The correct wiring of PLC is the prerequisite for PLC to function. It is necessary for every power operator to master the wiring of PLC input port and output port.

Generally, the PLC power input terminal is connected with AC220V to provide operation power for PLC. The output power port of PLC is generally DC24V, which is the power output of PLC. During the use of PLC, the correct wiring of input and output terminals is very important, and the correct wiring is the premise of PLC work. Let’s focus on the common wiring types of PLC input and output terminals:

1. Common wiring types and objects for input ports

Figure 1

2. The PLC input port is generally an input port

1. Switching signal: button, travel switch, change-over switch, proximity switch.

Figure 2

A simple example is easier to explain:

The wiring of button or proximity switch is shown as follows: PLC switching value wiring, one end is connected to PLC input terminal (x0, x1, X2, etc.), and the other end is connected to PLC common port (COM terminal).

2. Analog signal:

Generally, there are various types of sensors, such as pressure transmitter, liquid level transmitter, remote pressure gauge, thermocouple, thermal resistance and so on. Different analog signal acquisition equipment, different equipment wire system (two-wire system or three wire system), and slightly different wiring methods

3. Output port wiring

PLC output port wiring can generally be divided into the following three situations: 1. Relay output 2. Transistor output 3. Thyristor output

PLC output mode is different, and the type of power supply connected to the output load is also different. As shown in the figure: This is the basic wiring of PLC input and output, which belongs to the basic knowledge of PLC.

Figure 3

Three common sense in PLC wiring

1. PLC power circuit

In addition to AC power supply, the power supply of PLC control system also includes PLC DC power supply. Generally speaking, PLC AC power supply can be directly supplied by municipal power supply, while DC power supply of input equipment (switches, sensors, etc.) and DC power supply of output equipment (relays), it is best to adopt independent DC power supply. Most PLCs are equipped with 24V DC power supply. Only when the current required by input equipment or output equipment is not very large can the PLC’s own DC power supply be used.

Figure 4

2. Current rating of PLC input and output ports

The input port power supply of PLC is generally DC24V, and the current quota of each point of the input port is between 5ma-7ma. This current is the maximum current generated when the input port is short circuited. When the input port has a certain load, the current flowing through it will be reduced accordingly. The minimum current required for PLC input signal transmission is generally 2mA. In order to ensure the minimum effective signal input current, the total impedance of the equipment connected to the input port is generally less than 2K Ω.

That is, when the sensor power at the input port is large, it needs to be connected to a separate external power supply.

3. Generally, the maximum current that the PLC output port can pass varies with different PLC models, most of which are between 1a and 2A. When the load current is greater than the maximum rated current of the PLC port, it is generally necessary to add an intermediate relay to connect the external contactor or other equipment.

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