Hi Gang:
Here's the text of my writeup for the temp and fuel gauge article that's
on Marks site. Or it's pretty close, anyway. I adjusted it a bit.
Something I left out of the original text: The fuel and Temp gauges
have the same works, but different scales. The same number of ohms to
ground will result in the same pointer angle on both. This can be used
for troubleshooting. Fuel tank reading about half full, the pointer
straight up? Swap the sender lead to the temp gauge and you should get
about a half scale reading. If you get significantly different pointer
angles then one of the gauges is faulty.
Stu
*********
Temp and Fuel Gauge
I borrowed a "power decade box" from my employer at the time, and
substituted it for each of the senders. I fiddled around with the
resistance values until the gauges stabilized at each of the indicated
readings. The data was taken on my '67 1A Tiger, which was assembled in
the Fall of 1966 (according to Norman).
Fuel Gauge
Gallons Ohms
2 145
4 80
6 55
8 38
11 21
Temp Gauge
Degrees C Ohms
60 150
80 77
90 57
100 41
120 24
The thermostat mentioned yesterday opened at 180 F (82 C). So, if you
were to connect your ohmmeter to the sender, it should read in the mid
to low 70's when the thermostat opens. Remember, this is automotive
stuff, as well as being Lucas related, so don't panic if you can't
reproduce these numbers exactly. Close is fine.
Another point: While the gauges may seem to have adjustments, we don't
know what to do with them. At exactly what input level do you make each
of the adjustments? The factory probably had a procedure involving
simulating different input levels and tweeking the adjustments to give
the right readings, to wind up with reasonable accuracy over the whole
scale. If you don't know the procedure, you may end up with the "fat
lady and the girdle" scenario. Squeeze it in here, but it pops further
out over there. I once had great plans to tweek the accuracy of my
Smiths voltmeter (a thermal device not unlike our temp and fuel gauges),
and then going crazy for a while trying to get it back to the accuracy I
started with.
Stu Brennan
|