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4. Measurement Method
1. In order for the TDL 300 to detect a gas leak, three conditions
must be met:
• The gas plume concentration ans size must be greater than the
minimum sensitivity of the TDL 300,
• The detecting laser beam must pass through the gas, and
• The background target, i.e. building, ground, etc., has to
reflect the laser beam back at equal to or greater than the
detector's requirement.
2. Turn on the detector, press the trigger, begin detection by aiming
at the target area. Note: Detection begins only after the trigger
is pressed. Let the laser beam pass through the gas plume and
reflect the laser on the ground, a building, etc. Because the
detecting laser is invisible you should use the spotter laser to
line up the detector with the target. Note: the detecting laser and
spotter laser are in parallel and the spotter laser is above the
detecting laser. Keep the spotter laser above the target around 50
mm when detecting a gas leak.
3. Detection begins after pressing the trigger. Once a gas leak is
detected the gas concentration will show on the detector's LCD
display. The detector will light up and sound an audible alarm
once the gas concentration exceed the pre-set alarm threshold.
The louder the sound the higher the concentration.
4. Several factors affect the concentration and size of a gas plume:
• Windy weather or high temperatures will lead to rapid diffusion
of gas, decreasing the gas concentration.
• Methane's density is lighter than air, and leaking Methane will
diffuse upward causing the gas concentration to become lower
with increased height from the ground.
Operators should take the above factors into consideration
during inspections and make the right judgment according to
their experience.
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5. To determine the location of a gas leak, work the laser beam in a
stable "S" pattern route back and forth to ensure the laser passes
through the target area. A constant alarm sound indicates a leak,
and operators should check where the sound is the loudest.
6. The TDL 300 can detect gas leaks from up to 30 m. Actual
distance may vary due to target surface and environmental
conditions. As the scanning distance is increased, the laser light
returned will decrease. As the maximum distance is approached,
a low fault alarm will sound telling you to move closer or change
the scanning angle in order to continue detection. It is best to
scan within 10 m to 20 m of the target.
• Experience with the TDL 300 will make aiming at the target
position easier and ensure the laser beam passes through the
target are.
• Windy weather or high temperatures will lead to rapid diffusion of
gas. Scan against the wind
• Methane's density is lighter than air. Scan directly over places
where gas leaks are likely to occur.
• The detection beam is a cone-shape. The spot/beam width size
will become larger with increased scanning distance and is
around 50 cm at 30 m.
• Obstructions or variations in landscape can cause dark zones
where the laser cannot scan. Change to a better angle and scan
the location again.
• Strong reflection off certain types of surfaces, e.g. stainless steel,
glass, polished surfaces, reflectors, etc., may give false readings.
Rescan the area from a different angle.
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