Using programmable controller need to pay attention to what matters

the use of programmable controller is becoming more and more widely, schools, industrial everywhere in the programmable controller. Thus, the status of the programmable controller is gradually improving. To avoid using programmable controller went wrong, this article will be to the programmable controller and frequency converter connection about the matters needing attention.

introduction

the programmable controller ( PLC） Is a kind of digital computing and control device of the operation. PLC as a substitute for traditional relay products, widely used in various fields of industrial control. Due to the PLC can use software to change control process, and has small volume, flexible assembly, programming is simple, strong anti-jamming capability and high reliability etc, especially suitable for operation in harsh environment.

when using inverter control, automatic control system that composed many cases is USES the combination of PLC and frequency converter, such as our second catalytic automatic blowing system. PLC controller can provide control signals and instructions on and off. A PLC system consists of three parts, namely, central processing unit, input/output module and the programming unit. In this paper, the frequency converter and PLC to cooperate the matters needed attention.

1。 Switch input command signal

the inverter input signal includes the run/stop, forward/reverse, micro manipulation, running state switch type command signal. Converter is usually the use of relay contacts or relay contact switch characteristics of components ( Such as a transistor) With PLC) To get operation command, as shown in figure 1.

figure 1 run signal connection

in the use of relay contacts, often because of poor contact and bring the misoperation; 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 sometimes cause misoperation of frequency converter. For example, when the input signal circuit adopts the inductive load such as relay, relay open and close of surge current noise may cause misoperation of frequency converter, should avoid as far as possible. Figure 2 and figure 3 shows the wiring example of right and wrong.

figure 2 inverter input signal access

figure 3 input signal error connection

when the input switch signal into frequency converter, occasional external power supply and frequency converter control power supply ( DC24V时) The crosstalk between. The correct connection is power supply based on PLC, the external through the diode in the collector of a transistor to PLC. As shown in figure 4.

4 input signal against the interference connection

2. 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 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. 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 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 access to current limiting resistor in series way and method of partial pressure to open and close in order to make sure no more than the corresponding capacity of PLC and frequency converter. In addition, should be paid attention to in the attachment also separate wiring, ensure the noise on one side of the main circuit to control circuit.

usually frequency converter to the external output through terminal also corresponding monitoring analog signals. The scope of the electrical signal is usually of 0 ~ 10 v / 5 v and 0/4 ~ 20 ma current signal. In either case, all should be paid attention to: 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, due to the composition of the monitoring system for each other is not the same, have not clear place should consult factory.

in addition, in the use of PLC in sequence control, due to the CPU for data processing need time, there is a time delay, therefore, should be considered when more precise control.

because of frequency converter in the run will produce strong electromagnetic interference, in order to ensure the PLC not because the inverter main circuit breaker and switch devices such as noise and failure, the inverter when connected to a PLC controller should pay attention to the following:

( 1) 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.

( 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 reduce noise with access to the transformer, etc. , on the other hand, if necessary, at the side of the inverter also should 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 improve the level of noise interference.

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