Senders
Sharing Engine Senders
NTC resistors, resistive fuel level gauges, resistive fuel and oil pressure senders all use ground as common return (that would be the engine block and your battery minus). In order to measure the resistance, you need to send an electrical current of known value through the resistor, which causes a voltage level to appear accross the sender you want to measure. This voltage is then measured and used to calculate the sender reading.
The trouble comes in if you have two gauges trying to send current through the resistor (and each gauge will use different current values to add to the confusion). The voltage will be higher (probably significantly) as the two currents add up. As a direct result, both gauges will read incorrectly.
EGT/CHT thermocouples are different since they actually create a small (very small) voltage dependent on temperature. You could connect a single EGT probe to two of our RDAC units without trouble, but add an old "analog" gauge and the gauge will load the probe to such an extent that your Stratomaster will see less voltage and thus under
read. The analog gauge loads the probe to extract the tiny amount of energy required to move the needle (the power for that has to come from somewhere).
RPM, fuel flow and similar switched DC or AC signals can most of the time be connected in parallel without too much trouble. For example, it is quite common to connect a rotax (aviasport) rev counter in parallel to our RDAC unit.
Last update: 2006-11-13 12:45
Author: Rainier
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