PLC input and output wiring diagram

The input circuits of various PLCs are roughly the same, and there are usually three types. One is DC 12~24V input, another is AC 100~120V, 200~240V input, and the third is AC/DC input. External input devices can be passive contacts or active sensor inputs. These external devices must be connected to the PLC through the PLC terminals and form a closed active loop, so power must be provided.

1. Wiring of passive switch

FX2N series PLC only has DC input, and inside the PLC, the input terminal is connected to the positive pole of the internal 24V power supply, and the COM terminal is connected to the negative pole, as shown in Figure 1. In this way, its passive switch input does not need to provide a separate power supply. This is very different from other types of PLCs. When using other PLCs in the future, you must pay attention to reading their instructions carefully.

2. Wiring of proximity switch

A proximity switch refers to a switch sensor that needs a power source to drive itself and outputs a certain voltage or current. There are many types of switch sensors based on their principles, which can be used for detection in different occasions, but they can be divided into three categories based on their signal lines: two-wire, three-wire, and four-wire. Among them, the four-wire type may provide a make contact and a break contact at the same time, but only one of them is used in practice; or the fourth line is the sensor verification line, which will not be connected to the PLC input terminal. Therefore, no matter which situation, the three-wire wiring can be referred to. Figure 2 is a schematic diagram of the connection between PLC and sensor.

The two-wire type has a signal line and a power line. The three-wire type has the positive and negative poles of the power supply and the signal line. Wires with different functions are represented by different colors. There are different ways to define this color. Please refer to the relevant instructions when using it. Figure 2(b) shows a common color definition. When the signal line is black, it is a make type; when the break type uses a white wire.

The sensor shown in the figure is NPN type, which is a common form. For the connection of PNP type sensor and PLC, you cannot copy this connection and refer to the corresponding information.

3. Wiring of rotary encoder

Rotary encoders can provide high-speed pulse signals and are often used in CNC machine tools and industrial control. Different types of encoders have different output frequencies and phases. Some encoders output three-phase pulses A, B, and C, some only have two-phase pulses, and some only have one-phase pulses (such as phase A). The frequencies are 100 Hz, 200 Hz, 1k Hz, 2k Hz, etc. When the frequency is relatively low, the PLC can respond; when the frequency is high, the PLC cannot respond. At this time, the output signal of the encoder must be connected to a special function module, such as the FX2N-11C using the FX2N-11HC high-speed counting module.

4. Mitsubishi PLC terminal wiring diagram

In engineering practice, it is impossible for all input and output devices to be directly connected to the PLC. Moreover, multiple output terminals of the PLC share a common COM terminal, and it is impossible to connect several or even dozens of wires to one terminal, so they must be connected through terminal blocks.

The terminal block is usually composed of multiple terminals installed side by side on the guide rail. The two ports of each terminal are short-circuited, and the terminals can be short-circuited together as needed.