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DP Level Transmitter Elevation and Suppression Corrections

DP Transmitter Elevation and Suppression Corrections for Level Measurement

When installing a DP transmitter to measure liquid level, configuration of the transmitter often must include an adjustment for one of two conditions introduced by the mounting arrangement.

  • Elevated Span – The Lower Range Value (LRV) of the transmitter needs to be configured above “0.”
  •  Suppressed Span – The LRV of the transmitter needs to be configured below “0.”

Elevated Span and Suppressed Span

A brief discussion of how to make adjustments for elevation and suppression follows. Then two examples of the calculations needed to determine configuration parameters are given. Finally, a brief procedure that does not involve calculations is provided.

The range of the transmitter can be set anywhere, forward or reverse acting, as long as the following criteria are met:

LRL ≤ LRV ≤ URL
LRL ≤ URV ≤ URL
Span = [URV – LRV] ≥ Min Span

Note that the URL (Upper Range Limit), LRL (Lower Range Limit), and Min Span are transmitter dependent.

 ELEVATION CALCULATION EXAMPLE 

The below figure shows a sample transmitter installation.

Calculate Differential Pressure Transmitter

1. Calculate the differential pressure as follows. 

Pressure@DP = (H × SpG)High Side – (H × SpG)Low Side

where H = Height

2. Calculate the LRV when the tank is empty. 

LRV = (120 x 1.0)High Side – (0 x 1.0)Low Side

LRV = +120 inH2O

3. Calculate the URV.

URV = LRV + Span
URV = +120 + 100
URV = 220 inH2O

Therefore, transmitter range should be 120 to 220 inH2O

 SUPPRESSION CALCULATION EXAMPLE

The below figure shows a sample transmitter installation.

DP Transmitter Formula

1. Calculate the differential pressure as follows. 

Pressure@DP = (H × SpG)High Side – (H × SpG)Low Side

where H = Height

2. Calculate the LRV when the tank is empty. 

LRV = (0 x 1.0)High Side – (100 x 1.0)Low Side

LRV = -100 inH2O

3. Calculate the URV.

URV = LRV + Span
URV = -100 + 100
URV = 0 inH2O

Therefore, transmitter range should be -100 to 0 inH2O

Source : Siemens Pressure Transmitter

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13 comments

Masiyiwa Lewis Nyambabvu March 10, 2017 at 5:03 am

Would like to ask how these articles can be downloaded. Many thanks to you Sir, this information is very helpful to aspiring young technical personal.

Reply
Tamer ahmed March 10, 2017 at 11:27 am

very good description

Reply
Abdulkhaliq Albelushi March 18, 2017 at 3:21 am

Thank you for those very important calculation for DP transmitters presented in a very simple and understandable way.
How to save or download those valuable techniques ?

thank you once again

Best regards.
Abdulkhaliq Albelushi

Reply
lijo March 19, 2017 at 6:39 am

hii can you please tell what H2O SpG=1 means

Reply
S Bharadwaj Reddy March 19, 2017 at 1:52 pm

Specific gravity of the liquid inside tank. Here it is assumed sg=1

Reply
lijo March 20, 2017 at 11:35 am

thank you

Reply
manish wadia March 19, 2017 at 12:39 pm

dear, sir thank u very much for the calculation of level measurement

Reply
Abdel-rahman Sugar March 20, 2017 at 4:32 pm

thank you very much

Reply
Ghodbane April 15, 2017 at 8:35 am

Merci beaucoup

Reply
GERALD April 18, 2017 at 5:45 am

Please how do you calebrate the level transimeter when it is showing default on URV and LRV and and it ends at 46% as the maximum.

Reply
godfather December 22, 2017 at 4:44 pm

check all the specification on HART and then adjust the SPAN at 0%..25%..50..75..100%

Reply
godfather December 22, 2017 at 4:41 pm

sir ,what is catch spot phenomenon in level transmitter?

Reply
Channabasava October 29, 2018 at 3:14 pm

Very good info

Reply

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