Flowcon heating actuators on a 0-10 volt dc supply seem to be picking up voltage. It's on a knx system, and the switch actuator calls for 0-10 volts dc based on 0-100 %. The cable used is a screened 4 core. Though only using 3 cores as follows -0volts ground, 24volts dc to drive actuator, 0-10volts dc to tell actuator how much to open. Rooms are overheating , any ideas?
A ground loop between the control output and actuator input can generate enough current through AI's impedance to ground to offset what the actuator sees as an input (demand/control setpoint) value.
If you test the actuator input with a floating voltage source (battery powered), like a simulator or a calibrator) and find that a 'floating' source makes the problem disappear (the acutator does not drive higher than the input signal, then there's a ground loop.
It is usually most practical to defeat the ground loop with a galvanic signal isolator, 0-10Vdc input:0-10Vdc output where the output is isolated from the input.