Question for FACTFINDER, 'JUST ANOTHER ENGINEER', and FLINT

greenspun.com : LUSENET : TimeBomb 2000 (Y2000) : One Thread

Embedded issue has, at this point, been beaten to a pulp but not yet into submission. Let's get past the ROMs(and their evolved iterations)PLCs and directly to the DABs. Do they perform a true system command function? Is the DAB(or DABs) conducting this digital symphony orchestra? If so does it(or an array of DABs) communicate/interface with a mainframe? Are utility co. mainframes responsible for tasks other than accounting/billing,pensions and payroll or do they make decisions, based on information from embedded systems, with specific regard to load distribution, shutdown commands, fault detection and appropriate(programmed) response to those detected/perceived system faults or errors. In short, what is the role of the mainframe(if any) in getting the power to the customer? Just a quick personal note to Factfinder--Thanks for the e mail response to a question I asked a few days ago. I understand the reasons for your optimism but don't share your belief in those reasons. You work in a zero fault tolerance environment and are a perfectionist to boot. I simply doubt that others, outside of your highly specialized environment, have the same zeal, sense of mission and technical competence. Thanks for any replys.

-- Get Real (gaf@mindspring.com), December 09, 1999

Answers

Get Real:

As soon as you start to generalize about embedded systems, you're making false assumptions. There is no firm definition of what they are. If you install, say, some autodialer software and hardware in your PC for your business, and that's all that particular PC runs, you have an embedded system. Run a word processor with the autodialer running in the background, it's not embedded anymore, it's a PC again!

Gartner Group (and others) makes a distinction between standalone systems and LSES (Large Scale Embedded Systems). The vast majority of embedded systems stand alone, such as VCR's and other home appliances, or test equipment, etc. LSES are layered like an onion, or heirarchical like a tree. The "main trunk" of such a tree can be any kind of computer.

I've written lots of examples of such trees. As a brief example, your car may have a microcontroller at each wheel (for ABS, and to control other sensors). At this level, they're controlling the skid, temperature, vibration etc. of their own wheels. These microcontrollers each report to a higher level monitoring and controlling all 4 wheels (for example, to prevent the vehicle from slewing sideways by controlling braking differentially at different wheels). This controller reports up the chain of command to a controller that may monitor (and maybe control) the wheels, suspension, etc. There may be as many as 40 or more microcontrollers in your car. At the top level, dates may be handled for such purposes as keeping maintenance records.

Gartner estimated that the incidence of mishandled dates might run as high as 30-35% in LSES. This is partly because these systems are so extensive and complex, and partly because such systems tend to monitor complex processes in so much detail. Even here, though, most date anomalies take the form of incorrect logging or 2-digit year printouts and displays, unlikely to fool a human being.

The danger in such systems is that at the level where a critical decision is made, the data are not usually available to make a fully informed decision. So for example a sensor monitor (a microcontroller) might be integrating temperature over time looking for unusual (and therefore suspect) *rates* of temperature change. At rollover, it might calculate an absurd rate. But it doesn't pass the *rate* up the chain of command, it passes a message that says "emergency! Shut this process down NOW". The higher level has no information by which to judge the sensibility of this message. It only knows it has an emergency.

So the task with LSES is first to determine if they have any access to the date. If they do, do they use it? If they use it, HOW do they use it (i.e. to perform a calculation or make a decision, or just to display it and store it)? This is not always trivial to determine.

My understanding of power generation is that dates are used by SCADA systems, but these don't make shutdown decisions. Some processes DO automate the shutdown decision, regardless of the classification of computer making that decision.

So it's a case by case determination. Remember that embedded systems designers don't need to follow standards to be compatible with standard operating systems or applications, by and large. They can custom-design to fit the need, and they do. And there are as many different ways to fit a given need as there are possible love sonnets. It depends on the mood the designer was in that day.

-- Flint (flintc@mindspring.com), December 09, 1999.


Hi Flint,

I'm impressed! Nice, short explanation.

(Your prior messages implied, to me, a less than adequate understanding of embedded systems.)

-- Dean -- from (almost) Duh Moines (dtmiller@midiowa.net), December 10, 1999.


Thank you both for a thoughtful post and response. This was very informative, and filled in some gaps in my understanding.

I also really liked the "sonnet" analogy. ;-)

Mark

-- mark (mat_dc@hotmail.com), December 10, 1999.


Flint's explanation is why I prefer to refer to "automated processes" - rather than "embedded chips" or other such terms.

See, the total process is the key. If it (the process) can be salvaged, temporarily fixed by a manual override or by manual control, or if it doesn't break at all - and many won't; it really doesn't matter what you call the various parts and pieces and boards and chips and controllers and sensors and power supplies and interfaces inside: it's only one process.

To operate profitably in today's world, the process must be correct: to become more profitable; given modern industrial sensors, quality control, and dependence on statistical process control, it will generally lose money if not run as close to tolerances as possible. In other words, you loose money starting up a bad process, or loose customers by giving them bad quality (out of spec) "manually-done" parts.

And nobody makes enough money to throw it away on bad products, wasted material, incomplete material that got aborted when the temperature or pressure control was lost halfway through, etc.

Assuming even in the first place, that the process can actually be done with a failure somewhere in the middle. There aren't any redundancies and backup systems in a modern CNC or casting or plastics injection machine. and these can't be run "by hand"...power failure, cooling water, air or steam or compressed gas pressure, natural gas heaters, or coal, coke or steel, etc. are all remain vunerable to irregular supply system shutdowns.

-- Robert A. Cook, PE (Marietta, GA) (cook.r@csaatl.com), December 10, 1999.


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