16
5.
After calibration, the monitor will show
"CAL"
and the instrument will beep briefly.
Remove the probe from the gas outlet. The instrument is ready for use.
Note
: During calibration, the selector switch remains in the AUTO ZERO position. After
calibration is complete and
"CAL"
is displayed, the selector switch must be placed at
some other scale (or the OFF position) to return the monitor to a normal operating mode.
CAUTION:
Automatic calibration presupposes and depends on using Bascom-Turner's
calibration gas (Part No. MC-620). Do not use a gas of a different
composition for automatic calibration.
A-CAL Calibration with the Methane or System Gas
The thermal conductivity sensor is calibrated at the factory with methane. Routine re-
calibration of this sensor is not necessary. The thermal conductivity sensor is checked
operationally using air as the reference gas every time the AUTO ZERO routine is used.
However, should there be need to recalibrate the thermal conductivity sensor, proceed as follows:
1.
Place the selector switch on "AUTO ZERO" and zero the instrument in clean air.
The usual series of displays will appear on the monitor display. Note that if the
instrument had just been calibrated with the methane and CO calibration gas, the
selector switch must be moved to some other scale and given 30 seconds to purge
residual gas before the AUTO ZERO routine is repeated.
2.
After
"End"
appears on the display and the instrument beeps, block the probe tip
manually until
"bloc"
appears on the display. Now release the block. The display
will show
"go"
and the instrument is ready for calibration.
3.
Connect the probe to a source of pure methane or system gas. The gas pressure
should not exceed 6" or 7" of water column and gas must be delivered at the rate of
at least 2 liters per minute. The display will show
"GAS 1"
while the thermal
conductivity sensor is being calibrated. When calibration is complete,
"CAL"
will
appear on the display and the instrument will beep briefly.
4.
Disconnect the probe from the gas and let the instrument run briefly in clean air to
purge residual gas. Monitor the purging by placing the selector switch on the GAS
scale. When the reading on this scale returns to zero, the instrument is ready for
use.
Note that while the probe is being connected to a source of methane or system gas, "
bloc"
may appear briefly on the display, for example, if some time elapses between connection to the
gas outlet and opening of a valve that allows calibration gas to flow. This will not interfere with
proper calibration.
Models CGA-611 and 612 have a H
2
S sensor that is calibrated at the same time as the
thermal conductivity sensor. The proper calibration gas for these models is methane with 25
ppm of H
2
S (Part No. MH-620). For these models, the "GAS 1" display will be followed by
"H2S", while the H
2
S sensor is calibrated, and then by "CAL" when calibration is complete.
