Wiring issues on the control system side
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Actual on-site conditions: 1. The control system controls the start and stop of the on-site motors via the MCC； 2. The DCS allows manual control of motor start/stop via soft buttons, while the SIS provides interlock control for motor start/stop ； 3. The cables from the MCC to the system are listed and installed by the electrical department ； 4. The MCC side has only one pair of terminals for the corresponding start (or stop) signal, and the wiring to the system also uses just two wires ； Question: How should the wiring on the control system side be arranged to enable DCS and SIS to control the pump simultaneously?
There’s a problem with MCC; add a contact
In simple terms, the soft start/stop communication from the DCS side is sent to the SIS; after being processed by the interlock logic in the SIS, a DO signal is sent to the switchgear in the electrical MCC.
The issue is that if the DCS or SIS system only provides a stop function, the output contacts of the DCS and SIS are connected in series via a two-core wire and integrated into the electrical secondary circuit. If the DCS or SIS system only provides a start function, the output contacts of the DCS and SIS are connected in parallel via a two-core wire and integrated into the electrical secondary circuit. If both a start and a stop function are required from the DCS or SIS system, this cannot be achieved using a two-core wire
On the MCC side, motor start and stop are controlled separately
It can be achieved using the method from Floor 3; communication between DCS and SIS is possible via hardwiring
Could the original poster be more specific: Does the SIS control the “on and off” of the motor? Or just “stop”?
One cannot consider the two wires in isolation; it is necessary to know the control diagram for starting and stopping the control devices on the electrical secondary side, and then everything will become clear! Could you upload a diagram of the electrical secondary side? A wide range of knowledge is required to set up a DCS system