In the present production condition, when the use of frequency converter control, automatic control system that composed a lot of cases, PLC and frequency converter is required, such as bearing cleaning, paper printing, PCB production, etc.
PLC from dots or provided by the communication with kinds of control signals and instructions on off signal.
Below to introduce the frequency converter and PLC to cooperate the matters needed attention.
1, the switch command signal input converter input signal includes the run/stop, forward/reverse, speed, inching control on the running state such as switch type command signal.
Converter is usually the use of relay contacts or relay contact switch characteristics of components (
Such as a transistor)
Connected to the PLC controller
, operation instruction.
In the use of relay contacts, often because of poor contact and bring false action;
When using the transistor are connected, the transistor itself should be taken into consideration factors such as voltage, current capacity, to ensure the reliability of the system.
When designing the input signal circuit of frequency converter should also note that when the input signal circuit connection was not also can cause misoperation of frequency converter.
For example, when the input signal circuit adopts the inductive load such as relay, relay open and close the surge current may cause converter internal components of the damage or failure causing inverter misoperation, so should try to avoid the happening of this kind of situation.
When the input switch signal into frequency converter, occasional external power supply and frequency converter control power supply (
The crosstalk between.
The correct connection is power supply based on PLC controller, the external through the diode in the collector of a transistor to PLC.
2, there are some in the numerical signal input to the inverter numeric (
Such as frequency, voltage, etc. )
Command signal input, can be divided into analog input and analog output.
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.
The interface owing to the different input signal circuit, so we must 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 input signal is 0 ~ 10 v, and the output of the PLC is 0 ~ 5 v voltage signal range;
Or PLC controller on one 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, need to use and access resistance, series of way, way to limit or points to some voltage current, to open and close in order to make sure no more than the PLC and frequency converter capacity accordingly.
In addition, the attachment should also pay attention to the separate control circuit and main circuit, control circuit had better use shielded wire, ensure the noise on one side of the main circuit to control circuit.
Note: the size of the input impedance of PLC side to ensure the circuit voltage and current shall not exceed the allowable values of the circuit, to ensure the reliability of system and reduce errors.
In addition, in the use of PLC in sequence control, due to the data processing need time, and arrange the order of the different programming and instructions can result in system such as the use of different at runtime has certain time delay, so should be considered when more precise control of above factors.
Because the frequency converter in the run will produce strong electromagnetic interference, in order to ensure the PLC not because inverter main circuit breaker and switch device noise and failure
to the inverter connected to the PLC should pay attention to the following points: (
Of PLC itself should be grounded in accordance with the prescribed standards for wiring and grounding condition, and should pay attention to avoid using common grounding line and inverter, and in the ground to make the two separate as much as possible.
When power supply
condition is not very good, should be in the power supply module of PLC and the input/output module of power line access noise filter, reactor, and can reduce the noise with devices, etc, on the other hand, if necessary, at the side of the inverter input and the corresponding measures should be taken.
When the frequency converter and PLC is installed on the same operation ark, should as far as possible make wire and related to the frequency converter and PLC on separate wires.
By using the shielded wire and twisted pair to improve the level of noise interference.
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