Relay control circuit and PLC controller
ladder diagram, rounding 1, inching circuit function is introduced: as the name implies: the point is, the pine is motionless, or press the button to open, loosen the stop button 2, equipped with automatic stop holding circuit (
, function introduction to maintain a basic form of circuit state, is mainly used to keep the external signal status
, the working principle of normally open button boot = 0 to relay coil J0 to electricity, Lord J0 normally open contact closure - motor electric start-up, J0 normally open at the same time auxiliary contact self-locking and motor continues to run, as shown in figure 2-3
= normally closed button 1 downtime to relay coil J0 lost electricity, at the same time J0 auxiliary contact disconnect and motor electrical outages, as shown in figure 2
, circuit applications let's compare before and after the relay coil an unpowered and electricity: 02 relay control circuit is converted into a PLC
ladder diagram method relay contactor control system through long-term use, can have a complete system requirements and validated the control function of the control circuit diagram of the PLC control of ladder diagram is similar to relay contactor control circuit diagram, therefore, can be directly validated relay contactor control circuit diagram is transformed into ladder diagram.
The main steps are as follows: 1, familiar with the existing relay control circuit 3, the relay circuit diagram of intermediate relays, timers, with PLC of auxiliary relay, timer instead.
4, draw all the ladder diagram, and simplification and modification.
this method is of simple control system is feasible, more convenient, but more complex control circuit, it is not applicable.
Case 1 】
Y/delta decompression for motor starting control of main circuit and electric control principle diagram.
1, the working principle is as follows: press the start button SB2, energized KM1, KM3, KT and self-preservation, into Y type starter motor, 2 s, KT action, make KM3 blackouts, KM2 electric suction, motor into delta type operation.
Press the stop button SB1, stop running motor.
Y/delta decompression starting control main circuit of the motor and the principle of electrical control diagram 2, I/O distribution input and output stop button SB1: I0.
0 KM1: Q0处。
0 KM2： Q0.
Start button SB2:1 '.
2 overload protection FR: I0.
2 3, ladder diagram program after the conversion of ladder diagram program is shown in figure 2.
According to the grammatical rules of ladder diagram language simplified and modified ladder diagram.
In order to simplify the circuit, when more than one coil are all controlled by a series-parallel circuit, the circuit can be installed in the ladder diagram, control the storage such as M0.
As shown in figure 3 - simplified program
Case 1 ladder diagram program 3 -
Case 1 simplified ladder diagram program there are often many electrician in learning PLC much don't know why, the relay control, the PLC ladder diagram is not, in fact this is thinking.
Because PLC controller
ladder diagram is in principle by relay circuit transformation, relative to the relay circuit is more concise and clear, logical, and more readable.
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