms are correct, but you will also find you
meter is no way linear. They were not designed to be.
--
James Carpenter
Yellow '79 spit wired by a trained marmot
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