PLC Communication refers to the exchange of data between programmable logic controllers (PLCs) and other devices. It is an industrial-grade digital computer designed for control functions in various industries. It replaces older technologies like electromechanical relay systems. PLCs are modular, allowing users to add features like discrete and analog inputs/outputs, PID control, motor control, and more. One of the advantages of using the PLC is they are easier to troubleshoot, maintain, and cost-effective compared to relay banks.

How a Scale Can Help With PLC Applications

Our weighing scales play a crucial and significant role in enhancing PLC applications in several ways. Weighing scales integrated with PLCs can provide precise measurement at high speeds, which is essential to many industrial processes.

METHODS OF COMMUNICATING THROUGH PLC

Analog Output 4-20 mA, 0-5 VDC, 1-5 VDC

The Analog Output is utilized for communicating with programmable logic controllers and chart recorders. The setup menu offers full configuration options, allowing you to set the start and end currents or voltages. The Analog Output comes in two configurations: Current and Voltage output. Voltage Output: 0-5VDC, 1-5VDC scalable Current Output: 4-20mA scalable

In this section, we will try to understand how to communicate the PLC through Analog Output.

Understanding the analog output module on your PLC is a crucial step. This module is responsible for sending analog signals from the PLC to the external devices, making it a key component in successful communication.

Choosing the right signal type is a critical decision. Whether it’s 4-20 mA, 0-5 VDC, or 1-5 VDC, this choice directly affects the communication process.

You will write a program in the PLC to send the desired analog signal to the output module. This could involve setting a specific voltage or current level or more complex control algorithms.

Thorough testing is essential to ensure the PLC is correctly controlling the device through the analog output. This step guarantees the functionality of the system.

RS-232

RS-232 is a standard communications protocol used to transmit data from one computerized equipment to another. In the digital scale world, RS232 is utilized to communicate with printers, programmable logic controllers, and computers. Arlyn’s RS232 Option is a bi-directional interface that enables the Scale Indicator to both send data and receive commands from computers and other devices, providing full remote capability.

To communicate your PLC with RS-232, please make sure your PLC is powered on and that your PC is ready to install the necessary software.

Use an RS-232 cable to connect the PLC to your PC. Most computers and PLCs are DTE (Data Terminal Equipment) devices, so you will typically need a DTE-to-DTE interface cable also known as null-modem, model-eliminator, or crossover cable.

In addition, relating to RS-232 parameters, both PC and PLC must be set to use the same configuration for serial communication. This includes the following parameters like Baud Rate, data bits, handshake mode, number of start bits, number of stop bits.

Finally, once everything has set-up, you can test the connection by sending a command from you PC to the PLC and checking if the PLC responds correctly.

MODBUS

Arlyn Scales now offers Modbus Communication Protocol for scales equipped with the Arlyn UpScale Touchscreen Indicator. Modbus is a data communications protocol originally published by Modicon (now Schneider Electric) in 1979 for use with its programmable logic controllers (PLCs). Modbus has become a de facto standard communication protocol and is now a commonly available means of connecting industrial electronic devices.

The general way to set up the Modbus is firs is to make sure your PLC is powered on and your PC is ready with necessary software installation

Use a Modbus cable to connect the PLC to your PC. In addition, the PLC must be equipped with Modbus driver or a module supporting the Modbus protocol to communicate with Modbus driver.

Both PC and the PLC must be set to use the same configuration for Modbus communications.

Finally, once everything is setup, you can test the connection by sending a command from your PC to the PLC and checking if the PLC responds correctly.

Modbus address space is divided into four groups. Each group is defined by the data type that can be stored in it and its read/write permissions such as Coils, Discrete Input, Input Resister, and Holding Register.

EtherNet/IP

EtherNet/IP also known as Ethernet Industrial Protocol is a popular industrial network protocol that allows for high-speed data transfer and efficient exchange of critical control data across devices and systems . It is used in PLC communication systems and offers several advantages such as High-Speed data transfer, consistent communication, support of various devices, integration with other protocols, explicit and I/O messaging.

To set-up PLC communication via EtherNet/IP, you typically need to configure the IP address, Subnet mask, and default gateway according to you network settings. You will need to use specific software, such as SST configuration software for configuring and maintenance.

PROFINET

PROFINET also known as Process Field Net is an industrial communication standard for an industrial control system. Its often used for communication between a PLC and various devices.

Each device in a PROFINET network, including the PLC, is assigned a unique IP address and device name. This allows the PLC to identify and communicate with each device.

PROFINET supports real-time (RT) and isochronous real-time (IRT) communication which allows for precise synchronization and and fast response time, which are crucial in automation systems.

PROFINET provides comprehensive diagnostic information. This allows the PLC to monitor the status of all devices in the network and quickly identify and faults.

With each of the methods for the scales communicating with the PLC, all of them will vary depending on the PLC model, software, and network you are using. Always refer the the user manual or contact the manufacturer’s customer support for model-specific instructions.