Node-RED PLC Example

Node-RED web browser example of using python to communicate to Allen Bradley PLCs. Deployed on Raspberry Pi 2 with Raspbian Buster OS and with pylogix and pycomm3 open source libraries.

This is adapted version of the Node-RED pythonshell example, which made creating this project easy.

Required software for this example (try getting the latest versions):

• Node-RED and python3
  • On Debian/Ubuntu systems, you might need to install python3-venv package
• pylogix and pycomm3 will be installed by the flow (internet connection will be required until installed)

Required additional Node-RED packages (use "Manage Palette" option from within Node-RED to install, internet connection required until installed):

• node-red-dashboard
• node-red-contrib-pythonshell
• node-red-contrib-ui-artless-gauge

Optionally install any other Node-RED packages (like ui_level ; lineargauge ; ... etc).

Raspberry Pi 2 was used for this example but any other network enabled hardware, capable of running Node-RED and python3, should work as well. Linux operating systems, like Ubuntu, do have Node-RED package available.

Node-RED Screenshots

Setup Flow

Dashboard 1

Dashboard 2

Functionality

• Discover Devices on the network (this is using pycomm3 library).
• List ControlLogix PLC tags including UDT members (this is using pycomm3 library).
• Read ControlLogix tags and display their values in the dashboard (this is using pylogix library).
• Read SLC500 / MicroLogix tags and display their values in the dashboard (this is using pycomm3 library).
• Tags can be entered as either of:
  • Single tag, ex: CT_DINT
  • Multiple semicolon separated mixed tags, ex: CT_DINT; CT_REAL; CT_3D_DINTArray[0,3,1]{5}.
• Reading multiple elements of an array requires the following tag format:
  • tagName[startIndex]{elementCount}:
    • tagName should be the correct name of the tag as it is in your PLC program, a name like:
      • CT_DINT or CT_REALArray or My_INT
    • startIndex is the starting array index, which depending on array dimensions could be either of:
      • [x] or [x,y] or [x,y,z]
    • elementCount is the number of consecutive elements to read, for example:
      • CT_REALArray[0]{15} - this will request 15 elements starting at [0]
      • CT_DINTArray[0,1,0]{7} - this will request 7 elements starting at [0,1,0]
• The above tag rules are also generally applicable to SLC500 / MicroLogix, ex: N7:0 or N7:0{3}
• Automated or manual process for flow lines with pythonshell nodes
• Node-RED web browser access is generally via IP address of your device + the port, ex: 192.168.1.17:1880.
• Node-RED Dashboard web browser access is generally via IP address of your device + the port + ui, ex: 192.168.1.17:1880/ui.
• Debug nodes can be disconnected once you know that everything works.

Usage

• Install Node-RED, the required nodes and python3:
  • Additionally, python3-venv might also need to be installed
• Copy the Setup Flow.txt file's content to the clipboard and import it to Node-RED (just paste it)
• Make sure to read the comments and setup correct values for your IP Address / Processor Slot (Micro800 option is for pylogix only)
• Follow the flow from top to bottom and execute each line by using the inject button:
  • The indicator of success or failure of each step will be in the "Debug" window
  • Exercise patience before proceeding to the next line, especially while pylogix/pycomm3 packages are being installed since it might take a little while.
• Optionally, automate the Device Discovery / Tag Listing by checking the Inject once after option of the inject node
• Optionally, automate the Tag Reading by checking the Inject once after option (1, 2, 3 seconds respectively top to bottom) of the inject nodes and setting their Repeat option to interval (3, 3, 3 seconds respectively top to bottom):
  • Try using different intervals until you find the one that works the best for you
• More lines for tag reading can be added by following the existing pattern
• You can also remove whatever you want from the flow (like SLC500 / MicroLogix section if you don't need it)
• You can also convert the flow to only use either SLC500 / MicroLogix or ControlLogix / Micro800
• No special folder was set for this example and all the files / folders were created in the /home/pi/ folder
  • Any permission issues you might encounter would require that you set correct permissions on the folder you want to use
• After you make any changes to the flow then you will have to click the Deploy button

License

This is all MIT licensed.

Credits

All the credits go to Node-RED, its contributors and in particular rodened, the author of the original example, for making this an easy work for me.

Trademarks

Any and all trademarks, either directly or indirectly mentioned in this project, belong to their respective owners.

Useful Resources

Some Node-RED Library nodes specifically related to PLCs:

• OpenPLC
• redPlc
• plcindustry
• IO Simulation
• cip-ethernet-ip
  • you can also find it on GitHub
  • some insights from the AdvancedHMI Forum topic