PLCs are the industrial computers which run machines. They perform actions, instructing motors to run, pistons to operate and many other functions.
The actions are real life things and as such can and should be handled by competent and qualified persons only.
For the safety of users, among other reasons, communication with PLCs is not always the easiest.
Meteor Software Limited specialize in building systems upon the foundation of communication with the PLCs inside production factories.
Allen-Bradley family of PLCs
Write function
The most basic communication we use is to write to a table of Integers inside an Allen-Bradley PLC5, Control Logix or other similar machine. Using very well tried and tested techniques perfected through 20+ years of experience, we exchange information with specific tables and words, agreed with a PLC programmer. Transfers of information over ethernet are extremely fast, and allow us to make lots of changes which are not suited to the program within the PLC itself. We’re updating the data that the program uses to perform its actions, not modifying the program itself.
Listen function
Similarly, we typically run a dedicated service on a Virtual Machine hosted inside the client’s premises behind a secure firewall.This service is configured to listen for PLC messages, built by the PLC programmer according to our guidance.
A typical application listens, sorts, queues and handles these messages as they come in, to perform more complex operations such as database entries, further communication with other PLCs in the network etc.
Mitsubishi PLC
Similar to the functionality of the Allen-Bradley family of PLCs, we’ve build a framework which we have used to read and write to the data tables of commercially built systems. Again, the solutions created for the client has enabled things like automation of dimension changes at a rate that would not be possible for a human to perform.
The Mitsubishi communication is performed over ethernet using UDP.
Siemens PLC
The Siemens range of PLCs is extensive.
We have built a few systems to communicate with Siemens machines, the most recent of which used RESTful POST requests, with the body constructed as defined by the PLC programmer who set up the variable value names he expected to receive.
The communication had to be encrypted using TLS but worked very well.
The combination of these functions allows us to create sophisticated systems inside your plant. Typically the service that communicates with the PLC is multithreaded. It listens for and receives requests from PLCs on the network as well as a separate frontend application. It communicates with one or many databases and interacts with LDAP services.
