mensor PCS 400 - Head Pressure Correction; Gas Density (Table 9.6); Liquid Density (Table 9.7); Table 9.6 - Gas Density

HEAD PRESSURE CORRECTION
The accuracy of pressure measurement depends on several factors, one of which is the
consideration of the head pressure in the system. The pressure medium, whether a gas or liquid,
can cause an error in the measurement if not considered. In some cases the offset may be
insignificant, and it may be ignored. The following information provides instructions for
determining the density of the pressure medium and how to calculate the head pressure effect.
Gas Density
Liquids and gases have mass and are affected by gravity. The extent of the effect is dependent
upon the density of the pressure medium. Liquids normally have a constant density that does
not change with pressure. Gases, however, increase in density as the pressure increases. To
determine the density of a gas at a specific pressure multiply the absolute pressure by the density
per standard atmosphere from the following table. For gas the head pressure difference due to
temperature changes within the compensated temperature range will be insignificant.
Table 9.6 – Gas Density
Gas@23°C and
1 Standard Atmosphere
Density/Standard Atmosphere
ratio in lbs/in
3
(D
psi
)
Air,Dry
2.9314 X 10
-6
Argon
(A) 4.0443 X 10
-6
Carbon Dioxide (CO
2
) 4.4823 X 10
-6
Helium (He) 4.0461 X 10
-7
Hydrogen
(H
2
) 2.0379 X 10
-7
Nitrogen
(N
2
) 2.8355 X 10
-6
Liquid Density
In the table below, the density of water at various temperatures is given. The density of a liquid
is commonly specified in grams per milliliter (
g
⁄
ml
). To convert to
lbs.
⁄
cu.in.
multiply the density
by 0.036127292.
Table 9.7 – Liquid Density
Liquid Density Pounds/in
3
(D)
Pure Water @ 15°C
0.0360947
Pure Water @ 20°C 0.0360623
Pure Water @ 25°C 0.0360205
Pure Water @ 30°C
0.0359700
Pure Water @ 35°C 0.0359116
APPENDIX PCS 400
9-6 www.mensor.com