PLC how precise control frequency converter? The schematic diagram taught you -

Programmable logic controller is a specially designed for application in industrial environment and digital computing operations electronic systems. It USES a programmable memory, in its internal storage to perform logical operations, sequential control, timing, counting and arithmetic operations such as instruction, through digital or analog input/output control various types of machinery or production process.

common PLC control frequency converter three methods: 1. PLC of the multi-function terminal of frequency converter, frequency converter set in the multi-function terminal for speed function, and set the corresponding frequency. By the combination of PLC of the closing and opening, the inverter running under different rotational speed. Advantages: fast response, strong anti-jamming capability. Disadvantages: can't. 2. Through PLC controller and frequency converter, using the communication control. Advantages: can, smooth speed transformation, speed control precision, good adaptability. Disadvantages: poor anti-interference, response latency. 3. Through PLC and d/a, DA） Conversion module, PLC digital signal is converted into voltage ( Or current depending on the frequency converter set) Analog signal input to the inverter control terminal, control frequency converter. Advantages:. Disadvantages: low speed control precision, intuitive; D/a conversion module is more expensive.

inverter input signal includes the run/stop, forward/reverse, micro manipulation, running state switch type command signal. Inverter usually use relay contact or relay contact switch characteristics of components ( Such as a transistor) Connected to the PLC, operation instructions, as shown in figure 1. Figure 1

run signal connection when using relay contact, 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. Inverter input signal of right and wrong wiring, respectively, as shown in figure 2 and figure 3. When the input switch signal into frequency converter, occasional external power supply and frequency converter control power supply ( DC 24V） The crosstalk between. The correct connection is the use of PLC power supply will be outside after a diode in the collector of a transistor to the PLC, as shown in figure 4. Figure 2 inverter input signal access right

figure 3 converter input signal error access

figure 4 outside the collector of a transistor after

diode receiving PLC, there are some numeric signals in the frequency converter ( 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, 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. Inverter is usually through corresponding monitoring terminals to the external output analog signals, the scope of the electrical signal usually is 0 ~ 10 v / 5 v ( Voltage signal) And 0/4 ~ 20 ma ( Current signal) 。 In either case, 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 CPU for data processing need time, there is a time delay, therefore, should be considered when more precise control. Because inverter produces strong electromagnetic interference in the operation, in order to ensure the PLC controller is not due to the inverter main circuit breaker and switch devices such as noise and fault occurs, the frequency converter connected to the PLC when should pay attention to the following: 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 frequency converter. When the power supply condition is not very good, should be the power of the PLC controller module and input/output module of power line noise filter and noise reduction with access to the transformer, etc. , at the side of the inverter also should take corresponding measures. When the frequency converter and PLC is installed on the same operation ark, should as far as possible make lines and related to the frequency converter and PLC on separate lines. Between frequency converter and PLC of the transmission signal cable should be shielded cable or twisted-pair cable, in order to improve the level of noise interference.

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