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8.4 Gas Calibration
Before putting the system on-line, it is recommended that a
calibration check for the 'zero' reading is made using
calibration standard sample gas.
The 'zero gas' is permanently marked on the data plate on the
6548 001 katharometer unit. This gas when passed through
the katharometer gives a zero millivolt output. To provide a fail-
safe condition it is recommended that the zero gas is a 80% or
85% hydrogen in nitrogen mixture so that if power is lost to the
katharometer, an alarm condition will occur at the monitor unit.
Full scale output from the katharometer is obtained by a 100%
hydrogen gas sample and no adjustment of the katharometer
output is normally required. The maximum signal for the full
scale reading is sealed during manufacture and should not be
altered by users.
With the katharometer correctly adjusted using the 'zero gas'
hydrogen in nitrogen mixture. Carbon dioxide and air mixtures
are correctly displayed when the selector switch is in the
appropriate position.
8.4.1 Hydrogen Gas Calibration
Warning. Test for leaks in accordance with the
requirements of the responsible authority after making
any hydrogen connections.
1) Arrange to pass calibration quality Hydrogen gas through
the Katharometer Unit on the appropriate katharometer
analyzer panel, at the normal working pressure of the
sample gas system. This should give the correct flowrate of
gas, as set previously.
2) Power up the monitor unit, and the hydrogen katharometer
unit by switching on the appropriate power supply unit.
3) Set the range selector switch on the monitor unit to position
(1).
4) The display unit indicates the measurement parameter -
percentage by volume of hydrogen in air (%H2 in AIR) - on
the lower line. The upper line indicates a value for the
parameter.
5) With hydrogen calibration gas passing through the sample
system at the normal flowrate, the displayed value should
stabilize within 2 hours to read the correct value (80% or
85%) as appropriate.
Note. A zero adjustment facility is available from
the potentiometer adjacent to the display unit. Adjustment
is made by inserting a screwdriver through the hole
behind the small escutcheon plate.
8.4.2 Purge Gas Check Reading
Note. No adjustment of the zero potentiometer is
necessary. As any adjustment required will already have
been made while calibrating the hydrogen-in-air range.
With the calibration performed according to Section 8.4.1 the
purge gas readings (carbon dioxide, air) will be correctly
displayed when the selector switch is in the appropriate
position.
As a check, calibration quality carbon dioxide, air (or mixtures)
may be passed through the katharometer and the displayed
value compared to the stated mixture.
If adjustment is required, a hydrogen gas calibration (see
Section 8.4.1) must be performed to achieve the required
accuracy.
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