How to use the inverter properly

The connection of PLC and inverter becomes the key to the success of the system.

1. PLC switch command signal input

The input signal of the frequency converter includes switch type command signals for operation of running/stop, forward/reverse rotation, inching and other operating states. The frequency converter is usually connected to PLC by relay contact or components with relay contact switch characteristics (such as transistors) to the operation state command.

When relay contacts are used, they are often in poor contact and cause misoperation; When using transistors for connection, factors such as voltage and current capacity of transistors should be considered to ensure system reliability.

When designing the input signal circuit of the frequency converter, attention should also be paid to the fact that incorrect connection of the input signal circuit will also result in incorrect operation of the frequency converter. For example, when the input signal circuit adopts inductive load such as relay, the noise caused by surge current generated by relay opening and closing may cause malfunction of frequency converter, which shall be avoided as far as possible.

When the input switch signal enters the frequency converter, external power supply and frequency converter control will occur

Crosstalk between power supplies (DC24V). The correct connection is to use the PLC power supply to connect the external transistor collector diode to the PLC.

2. Inverter numerical signal input

When the voltage signal range of frequency converter and PLC is different, for example, the input signal of frequency converter is 0~10V, while the output voltage signal range of PLC is 0~5V; Or when the output signal voltage range on one side of PLC is 0 ～ 10V and the input voltage signal range of frequency converter is 0 ～ 5V, the allowable voltage, current and other factors of frequency converter and transistor are limited, and the current limiting resistor and voltage dividing method shall be connected in series to ensure that the corresponding capacity of PLC and frequency converter is not exceeded when opening and closing. In addition, the wiring shall be separated during wiring to ensure that the noise on one side of the main circuit will not be transmitted to the control circuit.

Usually, the inverter also outputs the corresponding monitoring analog signal to the outside through the wiring terminal. The electrical signal range is usually 0~10V/5V and 0/4~20mA current signals. In either case, it should be noted that 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 system reliability and reduce errors. （ http://www.diangon.com All rights reserved) In addition, the composition of these monitoring systems are different from each other, and those who are not clear should consult the manufacturer.

In addition, when using PLC for sequence control, CPU needs time for data processing, and there is a certain time delay, so it should be considered when controlling more accurately. Strong electromagnetic interference will be generated during the operation of the frequency converter. In order to ensure that PLC will not generate noise from the main circuit breaker and switching devices of the frequency converter, the following points should be noted when connecting the frequency converter to PLC:

(1) The PLC itself shall be connected according to the specified wiring standards and conditions. Attention shall be paid to avoid using common wiring with the frequency converter, and the two shall be separated as far as possible.

(2) When the power supply condition is not good, the power line of PLC power module and input/output module shall be connected with noise filter and noise reduction

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In addition, if necessary, corresponding measures shall be taken at the side of the frequency converter.

(3) When the frequency converter and PLC are installed in the same operation cabinet, the wires related to the frequency converter and PLC shall be separated as far as possible.

(4) Shielded wire and twisted pair are used to improve the noise interference level.

When connecting PLC and frequency converter for application, they involve using weak current to control strong current, so attention should be paid to the interference during connection to avoid the malfunction of frequency converter caused by interference, and PLC or frequency converter damage caused by improper connection.