I am always amazed at the dexterity of the poor operator who can hit the acknowledge/clear button with a rapidity that is truly awesome! Then there is the alarm printer that jammed or off-line with reaps of useless garbage stacked on the floor. In either case it is quite likely that any real alarms that may identify the root cause of plant outage are never noticed or ignored. Even if the alarms are posted to log file and not to decimating forests, they still create a search nightmare. The operations/maintenance staff lose confidence in the SCADA or OI and attack the problem in some other empirical fashion.
The list goes on ...and on...
- hardcoded limits and times that make it impossible to allow for valid process changes;
- mixing up routine events (NOT actual alarms) with alarms;
- 'clever' use of set-points that are meant to operate valves and pumps, but with the addition of a timer also produce an alarm;
- seven or more levels of set-points so that you have to create tags like LA4H-725 to accommodate the rare situation when - well, you fill in the situation;
- software suppliers who allow the creation of alarm log files, but use a binary format that is not searchable by any tool that a normal non-geek human can use;
- use of a dozen or more colours and shades to distinguish different types of alarms (Let's use light magenta to identify problems with acid feed system) (More on this in another post);
- meaningless or cryptic alarm messages, e.g. "PAH-123 High Pressure". This needs more description beyond the tag, like "PAH-123 High Feed Pressure at RO Inlet #1";
- …
In reality you can cover nearly everything with two types of alarms. Let's call the first warning variety "Alerts". These should be colour-coded YELLOW and offer advice about situations that are somewhat outside the normal operating band. A nice is example is pump that is running at higher than normal rpms and producing normal flow. At some point this will mean the need for a rebuild, but not just yet. The warning gives the operator some time to schedule maintenance on the pump. Remember the flow is still okay, but the pump is working harder than it should. This type of alarm implies knowledge of the pump curve and how to code deviations, but it can prevent an unscheduled outage and will definitely pay for itself.
Aside from alerts, there are actual alarms. These are coded RED and indicate that some piece of equipment has failed and shut one or more parts of the process. For me the terms 'Alert' and 'Alarm' are very clear. They correspond to yellow caution and red stop lights on traffic signals and I believe are universally understood using the analogy. They are also nice short words and are alliterative to boot! I understand that some customers don't like these terms and find them confusing. I have never met any of these people. Whenever I have been training customers, I offer the traffic light analogy and they get it right away. Still there might be some valid reason to go in another direction. Let me know if you come across it.
(Aside - while the RED is dangerous and GREEN is safe standard is entirely consistent and logical, it is intuitively opposite to any one who has motor vehicle experience. Why confuse people unnecessarily?? Just asking. You might have a valid reason, but I have not been convinced so far. I have used both according to customer spec, but still.)
What is the bottom line? Make sure you communicate clearly what the problem is, when it happened and if possible some readily available advice on what to do to fix the problem. This brings up the subject of interlocks, which will be the subject another post.
If you find this post alarming, or stupid, start a discussion. It might be fun!
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