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2.6.3.2 - Unpowered Isolated Signal

An example of an unpowered isolated signal would be a thermocouple or photocell where the sensor leads are not shorted to any external voltages. Such a sensor typically has two leads. The positive lead connects to an AINx terminal and the negative lead connects to a GND terminal.

An exception might be a thermocouple housed in a metal probe where the negative lead of the thermocouple is shorted to the metal probe housing. If this probe is put in contact with something (engine block, pipe, …) that is connected to ground or some other external voltage, care needs to be taken to insure valid measurements and prevent damage.