After passing through a one-input two-output safety barrier, the 4~20mA current signal shows inconsistent readings.
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Dear experts, I’m facing the following issue: The motor current is represented by a 4–20mA current signal generated by a current transmitter. This signal passes through a P+F two-input one-output safety barrier (model KFD2-STC4-Ex1.20), with one branch going to the Siemens 400 PLC and the other to the Heima SIS. However, only the Siemens PLC displays the correct value; the value shown in the Heima SIS is too high, and it often drops to 0. I would appreciate some advice from the experts. Thank you!
Measure whether the output currents are the same?
Too large to display? By how much? What is the current? Is the wiring on the HIMA side correct? It might be clearer if you first check these by yourself, or describe in detail the wiring inspection, before asking your question.
Swap the two output currents and make a judgment
It’s probably due to issues such as different loop resistances; in the loop with a higher resistance, adding a small adjustable resistor will do
It could also be that the supply voltages are at different levels, exceeding the allowable common-mode rejection ratio of the AI module. Consult the SIS manufacturer!
Measure whether the outputs are consistent, and check for any sources of interference such as high voltages like 220AC in the circuit that leads to the dark horse
Try changing the channel and see; check whether the output current values are the same
1. Check whether the impedance at the safety gate output matches that of the circuit downstream； 2. The safety barrier outputs a 4–20mA analog signal, and analog signals may experience deviations, thus requiring calibration.
Stop asking this question; go and find the faults yourself.
The system can be active or passive, or have different potentials.