3-4 | Model 120HD Hydrogen Analyzer
recalibration
Recalibration requires a known mixture of hydrogen and air or hydrogen
in nitrogen. Hydrogen gas is flammable, and in a mixture with air con-
centrations over 4% - 5%, it is explosive. For this reason, mixtures of 20%
hydrogen in air generally can’t be obtained from commercial sources.
Do not attempt to make such a mixture and recalibrate the analyzer
unless proper equipment, personnel, and expertise is available.
Follow these steps to recalibrate the analyzer.
1. Make sure that you have performed the
Current Adjustment
and
Electrical Zero Adjustment
if necessary.
2. Connect the inlet gas Swagelok tube fitting to the calibration gas.
3. Turn Knob 1 to either
TEST
position (non-backlit/backlit).
4. Set the flow through the analyzer at a rate of about 50 ml/min. A con-
tinuous, steady, flow rate of gas through the analyzer is preferred.
Calibration at 10% provides the most accurate results. However, cali-
bration at intermediate values (5 - 15%) should result in acceptable
performance.
5. The reading is stable when the digital readout does not increase for
30 to 60 seconds. If the reading is different from the calibration gas
value, you must adjust the
SPAN ADJUST
screw (Figure 3-2) until the
display reads the calibration value.
A decrease in the reading may indicate that there is a leak in the sys-
tem and should be invesitgated. Follow the procedure “Checking for
Leaks” in Chapter 1.
If the sample gas is forced through the analyzer by pressure at the
source and then vented to atmosphere, connect a short piece of rubber
tubing (12” x 18” long) to the outlet gas Swagelok tube fitting as a
precaution against ambient air diffusing back into the analyzer.
When the analyzer is not in use, be sure to turn Knob 1 to the
OFF
position, otherwise the battery will be decreased.
NOTE
NOTE
NOTE
