AQ: What if
Many years ago we used to call this the “what ifs?”. Part of the design phase is when we model what we think the system is meant to do. Just as important is how the system is meant to react when things are not going well, the abnormal situations or what ifs?
Your client will tell you how their machine or process works, well he will describe how he thinks it works. This is OK as a starting point but we need to consider the scenarios of “what If” something goes wrong? Scenarios is also a good word as scenarios paint a situation that can be described to the customer for his comment.
For example on a compressor control project what if the lube oil pump fails on the compressor, how do we alarm this to the Operator, should we trip the compressor or do we start the back-up oil pump (if there is one). As you look at the system you can pick out various components and generate likely scenarios that you can discuss with the client. Using this approach gives more of a real world feel to your client meetings that are likely to generate a deeper insight into how the system is meant to work.
All scenarios do not have to be centered around abnormal situations but can also relate to things that need to be considered as part of normal operation. For example we might look at how a duty/standby pump system works? One scenario might relate to duty pump failure but another scenario might consider rotating the duty and standby pumps to even out wear and tear? You might also have manual mode and auto mode scenarios to consider?
What you have to remember is that most clients are not control systems experts. They might and probably will struggle with flow charts or any other pseudo code expression type formats that describe how you think the client’s system is meant to work? You have to tailor your approach to match your audience and that is also very important when you produce your documentation, you do not want to lose valuable information just because the client doesn’t fully understand what you are trying to tell him? Also make sure that you spend time with your client. Walk the client through your design, do this face to face as much as possible and do it more than once! Getting feedback on a regular basis helps to eliminate the dreaded word “REWORK”! Also taking this partnership approach builds a good relationship with your client.
For the machine builders your client might be in your own company? Remember same company or not they are your client and your success in no small way depends on your relationship with them.
Add the modes of operation and abnormal situations to your system model and develop the methods of how you will flag these situations to the Operator and Maintenance Engineer. Alarm Management is dealt with by EEMUA 191. If you do nothing else then read this document it will help you to set up alarm workshops, alarm reviews, alarm prioritization and rationalization and how to develop an effective alarm management structure for your system.
