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8 comments
Member

Join Date: May 2011
Posts: 9

Instrument Loop Checking

03/14/2012 8:40 AM

Dear freiends! good afternoon, Here i am facing some problems regarding the loop checking, because our steam line operating pressure is 56 bar and we dont have the pneumatic hand pump of 56 bar range. we need to inject the pressure of 25,50,75, and 100% of working pressure. The boiler vendor is not allowing to use the hydralic pump with oil, and if we use the nitrogen cylinder i think we can't control the pressure input to the instruments because we dont get the proper availability of the regulator. And our all instruments are ROSEMOUNT smart transmitters. Shall we use the manual water injecting pump with proper size calibrated gauge? or anybody can tell the correct solution for this issue?

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#1

Re: Instrument Loop Checking

03/14/2012 9:05 AM

Presumably this instrument was ordered with a manufacturer's calibration certificate document? So why is there a need to re-test - after all, one is only checking the range span and zero. If they have been waxed into place at the factory, why is there any need to change them at site?

Always test with an incompressible fluid.

Presumably the test gauge has a calibration certificate too?

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Engineering Fields - Electrical Engineering - Been there, done that, still doing it. Engineering Fields - Control Engineering - New Member

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#2
In reply to #1

Re: Instrument Loop Checking

03/14/2012 10:55 AM

Very good points. Additionally at the manufacturing facility there is some calibration trace back to a real reference international standard. Any on site retesting of a measurement instrument with anything but a more precise, calibrated instrument done by somebody knowledgeable of proper measurement technique and tolerances will just destroy instead of correcting the calibration of the measuring device.

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Guru

Join Date: Jul 2010
Posts: 524
Good Answers: 114
#3

Re: Instrument Loop Checking

03/14/2012 11:45 AM

Google hydraulic dwad weight tester Dead weights are primary calibration standars, models range up to 1,000 bar Distilled water is typically the medium, with some alcohol, if I recall correctly. The others' warnings apply: understand what you're doing.

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Guru

Join Date: Jul 2010
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#4

Re: Instrument Loop Checking

03/14/2012 2:36 PM

that should have been "dead weight tester"

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Power-User

Join Date: Mar 2011
Location: oz
Posts: 166
Good Answers: 9
#5

Re: Instrument Loop Checking

03/14/2012 10:07 PM

Check your specs on your hand pump, Most of the hand pumps we have can easily achieve 56 bar with water.

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Active Contributor

Join Date: Dec 2011
Location: Alberta Canada
Posts: 24
#6

Re: Instrument Loop Checking

03/14/2012 10:25 PM

Are you trying to check the loop or calibrate the transmitter? If you are doing a loop check no pressure calibrator is necessary. You have stated you have a Rosemount smart transmitter so all you have to do is hook up to it with a hand held communicator and put the transmitter into loop check and it select 4ma and you check your dcs or plc screen for 0 then select 8ma 12ma and so on.

If you are trying to recalibrate the transmitter I agree with some of the other posters unless you have a dead waight tester or some other high accuracy calibration equipment that is traceable you are doing more harm than good. That being said new smart transmitters generally don drift much. Some times you get a little bit of zero drift. If you have a block and bleed before your transmitter This can easily be checked and fixed by doing a zero trim with you hand held

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Member

Join Date: Mar 2012
Posts: 9
#7

Re: Instrument Loop Checking

03/14/2012 10:38 PM

Do not confuse yourself between loop check and functional test or calibration check. Loop check is to ensure the circuit continuity so that when you simulate input you will get the output at the other end. What you are trying to do at different pressure is to calibrate I guess. You can take the device to supplier's test bench for pressure calibration during your next shutdown.

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Participant

Join Date: Feb 2012
Posts: 1
#8

Re: Instrument Loop Checking

03/15/2012 10:25 AM

Totally agreed. Loop check and site calibration are different. Loop check is only check the circuit.

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