Interference in the 4-20mA signal feedback from field instruments (causes and solutions)
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Hello everyone! Please share your views on the interference issues related to the 4-20mA signal feedback from on-site instruments (the causes and solutions)
The cable shielding must be good, and the grounding must be good
This is a fairly common issue: the feedback signal is a current signal, and current signals are analog values; therefore, even slight fluctuations (such as 4.002 mA) can cause the feedback value to fluctuate as well. Three recommendations are offered: 1: Ensure a firm connection between the actuator feedback rod and the valve; 2: Maintain a stable air supply (the pressure regulator must not leak); 3: Properly shield the cables (the shielding layer is usually connected at the cabinet). These are personal experiences gained from practical work
It means the issue of interference with the “4-20mA signal feedback”; I’m sorry, maybe I didn’t explain myself clearly.
Reasons for signal interference: 1) Shielded cables are not used, 2) The shielded cables are not grounded at one end or the grounding is poor, 3) Signal cables are laid together with power cables, 4) Faults in the instruments themselves
Electromagnetic interference has no effect on 4-20ma signals; it makes no difference whether shielded cables are used or not for these signals. To be more specific, there’s no need to keep bringing up the issue of shielding
I’ve learned from it; I experienced firsthand the interference caused by poor power supply, and it was quite serious – the instruments could hardly function properly. Is it power supply interference? What exactly is this interference? I’m not quite sure.