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Question
```how can we caliberate interface
level troll```
Question Submitted By :: Instrumentation
I also faced this Question!!     Answer Posted By

# 1
Level troll calibration
0% Zero 100% Span
Liquid Level Displacer out of liquid Displacer in liquid
Interface Level Displacer in lighter liquid Displacer in heavier liquid
Wet Calibration with Water For Liquid level
Zero :
Hang displacer on torque tube arm rod.
Adjust Zero to 3 psi .
Span :
Fill up water into the chamber.
Adjust Span to 15 psi .
0%, 25%, 50% , 75% & 100%. Mark on chamber.
Fill up & Drain water to check 0%, 25%, 50% , 75% & 100%.Check output.
Check function two three times.
Note: Compensate specific gravity difference of water & process liquid.
Process liquid specific gravity is 0.7
Water specific gravity is 1.0
To calibrate level transmitter 100% level.
Water level to be fill up in chamber = 0.7/1.0 x 100 %
= 70 %
Dry Calibration with Weights
Find out Displacer
W = Displacer weight in 2400Gram (2.4 kg)
Specific gravity of process liquid. (WATER)= 1.0
V = Volume of displacer. 1620.84
Displacer diameter 7.620 Centimeter (3 inch).
Length of Displacer 35.56 centimeter (14 inch)
Volume= 3.14 X rē X h
= 3.14 X 3.81 X 3.81 X 35.56
= 1620.84
Zero :
For 0% Hang displacer or 2400 gram weight on torque tube arm rod .
Adjust Zero to 3 psi .
Span :
For 100% Hang weight= Displacer weight  Volume X Specific gravity
= 2400  1620 X 1
= 780.
Adjust Span to 15 psi .
Check function two three times for calibration.
Level
%
Hang weight
(Gram)
Transmitter O/P
(PSI)
0 2400 3
25 1995 6
50 1590 9
75 1185 12
100 780 15
For each 25% step subtract 405 Gram weight from hang weight.1620/4=405.
Note: Compensate specific gravity difference of water & process liquid.
Wet Calibration with Water For Interface level
Zero : Displacer in lighter liquid
Process liquid specific gravity is 0.7
Water specific gravity is 1.0
Mark chamber at 70%
Fill up water in chamber.
To calibrate level transmitter 0% level.
Water level to be fill up in chamber = 0.7/1.0 x 100 %
= 70 %
Adjust Zero to 3 psi .
Span : Displacer in heavier liquid.
Process liquid specific gravity is 1
Fill up 100% water into the chamber.
Adjust Span to 15 psi .
Dry Calibration with Weights
Find out Displacer
W = Displacer weight in 2400Gram (2.4 kg)
Specific gravity of process liquid. Oil= 0.7
V = Volume of displacer. 1620.84
Displacer diameter 7.620 Centimeter (3 inch).
Length of Displacer 35.56 centimeter (14 inch)
Volume= 3.14 X rē X h
= 3.14 X 3.81 X 3.81 X 35.56
= 1620.84
Zero : Displacer in lighter liquid
For 0% Hang weight on torque tube arm rod .
Hang weight= Displacer weight  Volume X Specific gravity
= 2400  1620 X 0.7
= 2400 - 1134
= 1266
Adjust Zero to 3 psi .
Span : Displacer in heavier liquid.
For 100% Hang weight= Displacer weight  Volume X Specific gravity
= 2400  1620 X 1
= 780
Adjust Span to 15 psi .
Check function two three times for calibration.
Level
%
Hang weight
(Gram)
Transmitter O/P
(PSI)
0 1266 3
25 1145.5 6
50 1023 9
75 901.5 12
100 780 15
For each 25% step subtract 121.5 Gram weight from hang weight.(1620-
1134=486)
486/4=121.5.

 Is This Answer Correct ? 33 Yes 4 No
Jayesh Manani

# 2
Interface level troll means: When a vessel is filled with
two liquids of two different specific gravities the level
measurement refers to as interface level.
DP = H (D - d)

Calculation # 1 If the calibrating liquid is water:
Process Liquid Density / 1* Displacer height = mm of H2O.

Calculation # 2 If the calibrating liquid is other liquid:
Process Liquid Density / Calibrating liquid density *
Displacer height = mm of H2O. (Calibrating liquid height in
mm).

1. First close both the primary isolation valves and drain
the liquid inside the chamber.
2. Adjust the zero to get 0% output.
3. Connect a transparent PVC tube to the drain point as
shown in hook up.
4. Fill it to the center of the top flange.
5. Adjust the specific gravity or span adjustment
(Electronic Level).
6. Fill it up to 50 %, check linearity.

40. How will you calibrate on interface level control. ?
On an interface leveltrol there are two liquid of two
different specific gravities.
1. The level will be zero when it is full of lighter liquid.
Zero % level = H X d.
H = Displacer length
d = Specific gravity of lighter liquid.
2 The level will be 100 % when it is full of heavier liquid.
100 % level = H X D.
D = Specific gravity of heavier liquid.
Calibration with water:
1. Fill H X d level with water adjust zero.
2. Fill H X D level with water adjust Sp. gravity or span.
3. Check linearity.

Displacer length: L in mm
Density Low : dl in Kg / 1
Density High : DH in Kg / 1
Alarm / Trip point %: X
HH Trip Point: Y in mm

 Is This Answer Correct ? 36 Yes 9 No
Mohammad Reyaz A Nsari

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