The PLC control principle is introduced at -

To popularize the inching control principle of PLC, easy to learn technical knowledge.

so, everybody please see below, as shown in figure 1:

first of all, what is inching control? You look at the picture 2:

this is a traditional control circuit, this circuit it is divided into: the main circuit and control circuit.

1, the main circuit are: QS ( Circuit breaker) 、FU( The fuse) 公里( Contactor main contact) M（ Motor) . 2, control circuit (

Also known as the auxiliary circuit) By FU (: The fuse) 某人( Normally open contacts) 公里( Contactor coil) Composition.

everybody, look at the following diagram, as shown in figure 3:

when working in the circuit, we press the button SB1, contactor coil electricity, armature and the three of the main contact closure, motor starts on three-phase power supply is go, when we release the button, contactor coil power, motor power stop running, this kind of control mode we call dynamic control points. It is mainly used for lifting equipment, fixed-point mobile control, as well as the production equipment debugging, in our actual application, the contactor control circuit is relatively large, the mechanical games for a long time results in the decrease of the reliability of the button, contactor and other components, the use of contact is limited, if we want to change the control function of the circuit are also required to build, the workload is bigger and error-prone, are these deficiencies, we cite PLC to realize, so what is a PLC?

please take a look at this chart, as shown in figure 4:

here we FX2NPLC mitsubishi company production, for example: there are so many screws on the left is the PLC signal input point X is mainly suitable for buttons, switches, sensors, etc. The input signal. On the right side of the block, it is Y, PLC controller output point to external contactor, solenoid valves, lights, alarm output devices such as signal, there is the CPU and memory, main is to control the internal parts of the system as a whole, coordinate system, and the function of store programs and data. If change control function, only need to modify the internal program, don't need to go we readjust the external circuit, in order to facilitate our debugging, hardware and less error, the use of PLC relay internal program is not restricted. Then we use the PLC how to implement the inching control?

everybody below, as shown in figure 5:

normally open button SB1 received the PLC input point X1, when we put the SB1 button input circuit is connected, the X1 will get an IO signal, the X1 IO signal to the PLC internal operations, it outputs a signal, the output signal will output loop through to Y1, KM1 coil electricity, corresponding to the main circuit of KM and main contact.

we look at the following diagram, as shown in figure 6:

and we compare the above diagram. Inside the PLC is to control the operation according to what?

we looked down again, as shown in figure 7:

we look, on the left side of the vertical bar is the left bus bar and the right that is the right bus, bus we can paint is not right, we are supposed to do bus to connect power of the anode, the right bus to connect power of the cathode, input relay X1 is set in the form of a normally open contact, serial output coil Y1, when the X1 is equal to NO state, like the circuit connected between the two bus bar, we can think of a hypothetical current flows through the circuit.

see below, as shown in figure 8:

coil conductance through, you see, the upper right corner of the ladder diagram the red thread, the corresponding Y1 contact ( Coil) Will, in the main circuit contactor KM1 is main contact and motor's work. See? Left KM1 main contact and, become a straight line, at the same time turned red prove to electricity, when we release button, then at the following figure.

as shown in figure 9:

figure is a little bit more, main is to want to let everybody understand understand.

as shown above, we loose button, that is to say, the X1 is OFF when the bus between the circuit broken, Y1 coil power, main contact reset disconnect, motor will stop losing electricity work. Inching control design is completed, we put the design of this figure is called 'ladder diagram', that is the internal of PLC control. Finally we use GX simulation software to design good write into the PLC ladder diagram.

as shown in figure 10:

connection good external power supply circuit of X and Y, press the start button, motor start, loosen the button of the motor stop working.

here, to realize the function of electric control.

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