, when many beginners just learned PLC , they didn’t know how to use PLC to control the equipment, why such wiring and control methods are needed. Here, the editor uses PLC control by transforming the "double interlocking forward and reverse circuit" An example to explain how to transform a traditional electrical circuit.
First we look at the traditional circuit, as shown in the figure below.
double chain forward and reverse circuit diagram
Which part of the circuit does the PLC transform? Transform the control circuit, as shown in the figure below after the transformation.
The main circuit has not been changed. The control circuit uses a 24V switching power supply. The function of the 24V switching power supply is to convert the input 220V AC power into a DC 24V power output, mainly to supply 24V electrical equipment. . The PLC connection is connected according to the standard wiring diagram in the 200smart sample manual. Here, the stop button SB3 is connected to normally closed. The advantage of connecting to normally closed is that it is convenient to check whether there is any disconnection in the circuit. If it is disconnected, it will stop the device. Play a protective role, if you say that you are using a normally open, there is a disconnection in the line, because only when the stop button is triggered can you know whether the button can form a loop, so such equipment is very unsafe and may be Cause personal safety and damage equipment. Because ST40 is a transistor type output, it is necessary to use the output point to control the 24V intermediate relay , the 24V intermediate relay then controls the AC contactor , the AC contactor controls the start and stop of the motor, this is the method of small current control large current .
When the PLC program controls Q0.0 output, the KA1 intermediate relay coil is closed, KA1 in the control circuit is normally open, KM1 contactor coil is closed, KM1 auxiliary normally open and main contact are closed, KM1 auxiliary normally closed open. When the KM1 main contact in the main circuit is closed, the motor is forwarding. If the output principle of Q0.1 is the same, when the main contact KM2 in the main circuit is turned on,The motor reverses. The normally closed of KM1 and KM2 in the control circuit is an interlock for safety. If your program is not written correctly and the device is output at the same time, it will be a problem, so the external hardware should be protected. The main function of
IO table is to draw wiring diagrams, write programs, annotate programs, read programs, and equipment selection.
I/O table
The program in the PLC is written according to the control circuit. Here, the stop and thermal relay contacts are normally open, because the external wiring is normally closed and not triggered When the button is pressed, the corresponding channel has a signal, so a normally open contact is required for disconnection.
Finally, to summarize, the electrical equipment is transformed into PLC control, the corresponding button signal is connected to the output of the PLC, and the control equipment is selected according to the type of PLC. Here, because the transistor output can only be connected to 24V Therefore, it is necessary to use a 24v intermediate relay to control the AC contactor, so as to achieve PLC control of the motor.
(original of Jicheng Training Network, author: Zou Zhirui, no reprint without authorization, offenders must be investigated)
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