How to deal with interference!
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In the pure water system, the high-voltage and low-voltage circuits are in the same cable tray; it worked normally before. However, recently, the level gauges of the raw water tank and the pure water tank have experienced fluctuations of around 0.3M whenever the raw water pump, the primary and secondary high-pressure pumps, or the booster pump is started or stopped. At first, the liquid level was 4.7M; as soon as those pumps were started, it rose to 5M. Once the pumps reached a stable operation state, the liquid level dropped again! ! I think it’s a interference issue, but how can I confirm and fix it? ! !
The possibility of interference cannot be ruled out, but based on the description, when the pump is first started, sudden inflow of water causes fluctuations in the liquid level, which leads to an increase in the measured values; once operation stabilizes, everything returns to normal, indicating that the instrument is functioning properly.
It’s not a problem of interference at all; look for other reasons.
I’m also very confused by what the original poster said. It is generally believed that the starting current of an asynchronous motor is 4 to 7 times its rated operating current, and it’s completely normal for such a current to cause interference with the instrument signal cables. But there shouldn’t be any interference when the pump is stopped. Are the primary water pump, the primary and secondary high-pressure pumps, and the booster pump new additions? Were these pumps already present when the owner mentioned those abnormalities? As for the verification method, I don’t really have any good ideas either. Whether this approach will work is just a rough idea; there are many aspects that need to be improved: the cable connected to the liquid level transmitter on-site should not be used; instead, a load resistor of around 1000 ohms should be connected in series, followed by an ammeter. Then, the several pumps mentioned by the original poster should be operated, and the current values should be recorded. If there is a change in current on the order of mA, it can be confirmed that the motor cable is causing the interference.
I’ve encountered a similar problem as well: when starting and stopping the motor (driven by an inverter), there were significant fluctuations in flow rate and liquid level. The issue was resolved by replacing the cable and running it through a new tray. You can give it some thought
Consider the interference from contactors or frequency converters.
Strong and weak cables cannot be placed in the same tray. . Over time, the instruments are prone to damage
This happened to us as well; once we kept them separate, the problem disappeared.
There’s no good solution; we should separate them. We can also try grounding the instrument shielding layer, as this is necessary
Instrument signal cables must not be stored together with electrical cables; they should be routed in separate trunking.
Separate strong current from weak current, separate strong current from weak current, separate strong current from weak current. Otherwise, the interference simply cannot be dealt with. Power, control, and measurement cables run in their respective cable trays; the measurement cables and some of the control cables are shielded cables, with their shielding layers properly grounded.