Yamatake Corporation
5-50
ST3000 Smart Transmitter Series 900 Electronic Differential Pressure/Pressure Transmitter
5-10 : Set Range Calculation for Liquid Level Measurement
5-10-1 :Open Tank or Closed Tank (Dry Leg) or Remote Seal Set Range
Calculation
Set range calculation Ex. STD Type
Calculate the set range using these procedures:
The following symbols are used to express density and distance.
It is assumed that the density is fixed, during liquid level measurement.
: Specific gravity of liquid in tank
: Specific gravity of liquid in high pressure side connecting pipe
l
: Distance between 100% liquid level and 0% liquid level (measurement range)
h
: Distance between 0% liquid level and high-pressure outlet port
d
: Distance between high-pressure outlet port and transmitter
Figure 5-6 Open Tank
Figure 5-7 Closed Tank
Differential pressure at 0% liquid level (Pressure on high-pressure side - Pressure on
low-pressure side)
= h + d
=
LRV
Differential pressure at 100% liquid level (Pressure on high-pressure side - Pressure
on low-pressure side) =
l + h + d
= (l+h) + d
= URV
Therefore, set the range as follows:
Low limit (LRV):
h + d
; High limit (URV): (l+h) r+ dr0
Example of calculation: l = 1500 mm, h = 250 mm, d = 500 mm = 0.9,
= 1.0
If the above conditions are assumed, the following results are obtained:
Differential pressure at 0% liquid level = (250 x 0.9) + (500 x 1.0) = 725 mmH2O =
7.110 kPa
Differential pressure at 100% liquid level = {(1500 + 250) x 0.9) + (500 x 1.0) = 2075
mmH
2
O = 20.35 kPa
Therefore, set the range as follows:
Low limit (LRV): 7.110 kPa{725 mmH
2
O}, High limit (URV): 20.35 kPa{2075
mmH
2
O}
ρ
ρ
0
STD
d
h
ρ
l
ρ
o
High-pressure outlet port
100% liquid level
0% liquid level
Open tank
High-pressure side
Low-pressure side
STD
d
h
ρ
ρ
o
l
100% liquid level
0% liquid level
Closed tank
High-pressure
outlet port
High-pressure side
Low-pressure side
ρ
ρ
0
ρ
ρ
ρ
0
ρ
ρ
0
ρ
ρ
0
ρ
ρ
0
