8
3.
INSTRUMENT CHECKS
Automatic Battery Check
If the battery life is less than about 1 hour, the display flashes
"Lo"
(low) between
readings. The batteries should be changed at a convenient time. If the battery life is over, the
display stays on
"Lo"
. The batteries must be changed to make the instrument operational.
Automatic Pump Check
If the intake is blocked, the display shows
"bloc"
(block) and the detector beeps until the
problem is cleared. This check is carried out whether or not a probe is being used.
If the intake is blocked during AUTO ZERO (see below), the display shows
"bloc"
but
the detector does not beep.
Check for Tight Connections
To check for tight connections, block the probe inlet to observe
"bloc"
on the display. If
"bloc"
fails to appear, there may be a leak (see Section 6, "Troubleshooting").
WARNING:
The instrument should not be operated if it fails to display
"bloc"
when the air
intake is blocked.
Automatic Zero
To adjust the zero automatically, advance the selector switch to "AUTO ZERO". Zero
adjustment, which takes 60 seconds, is typically required only once a day.
Models CGA-611 and CGA-612 do not have a separate position marked AUTO ZERO.
For these models, the AUTO ZERO mode is entered by switching from the % Oxygen position to
the PPM H
2
S position while holding down the RESET button.
Display
Automatic Operation
Air, O2
The oxygen sensor (if present) is adjusted.
GAS 1
The zero of the thermal conductivity sensor is adjusted.
CO
The zero of the CO sensor (if present) is adjusted.
GAS 2
The zero of the combustion sensor is adjusted.
H2S
The zero of the H
2
S scale (if present) is adjusted
.
End
The instrument beeps briefly denoting that it is ready for use.
If automatic adjustment of zero cannot be carried out, for example, because the methane
concentration is too high, the display shows
"nogo"
(no go) and the name of the scale that failed
to zero, and does not advance to
"End"
(see Troubleshooting Section).
CAUTION:
Zero adjustment
must
be carried out with clean air. If the air is not clean, a systematic
error will be introduced in subsequent measurements. The instrument will auto zero in
concentrations of methane below 0.25% (5% LEL) and concentrations of CO below
20 ppm. If higher concentrations of methane or CO are detected, the instrument will
not change its zero, and the display will show
"nogo"
(no go).
Automatic Sensor Check
If a gas sensor fails (opens up), the display shows
"FAIL"
along with the name of the
sensor that failed, e.g. GAS1, GAS2, or O
2
(see Troubleshooting Section). CO or H
2
S failures do
not produce the
“FAIL”
message.
