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 now be looking at simple data logging using a Click PLC with an Ethernet port. Node-RED will be used to communicate to the controller via Modbus TCP protocol. Information collected will be then stored in an SQLite SQL database. A Raspberry Pi 4 single-board computer will be used for the Node-RED collecting and storing. The update time will be two times a second (500 mSec). This method is ideal for quickly determining how things are operating.
Analysis or display of the information will be done with a spreadsheet. The spreadsheet will be run on a windows computer. 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.
We will now be installing Node-RED on a Raspberry Pi 4 single-board computer. A static IP address will also be given for both the WiFi and Ethernet connections.
The Raspberry Pi has quickly become a fixture in the industrial environment when utilizing the internet of things. (IoT) We will be utilizing this low-cost computer to poll and log information from our PLCs using Modbus and MQTT protocols. Node-RED will be the IoT enabling software that will allow us to utilize this hardware.
Let’s get started with installing Node-RED and setting up a fixed IP address on our Raspberry Pi 4 computer.
Node-RED HTTP Request can be used to read any BRX Do-More PLC memory area. This HTTP (Hypertext Transfer Protocol) communication will only read information from our controller.
The BRX Do-More REST API is used to read information using a URL (Uniform Resource Locator) or web address. We will be using the HTTP request node in Node-RED to read information from our BRX Do-More REST API-enabled controller. Writing using Modbus will also be shown. This will all be done on our Raspberry Pi 4 single-board computer. Let’s get started.
We will now look at the connection to our SQL database using a spreadsheet application. Previously we used Node-RED to communicate Modbus TCP and RTU to our Click PLC and Solo Temperature Controller. The information collected from the controllers was then put into an SQLite SQL database.
Spreadsheets like Excel are great for analysis of the data. We will be connecting to our SQLite SQL database with WPS spreadsheets. This will be accomplished by using an ODBC driver as the translator between the database and spreadsheet. Let’s get started.