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How is D.P transmitter applied to a close tank & open tank with dry leg or wet leg?

Span   =  ( X ) ( GL )
HW at minimum level   =  ( Z ) ( GS )  +  ( Y ) ( GL )
HW at maximum leve l  =  ( Z ) ( GS )  +  ( X + Y ) ( GL )
                 
Where :
GL  =  Specific gravity of tank liquid.
GS  =  Specific gravity of seal liquid.
HW = Equivalent head of water.
X, Y & Z are shown in fig (1.1)

Open Tank and Close Tank with Dry Leg

Example :
Open tank with X   =  300 inches
Y    =  50 inches
Z    =  10 inches
GL  =   0.8
GS  =   0.9
Span   =  ( 300 ) ( 0.8 )  =  240 inches
HW at minimum level =   ( 10 ) ( 0.9 )  +  ( 50 ) ( 0.8 )  =  49 inches
HW at maximum level =  (10 ) ( 0.9 )  +  ( 50 + 300 ) ( 0.8 )  =  289 inches
Calibrated range =  49 to 289 inches head of water


Close tank with wet leg:
Span   =  ( X ) ( GL )
HW at minimum level    =  ( Y ) ( GL )  –  ( d )( GS )
HW at maximum level   =  ( X + Y ) ( GL )  –  ( d ) ( GS )
Where : GL  =  Specific gravity of tank liquid
GS  =  Specific gravity of tank liquid
HW   =  Equivalent head of water
X, Y and Z are shown in fig.  

Close tank with wet leg

Example :
 X  =  300 inches
Y  =  50 inches
d  =  500 inches
GL =  0.8
GS  =  0.9
Span  = ( 300 ) ( 0.8 )  =  240 inches

HW minimum level  =  ( 50 ) ( 0.8 )  -  ( 500 ) ( 0.9 )  =  - 410 inches
HW maximum level =  ( 300  +  50 ) ( 0.8 ) – ( 500 ) ( 0.9 )  = - 170 inches
Calibrated range  =  - 410 to –170 inches head of water.
( minus sings indicate that the higher pressure is applied to the low pressure side of the transmitter )

Comments (1)Add Comment
0
level transmeter
written by Bilalkhan, August 29, 2017
Instrument tecnicean

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