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panamattam
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Join Date: Aug 2011
Posts: 10

Flow Transmitter Range

10/16/2011 1:19 PM

Dear,

I would like to know how to calculate a new differential pressure range of a DP type flow transmitter with the following datas.

Existing flow range in DCS = 0-7 Tons/Hour

Existing Differential Pressure Range = 0-250 mBar

New flow range in DCS = 0-15 Tons/Hour

What is the new DP range to be set to the transmitter

Please advice me in this regard
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panamattam
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Join Date: Aug 2011
Posts: 10
#1

Re: Flow Transmitter Range

10/16/2011 1:42 PM

For Your Information That the transmitter itself has a square root extractor.
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2
Carl_E
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Join Date: Nov 2009
Posts: 335
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#2

Re: Flow Transmitter Range

10/16/2011 5:23 PM

15 tph is 214.28% of the 7.0 tph design size flow rate of the primary flow element which drops 250mbar at 7.0 tph. 214.28% = 2.1428

Flow rate is the square root of the percentage of DP, where 100% DP is the design size.

Square root of what (x) = 2.1428 ?
x = 4.591 = DP in percent full scale in relation to the design sized 250mbar = 459.1% of 250mbar

250mbar * 4.591 = 1148mbar DP at 15 tph.
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panamattam
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Join Date: Aug 2011
Posts: 10
#3
In reply to #2

Re: Flow Transmitter Range

10/17/2011 9:25 AM

Thanks for the valuable reply
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Bud
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Join Date: Jul 2010
Posts: 136
Good Answers: 19
#4

Re: Flow Transmitter Range

10/17/2011 10:03 AM

If his answer is so valuable, doesn't Carl_E deserve a GA?

For the casual observer, note that the flow rate increased by slightly more than double, from 7 tph to 15 tph.

But the DP went up over a factor of 4, from 250 mbar to 1148 mbar.

Had the flow doubled from 7 tph to 14 tph, the DP would have gone up by exactly 4x to 1000 mbar, because √4 = 2.
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ajwinemaker
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Join Date: Dec 2008
Location: Australia
Posts: 143
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#5
In reply to #4

Re: Flow Transmitter Range

10/17/2011 6:31 PM

Indeed he does. Clear, concise and more importantly correct. GA from me.
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tonykuphaldt
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Engineering Fields - Instrumentation Engineering - New Member Engineering Fields - Control Engineering - New Member Technical Fields - Technical Writing - New Member Technical Fields - Education - New Member Fans of Old Computers - Apple II -

Join Date: Sep 2011
Location: Bellingham, WA
Posts: 191
Good Answers: 46
#6

Re: Flow Transmitter Range

10/20/2011 9:04 AM

The basic principle you need to keep in mind here is that the differential pressure is proportional to the *sqaure* of the flow rate, all other factors remaining constant. With double the flow, you're going to get four times the DP.

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ajwinemaker (1); Bud (1); Carl_E (1); panamattam (2); tonykuphaldt (1)

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