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Active Contributor

Join Date: Oct 2010
Posts: 16

# DP transmitter Calibration

01/04/2011 12:42 PM

please help me. How to calibrate a Differential Pressure Transmitter,range is -1 to 25 BAR, 0 to 20 mA output.in 0.8 bar how to calculate the mA,and all ranges.

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Guru

Join Date: May 2009
Location: Richland, WA, USA
Posts: 20971
#1

### Re: DP transmitter Calibration

01/04/2011 3:33 PM

mA = (P+1)/1.3

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Commentator

Join Date: Apr 2008
Location: Rhode Island, USA
Posts: 56
#2

### Re: DP transmitter Calibration

01/04/2011 4:59 PM

You have 1.8 bar signal out of a span of 26 bar. The transmitter span is 16 Ma., with a 4 ma. zero.

Your output will be 1.8/26 bar times 16 ma. span plus 4 ma. zero equalling 5.108 ma.

Active Contributor

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#3

### Re: DP transmitter Calibration

01/04/2011 9:26 PM

can u explain me deeply

Guru

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#4

### Re: DP transmitter Calibration

01/04/2011 11:04 PM

Let pressure P be like an x-axis, and mA be like a y-axis.

Pressure of -1 corresponds to 0 mA; this point is (-1, 0).
Pressure of 25 corresponds to 20 mA; this point is (25, 20).

Using the algebra for a line through two points, you get mA = 20(P+1)/26, or (P+1)/1.3

The range of 0-20 mA is unusual, but I used it anyway. More common is 4-20 mA, as shown in the other computation.

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Anonymous Poster
#8

### Re: DP transmitter Calibration

01/07/2011 6:22 AM

can you explain me with example,please

Anonymous Poster
#5

### Re: transmitter Calibration

01/05/2011 1:15 PM

Commentator

Join Date: Apr 2008
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#6

### Re: transmitter Calibration

01/05/2011 1:43 PM

I didn't read your original post carefully enough. You stated that the transmitter span wa 0 to 20 ma. If it's a typical industrial control transmitter, the range would be 4 to 20 ma. This is used so the transmitters can be self powered on a 2 wire line. Would you check your transmitter specs and let us know whether it is 0 to 20 or 4 to 20 ma?

I also presume that your pressures are gauge pressure, not absolute pressure. Is that correct?

Anonymous Poster
#9

### Re: transmitter Calibration

01/07/2011 6:25 AM

i am sorry it was 4-20 mA output,

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#13

### Re: transmitter Calibration

02/04/2011 5:11 AM

Hi,

if this instrument is in the workshop or in the field, please get the senior tech to do the work? he will be able to help your problem solving????

Regard's

Guru

Join Date: May 2009
Location: Richland, WA, USA
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#7

### Re: transmitter Calibration

01/05/2011 3:26 PM

[P-(-1)]/[25-(-1)] = (mA-4)/(20-4).

(P+1)/26 = (mA-4)/16.

P = (26/16)(mA-4)-1; throughout the respective ranges.

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Anonymous Poster
#10

### Re: transmitter Calibration

01/07/2011 6:46 AM

can u explain me in -1 to 25 bar ptx,in -0.8 bar and 0 bar how i calculate ,please help me,i am fresh in instrumentation.b4 u given me many equation but i can not understand.

2
Commentator

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#11

### Re: transmitter Calibration

01/07/2011 10:11 AM

Let's see if I can explain this.

Your transmitter pressure span is 26 bar. From -1 to 25 bar

Your transmitter current span is 16 ma., From 4 to 20 ma.

To calculate the current output for any measured pressure, (Pm) do this.

1. Add 1 to the Pm, because your pressure span starts at -1.

2. Divide the the number from step 1 (Pm+1) by 26, which gives the part of the pressure span represented by that pressure.

3. Multiply the number from step 2, (Pm+1)/26, by 16, which is the ma. span of the transmitter.

4. Add 4 Ma. which is the zero signal of the transmitter. (Pm +1)/26*16+4.

For 0.8 bar, the calculation is 1.8/26*16+4= 5.11 ma.

For 0 bar, it's 1/26*16+4= 4.62 ma.

4ma.=-1 bar

8 ma.= 5.5 bar

12 ma.= 12 bar

16 ma.= 18.5 bar

20 ma. = 25 bar.

Does that help?

Anonymous Poster
#12

### Re: transmitter Calibration

01/07/2011 9:29 PM

very very thanks sir,i will remember u every time ,may god bless u, thanks.

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Join Date: Jan 2010
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#14

### Re: transmitter Calibration

02/07/2011 7:07 PM

then give him a GA like i did, then learn the math so you can understand the others who gave you GA's you didn't understand, look back at their formulas, same thing.

Good job Dave, do you teach, if not you should, more patience than the rest of us?

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#15

### Re: transmitter Calibration

02/07/2011 9:22 PM

Thanks KWcharlie.

I don't teach, but I spent many years designing that type of equipment.

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#16

### Re: transmitter Calibration

02/12/2011 12:08 PM

You teach them everything you know and they STILL don't know anything , A Saleem still hasn't seen your explication of pu as a GA to his question and at his level.

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Why do they make manhole covers round? so they won't fall in [before asking "Who is John Galt?"]
Commentator

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#17

### Re: transmitter Calibration

02/19/2011 9:03 PM

I agree that the explanation was excellent but that does not answer the real problem that I have seen mostly overseas that people are in instrumentation positions and have no or very little training what so ever. I know that in some places of the world that the school systems and internet service are not up to the same standards as maybe in the US and Europe, but that is not an excuse to not be truthful on a resume. I have had to come in after someone has designed and or calibrated an instrument, and have found out that the person(s) do not have even the elementary knowledge of basic instrumentation. I believe if this person is an instrumentation engineer and does not know how to derive the calibration values for a 4-20 mA loop, either they are in the wrong position or needs to get their money back from the school they went to. Sorry to rant but I have seen this type of question numerous times and it is very tiresome to go over this explanation again and again.

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#18

### Re: transmitter Calibration

02/19/2011 10:12 PM

The level of some of the questions that come from people who are working with very high energy processes is enough give you some pause for thought. I guess the only saving grace is that they are mostly far enough away that we should be out of the blast zone.

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