The oxygen level is indicated stably on the local screen, while the signal at the remote output fluctuates
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I encountered a strange phenomenon: the oxygen analyzer generated a 4–20mA signal, which was connected to a PLC card via a cable, and the scale settings were adjusted accordingly. However, on the PLC’s display, the current value kept fluctuating within its range. By using a signal generator to send signals to the input terminal of the card, the fluctuations stopped and the corresponding input signal value was displayed steadily. I then tried sending signals from the oxygen analyzer side using a signal generator, and the output value on the PLC display also became stable. Additionally, the current output from the oxygen analyzer remained stable as well. Since I didn’t have a multimeter with an analog needle, I had no choice but to give up for now. I checked the connection points for the current output of the oxygen analyzer; as it involved multiple wires, I suspected interference, but the fluctuations continued. I consulted two different technical staff members from the manufacturer, but they said there was nothing they could do and suggested that I contact their sales team. However, the sales staff wouldn’t answer the phone. What should I do?
First is to endure, second is to wait, third is to change. The above are solutions that require no initiative on your part.
There’s no problem when current is applied at the input terminal of the card, but there’s still an issue when current is applied at the output terminal of the meter. I tried measuring the resistance of the multi-wire cable relative to ground using a megohmmeter; it seems that the cable may be damaged or subject to electromagnetic interference. Is there any junction box or connector somewhere in between?
Based on this situation, check the insulation of the cables; the wiring terminals also need to be inspected for insulation issues, as well as whether there is any interference caused by large equipment in the vicinity.