5
WARNING:
The operation check is NOT equivalent to calibration and cannot be used as
a substitute for calibration.
If two or more bars are consistently absent, replace the natural gas sensor or
return the instrument for repair.
CAUTION:
Operational Modes.
The instrument operates in four distinct modes: “Survey”, “Truck
Survey”, “Bar Hole” and “Monitor”. An operating mode may be entered from another by pressing
the appropriate button either during warm-up or regular operation. For example, the Bar Hole
Mode can be selected when the instrument is first turned on by pressing the left “BH” button during
the warm-up period for the Survey Mode.
Survey:
Connect an appropriate probe and power the unit. Following the preliminary
displays (see above),
“Survey PPM”
is shown for about 20 seconds. At the end of the warm-up
period “
Operation Check
” is available. To use it, present a source of at least 100ppm methane in
air to the probe intake. The Rover will automatically carry out the operation check and, if
satisfactory, will display “
Operation Check OK
”. If the check is not satisfactory, a “
Please
Calibrate
” message will appear. Calibration can be carried out as described in Part 2.
The Operation Check is offered when the instrument is first turned on. It is not offered
when the Survey mode is re-entered subsequent to bar-holing or monitoring. The time window
for carrying out the calibration check is 30 seconds; the test can be bypassed by pressing the
“Override” button in the initial screen or subsequently in the “
Please Calibrate
” screen.
After the instrument enters the Survey mode, it shows the concentration of gas in air in
parts per million by volume (ppm). The beeper will sound if the ambient concentration of gas rises
above a user selected value (see Part 2, Section 1). The factory set value is 10ppm. If it is desirable
to silence the beeper during a leak survey, the middle switch mutes the instrument (“
Mute
” appears
on the display). If the gas concentration is over 10,000 ppm (1% gas by volume), the unit
automatically enters the Monitor mode (see below).
Under some circumstances, it may be necessary to re-zero the survey mode. If a “fresh”
zero is required, for example, if the zero has drifted with the result that the instrument shows a
reading when sampling clean air, press the right switch after raising the probe away from the
ground, then press the right “Zero” button. The reading will be reset to zero within a few seconds.
The
Symbol.
The symbol depicted here is used in the “Survey” mode to indicate
sensitivity at any particular instant. In general, sensitivity is an inverse function of background
noise – the lower the noise, the greater the sensitivity. The noise is primarily thermal and is caused
by convection.
Under most circumstances, all three vertical bars should be present. If the background
noise increases, one or more bars will be missing and in extreme circumstances, the whole symbol
may disappear. If the noise level rises so that more than two vertical bars are deleted, the
instrument should be allowed to return to its normal state by holding it steady for about two to
three seconds.
Survey by Truck:
If a survey is to be conducted by truck, turn the instrument on as above
and carry out a calibration check. Connect the instrument, using an appropriate filter, to the
sampling system of the truck (see Appendix 2) and select the Truck mode.