GasTech D-Guard2, Operator'S Manual

Page: 39 / 77

D-Guard
2
36
12.4.1 Auto Span Calibration
After entering the calibration system The 'Calibrate Span' information page is now shown
When entering the calibration functions, the zero calibration
page is the first one seen. Operate the 'Span Cal' soft-key to
move on to the span calibration pages. This page provides information and guidance on using the
span calibration functions available.
Operate the 'Settings' soft-key to continue.
Auto Span Page - No Gas Applied Auto Span Page - Target Gas Applied
The 'Settings' soft-key moves to the auto-span function. From
here automatic span calibration can be started, or the manual
span function accessed. A warning to apply the target gas is
indicated. The expected span gas concentration is
programmed into D-Guard
2 during manufacture. This can be
user modified if required (see section 12.1.4 on how to do
this). Until a valid target gas is applied, the warning message
and gas cylinder icon will be displayed and the calibration
process disabled.
Target gas must be applied at this point to
continue.
Once the target gas has been applied, the warnings will stop
being indicated and the 'Run auto Cal' soft-key will become
active. Observing the trend indicator will show when the gas
reading has stabilised. If the marker is in the centre position,
then the auto-span process can be started. If the marker is
not in the centre position, the sensor has not stabilised and
auto-span is not possible.
To continue, operate the 'Run Auto
Cal' soft-key.
Running the Auto Span Process Unstable Reading Warning
After the 'Run Auto Cal' soft-key has been operated, a
countdown period starts before the span calibration process
begins. During this time D-Guard
2 checks the stability of the
gas readings. The stability of the readings can be observed on
the trend indicator. If the readings are stable and the trend
marker is in the mid position, the auto-span process will start.
If however, the readings are not stable a warning message will
be shown.
If the sensor is old and has become electrically noisy, it is
possible for the readings to be unstable. D-Guard
2
checks
stability and shows a warning if instability is too great to
perform an auto-span calibration. The extent of the instability
can be gauged by the distance the trend marker moves from
the centre. If the sensor stability is variable, the detector may
revert back to the auto-span countdown. If instability returns,
the stability warning screen will again be shown. D-Guard
2
re-
tries the auto-span process a number of times before
stopping.