PLC - Programmable Logic Controllers

PLCs (Programmable Logic Controllers) are the purpose-built computers that control the Plant. They monitor and activate devices in a controlled safe manner. The connections to devices can be dedicated (hard-wired) or by networks such as CANBus or DeviceNet.

As a simple example, a light switch (with two wires) can be wired to a PLC’s digital input, a light (with two wires) can be wired to a digital output. A simple PLC Program would emulate what happens if the PLC was not present, i.e. when the light switch is turned on, turn the light on, and when it is turned off, turn the light off. Having the devices wired into a PLC enables more complicated operation; e.g. turn the lights off at 5:00pm every day.

Many operators consider the PLC as a mysterious black box that has a mind of its own. PLCs are often programmed in a way that assumes everything is running smoothly; as such, they don’t handle abnormal circumstances well. At Mescon, we reduce the mystery by programming in a robust manner that ensures the machine operates smoothly. When things go wrong (e.g. a sensor gets knocked and no longer detects product), you need to be able to diagnose this quickly and rectify the situation. When you don’t have to look inside the PLC to know what is happening, you will be able to rectify many issues yourself, therefore reducing the number of callouts you will need to make. This will save you time and money.

At Mescon we produce robust and easily diagnosable PLC programs through:

  • Consultation with the client to achieve desired functionality
  • Functional Description written in plain English
  • Informative alarming (e.g. product not detected)
  • Documented online comments
  • Consistent terminology, reflecting the Functional Description
  • Unlocked code
  • Modular programming
  • Preconditions animated on associated graphics
  • Numbered sequence steps

Mescon has several years’ experience over a multitude of PLCs, mostly programming in ladder logic, but we have also used Flow Chart, Statement List, Function Block and Sequential Function Charts. Each PLC manufacturer has their own unique ‘features’. We regularly program the popular brands such as Rockwell, Omron and Schneider, but we have also programmed less common varieties such as Toyo, Honeywell, Hitachi, Mitsubishi, Texas Instruments, Siemens, and Horner.

Prior to commissioning, our PLC programs undergo simulation and testing to ensure they operate on site as intended. You can be confident that the PLC software is acting as described and agreed. Many clients undergo FAT (Factory Acceptance Testing) with the PLC and SCADA system to verify that operations occur as expected. This gives the end client the confidence that the software and the graphics are telling a true story. It removes a lot of mystery and unnecessary fault finding during commissioning. Factory Acceptance Testing includes simulation of feedback and normal operation. Within the FAT or simulated environment, it is possible to see your plant running before it goes live. This allows you, in a timely and safe manner, to identify shortcomings in design and operation, and even test scenarios without affecting equipment operations.

Get in touch with us and see how we can help your business by moving data and information between the factory floor and the corporate decision makers. CONTACT US