It's difficult to PLC programming? Instance to explain how the PLC programming simplification -

According to the chart of the three-phase ac motor and reversing control of main circuit, design a control system of PLC controller control motor is stopped. Control requirements are as follows:

1) Under normal circumstances, press the start button SB1, motor forward, reverse start button SB2, motor reversal.

( 2) After motor start, press the stop button SB3 and wait for 5 seconds later, can change the direction of rotation of the motor;

( 3) If the SB1 and SB2 press at the same time, the motor stop running, and don't start, at the same time alarm light L1 on 1 second dark flashing 1 SEC. Press SB3 stop button to reset at this time.

first we confirm button, use the auxiliary contact situation of KM, there is a positive &negative main circuit, main circuit must have an interlock circuit, the other button with normally open contacts.

it's PLC controller input and output point table:

according to the question ( 1) Programming: according to the question 1 here, and just over two since the hold circuit can be.

the question 2 for 5 seconds press the stop button to change the direction of motor, so there should be a flag bit in the set, here use M0. 0.

and interlock circuit and program, specific as follows:

in the first two since added to keep the loop interlock circuit - — Networks 1 Q0. 1 normally closed point, Q0 and network 2. 0 normally closed. Question 2 say 5 seconds after press the stop button, can press the start button, so the network 3 press I0. 2 after the stop button, M0. 0 to keep, timer T37 timing after 5 s, M0. 0 loop since hold off. And M0 are added into the network 1 and 2. 0 normally closed point, M0. 0 to electric network 1 and 2 even when pressing the forward button or reverse button didn't make Q0. 0 or Q0. 1 have to electricity.

the question 3 for SB1 and SB2 press at the same time, the motor stop running, and don't start, at the same time, the alarm light L1 on 1 second dark flashing 1 SEC. Programming is as follows:

this 4/5/6 increased network, network 5 and 6 is to use two timer to produce a small program for a second pulse, SM0. 0 for special, its function is always have electricity. Networks are 4 using M0. 1 will network 1/2/3 lock, that is to say, M0. 1 have to electric network. 2. 3 is not effective. A summary on its principle and M0. 0.

above all the programming is the instance. Is the so-called great oaks grow from little acorns, if you call small make up a breath made up, small make up also is very difficult. However, the question a little break up, a little to write the function of the required, finally certainly can satisfy your heart. Finally you see make up the program and the initial difference how much

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