Introduction of PLC input port and output port wiring and common wiring types

At present, PLC is a centralized control device with a very high usage rate in industrial production and automation control. PLC replaces heavy relay cabinets, AC contactor cabinets, etc., and is gradually popularized in production and control. In the design of PLC control system, although the proportion of wiring work is small, most of the work is PLC programming and design work, but it is the basis of programming and design, as long as the wiring is correct, the programming and design work can be carried out smoothly. The correct wiring of PLC is the precondition for PLC to function, and it is necessary for every electric power operator to master the wiring of PLC input port and output port.

Under normal circumstances, the PLC power input terminal is connected to AC220V to provide the PLC with running power. The PLC output power port is generally DC24V, which is the power output of the PLC. During the use of PLC, the correct wiring of input and output terminals is very important, and correct wiring is the premise of PLC operation.

Let's focus on analyzing the common wiring types of PLC input and output:

First, the common wiring types and objects of input ports:

PLC input ports are generally input:

1. Switch signal:

Buttons, travel switches, transfer switches, proximity switches, DIP switches and more.

PLC switch value wiring, one end is connected to the input end of the PLC (X0, X1, X2, etc.), and the other end is connected to the PLC public port (COM end) together.

2. Analog signal:

Generally, various types of sensors, such as pressure transmitters, liquid level transmitters, remote pressure gauges, thermocouples and thermal resistances, etc.

The analog signal acquisition equipment is different, the equipment wiring system (two-wire system or three-wire system) is different, and the wiring method is also slightly different. as the picture shows:

Second, the 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. This is the basic wiring of PLC input and output, which belongs to the basic knowledge of PLC.

Three, three common sense in the PLC wiring process:

1. PLC power supply circuit.

In addition to the AC power supply, the power supply of the PLC control system also includes the PLC DC power supply. Generally speaking, the PLC AC power supply can be directly supplied by the mains, while the DC power supply of the input devices (switches, sensors, etc.) and the DC power supply of the output devices (relays) Power supply, etc., it is best to use an independent DC power supply. Most PLCs have their own 24V DC power supply. Only when the current required by the input device or output device is not very large, the PLC's own DC power supply can be used.

2. Current rating of PLC input port and output port.

The power supply of the input port that comes with the PLC is generally DC24v, and the current rating 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, its current The passing current 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 ohms.

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

3. The maximum current that the PLC output port can pass varies with the PLC model. Most of them 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 external contactors or other devices.

The correct wiring of PLC is the premise of the effective operation of PLC, and it is also the basic skill of PLC. It is very necessary to master the common sense of PLC wiring.