The Value of Messaging in Industrial Control Systems

The following tip is from the ISA book by Greg McMillan and Hunter Vegas titled 101 Tips for a Successful Automation Career, inspired by the ISA Mentor Program. This is Tip #17.

101 Tips for a Successful Automation CareerThis is one of those tips that you cannot appreciate until you have worked on a control system that did NOT have adequate messaging programmed in it. Operators want to know what is going on, and system messaging is usually their only clue. Imagine running a complex or dangerous process and not having any feedback to tell you what is happening or if anything is happening at all! Or perhaps just as bad, imagine having the process sequence stop with such useless messages as “Sequence on Hold.”

Concept: Nothing frustrates an operator more than working on a control system that provides vague, generic messages, or worse, provides no clue that anything is happening at all. Tell the operator what is going on! If a phase goes to hold, the system should tell the operator why. If the system is on hold for 10 minutes, the operator should see a countdown. The extra effort to do this is minimal, and the positive impact on operations personnel is immeasurable.

Details: Creating detailed messaging is easy once the phase templates have been configured to include it. The messaging can be displayed in a two line message bar at the bottom of the screen that is used for active phase messaging and for operator questions and responses. Two lines are usually necessary because many batch processes have multiple operations occurring simultaneously and providing two message areas avoids overlap.

Here is a sample of some of the messaging an operator should see:

• During timed holds, the system should provide a countdown: “10 minute hold, 6:33 minutes remaining.”
• During material charges the message should indicate the amount and type of material charged and the amount remaining. For instance, the message might read: “Charging 200 gal caustic, 52 gal remaining.”
• If a phase goes to hold, the system should always indicate WHY it went to hold in a detailed manner. For instance, the message might read: “Rx 300 to storage transfer held due to high level in product TK 301.” Resist the urge to write generic messages such as “Phase on hold due to valve misalignment.” Indicate WHICH valve is the problem.
• During equipment setup, the system should indicate what actions are being performed. For instance, the starting of an agitator might generate these messages: “Starting Agitator,” “Ramping speed to 75%,” “Agitator at Speed” etc. Generic messages such as “Setting Up Equipment” do not give much indication of what is happening.

Take the time to do messaging right. The improved operability and increased information to the operator will reduce downtime and allow the operators to quickly identify problems and resolve them without outside maintenance and/or engineering help.

Watch-Outs: If a programmer is not a good speller, do not have him or her doing the messaging! A couple of misspelled words will dramatically lower the perceived quality of the control system in the operator’s eyes. (See Appearance Matters Tip #30.)

Exceptions: There aren’t any. Even a simple sequence can be programmed with a short message bar that is populated as logic is executed.

Insight: A trick to making messaging easy is to create one (or two) operator message variables that appear in the message lines on the bottom of the page. The various phases write to these variables so that the operator gets used to seeing phase related messaging in the same place. These message bars can be placed on several graphics as appropriate.

Rule of Thumb: Messaging can make or break a control system. If the information is detailed and useful, the operator will be able to run the system much more independently and resolve problems without any outside help. If the messages are generic or non-existent, Operations will be calling Engineering all night long looking for help to identify problems and get the process running again.


Hunter Vegas

About the Author
Hunter Vegas, P.E., holds a B.S.E.E. degree from Tulane University and an M.B.A. from Wake Forest University. His job titles have included instrument engineer, production engineer, instrumentation group leader, principal automation engineer, and unit production manager. In 2001, he joined Avid Solutions, Inc., as an engineering manager and lead project engineer, where he works today. Vegas has executed nearly 2,000 instrumentation and control projects over his career, with budgets ranging from a few thousand to millions of dollars. He is proficient in field instrumentation sizing and selection, safety interlock design, electrical design, advanced control strategy, and numerous control system hardware and software platforms.
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