Ametek 5000 Instrument Manual page 104

Interferences Caused by Gases Other Than Air
The system is factory calibrated to read directly for air, oxygen, and nitrogen. The instrument will analyze mois-
ture in hydrocarbons, refrigerants, and other various gases (some are listed in Table B2).
The background interference is present when the sample is a gas other than air and the reference is dry air or
nitrogen. This interference is caused by the physical and chemical differences of the sample and reference gases.
Of the gases in Table B2, only carbon dioxide causes an interference which can be attributed to sample sorption
on the crystal coating. Data in Table B2 shows typical amounts of interference between a dry sample gas and a
reference gas of dry air or nitrogen.
These values are pressure dependent. It is suggested that the interference for a particular sample be determined
by temporarily running the analyzer with a sample gas dried with a 3A molecular sieve or other appropriate
desiccant, against a reference gas of instrument air or nitrogen passed through the 3A sieve dryer supplied. As-
suming that both gases are then dry, any apparent "moisture" indicated by the analyzer will be the interference.
This error can be subtracted from readings by adding the measured error to the value programmed for Poly
Coeff 0 (refer to 4-5).

Interferences can be avoided by using dried sample gas as the reference as shown in Figure 9a, Page
2-15. Using this method eliminates this interference.
NOTE
Table B2: Typical Interference Values for Gases Other Than Air
Sample gas
100 %
Oxygen
Nitrogen
Carbon Monoxide
Propane
Ethane
Ethylene
Methane
Hydrogen
Isobutane
Butane
Isobutylene
F-22
F-12
Carbon Dioxide
B-6 5000 Multi Point Moisture Analyzer
Indicated
ppm v/v
0.0 Heptane — air
0.0 Benzene — air
0.7 Methanol — air
0.7 Ethanol — air
1.3 Perchloroethylene — air
1.3
1.7
2.6
2.6
2.6
5.0
10.0
7.5
44.0
Vapors Concentration
% Indicated
ppm v/v
4 10
9 10
12 150
1 1
3 8