PLC control motor forward stop and reverse control control system design case

According to the main circuit of the three-phase AC motor forward and reverse control in the figure below, design a PLC control system for the motor forward, stop and reverse. The control requirements are as follows: (1) Under normal circumstances, press the start button SB1, the motor rotates forward, and press the reverse start button SB2, the motor rotates reversely. (2) After the motor starts, press the stop button SB3 and wait for 5 seconds before changing the direction of rotation of the motor; (3) If SB1 and SB2 are pressed at the same time, the motor stops rotating and does not start, and the alarm light L1 flashes continuously for 1 second on and 1 second off. At this time, press the stop button SB3 to reset.

First, let's determine the use of auxiliary contacts for buttons and KM. This is the main circuit for forward and reverse rotation. The main circuit must have an interlocking circuit. Other buttons use normally open contacts. The following is a table of PLC input and output points:

Programming according to question (1): Here, according to question 1, only two self-holding circuits are needed.

Question (2) requires that the motor direction can only be changed after pressing the stop button for 5 seconds, so a flag needs to be set here, and M0.0 is used here. And a program interlock circuit is added, as follows:

First, add an interlocking circuit to the two self-holding circuits - the normally closed point of Q0.1 in network 1 and the normally closed point of Q0.0 in network 2. Question 2 says that the start button can only be pressed 5 seconds after the stop button is pressed, so after the I0.2 stop button is pressed in network 3, M0.0 is energized and self-held. After timer T37 counts for 5 seconds, the self-holding circuit of M0.0 is stopped. And add the normally closed point of M0.0 in network 1 and network 2, so that when M0.0 is energized, network 1 and network 2 will not energize Q0.0 or Q0.1 even if the forward or reverse button is pressed. Question (3) requires that SB1 and SB2 are pressed at the same time, the motor stops rotating and does not start, and the alarm light L1 flashes continuously for 1 second on and 1 second off. Program as follows:

This time, network 4/5/6 is added. Network 5 and 6 are small programs that use two timers to generate a one-second pulse. SM0.0 is a special bit, and its function is to always be powered. Network 4 uses M0.1 to lock network 1/2/3, which means that when M0.1 is powered, network 1.2.3 will not work. The principle is the same as M0.0 in the previous summary. The above is all the programming for this example. As the saying goes, a tall building starts from the ground. If you ask me to program it all at once, I will find it difficult. However, if you split the question bit by bit and write the required functions bit by bit, you will definitely be able to meet your needs in the end. Finally, see how much the finished program differs from the original program?