PLC and frequency converter connected the matters needing attention when inventory -

PLC is a kind of digital computing and operation of the electronic control device, it through the software to change control process, with small size, flexible assembly, programming is simple, strong anti-interference ability and high reliability, etc. The operation is very suitable for bad work environment, so popular.

using the inverter automatic control system, many things is to use and PLC. PLC controller can provide control signals ( Such as speed) And instructions on off signal, Start, stop, reverse) 。 A PLC system consists of three parts: the central unit, input/output module and the programming unit. Switch input command signal

the inverter input signal includes the run/stop, forward/reverse, inching operation on the running state such as switch type command signal ( Digital input signal) 。 PLC usually use relay contact or relay contact switch characteristics of components ( Such as a transistor) Connected to the converter, operation instructions, as shown in figure 9 14.

FIG. 9 14 of PLC and frequency converter connected

when using relay contact, often lead to misoperation due to poor contact; When using the transistor are connected, you may need to consider factors such as voltage, current capacity of the transistor itself, ensure the reliability of the system.

when designing the input signal circuit of frequency converter should also be noted that when the input signal circuit connection was not sometimes cause misoperation of frequency converter. For example, when the input signal circuit use the inductive load, such as relay relay on and off when the surge current of noise may cause misoperation of frequency converter, should avoid as far as possible. The numerical signal input

in frequency converter, there are some numeric ( Such as frequency, voltage, etc. ) Command signal 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 PC to set; Analog input is through given by external terminals, usually through 0 10 v ( Or 5 v) The voltage signal or 0 ( Or 4) - - - - - - 20 ma current signal input. The interface owing to the different input signal circuit, it is necessary to choose according to the input impedance of transducer output module of PLC. Figure 9 - 15 for signal connection between PLC and frequency converter.

FIG. 9 15 signals between PLC and frequency converter connection diagram

when the voltage signal range of frequency converter and PLC is not at the same time, for example, the inverter input signal in the range of 0 10 v and PLC output voltage signal in the range of 0 5 v, or PLC output signal voltage on one side of the range of 0 - 10 v and frequency converter input voltage in the range of 0 5 v, because of the frequency converter and transistors allow the limitation of factors such as voltage, current, you have access to current limiting resistors in series and the partial pressure, in order to make sure to connect and disconnect when less than the corresponding part of the PLC and frequency converter capacity. In addition, the attachment should also pay attention to the separate wiring, ensure that the noise is not on one side of the main circuit to control circuit.

usually inverter also to the external output through terminal corresponding monitoring analog signal, signal range of 0 - usually 5 v ( Or 10 v) And 0 ( Or 4) - - - - - - 20 ma current signal. In either case, must pay attention to the size of the input impedance of PLC side ensure the voltage and current in the circuit does not exceed allowable values of the circuit, to ensure the reliability of system and reduce errors. In addition, because the composition of the monitoring system is not the same, as have not clear place best advice to the manufacturer.

in the use of PLC in sequence control, because when the CPU to process takes time, there is always a certain time delay.

due to the frequency converter in the running process leads to the strong electromagnetic interference, in order to ensure that the PLC is not due to the inverter main circuit breaker and switch devices such as noise and fault occurs, the frequency converter and PLC controller and PC with when using must also note:

1) Ontology of PLC in accordance with the prescribed standards and earthing conditions for grounding. At this point, should avoid using common grounding line and frequency converter, and grounding as far as possible make them apart.

2) When the power supply condition is not very good, should be the power of the PLC module and input/output module of power line noise filter and noise reduction with access to the transformer, etc. In addition, if necessary at the side of the frequency converter should also take corresponding measures.

3) 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.

4) By using the shielded wire and twisted pair to achieve the purpose of raise the level of noise resistance.

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