GasCheck
Operating Manual V2.4
14
When using balloons, take the gas balloon, release the clip valve and expel
any air by squeezing it, then close the clip valve. To purge the balloon attach
the balloon assembly to the gas cylinder, open the clip valve and allow the gas
to flow into the balloon so that the diameter of the balloon increases
somewhat. Stop the gas flow and empty the balloon by squeezing it to expel
the gas. Close the clip valve.
Again, attach the balloon assembly to the gas cylinder, open the clip valve and
fill to a diameter of approximately 20 cm. Then stop the gas flow and close the
clip valve. Connect the balloon to the calibration port and after al lowing a
settling time check the calibration. Check that the balloon is still inflated at
the end of the procedure.
Because the sensor fundamentally measures mole density and not volume
percent (see Chapter 3.2), it is advisable to calculate the targeted i nstrument
reading corresponding to the span gas concentration with the ambient pressure
taken into account in order to achieve maximum accuracy from the GasCheck
sensor.
The targeted concentration reading is given by equation
Po
Po
P
BC
TCR
)
5
.
0
5
.
1
(
(2)
where:
TCR = targeted concentration reading (ppm or %),
BC
=
bottle concentration (ppm or %),
P
= ambient pressure (hPa or mbar)
P
0
= 1013.25 (mbar)
EXAMPLE:
If the GasCheck 3000 is to be calibrated with 3000 ppm gas on a day when the
ambient pressure is 980 hPa, using equation (2) the output reading should be
adjusted to read an equivalent to
ppm
2852
25
.
1013
)
25
.
1013
5
.
0
980
5
.
1
(
3000
TCR
ppm
.
From the linearisation curve, this corresponds to 0.978V.
NOTE
All units are factory set to the corrected gas
concentration on the day of manufacture. For maximum
accuracy all field calibrations should also use pressure
and temperature correction.
