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Scan Time Difference?

03/15/2017 12:39 AM

Why ESD scan time is faster than DCS scan time?

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#1

Re: Scan time diffrence?

03/15/2017 12:48 AM

Do you know what the initials stand for?

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#2

Re: Scan time diffrence?

03/15/2017 4:56 AM

Assumption 1: <...ESD...> is defined as Emergency Shutdown System, usually automated.

Assumption 2: <...DCS...> is defined as Distributed Control System, usually involving a human element to analyse and make decisions

Question for Original Poster: why would one want the EDS to operate faster than the DCS, eh? Has it got something to do with the word Emergency?

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#3

Re: Scan time diffrence?

03/15/2017 5:48 AM

Sorry, my crystal ball just isn't working today.

DCS?

Distributed Control System

Distributed Computer System

Device Control String

Digital Communication System

Digital Control System

Distributed Communication System

ESD?

Electrostatic Discharge

Electronic Software Distribution

Embedded Systems Design

Electronic Software Download

Emergency Shutdown

Energy Spectral Density

CRIMINAL

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#4
In reply to #3

Re: Scan time diffrence?

03/15/2017 11:30 AM

extra good answer! ESD is faster than DCS because it wants to take action more quickly, there, is that simple enough?

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#5
In reply to #4

Re: Scan time diffrence?

03/15/2017 11:54 AM

Ahem - actually, it's the System Designer who wants it to work more quickly, not the inanimate ESD, which really cannot express preference, desire or opinion.

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#6
In reply to #5

Re: Scan time diffrence?

03/15/2017 12:20 PM

Dear PW - having a frog in your throat today when addressing me? LOL I thought so.

WOW! Two air balls in a row during March Madness (basketball crazies over here), not good form!

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#7

Re: Scan Time Difference?

03/16/2017 1:38 PM

I have found ESD and DCS together in the specification for an industrial plant here. DCS is specified as Distributed Control System, and DCS "Scan time means the sum of total time required for reading an input, running control algorithm and writing the output values) shall be better than 250 milli-seconds for any type of channel".

ESD is Emergency Shutdown System. In paragraph 5.3.9

"The emergency shut down system shall be independent of DCS. It shall be a state-of-the-art, Programmable Logic Controllers with Quadruple Modular Redundancy (QMR) based Fail Safe architecture. Irrespective of process hazards/safety class, the ESD (Emergency Shutdown System) or ESD system shall be certified for Safety Class – AK- 6 as per TUV and DIN19250/VDE0801 and SIL3 as per IEC61508 (without limitation in repair time on single point error) as a minimum. The complete application cycle time of ESD / ESD shall be less than the 25% of the Process Safety Time, when system is fully loaded and running at peak load. ( i.e. if Process safety time is 1 second, complete application cycle time of proposed safety ESD shall not be more than 250 milliseconds) "

Seems an entirely reasonable specification to me, that the emergency shutdown procedure should react faster than the normal process scan.

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#8
In reply to #7

Re: Scan Time Difference?

03/16/2017 1:45 PM

I was worried that was the control and data acquisition with sequel server for a hospital imaging system using Unobtainium excitation elements. Those machines can see right through underwear. Excess exposure results in babies being born naked.

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#10
In reply to #8

Re: Scan Time Difference?

03/17/2017 7:06 AM

Almost but not quite right. I often prescribe a tot of whisky to aid the thought processes, but in this case I fear the remedy has already been overused.

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#11
In reply to #10

Re: Scan Time Difference?

03/17/2017 10:25 AM

I ne'r touch the stuff, without exception, except for day that end in Y.

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#9

Re: Scan Time Difference?

03/17/2017 5:36 AM

I give up! Why is it faster? Do tell us.

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