6
WARNING: If a check is to be made for trace amounts of gas, for example around the
foundation of a structure, the Survey or the Monitor – not the Bar Hole -
mode should be selected.
The Truck mode is faster and more sensitive than the Survey mode and as such, it may
require occasional re-zeroing. To re-zero, press the right key and then choose “Zero” by pressing
the right key again.
Survey to Truck Survey and Truck Survey to Survey:
Once either Survey or Truck
Survey modes have been entered, the transition from one to the other is relatively rapid (20
seconds). Either can be selected from the other by using the right button in each screen and
selecting Survey or Truck, as the case may be, in the screen that follows. It should be noted that
if another mode is selected in between, that is, either Bar Hole or Monitor, a warm-up period is
necessary when re-entering the Survey or Truck Survey modes.
Bar Holing:
The detector measures gas levels in sampling holes used for locating
underground natural gas resulting from seepage or leaks in a conduit. Gas concentrations in a bar
hole near a significant leak will exceed several percent. Therefore an alarm for gas is likely, but
since it is not relevant to the ambient atmosphere above ground, it is automatically suppressed.
During bar-holing, the alarms for all gases are automatically turned OFF.
To bar hole, select an appropriate probe (see Part 1, Section 7) and set the front panel to
Bar Hole (BH). The instrument automatically clears any residual gas and checks for clean air. The
pump is then turned off and the instrument is ready for bar holing. After inserting the probe into
the bar hole, press the “Go” button. The pump is turned on and the instrument samples gas for a
fixed time
(factory set time is 15 seconds)
. Readings during sampling are shown on the display.
At the end of the fixed time for sampling, the instrument turns off the pump, and displays the peak
and sustained readings. Both values are in % GAS.
If in the course of bar holing, water is encountered, press the left “Stop” button to stop the
pump. Use of a water-stopper (see Figure 2 in Section 8) will prevent water from entering the
instrument.
Monitor:
The detector shows the concentration of natural gas (methane) in air in steps of
0.05% GAS (1% LEL) up to 5% GAS (100% LEL) and then in steps of 1% GAS up to 100% GAS.
The concentrations of CO and O
2
are also shown if the unit is equipped with the corresponding
sensors (see below). To mute the alarm, press the middle button (mute is displayed). Pressing any
button backlights the display for 20 seconds. To backlight while in the Monitor mode, press the
middle (mute) button twice.
The peak reading for GAS is retained and displayed along with the current readings until
the unit is turned off, another mode of operation (e.g. Survey) is chosen, or a new zero is obtained.
To return from ‘Monitor” to the “Survey” mode, press BH and after the bar holding screen appears,
press Survey. Occasionally, the Survey mode may have to be re-zeroed (press Zero/off and then
Zero) after this transition.
