You can deal with “grounded at the sensor end” by running a twisted pair, and inserting a resistance to ground and an equal resistance to the signal. That gives you a balanced (but not differential) signal. Any differential line receiver or other differential amplifier will happily amplify the difference (the signal you want) and ignore common mode noise which should be picked up equally in both wires of the twisted pair as they are now both at the same impedance.

UNFORTUNATELY, twisted pair is not an available option: "My guess is that that the signal will pick up a lot of noise and interference from outside the cable (ordinary flat cable)" is what the TS explained after a few questions.

 

UNFORTUNATELY, twisted pair is not an available option: "My guess is that that the signal will pick up a lot of noise and interference from outside the cable (ordinary flat cable)" is what the TS explained after a few questions.

Your right.It’s ribbon. What he didn’t tell us was what else was on that ribbon. Maybe what’s on there makes it even worse. Probably the gate drives to the MOSFETs.

 

Interleaved grounds would help with both noise and impedance control. In a football stadium, I once ran multi-hundred-kilohertz TTL through flat ribbon cable over 60 feet with no problems. That system was used for years.

ak

 

Since we now know that "the signal" is the current thru a photo-transistor in an opto-isolator, we hace a clue. One of the pair is the voltage source and the other is the return current from the photo-transistor. So it should be the same current on both sides. AND, if it is done right, the sensor end is not connected to anything else, such as a "ground."