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Level Measurement with Wet leg and Installed Below Tapping Point

Closed Tank Level Measurement with wet leg and Transmitter installed below Tapping Point
Level Measurement with Wet leg and Installed Below Tapping Point
This calculation used for closed tank level measurement with wet leg type calibration

The formulas for calculating transmitter URV and LRV are as follows:

HP Side or LRV or Transmitter 0% = X.S1 – Y.S2

LP Side or URV or Transmitter 100% = S1(X+H) – Y.S2


S1 = Specific gravity of tank liquid or process liquid.
S2 = Specific gravity of wet leg
H = Tank Height
X = Distance between transmitter and HP tapping point.
Y = Wet Leg Height


1. The Parameters H,X can be entered in any units like mmh20, inh20 but must be same

2. If wet leg Y is filled with same process liquid in the tank then S2=S1.

3. If wet leg Y is filled with different liquid (other than tank process liquid) then enter specific gravity of wet leg liquid in S2.

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Anonymous April 18, 2015 at 6:46 am

Nice tool Mr.Bharadwaj.

Really helped me.Please share more tools.

Micheal Tram April 20, 2015 at 4:59 am

Instrumentation made easy……Now Level Transmitter wet leg calibration/configuration is equal to a simple PT or TT configurastion

Anonymous May 13, 2015 at 10:58 pm

This is a very helpful tool. So much easier than having to do the calculations manually. Please don't take this link down. Thank you.

S Bharadwaj Reddy May 14, 2015 at 9:55 am

Thanks for the comment. These all instrumentation tools available all the time.
Thank you,
S Bharadwaj reddy

Sathish September 25, 2015 at 9:58 am

Really very usefull ,,thanks to Reddy,,,

Zahid March 31, 2016 at 11:50 am

I’m confused about culculation because I thinking in suppression
X.s1 + y.s2= lrv
But you used minus that why I confused
Maybe I’m wrong please send me details of proper culculation and reson. Thanks

muhammad sadiq October 12, 2015 at 11:19 am

Wonderfull very usefull for instrumentation

aji January 7, 2016 at 11:41 am

how to measure level steam drum use dp transmitter

manoj February 16, 2016 at 4:00 pm

Dear sir,
In what case Dpt transmitter range need to be in -ve say -1000mmwc to0
1.if tank is closed and have vapour or steam in upper side and cond.pot is installed or every close tank needs cpot and _ve range steam doesent matter?
2.if tank is open can I take o to 1000mmwc
Both have CTo c dist. 1000mm density 1.0

S Bharadwaj Reddy February 16, 2016 at 4:15 pm


When you do the LRV & URV calculation, lets say for Open tank & Closed tank you will get negative values also. So we need Negative mmwc range of instruments for this case.Thats it. Simple if we have negative value in either LRV or URV then we need negative mmwc range of instrument. Also Depends on Calculated URV & LRV Ranges we have to select our instrument range. Either Open tank or Closed tank if your calculated LRV & URV values are withing the instrument mmwc range then we can use the instrument. Remember Negative mmwc also considered.

arshad September 19, 2016 at 3:45 pm

hi sir
LT installed at Dearator tank is showing high alarm while actually tank level is low?? what must be the reason.??

regards, Arshad

manoj February 16, 2016 at 4:25 pm

with ref to your answer how can be open tank have -ve mmwc at hp side since tank is at atmosephric pressure . Also talk more about condensing pot we use it only for high temp. steam vapour so if we fill pot side that is lp side to maintain head and close tank then only its -ve mmwc and if close tank , correct me if i am wrong .

S Bharadwaj Reddy February 16, 2016 at 4:40 pm

Hello Manoj, Actually it depends on how your field instrument mounted in the field. Say For open tank case if the field Tx mounted above the HP tapping point and then we can get Negative mmwc range also. Its mainly depends on Tx installation also. As Open/Closed Tank Calculations also considered. Pl Click Here For Example.

Chetan Dileep Singh September 27, 2016 at 5:19 pm

Sir is there any case when height ‘y’ and h+x will be equal?

S Bharadwaj Reddy September 27, 2016 at 6:12 pm

of course it’s possible.

Mark May 26, 2017 at 11:20 am

Great tools and examples, thanks for all your sharing!!

I have a remote diaphragm coupled DP Tx, but the Tx is mounted at the mid-level of the tank, so NOT below or level with the bottom flange connection.

How do i apply this to the formula, i was entering “X” as a negative value, but this isn’t giving me good results 🙁

S Bharadwaj Reddy May 26, 2017 at 4:02 pm


Please check these : Article 1 (click here) and Article 2 (click here), these may help you.

quy June 25, 2017 at 1:05 pm

thats so great. thanks for your post!!
and plss. i have a closed tank wet leg with H = 103in, X = 100in, Y = 203in,
i have been calculated URV = 0kpa and LRV = – 27.56kpa. but why in datasheet they maked thats +4.8 to +31.3 thanks you.

jadav chirag April 2, 2018 at 3:38 pm

Sir, first of all thank u for this wonderful site.
Q.: where should we use dry leg and where to wet leg I mean application wise.

jadav chirag April 2, 2018 at 3:58 pm

Q-2: can u plz give me some idea about when should we install DP Tx 1)below HP, 2) Parallel to HP and 3) above HP? (with some industrial example)


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Level Measurement with Wet leg and Installed Below Tapping Point

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