Since distributed control systems are a potential weakness, is there a way to manually work around them?

-- Anonymous, February 10, 1999

Answers

Sometimes.

The Instrument Society of America (ISA) defines 4 levels of a typical control system (0-3). DCS typically resides at level 3. If you'd like, I'll email you a copy of a powerpoint presentation that I have that describes the levels in a bit more detail.

The bottom line is that the ability to manually operate process control systems, if available, resides at level 1, which is typically at the component level rather than loop (level 2) or system (level 3) levels.

Here's a text breakdown of the levels:

Level 3: DCS Level 2: Instrument loops Level 1: Individual components Level 0: Process monitoring

It's like a pyramid - a single DCS can control many individual loops, which in turn can control many individual components, which in turn receive process monitoring inputs from many individual process monitors (for example, pressure, temperature, voltage, frequency, etc.).

Hope this helps!

-- Anonymous, February 12, 1999

Thank you Rick for answering this question. I hope you have time to continue this dialog or move me to a place where I can get answers to these specific questions....

1) How many people operate a single functional DCS?

2) If a DCS were found to be able to be operated manually, On average how many people do you think would be required to do the job?

I greatly appreciate your response.

-- Anonymous, February 12, 1999

Whenever I see the manual overrides question pop up (anywhere), I think of this thread that's filed waaaaaaaaaaaaaaaay down in the "Electric Utilities Business Issues" category. Interesting posts by Rick, Kim Smith (a controls expert, I believe), and Roleigh Martin...

http://www.greenspun.com/bboard/q-and-a-fetch-msg.tcl?msg_id= 0001Wf

-- Anonymous, February 13, 1999

I am really hoping for a quantitative answer on the questions I have. This would help me to investigate the risk of not having an appropriate contingency. The link is helpful, though. Thank you.

-- Anonymous, February 16, 1999