Electrical – Twisted pair for long distance voltage measurement

adccurrent measurementinstrumentation-amplifieroperational-amplifiertwisted-pair

I want to measure the voltage drop across a shunt, but the ADC performing the measurement will be far from the actual shunt – perhaps five meters.

I'll need to measure voltage drops across the shunt to about 0.1 mV, so stray signals of that magnitude could be a problem.

Can I just run two pieces of 22 AWG wire from the shunt to the ADC, or would something like twisted lair help cancel out noise, and ensure the wire runs are the same length (the latter may not matter since the current flow is minimal – only enough to satisfy the ADC cap).

The environment is a camper van – so it is fairly noisy as it has various DC and AC wiring running all over the place.

Best Answer

Common mode voltage (DC and noise on whatever it turns out to be) is likely to be your biggest problem. A shunt is a very low impedance source and is easily filtered if you don't need fast response. You don't need a twisted pair in that case, though it won't hurt.

If you filter the shunt voltage well at the ADC end and use a differential amplifier with a bipolar supply (such as an instrumentation amplifier) to amplify the voltage up into the ADC range you should be okay.

If you're planning on going directly into an ADC with an on-board PGA and unipolar supply, I think you're going to have serious problems.