We will be using an MQTT broker in Node-RED to communicate to the productivity PLC clients. MQTT stands for Message Queuing Telemetry Transport. This simple ‘publish and subscribe’ communication protocol does not take too many resources.
Constrained devices with low bandwidth are ideal for MQTT. This protocol provides machine-to-machine (M2M) connectivity, perfect for the Internet of Things. (IoT) This protocol is not for remote IO or real-time (deterministic) applications. MQTT is a good solution for applications that move data from hundreds or thousands of machines (sensors) to clients in many networks.
We will be installing and programming the AEDES MQTT Broker in Node-RED. A productivity P2000, P1000, and Node-RED will be the clients communicating to the broker. The PLC simulator inputs on each controller will control the outputs on the other controller. This will demonstrate the communication capability for publishing and subscribing to this IoT platform. Let’s get started.
A human-machine interface (HMI) is present in some form for every PLC. The HMI connects a user to a machine system to exchange information or control data. This interaction with the system can be through hardware or software.
HMIs offer different people information and control in many ways for the automated system. Operators, supervisors, mechanics, electricians, engineers, and programmers all have different needs. The machine HMI(s) must provide or make the information easy for all the people who use the system.
We will now look at some of the ways that human-machine interfaces (HMI) are used in automated systems today. Let’s get started.
All Solo Standard Process Temperature Controllers that support RS-485 serial communications can use the SL-SOFT configuration and monitoring software. This free package will communicate to monitor multiple SOLO controllers using Modbus RTU or Modbus ASCII protocols.
We will be installing the SL-SOFT configuration and monitoring software package on our Windows 10 PC. Communicating through our Waveshare USB to RS485 adapter, Modbus RTU will be used as the protocol to establish communication. Let’s get started.
Node-RED will be used on the Raspberry Pi 4 to communicate serial Modbus RTU to a Solo process temperature controller and Click PLC using twisted pair RS485. This will be done on the same serial network so the devices will be daisy-chained together on the two wires.
We will be reading the PV (present value) and SV (set value) of the Solo temperature controller and then writing these values into the Click PLC. An SV value will then be read from the Click PLC and if it has changed, the value will be written to the SV of the Solo controller. Let’s get started.
Node-RED Modbus TCP can recover from communication errors automatically. Options are available to you the programmer to continue the Node-RED flow upon detection of these errors.
Broken Ethernet cable, Modbus Server power, and Node-RED Client offline are just a few of the errors that can occur on the industrial plant floor. Our Node-RED program must account for and be tested for each of these conditions.
We will be communicating Modbus TCP (Ethernet) to our Click Plus PLC. Using the catch node we will detect and display errors that may occur. Let’s get started.
We will be installing an industrial USB to RS485 converter on our computer. The Waveshare USB to serial port is a 2-wire USB to RS-485 serial communication adapter for RS485 use. It does not require an external power supply or complicated configuration.
It has a Type A (plug) USB connector for the computer side and screw terminals for the RS485 connections. This is an industrial USB to RS485 converter that has an FT232RL chip inside. It features embedded protection circuits such as lightning-proof, resettable fuse, ESD (Electrostatic Discharge) protection, and TVS (Transient Voltage Suppression) diode, etc. All of these features are packed within a small form size.
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We will be installing the driver for this USB to serial converter and connecting it to our computer. Node-RED will be used to communicate Modbus RS485 protocol to a Solo process temperature controller. Let’s get started.