In the ISA Automation Week Mentor Program, I am providing guidance for extremely talented individuals from Argentina, Brazil, Malaysia, Mexico, Saudi Arabia, and the USA. We will be sharing a question and the answers each week. If you would like to provide additional answers, please send them to Susan Colwell at ISA. The twentieth question is from Bill Thomas in the USA:
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.
Answer from Hunter Vegas, project manager at Avid Solutions, Inc.
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.
Assuming you are asking about an I/O checkout then here is my answer:
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.