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 CAN A SCALE 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 TO PLC

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

The Analog Output utilizes voltage and current signals to communicate quantities (such as weight) to programmable logic controllers and chart recorders. Analog Output comes in two configurations: Current or Voltage output. Voltage Output signals can be 0-5VDC, 1-5VDC, 0-10VDC scalable. Current Output signals can be 4-20mA and 0-20mA scalable.

In terms of integrating a scale to a PLC using analog output, understanding how the analog output module works on your PLC is a crucial step. This module is responsible for receiving analog signals from the scale and having PLC re-interpreting it back to weight.

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. The PLC will also need to be calibrated to match the scale’s weight capacity. This way the PLC will know the signal value corresponding to the minimum and maximum weight reading of the scale (e.g. 4mA = 0 lb, 20mA = 1000 lb).

It is also important to know whether the PLC’s analog output module accepts self-powered analog outputs, line powered or loop powered analog outputs.

For more information on the differences of each of these signal types and various other documentation, visit the Wiring Diagrams section in User Manuals and Specifications page.

Arlyn Scales supports all kinds of analog output configurations. Contact us for more details.

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 ASCII/RTU and TCP

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 MODBUS communication 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.