I’ve always been confused about the issue related to the negative terminal of the 24V power supply in DCS systems. We are currently using a CS3000 system – is the negative terminal of the power supply connected to the signal ground? In the end, all grounds were connected using a ground bar; does that mean it’s equivalent to the negative pole of the power supply?
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Problem with the negative terminal of the 24V power supply in the DCS system?
There are two types of common terminals for signal circuits: one is floating, and the other is grounded. Generally, the negative terminal of 24V DC is connected to the signal ground, and this connection method is quite common.
According to the standards for working signals set by the International Electrotechnical Commission, the point with the lowest potential in a system should be chosen as the signal common ground. In a DCS system, the negative pole of the 24V power supply has the lowest potential, and it serves as the signal common line. If the signal negative wire is not connected to this common line, it can lead to unnecessary interference or errors.
So ours should be grounded; in each cabinet, there is a signal ground terminal block, and then a grounding wire is used to connect to that terminal block.
During the rainy season, if water gets into one of the instruments on site, it affects all 16 instruments on that card; some of their readings increase while others decrease. This is very troublesome, and the only way to identify the problem is by turning off each instrument individually. So I’m really confused when it comes to grounding.
If possible, separate the switching power supplies for these instruments.
The negative electrode is left floating in this way; it’s a common practice in UPS systems and control systems.
Under normal circumstances, the power supply itself has a working ground and a protection ground, and this ground must be connected to the grounding terminal to form a common ground
It might be caused by humidity; if there is water present, the grounding effect should be better
It might be caused by humidity; if there is water present, the grounding effect should be better
This is the drawback that remains from the installation process; it’s why people try to simplify things by avoiding extra wires. Here, in some cases, the wiring is done behind the panel, and all the negative terminals from the wiring connectors there are shorted together. This type of wiring leads to the problem you mentioned. Normally, the positive and negative terminals from the connectors should be separated. Someone else has already suggested separating all the negative terminals, but this can only be done during installation. Our system from LSYS is wired in exactly this way, and it’s really annoying