To List - the following comments were made to me by 'Tiger' Tom Ehrhart and
are passed on as added, quality information on the topic currently in
discussion. To quote Tom:
"Over the years, I have repeatedly seen/heard similar comments. Here's my
quick spin to check gauge accuracy. It's quite different from others. Since
I calibrate gauges I needed a calibration standard. I do not have any
factory info on electrical calibration, so I made my own.
About 15 years ago when I was selling parts, I placed 10 new temp sender
units in a temperature chamber at the same time and tested them for
electrical characteristics at three specific temperatures. I also compared
with some used units as well. I was a manger of an environmental laboratory
at the time and had access to accurate chambers and measurement equipment.
I predetermined what the meter current of our gauges is. This is a fixed
value for all gauges. I than applied the same current to all sender units
and measured the voltage drop across each sender at the three specific
temperatures. The temperatures were at the low, mid and high end of our
gauges. I took the results of the 10 readings and statistically determined
what the voltage drop at each temp should be. I than used this value to
calculate what voltage is required to make a gauge indicate a specific
value.
If you look along the outer edge of the gauge face you will see three sets
of two dots each at the low, mid and high points. It's the same for fuel or
water. Using the data from the new sender units I have calculated that it
takes the following voltages applied across the gauge to produce the
low/mid/high indications. They are 2.0/4.8/7.6 volts respectively. All this
is based on using new Smiths senders units. If they were wrong, then we are
all in trouble.
I have considered the relationship of owner misidentification of overheating
because inaccurate gauge indications. While I have found most Alp/Tgr
instrumentation to be quite accurate for the most part, there are many
factors that cause many owners to have inaccurate readings. And that is
another entire topic in and of itself. TT"
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