AQUATRAN 3/38 Operator’s Manual
Preparing RH Calibration Standards
MOCON, Inc.
Revision G
F-1
Appendix F: Preparing RH Calibration Standards
To calibrate or check the RH probes used in the AQUATRAN 3/38, requires RH reference values (or
standards). A RH Calibration Standard consists of a saturated salt solution or molecular sieve in a
“Calibration Flask”. Calibration Standards should be kept tightly sealed using the “Flask Stopper” when not
in use. The molecular sieve should be regularly replaced.
RH Calibration Equipment
MOCON has available the following materials to facilitate the preparation of RH reference standards
suitable for the calibration of the RH Probes in the AQUATRAN 3/38.
•
Calibration Flask
MOCON Part Number
030-802
•
RH Probe Stopper
MOCON Part Number
030-803
•
Flask Stopper
MOCON Part Number
030-804
Choosing a Salt Solution
Warning!
Some salts will produce exothermic or endothermic reactions when mixed
with water. Failure to use proper safety equipment when mixing salt
solution can result in frostbite or burn injuries. Salt solutions should be
prepared only by qualified people with proper safety equipment.
RH sensor calibration will be performed at a specific temperature. A salt must be chosen that will produce
the desired RH at that temperature.
For most salt solutions the RH produced by the solution is dependent on temperature. To choose the
correct salt solution for your application, consult one of the following resources:
•
Table F.1, Salt Solution Humidity Standards in Percent RH shown below.
•
Handbook of Chemistry and Physics.
•
The National Bureau of Standards.
Salts
15 °C
20 °C
25 °C
30 °C
35 °C
Lithium Bromide
6.86
6.61
6.37
6.16
5.97
Lithium Chloride
11.30
11.31
11.30
11.28
11.25
Potassium Acetate
23.40
23.11
22.51
21.61
21.61
Magnesium Chloride
33.30
33.07
32.78
32.44
32.05
Potassium Carbonate
43.15
43.16
43.16
43.17
43.17
Potassium Iodine
70.98
69.90
68.86
67.89
66.96
Sodium Chloride
75.61
75.47
75.29
75.09
74.87
Ammonium Sulfate
81.70
81.34
80.99
80.63
80.27
Potassium Chloride
85.92
85.11
84.34
83.62
82.95
Ammonium Monophosphate
93.85
93.32
92.65
92.00
91.42
Potassium Nitrate
95.41
94.62
93.58
92.31
90.79
Table 9-7: Salt Solution Humidity Standards in Percent RH
