Pantera DeTomaso Temperature Gauges
Figure 5 – Circuit Model
Note, I included the “+” and “Term” labels from the back of the meter on the diagram above to designate where wires went. See Figure 9 for a shot of the back of the meter.
I then mathematically modeled the circuit, knowing that resistors in series add and resistors in parallel add the inverse. Note – the meter is set up such that there is battery voltage across one coil while the temperature sender powers a separate coil in the meter. As such, the meter reading is proportionate to the difference between battery voltage and the reduced voltage due to the temperature sensors resistance.
Next I experimented with various resistance values for R0 and R1 until I got the resistance the meter saw at a given temperature (combination of the temperature sensor resistance (R) plus, R0 plus R1) closer to the resistance generated by the temperature sensor at the same temperature.
OK, I know this is complex – and likely confusing. Don’t get the idea I figured this out on my first try. Initially I sort of figured I’d possibly need a resistor in parallel with the coil in the meter that senses the temperature sensor, and might also need a resistor in series with the coil in the meter that senses the battery voltage. Turned out I didn’t need either.
My modeling suggested that I needed around 200 ohms in parallel with the sensor (R0). Turns out, after experimenting with resistors and the gauge, I needed 220 ohms in parallel (R0) and 1/2 ohm in series (R1). I did not need R2 or R3.
The resultant data are plotted on Figure 6.
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