The following technical discussion is part of an occasional series showcasing the ISA Mentor Program, authored by Greg McMillan, industry consultant, author of numerous process control books, 2010 ISA Life Achievement Award recipient and retired Senior Fellow from Solutia Inc. (now Eastman Chemical). Greg will be posting questions and responses from the ISA Mentor Program, with contributions from program participants.
In the ISA Mentor Program, I am providing guidance for extremely talented individuals from countries such as Argentina, Brazil, Malaysia, Mexico, Saudi Arabia, and the U.S. This question comes from Bill Thomas from the U.S.
Bill Thomas' Question
Is there a way that I can check out my DCS I/O while at the panel shop? I know how to do this for PLC (programmable logic controller) and HMI (human-machine interface) software but haven’t figured out how to do it for a DCS (distributed control system). As you know, there is a certain luxury and lack of stress when checking out the software and panel hardware while at the panel shop.
Hunter Vegas' Answer
I absolutely agree with you that a good panel checkout prior to leaving the shop is extremely important. When I go into a retrofit turnaround, it is nice to know that everything from the terminal blocks in has been tested and is 100% functional and all I need to worry about is the field wiring. I also have been seeing increasing numbers of defective DCS equipment “out of the box” due to manufacturing difficulties over in Indonesia so a point-to-point checkout is a worthwhile activity. This is especially true if you are using Flexconnect I/O as those cables are handmade, and I’ve had several of them arrive with swapped pins, etc.
I assume you mean an I/O checkout of the equipment and not a functional test of the software logic itself. We usually test the logic using simple tie-back simulation and some basic simulation logic blocks. With that additional software we are able to run the system configuration through its paces. (For instance we actually run recipes on a batch process, charging reactors, reacting batches, transferring product, etc.) The little bit of extra time to do this is easily justified by the resulting extremely low error rate and the operators often use our simulation as a training tool prior to start-up.
ISA Mentor Program
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Greg McMillan's Follow-Up
An I/O checkout on a DCS system is rather difficult because there is no means to “force” the I/O as you can most PLCs. Therefore if you have an active configuration in the controller, you cannot toggle and/or manipulate the outputs without having to go to each device module, force whatever interlocks and logic you need to make the system work, and then actually toggle the device. This can be EXTREMELY time consuming. Rather than do that we do the following:
- We perform all the logic functionality testing in simulation as mentioned above. (That is where we check interlocks, general logic function, etc.) During that functional checkout, we also carefully check the I/O assignments to make sure they are correct.
- In order to do the panel checkout, we create a dummy checkout configuration, which we download to the controller. In this configuration, we accept the default I/O names and tags and create modules that have parameters pointed to each digital and analog output. (We don’t use DO or AO blocks as these take longer to toggle. Instead we just drop down a parameter and externally reference that flag directly to the digital/analog I/O point.
- In order to check analog and digital inputs, we just open up Diagnostics and read the values on the card as we apply an external analog/digital signal to each point.
- In order to check the analog and digital outputs, we open up the dummy modules in On-line mode and double click and set each parameter flag to the value we desire (On/off, 0, 25%/50%/75%/100%).
Note: As each DCS system is different and would require a more in-depth explanation, the above question and answer provided pertains to DeltaV and may (or may not) apply to other DCS systems.
Additional Mentor Program Resources
See the ISA book 101 Tips for a Successful Automation Career that grew out of this Mentor Program to gain concise and practical advice. See the InTech magazine feature article Enabling new automation engineers for candid comments from some of the original program participants. See the Control Talk column How to effectively get engineering knowledge with the ISA Mentor Program protégée Keneisha Williams on the challenges faced by young engineers today, and the column How to succeed at career and project migration with protégé Bill Thomas on how to make the most out of yourself and your project. Providing discussion and answers besides Greg McMillan and co-founder of the program Hunter Vegas (project engineering manager at Wunderlich-Malec) are resources Mark Darby (principal consultant at CMiD Solutions), Brian Hrankowsky (consultant engineer at a major pharmaceutical company), Michel Ruel (executive director, engineering practice at BBA Inc.), Leah Ruder (director of global project engineering at the Midwest Engineering Center of Emerson Automation Solutions), Nick Sands (ISA Fellow and Manufacturing Technology Fellow at DuPont), Bart Propst (process control leader for the Ascend Performance Materials Chocolate Bayou plant) and Daniel Warren (senior instrumentation/electrical specialist at D.M.W. Instrumentation Consulting Services, Ltd.).
About the Author
Gregory K. McMillan, CAP, is a retired Senior Fellow from Solutia/Monsanto where he worked in engineering technology on process control improvement. Greg was also an affiliate professor for Washington University in Saint Louis. Greg is an ISA Fellow and received the ISA Kermit Fischer Environmental Award for pH control in 1991, the Control magazine Engineer of the Year award for the process industry in 1994, was inducted into the Control magazine Process Automation Hall of Fame in 2001, was honored by InTech magazine in 2003 as one of the most influential innovators in automation, and received the ISA Life Achievement Award in 2010. Greg is the author of numerous books on process control, including Advances in Reactor Measurement and Control and Essentials of Modern Measurements and Final Elements in the Process Industry. Greg has been the monthly "Control Talk" columnist for Control magazine since 2002. Presently, Greg is a part time modeling and control consultant in Technology for Process Simulation for Emerson Automation Solutions specializing in the use of the virtual plant for exploring new opportunities. He spends most of his time writing, teaching and leading the ISA Mentor Program he founded in 2011.
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