Operation of the Transmitter Yamatake Corporation
5-56 ST3000 Smart Transmitter Series 900 Electronic Differential Pressure/Pressure Transmitter
Set range calculation Ex. STC Type
Calculate the set range using these procedure:
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 sealing liquid
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 5-14 Closed Tank (Wet Leg)
Differential pressure at 0% liquid level (Pressure on high-pressure side - Pressure on
low-pressure side) = d - h = LRV
Differential pressure at 100% liquid level (Pressure on high-pressure side - Pressure
on low-pressure side) = d - (l+h) = URV
Therefore, set the range as follows:
Low limit (LRV): d - h , High limit (URV): d - (l+h)
Example of calculation:
l = 1500 mm, h = 250 mm, d = 2000 mm, = 0.9, = 1.0
If the above conditions are assumed, the following results are obtained:
Differential pressure at 0% liquid level = (2000 x 1.0) + (250 x 0.9) = 1775 mmH
2
O =
17.41 kPa
Differential pressure at 100% liquid level = (2000 x 1.0) + (1500 x 250) x 0.9 = 425
mmH
2
O = 4.168 kPa
Therefore, set the range as follows:
Low limit (LRV): 17.41 kPa{1775 mmH
2
O}, High limit (URV): 4.168 kPa {425
mmH
2
O}
ρ
ρ
0
h
P
ρ
100% liquid level
0% liquid level
Tank
Blow valve
Stop valve
ρ
0
ρ
ρ
0
ρ
ρ
0
ρρ
0
ρ
ρρ
0
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