Can an optical cable be used as the control cable for remote start/stop of a PLC?
Thread Content
For VOC projects, the PLCs are installed on-site by the manufacturers. Now, it is desired to establish start/stop points in the DCS in order to enable emergency shutdown control of the PLCs. Is it necessary to use hard-wired connections for the control cables? I want to use fiber optics; is that possible? If possible, how can it be achieved via fiber optics? Thank you, experts, for your answers!
Fiber optic communication is used between the PLC and the DCS, and there are two types of wired connections: 1) Indirect connection – the DI/DO wires of the DCS are connected directly to the PLC, allowing control over the start and stop of motors through the PLC. 2) Direct control: The feedback signals indicating whether the motor is running or stopped are obtained directly from the auxiliary contacts of the contactors on the local panel. DO signals are connected in series within the motor’s closing and opening circuits. This method is somewhat complicated, as corresponding changes need to be made to the motor’s electrical circuit; however, its advantage is fast direct response.
Hello, do you mean the 2-core control cable when you talk about the DO hard wire? I would like to ask whether it is possible to control the start and stop of a PLC using fiber optic communication instead of a 2-core cable
Optical fibers are used for communication. It depends on whether the agreement can be finalized.
Communication between DCS and PLC works fine using optical cables.
It’s possible, as long as the communication system supports control. It’s similar to two remote control stations in a DCS system that communicate using light, the same principle applies
The optical fiber is just a medium; what’s important is whether DCS and PLC can communicate. It’s crucial whether the manufacturer provides the source code for the PLC – if so, it’s possible to modify the program or add hardware, using either communication or direct wiring； If there is no source code, it seems that hard interlocking is the only option
For communication optical cables themselves, there is no problem; optoelectronic signal converters are needed at both ends, and then the DCS system can be used to initiate and stop the corresponding processes
No fiber optic is needed; 485 communication can be used. However, it is not recommended to rely on communication for this purpose, although it is possible to achieve the desired outcome in that way
Does the PLC control cabinet have a touch screen? ? We use an OPC server; the DCS and PLCs communicate via OPC, and configuration on the DCS can be exactly the same as that on the touch screen. It’s because OPC isn’t set to a redundant mode; once the OPC server crashes or shuts down, the OPC data is lost, and it becomes impossible to operate the field PLC system (the field touch screen can still be used for operation).
Using fiber optics is no problem; the key factor is the communication protocol – whether it’s MODBUS, DP, or TCP/IP. It is recommended to use DP or TCP/IP, as they offer faster and more stable data transmission. It mainly involves adding corresponding communication modules as well as photoelectric conversion modules to PLCs and DCS systems