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Input of numerical signal for PLC and inverter

Dec 10, 2020

Input of numerical signal for PLC and inverter

There are also some numerical command signal inputs (such as frequency, voltage, etc.) in the inverter, which can be divided into two types: analog input and analog output. The analog input is given externally through the wiring terminal, usually through a voltage signal of 0~10V/5V or a current signal of 0/4~20mA. Since the interface circuit varies with the input signal, the output module of the PLC must be selected according to the input impedance of the inverter.

When the voltage signal range of the inverter and the PLC are different, for example, the input signal of the inverter is 0-10V, and the output voltage signal range of the PLC is 0-5V; or the output signal voltage range of one side of the PLC is 0-10V When the input voltage signal range of the inverter is 0~5V, due to the limitation of the allowable voltage and current of the inverter and the transistor, it is necessary to connect the resistor in parallel or series to limit the current or divide part of the voltage. , To ensure that the corresponding capacity of PLC and inverter is not exceeded when opening and closing. In addition, you should also pay attention to separate the control circuit and the main circuit when wiring. It is better to use shielded wires for the control circuit to ensure that the noise on the side of the main circuit is not transmitted to the control circuit.

Note: The size of the input impedance on the PLC side should ensure that the voltage and current in the circuit do not exceed the allowable value of the circuit to ensure the reliability of the system and reduce errors.

In addition, when the PLC is used for sequential control, the time required for data processing, the different sequence of program writing and the different use of instructions will cause a certain time delay when the system is running, so in more precise control The above factors should be considered.

Because the inverter will produce strong electromagnetic interference during operation, in order to ensure that the PLC does not malfunction due to the noise generated by the inverter's main circuit breaker and switching devices.

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