Motor DCS signals and instrument DCS signals
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I only work with instrument DCS systems and don’t know much about electrical aspects. In the systems I worked on before, it seemed that all kinds of signals related to the motors were sent to the DCS via communication. I would like to ask: how are these various motor signals (such as current, start/stop commands, etc.) connected to the MCC? And once they are there, how does the MCC process these signals before sending them over via bus communication? Are there also cards similar to those in DCS in MCC to collect these signals and transmit them to the DCS side? Is there still something similar to PLCs or frequency converters that collect and process signals before sending them to the DCS? Also, if these motor signals are to be connected to the DCS system, can they be connected directly? Is it necessary to add barriers or something? Can it share a DCS cabinet with the instruments? A simple question; thank you all for your guidance.
The start and stop of motors are generally controlled using contact signals, without the need for communication. If ensuring a safe voltage is important, it is best to use an intermediate relay in the electrical circuit to isolate the 220V voltage; however, many designs these days connect directly to the DCS cabinet (the DCS side uses dry contacts, and the voltage in the circuit is usually around 220V). For important pumps, especially those equipped with interlocks, it is advisable to use cables for signals related to operation and faults as well. Communications are generally used only for displaying signals such as current, faults, frequency conversion, and so on.
For normal start/stop operations, feedback, and current measurements, it’s sufficient to connect them directly to the DCS; communication is only necessary if you need very comprehensive parameter settings or something similar
The electrical side is divided into low-voltage and high-voltage systems, with signals collected via a SCADA system, just like with our instruments. If communication with the instruments is to be carried out, it is done through a SCADA system; generally, the points involved in interlocking and control, as well as those in the high-voltage system, are connected via hard wiring, while communication can be considered for other indicator points. When it comes to communication, attention must be paid to the quality and routing of the communication cables; at the same time, the communication hardware on the electrical side must also operate properly.
It can be connected directly to the DCS; the AO and AI signals from the frequency converter can be handled by installing isolated safety gates on the DCS side.