Why the PLC can replace the traditional relay and contactor control PLC have what advantage

PLC is very popular, now almost universal in industrial production and the development of science and technology, gradually replaced the traditional contactor control and relay control system, a lot of people can not help but ask: how the PLC to replace the traditional relay control and contactor control system?

PLC has many functional components.

PLC internal many components with different functions, these components are composed of electronic circuits and memory. For example, input relay ( X） Is composed of input circuit and the input image register, output relay ( Y） Is composed of output circuit and output image register, the timer ( T） And counter ( C) , auxiliary relay ( M） , state relay, S） , data register ( D） , the index register ( Ⅴ,Z) Is composed of memory.

in order to distinguish what it and usually hardware components, these components often called soft components, they are the simulation of equivalent abstract element, not the actual physical components. To work in the process, only pay attention to the function of components, according to the function of the components given name, and there are certain address each element number.

1, input relay ( X） ; It is connected with the input terminal of PLC, PLC receives the external switch signals, PLC through the external signal input terminals state read and stored in the input image register. Connected to the input terminals of input relay is photoelectric isolation electronic relay, the moving contact in the PLC program, moving off a lot of a lot of contact.

FX2NPLC input relay the octal address code, for example, such as the Xo ~ X7, X10 ~ X17, X20 ~ X27, etc. Wiring diagram of PLC input signal reference icon below:

as the start button and stop button SB2 SB1 signal to PLC controller, respectively and send its one end to the Xo X1, on the other side on the input side CoM field, can put the button to switch the corresponding signal is sent to PLC. If 0 ff SB1 button state, all contact Xo in the PLC program is to keep the original state, namely dynamic contact remain disconnected, moving off keep close contact. If SB1 button 0 n state, in the program X0 all contact action, which cut off contact, close contact closure.

2, output relay ( Y） ; The output connected to the output terminal of relay with PLC controller, it is the window of the PLC sends a signal to the external load. The output relay is used to output signal is transmitted to the output unit of the PLC, then driven by output unit to external load. In the PLC program output relay coils and contacts. The coil in the process, generally only once, and the contact may not be restricted. Its address number is similar to the input relay, USES the octal number address, such as Y0 ~ Y7, Y10 ~ Y17, Y20 ~ Y27, etc.

when the state of PLC controller program, Y0 coils connected to 0 n, the program Y0 all contacts will be in action, move close contact closure, cut off contact. And in the peripheral circuit ( See the picture above) , Y0 terminals and C0M1 terminals will be connected, Y0 load control by the HL1 work will connect the power supply and light. When the program Y0 coil in the disconnection of 0 ff, program Y0 all contact to maintain the original state, dynamic contact disconnect, dynamic contact closure. And in the peripheral circuit, Y0 terminals and C0M1 terminals will be disconnected, is controlled by Y0 load HL1 did not get through, its light is not on work power control.

learning PLC by a part of the teacher taught mainly by themselves, and the system of PLC of the series of learning. First introduction to feel a bit hard for you, waiting for you to taste it with pleasure, to say the reluctant to go. When studying one step a footprint, from the shallow and deep, from simple to complex, technology is no shortcut

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