BT CGA-411 Operation Manual page 12

B. Leak Detection
The TRACK GAS scale may be used to test for gas leaks and to locate their source. To
use this feature, connect an appropriate probe and turn the selector switch to the TRACK GAS
position. The display will show "Snif" (sniff) for about 10 seconds. After this initial warm-up,
the display shows the concentration of methane (natural gas) in air in % LEL (Model CGA-411)
or in % GAS (Model CGA-412). If ambient air is clean (contains no methane), the display
should read zero. If it does not, use the AUTO ZERO to adjust the instrument zero.
To locate a leak, advance the probe along a pipe or other conduit at a rate of about one
foot per second. Since methane is lighter than air, track a gas pipe from above wherever
possible. The beeper will sound once every two seconds at ambient concentrations of natural
gas, will speed up with rising concentration, and will beep continuously at 2% LEL (or 0.1% gas)
above ambient. By listening to the beeper or by reading the display, the source of the gas leak
can be located.
The TRACK GAS scale displays readings in increments of 0.2% LEL (CGA-411) or
0.01% GAS (CGA-412). The ambient gas concentration used to establish the lowest beep
frequency is automatically reset every time the TRACK GAS scale is selected.
The instrument response time depends on the length of the probe attached to the detector.
To shorten the response time (to about half a second) use a gooseneck probe and filter (see
Section 9). A gooseneck probe is also convenient for one-hand operation of the detector.
C. Bar Holing
The CGA-411 and CGA-412 may be used to measure gas levels in sampling holes used
for locating underground natural gas resulting from seepage or a leak in a conduit. Gas
concentrations in a bar hole near a significant leak will be several percent. Therefore, an alarm
for gas is likely, but it has no relevance to the ambient atmosphere above ground. Under these
conditions, the alarm for the % GAS display may be set to OFF (see Section 11). The % GAS
display is now a measuring scale. Alarms for CO and low or high oxygen will still be given, but
at a reduced frequency (once every fifteen seconds) so as not to interfere with the display of gas
concentrations.
Bar holing may be done with optional probes available from Bascom-Turner. These
include a 36" long plastic probe, a fiberglass probe, and a steel probe with an electrically
insulated handle (see Section 9). An optional accessory, the Water-stopper, may be used to
minimize interruptions from accidental aspiration of ground water (see Accessories).
D. Ambient and Flue Gas Testing for Carbon Monoxide
Ambient Air. The PPM CO display is used for measurements of carbon monoxide in
ambient air. Accessible concentrations are 1 ppm to 9999 ppm. Readings above 1000 ppm are
precise to about ±10%.
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