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suhasdh
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For DPT only URV & LRV applied to HP & LP side individually (seperately/one at a time) what will be mA output.)

08/30/2022 8:32 AM

For any DPT, only at a time either URV or LRV applied in terms of 25%, 50%, 75%, 100% what will be mA output.

e.g. 1) if URV is 100mmwc (& if only URV applied to DPT at HP side) applied in %age wise like above what will be mA output.

2) if LRV is 80mmwc (& if only LRV applied to DPT at LP side) applied in %age wise like above what will be mA output.
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PWSlack
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#1

Re: For DPT only URV & LRV applied to HP & LP side individually (seperately/one at a time) what will be mA output.)

08/30/2022 9:39 AM

Refer to the instrument calibration check sheet in the commissioning records, for that is where the answer can be looked up.

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Iris
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#2

Re: For DPT only URV & LRV applied to HP & LP side individually (seperately/one at a time) what will be mA output.)

08/30/2022 9:42 AM

LRV and URV are values used to define what value the 4mA output represents in engineering units (LRV) and what value the 20mA output represents in engineering units (URV).

Applying a pressure equal to an LRV or URV value is possible but it isn't clear from your description exactly what the configured LRV and URV values are in your case, so I'll use the values given, LRV = 80mmwc and URV = 100mmwc.

Also, differential pressure transmitter has two ports, a high side and a low side. The DP xmtr reports the pressure difference: low side pressure subtracted from the high side pressure.

To provide answers to questions about what the output is, the LRV and URV need to be specified AND the pressures at both ports need to be known.

Assuming (from your stated LRV and URV values)

1. that LRV = 80.0 mmwc and URV = 100mm wc (LRV is NOT 0.0mmwc)

resulting in an output span of 20mmwc DP (your transmitter can do this?)

where
0.0mmwc DP = 4.0mA
20.0mmwc DP = 20.0mA

AND

2. that the port that does not have the specified applied pressure is open to atmosphere

then

100% 100mmwc applied at the High side port then high side 100mmwc minus low side 0.0mmwc (atmospheric pressure) = 100mmwc DP = 20.5mA or output saturation because the span is only 0-20.0mmwc DP and the applied pressures is 5x the configured range

75% 75mmwc applied at the High side Port then high side 75mmwc minus low side 0.0mmwc (atmospheric pressure) = 75mmwc DP = 20.5mA or output saturation because the span is only 0-20.0mmwc DP and the applied pressures is 3.75x the configured range

50% 50mmwc applied at the High side Port then high side 50mmwc minus low side 0.0mmwc (atmospheric pressure) = 50mmwc DP = 20.5mA or output saturation because the span is only 0-20.0mmwc DP and the applied pressures is 2.5x the configured range.

25% 25mmwc applied at the High side Port then high side 25mmwc minus low side 0.0mmwc (atmospheric pressure) = 25mmwc DP = 20.5mA or output saturation because the span is only 0-20.0mmwc DP and the applied pressures is 1.25x the configured range.

To get an output value within the range of the transmitter, the applied value would have to be less than 20.0mmwc, for the configured conditions stated.

100% 80mmwc applied at the Low side port; then high side 0.0mmwc minus low side 80.0mmwc (atmospheric pressure) = -80mmwc DP (negative 80.0mmwc) = ~3.5mA output or whatever the low output saturation value is for that transmitter because the span is only 0-20.0mmwc DP and the applied pressures is way below the configured range of 0-20.0mmwcDP

The same applies to all the other percentage of LRV outputs: low saturation value because the applied pressure is way below the configured range of 0-20.0mmwcDP
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PWSlack
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#3
In reply to #2

Re: For DPT only URV & LRV applied to HP & LP side individually (seperately/one at a time) what will be mA output.)

08/30/2022 11:39 AM

Er, um, assumption 2 does not correspond with the original poster's thread opener:

<... if LRV is 80mmwc (& if only LRV applied to DPT at LP side)...>.

If the latest commissioning record cannot be relied on to give the tested range of the instrument, then the only thing to do is to test it again, and set the range up as required; the original thread does not reveal this information, which is why the posted question is unanswerable.

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rwilliams
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#15
In reply to #2

Re: For DPT only URV & LRV applied to HP & LP side individually (seperately/one at a time) what will be mA output.)

09/05/2022 10:59 AM

Nice explanation, but a differential pressure transmitter can not be calibrated in gauge pressure, so when you state 0.0mmWC at the open port, the sensor in the transmitter is seeing 10,300 mmWC pressure. So in this case, unless you apply 10,320 mmWC or 10,280mmWC to the various ports, your transmitter output will be saturated at 4mA or 20mA.

The answer to this particular question is No, you can’t do this, it is a meaningless exercise. You will get either 4 mA or 20mA, and it will tell you nothing. You need to apply test pressures with 0-20mmWC differences to both ports for the instrument to respond as it was calibrated.
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suhasdh
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#4

Re: For DPT only URV & LRV applied to HP & LP side individually (seperately/one at a time) what will be mA output.)

08/31/2022 3:13 AM

Thank you all for your answers. And apology for the trouble for the low range values (100 & 80).

Let's change URV from 100mmwc to 20000mmwc & LRV from 80mmwc to 12000mmwc.

Then how will be the mA output as per the question.
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PWSlack
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#5
In reply to #4

Re: For DPT only URV & LRV applied to HP & LP side individually (seperately/one at a time) what will be mA output.)

08/31/2022 4:31 AM

An explanation is needed as to why the <...LRV...> is connected to the <...LP...> side.

If in doubt, consult an Instrument Technician, who will be able to interrogate the instrument locally, determine the range setting at any given time, and answer these questions. The instrument is, after all, very difficult to see from here.

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#6
In reply to #4

Re: For DPT only URV & LRV applied to HP & LP side individually (seperately/one at a time) what will be mA output.)

08/31/2022 9:39 AM

Friend,

As answered by others, your DPT is providing an output based on the difference of pressures between the two input ports (high minus low). Assuming your questions are for mmwc pressures relative to atmospheric pressure, then you will see an output in the 4-20mA range only when the pressure difference is within the positive range of 20000-12000 = 8000mmwc. As answered already, with a test pressure of any value up to 12000mmwc applied to only the low pressure port all pressure differences are negative and the output will be always below scale. With only a test pressure applied to the high pressure port, the output will be above scale for all applied pressures greater than 8000mmwc--which occurs at the 40% test point in your original question.

JMM
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PWSlack
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#14
In reply to #4

Re: For DPT only URV & LRV applied to HP & LP side individually (seperately/one at a time) what will be mA output.)

09/05/2022 9:41 AM

Did the Instrument Technician re-range the instrument at that juncture or not? Where is the record of that having happened?

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Randall
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#7

Re: For DPT only URV & LRV applied to HP & LP side individually (seperately/one at a time) what will be mA output.)

09/01/2022 5:20 AM

https://instrumentationblog.com/calibrate-a-differential-pressure/

The trouble with all these TLAs is that no one tells you what they mean. The above link does, and so is probably quite a good introduction to the subject.

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PWSlack
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#8
In reply to #7

Re: For DPT only URV & LRV applied to HP & LP side individually (seperately/one at a time) what will be mA output.)

09/01/2022 5:37 PM

TLAs. Who needs ‘em?

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#9
In reply to #8

Re: For DPT only URV & LRV applied to HP & LP side individually (seperately/one at a time) what will be mA output.)

09/01/2022 6:13 PM

LOL.

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PWSlack
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#10
In reply to #9

Re: For DPT only URV & LRV applied to HP & LP side individually (seperately/one at a time) what will be mA output.)

09/02/2022 7:24 AM

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#11
In reply to #7

Re: For DPT only URV & LRV applied to HP & LP side individually (seperately/one at a time) what will be mA output.)

09/04/2022 7:43 AM

TLA? Please define.These acronyms have got to stop..ASAP!

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PWSlack
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#12
In reply to #11

Re: For DPT only URV & LRV applied to HP & LP side individually (seperately/one at a time) what will be mA output.)

09/05/2022 2:52 AM

TLA = Three-Letter Abbreviation

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Anonymous Poster #1
#13

Re: For DPT only URV & LRV applied to HP & LP side individually (seperately/one at a time) what will be mA output.)

09/05/2022 9:38 AM

Duplicate thread.
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Previous in Forum: IS Barriers   Next in Forum: What will be mA output if 50% & 100% span value applied to the LP side of a DPT by keeping HP side open.

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