INFICON Sensistor ISH2000 Hydrogen Leak Detector - Manual (Page 56)

Sensistor ISH2000 Technical Reference Manual (TRM) EN- 56
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When the probe is moved around and over the product, the signal will increase
as the probe approaches the leak. If the signal goes out of scale, simply reduce
the sensitivity setting to bring the signal within the scale. Working with the sen-
sitivity setting this way you will be able to locate multiple leaks that are in close
proximity to each other.
Note: Working inside a confined space such as, for example, a cabinet or a nar-
row passage on a combustion engine there is a risk that the background con-
centration accumulates to levels close to the upper detection limit of the
detector. In such case it will not be possible to locate leaks as easily as in open
spaces.
Hint: Do not expose the probe to more gas than is necessary, because it will
slowly saturate with time. It is good practice to detect a leak, locate it, and
immediately remove the probe to avoid saturation. The probe is not damaged
by the exposure but it will recover more slowly. After excessive exposure it will
be less sensitive for a short period of time.
To quantify leaks
The Analysis Mode (or use the analysis figures in Combined Mode) is used
for measuring the size of a leak (or the concentration of a gas sample). To be
able to do this measurement and obtain correct values, the instrument must
first be calibrated using the calibration function.
In the Analysis Mode the detector determines the gas concentration from the
change, as the probe goes from being exposed to background to being
exposed to a certain gas concentration. The detector does not continuously
monitor the gas concentration but takes just one reading instead. Another suit-
able alternative name for this mode could be Sampling Mode. It is important to
keep this in mind when using the detector in this mode.
In Analysis Mode the probe should be moved directly from a background situ-
ation to the test point. The size of the leak in PPM, or any other selected units,
is shown on the display. The probe can and should be removed from the mea-
suring point as the measured value steadies and remains on the display. The
period during which the measured value is displayed can be adjusted in the
Analysis Mode Settings menu.
The leak detector operates in the range 0.5 - 2000 ppm H2 giving linearity
between 0.5 and 500 ppm. To obtain greatest accuracy over this range, follow
the calibration recommendation. See "Calibration of the leak detector" on
page page 57.