Frequency converter and PLC connection generally has the following several ways: (1) using analog output module of PLC
control inverter PLC analog output module of 0 ~ 5 v voltage signal or 4 ~ 20 ma current signal, as analog input signal of the inverter, control inverter output frequency.
This way of control wiring simple, but need to select output module of PLC and frequency converter input impedance matching, and the PLC analog output module prices more expensive, in addition to partial pressure measures to adapt frequency converter to the PLC voltage signal range, in separate wiring, when connected guarantee of noise on one side of the main circuit to control circuit.
(2) the switch output control frequency converter based on PLC.
The switch of PLC output can generally attached directly to the inverter switch input.
This kind of control mode of wiring is simple, strong anti-jamming capability.
Switch output using PLC to control frequency converter of start/stop, is/reverse and point move, rotation speed and add and subtract time, can realize more complex control requirements, but there can only be used.
using relay contact connection, sometimes have the wrong operation due to poor contact.
When using the transistor are connected, you may need to consider the transistor's own factors, such as voltage, current capacity to ensure the reliability of the system.
In addition, in the design of inverter circuit, the input signal should also be noticed that the input signal circuit connection is undeserved, sometimes also can cause misoperation of frequency converter.
For example, when the input signal circuit use the inductive load, such as relay relay when open and close, the surge current of noise may cause misoperation of frequency converter, should avoid as far as possible.
- (3) PLC and RS
485 communication interface connection.
All the standard has a RS - Siemens frequency converter
485 serial interface (
Some RS - are also provided
, using the double connection, the application of its design standards applicable to the industrial environment.
Single RS -
485 link up to 30 frequency converter can be connected, and according to the address or the broadcast information of frequency converter, inverter can find need communication.
In the link needs to have a main controller (
And the frequency converter is the subordinate control object (
From the stand)
and frequency converter communication methods: 1, the switch signal control frequency converter and can be programmed control frequency converter of start, stop, reset;
Can also control the different combination of frequency converter speed, medium speed and low speed terminal implementation period of speed.
However, because it is using switch to implement and control, the speed curve is not a continuous smooth curve, also cannot achieve fine speed regulation.
2 in the analog signal control frequency converter, PLC frequency converter, there are some numeric instruction signal (
Such as frequency, voltage, etc. )
Input, can be divided into two kinds of, digital input and analog input.
Digital input used more frequency converter on the front panel keyboard and serial interface to a given;
Analog input is through given by external terminals, usually by 0 ~ 10 v / 5 v voltage signal or 0/4 ~ 20 ma current signal input.
Owing to the different input signal interface circuit, so you have to choose according to the input impedance of transducer output module of PLC.
When the voltage signal range of frequency converter and PLC is not at the same time, such as frequency converter and PLC input signal range of 0 ~ 10 v output voltage signal in the range of 0 ~ 5 v, or PLC on the side of the range of 0 ~ 10 v output signal voltage and frequency converter input voltage signal in the range of 0 ~ 5 v, because of the frequency converter and transistors allow the limitation of factors such as voltage, current, to access current limiting resistors in series and branch voltage circuit, adjust the frequency converter parameters and jump line change the inverter voltage and the analog signal, to open and close in order to make sure no more than the PLC and frequency converter interface circuit of the corresponding capacity.
In addition, should be paid attention to in the attachment also separate wiring, ensure the noise on one side of the main circuit is not to control circuits.
analog advantages: simple and convenient PLC programming, speed control curve smooth continuous and stable operation.
Disadvantages: in mass production line, the control cable is longer, especially the DA module USES the voltage signal, the output of the circuit has a larger voltage drop, influence the stability and reliability of the system.
3, PLC adopts RS -
485 communication control of frequency converter which is by far the most common use of a method of PLC serial communication using RS instruction programming.
Advantages: simple hardware, low cost, can be 32 inverter control.
Weakness: programming larger workload.
4, PLC adopts RS -
Modbus - 485
The control frequency converter RS - RTU communication method
Terminal using Modbus - 485
RTU protocol to communicate with PLC.
Advantages: the Modbus communication ways of PLC controller
programming than RS -
485 no agreement as to simple and convenient.
Weakness: the PLC programming still larger workload.
5, PLC using fieldbus control inverter mitsubishi inverter can be built-in various types of communication options, such as used for CC -
The Link of the fieldbus FR -
FR - for Profibus DP fieldbus
Used for FR - DeviceNet fieldbus
A5ND option, and so on.
Mitsubishi FX series PLC has a corresponding docking with the communication interface module.
Advantages: high speed, distance, high efficiency, stable operation, simple programming and can be connected inverter.
Weakness: the cost is higher.
6, the extended memory advantages: low cost, easy to learn and easy to use, reliable performance disadvantages: can only be used for no more than eight frequency converter system.
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