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Accuracy Considerations 3098 Technical Manual
4-2
3098 SPECIFIC GRAVITY METER
CONTROL PRESSURE SELECTION
Date: ................................. Type of Gas: ................................... Specific Gravity Range: ............. to ............
3098 Serial No. ................... Temperature Coefficient of Density Meter: ............................................. kg/m
3
/°C
CONTROL PRESSURE AT 20°C (lb/in
2
abs.)
(bars abs.)
18
1.2
30
2
60
4
100
7
DENSITY RANGE AT 20°C (kg/ m
3) 0.79 - .15 1.32 - 2.0 2.66 - 3.8 4.58 - 6.72
Measurement Errors (% of FS Specific Gravity/°C)
due to:
Density Meter Temp. Coefficient
Gas Compressibility of Sample Gas
Velocity of Sound in Sample Gas
Reference Chamber/Relief Valve +0.007 +0.007 +0.007 +0.007
Total Error
Table 1
Calculating the parameters
Density Range at 20°C
Calculated using equation:
Density range = to PG PG
air air
ρ
ρ
min max
where P = Absolute pressure in bars.
ρ
air
= Density of dry clean air (1.2kgm
-3
approximately)
GG
min max
& = Specific Gravity minimum and maximum values.
Density Meter Temperature Coefficient Error
Inversely proportional to density (therefore pressure) and is calculated as follows:
Temperature coefficient from calibration certificate = x kgm
-3
/°C
At maximum density value of y kgm
-3
:
Sensor equivalent temperature coefficient =
x
/
y
x 100%/°C
Gas Compressibility Error
This describes the deviation in gas compressibility of the sample gas compared with that of the reference chamber gas.
The error is taken as 2/3 of the deviation caused by temperature change on the two gases at the reference pressure and
is typically proportional to this pressure.
For information on the gas characteristics see the Gas Tables.
Velocity of Sound Error
This error is taken as - 0.0034 G %/°C with G taken at maximum specific gravity
G
max
.