GMI PPM Gasurveyor 500, User Handbook Manual

Page: 15 / 90

5
GENERAL INFORMATION
PPM Flammable 0 – 1000 ppm
This range is used to measure very low levels of gas and
indicates the parts per million concentration of the gas in
air (1000 ppm is equivalent to 0.1% Volume Gas).
The digital display reading resolves to 5 ppm with the
analogue bargraph following in steps of 40 ppm. The ppm
range is more sensitive than LEL and Volume ranges and
takes longer to stabilise. The detection principle is a
catalytic reaction with the sensitivity of the sensors greatly
enhanced compared to the LEL range. Digital signal
correction techniques are used to minimise drift. The ppm
range includes a manual zeroing procedure.
The ppm range has the option of using a ‘threshold’. By
this, we mean that we can display either a blank screen
or simply a zero (0) on the display, up to a pre-set level.
This allows small readings, which may not be due to the
gas we wish to find or very small amounts of gas, to be
ignored if they fall below any pre-set action levels. This
allows the operator to react only to significant levels.
The ppm range has no threshold set by default. If your
instrument has a threshold, write the level here:
.......................................................................................
The ppm range, by default, has the audible and visual
Geiger indication configured which provides indication
of gas concentration increase via the increased rate of
sounder and LED pulse.
When the instrument is switched on, the visual Geiger
indication is enabled and the audible Geiger indication is