Have you ever gone online with a PLC and realized it contained no structure, the I/O was all over the place, and there were no comments in the logic? Fortunately, all projects are not retrofits or adding code to an existing PLC program. Sometimes you get to start from scratch. There are some good practices to follow when launching a new project that will help simplify a complicated program and make it easier to follow should someone else need to edit the code in the future.
I often say, “Levels are devils to control.” Why? They’re integrating variables; that is, if the level in a vessel is constant, and the valve is opened or closed and then brought back to its original opening, the level will be at a different place in the vessel. Levels are non-self-regulating – they represent an imbalance between the flow of material into and out of a vessel. The tuning challenge is to find the best combination of gain (or proportional band) and integral time (or reset) that attempts to react to material flow imbalances and maintain the level reasonably close to a set point. For a variety of reasons, using derivative is not a good idea for level control. Gain alone or PI control handles PV trajectory changes quite well.
Traceability is one of those words that’s been around for awhile now in manufacturing and the supply chain and has lots of different meanings. It just means different things to different people.
As I walked into the control room the first thing I heard was, “Why can’t I commission this transmitter?” The technician was pointing to the screen where he was trying to commission some Foundation fieldbus transmitters that had been taken out for service. At least this time he’d remembered to decommission them first.
A major part of today’s communication revolves around Ethernet networking. In our world, this is used for either communications or I/O control. The current state-of-the-art network hardware makes the implementation of these types of networks extremely easy and secure. The fact that this is the same technology that is used in every corporation’s IT department makes it even more attractive.
In the last post I gave you some homework around the idea of operational excellence. I hope you did your homework and learned some things.
Leaving Project Specifications Blank or TBA is a Recipe for Project Trouble
Much has been written on the subject of creating legal contracts, often including statements like, “Good contracts make for good clients,” and “Good contracts lead to good customer relationships.” Contracts are important. In addition to stating legal and financial requirements, contracts define what is to be done for the client. Just as important as contracts, proper specifications are needed to identify clearly how the contract requirements are to be satisfied.