The combination of PLC and frequency converter application

The combination of PLC and frequency converter application newmaker welcome to e hall exhibition hall 3 PLC PLC programmable controller, PLC programming cable. 。 。 The introduction programmable controller ( PLC controller） Is a kind of digital computing and control device of the operation. PLC controller 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 the 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 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 controller to cooperate the matters needed attention. 1. Switch command signal input converter 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. 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. Figure 1 run signal converter connection mode in the design of the input signal circuit 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. Figure 4 connection 2 anti interference of the input signal. There are some in the numerical signal input to the inverter 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. Figure 5 for signal connection between PLC and frequency converter. 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 the frequency converter in the run will produce strong electromagnetic interference, because the inverter main circuit breaker and PLC in order to ensure the noise and fails, switch devices, etc will be the inverter connected to the PLC 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. 3 conclusion application of PLC and frequency converter connection, because the two involved with high voltage and low voltage control, therefore, should pay attention to the connection of interference, avoid the interference caused by error action of frequency converter, or cause the damage of the PLC and frequency converter because of improper connection.
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