If you don't plug in the PG card, do you use PLC's PID control?Plug in the PG card and the PLC PID control, which is reliable and precise?
Mainly depends on what you want closed loopIf it is speed closed-loop, with PLC, you can not use PG card, direct PLC acquisition speed as a negative feedback signalIf it is a closed loop of ordinary process variables, such as pressure, temperature, etc.Neither PLC nor PG cards are requiredThe PG card is mainly used in the speed closed loop of the converter to collect signals
Using PG card of frequency converter to realize closed loop vector controlFor example, vertical motion loads, such as cranes and elevators, require closed-loop vector controlIn this case, the frequency converter must install the PG card, and the encoder signal will be connected to the PG card, using the frequency converterPID instruction.In this application, the PID function module of PLC can not realize the vector control function.
If there is a PLC encoder as a speed sensor signal, you can access the PLCPLC analog output (or communication) as a given value of the inverterUse PLC's PID instruction to complete the speed closed loop control of the converter.Note: if you are not using vector control of the inverter, you can.For example: horizontal transmission of non vector control or pump fan class.
There are several kinds of closed loop, speed closed loop, temperature / pressure / flow closed loop.Since you're talking about PG cards, then obviously you have to control speed.Generally speaking, the control precision is related to the hardware, and the PLC can also output pulses.If you are small system, simple control, it is recommended that you use PG card + encoder to save the cost, you can inverter internal PID, and control accuracy is also ok.My feeling, as if the speed control precision is high, is PG card.
