Complete PLC Wiring Diagram with SMPS, Relay Card, Contactor

Hey, in this article we are going to see the complete PLC wiring Diagram and Connection with SMPS, Relay Card, Contactor, Input Devices(such as sensors, and switches), Output Devices, Motor, VFD, and other networking or communicating devices such as PC, HMI, Router, Network or Internet, etc. You may not need all these connections but you can get ideas for all the possible connections for the PLC. So whatever you require you can make your wiring.

PLC means Programmable Logic Controller. It is basically a processing or automation system built with a central processor and some input and output devices. The processor takes input from the input devices and after processing, it generates outputs and sends them to the output devices. PLC systems are used in so many places such as industrial automation, transportation systems, security system, traffic light control, and many more places. Anyway in this article, our main focus is to control electrical motors using PLC.

Wiring Diagram

Here, you can see the wiring diagram and connection of PLC.

Connection Procedure

PLC Connection with Input Devices for Different Modes

PLC operates in two modes Sinking and Sourcing Modes. These are also known as NPN or PNP  modes. In the Sinking or NPN mode, a negative supply is common whereas, in the Sourcing or PNP mode, a positive supply is common.

In the above wiring diagram, the PLC operates in Sinking or NPN mode. That is why the negative terminal from the SPMS is directly connected to the PLC Common terminal for Digital Input and Ground Terminal for Analog Input.

Switch Connection

Switches are to be connected to the PLC Digital Input Terminals. For the NPN mode connection, the positive terminal from the SMPS is to be connected directly to the Switches and the output from the switches should be connected to the digital input terminals.

Sensor Connection

Here, we have connected a Speed Sensor(It may be an NPN proximity sensor). So the negative terminal from the SMPS is connected to the negative(blue) terminal of the sensor and the positive terminal of the SMPS is connected to the positive(brown) terminal of the sensor. The output terminal(black) of the sensor is connected to the Analog Input terminal of the PLC.

How to connect PLC with SMPS

Some PLC Modules come with inbuilt SMPS and they are designed to operate with 120V or 230V AC supply. But most of the PLCs are designed to operate with a 24V DC power supply and need an external power supply for their operation. So, an external power supply can be provided to the PLC by using a 24V SMPS. So connect the 24V output power supply from the SMPS to the PLC Module using a power connector whatever it supports.

PLC Connection with Output Devices

The output connection of the PLC also has two types - NPN and PNP. Here, in the above wiring diagram, all the outputs are connected in PNP mode. The 24V positive terminal is directly connected to the PLC unit and the negative terminal of all the output devices is connected to the negative terminal of the SMPS.

PLC and Relay Card Connection

Here, we have used a five-channel relay. We can short all the positive terminals or all the negative terminals in the relay card using a jumper connector. Here, we have shorted only three relays by the negative terminal. The negative terminal of the relay is connected to the negative terminal of the power supply(SMPS) and the positive terminal of the relay is connected to the digital output terminal of the PLC.

PLC and Contactor Connection

If your contactor has a 24V DC coil and its current rating matched the PLC current rating then you can directly connect to the PLC module. This connection will similar to the relay card connection. But if your contactor has a high voltage coil such as here 230V AC coil then you need to connect the contactor with PLC through the Relay card.

One terminal (here neutral terminal) of the Contactor coil is to be directly connected to the power supply and another terminal is to be connected to the NO terminal of the relay card. And one terminal of the power supply(here 230V phase) is to be connected to the common terminal of the relay card. So when the PLC operates the Relay card by providing a 24V DC supply the relay card will operate so the Contactor coil will get energized by the power supply connected to it.

PLC and VFD Connection

VFD takes digital inputs for its Start/Stop, Forward, and Reverse operations and sometimes for frequency varying. So the digital output of the PLC is to be connected to the Digital input of the VFD for its Start/Stop, Forward, and Reverse operations. So before connecting identify the proper terminals on the VFD and read the manual carefully. Because different models have different specifications and terminal identifications.

The Analog input of the VFD can be connected to the Analog output of the PLC, so PLC can send an analog signal to the VFD to vary the speed or frequency.

The analog output of the VFD also can be connected to the analog input of the PLC so the VFD can send the motor running status to the PLC through an analog signal.

PLC and VFD also can be connected using an RS485 connector for serial communication. Even modern VFD and PLC module supports RJ45 Connector also.

How to connect PLC with Networks such as the Internet

PLC can be connected to the local network or the Internet by connecting a router to it. And the Router can be connected to the PLC using RJ45 connectors and an ethernet cable.

How to Connect PLC with HMI or PC/Laptop/Computer

PLC can be interfaced with HMI using RS485 Connectors. Similarly, PLC can be connected to a PC/Laptop/Computer using RS485 Connectors or RJ45 connectors. If your computer does not have an RS485 port then you need USB to RS485 converter.

Read Also: 

• VFD Wiring Diagram with Motor, Switches, and External Devices
• Automatic Water Pump Control with Moisture Sensor Circuit Diagram
• Submersible Pump Starter and Water Level Controller Wiring Diagram
• Soft Starter Wiring Diagram and Connection Procedure
• Automatic Water Pump Control with Moisture Sensor Circuit Diagram

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