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Accuracy 4-20 mA signal loop calculation

Created by: AutoGen_285321 at: 7/10/2014 6:34 PM (7 Replies)

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7/10/2014 6:34 PM	Rate (0)
AutoGen_285321 Posts: 4 Rating: (0)	I am looking for a document or template to be used in order to calculate the accuracy and measurement error for a typical measurement current loop constituted by Analog Imput card,signal conditioner, instrument. An help in this matter would be really helpfull. Regards Norberto
AutoGen_285321 Posts: 4 Rating: (0)	Last edited by: AutoGen_285321 at: 7/10/2014 6:35 PM
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7/11/2014 10:36 PM	Rate (0)
RugbyGuy Silver Expert Joined: 1/15/2009 Last visit: 4/19/2024 Posts: 316 Rating: (40)	Hi AutoGen, Please see the following link for the ET200 IO modules, specifically Chapters 4, 5 and 6 where Analog measurement principles, and specific IO module technical details are discussed. http://support.automation.siemens.com/WW/view/en/8859629 Have a great day!
	The best location for all PCS 7 content (manuals, guides, application notes, FAQs, and videos). https://support.industry.siemens.com/cs/ww/en/view/63481413
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7/14/2014 5:32 PM	Rate (0)
AutoGen_285321 Posts: 4 Rating: (0)	Hi RugbyGuy, The document take in account only the AI Card error, in my case i have to calculate the total error wich is composed by the AI card+the external signal conditioning device+instrument. I gues theaccuracy errors cannot be simplyadded but some other alghorithm have to be used. Let me know whehter you have any reference document. regards Norberto
AutoGen_285321 Posts: 4 Rating: (0)
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7/14/2014 5:44 PM	Rate (0)
RugbyGuy Silver Expert Joined: 1/15/2009 Last visit: 4/19/2024 Posts: 316 Rating: (40)	Hi AutoGen, Yes you are correct. This is only for the IO module. You do still need to get the same technical details for anything external to it (instrument, signal conditioner...etc), however that information you will likely have to find at their manufacturer's websites.
	The best location for all PCS 7 content (manuals, guides, application notes, FAQs, and videos). https://support.industry.siemens.com/cs/ww/en/view/63481413
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7/14/2014 5:58 PM	Rate (0)
AutoGen_285321 Posts: 4 Rating: (0)	No i dont need the same details, i just need to know how to calculate the total accuracy error taking into account the single errors of each component. regards Norberto
AutoGen_285321 Posts: 4 Rating: (0)
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7/14/2014 7:20 PM	Rate (0)
RugbyGuy Silver Expert Joined: 1/15/2009 Last visit: 4/19/2024 Posts: 316 Rating: (40)	Hmm, I am not certain what is best. But, my expectation is that you may use the rule for mutually independent quantities being added. Maybe someone else has can confirm.... Attachment Mutually independing being added.jpg (182 Downloads)
	The best location for all PCS 7 content (manuals, guides, application notes, FAQs, and videos). https://support.industry.siemens.com/cs/ww/en/view/63481413
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7/14/2014 7:23 PM	Rate (0)
cabreytj Silver Member Joined: 5/18/2006 Last visit: 10/21/2020 Posts: 170 Rating: (64)	If the various elements have independent accuracies (an inaccuracy in one device doesn't influence the accuracy of another device) you can typically use the Square Root of the Sum of Squares (SRSS) method to statistical combine all the errors to determine an overall loop accuracy. All the device accuracies should be based on the same sigma level so the result of SRSS yields the same level. If device accuracies are mixed the over accuracy will be the lowest device level (e.g. 1 sigma lower then 2 sigma). Keep in mind the device accuracy may need to consider more then just the vendor published accuracy but also environment, process (over pressure), vibration/seismic, EMF/EMI, Radiation, etc. Loop Accuracy = +/- (A₁² + A₂² + … + A_n²)^1/2Where A₁= Devise #1 Accuracy (etc.) Can find more information about this topic in the ISA 67.04 for Nuclear Power Plant Instrument Setpoint Calculation Methodology.cabreytj

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This contribution was helpful to 1 thankful Users RugbyGuy

7/15/2014 8:42 AM	Rate (0)
AutoGen_285321 Posts: 4 Rating: (0)	Tank you for the information, is now more cleare how to proceed in this matter. Norberto
AutoGen_285321 Posts: 4 Rating: (0)
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