My analog amplifier is having issues with the AIO

[thestumbler]

Hello,

I have a load sensor that the OEM has installed this analog amplifier in: https://www.mantracourt.com/products/an ... -amplifier

The sensor cable, which was also supplied by the OEM has a length of 100ft and is a 22awg 4C with overall shield, but notably is not twisted pair.

I have attached a photo of our wiring.

We have a number of these units in the field. We have observed intermittent noise, sometimes very small, sometimes much larger and very random. At other times, the signal comes in clearly with no change to the system noted. Most of the time it seems like we are losing a few ma somewhere when the noise presents itself.

To illustrate I have attached two plots. The first plot, "rawsignal" is the raw signal from the load cell measured against time. The second plot, "B4NAFTR" is the signal plotted along the Y-axis, with another position signal along the X-Axis, right after we made the connection, and the deteriorated signal we measured later. The signal deteriorated after about 1.5hrs. The blue is the Before, which we consider good quality for our computations, and the green is after deterioration.

We are sampling at 25Hz. The other signal you see on B4NAFTR is along the X-Axis is also 4-20ma and we are not having an issue with this signal - but the sensor is of course different.

We don't suspect this is actually a problem with the RevPi AIO card, but I know there are a lot of talented people on this forum from all over the world, and maybe somebody would be kind enough to take a quick look and offer a bit of insight.

Thanks very much Forum.

[dirk]

Dear thestumbler, thank you for this good piece of information you have provided. Please modify your wiring as follows:
Change the AIO channel ground wiring. Avoid using the common ground. Because every voltage drop in the ground line that is caused by the system then influences the measurement.
Instead please connect the AIO channel ground to the sensor AIO ground.