15
(3) Insert the end of the sample probe into
the location to be sampled.
(4) Squeeze the aspirator bulb several times
to draw air from the remote location to
the sensor compartment. Allow one
squeeze of the bulb for every one foot of
sampling hose for the sample to begin
reaching the sensor compartment. Once
the sample has reached the sensor,
continue to squeeze the bulb at a rate of
once per second for another full minute
until readings stabilize.
Caution: Hand aspirated remote
sampling only provides continuous gas
readings as long as the bulb is being
squeezed.
2.5 Combustible gas sensor
The Ex Chek contains a single combustible
gas sensor.
It is important to note that catalytic "hot
bead" type combustible sensors require the
presence of oxygen (at least 10 percent by
volume) in order to detect accurately. A
combustible sensor located in a 100 percent
pure combustible gas or vapor environment
containing no oxygen will be unable to burn
the combustible gas and will produce a
reading of zero percent LEL.
For a detailed discussion of the theory
behind the Ex Chek combustible sensor,
see section 1.3 above.
2.5.1 Detection of missing or
damaged Ex Chek sensor
If the Ex Chek sensor has been
inadvertently removed or has sustained
internal damage the Ex Chek will sound an
audible alarm and flash the visible alarm
LED while displaying “F L T” on the LCD
display. The Ex Chek will stay in alarm
mode until the unit is shut off and an
operational sensor is installed.
Chapter 3. Calibration
The Ex Chek detector has been designed
for easy calibration. The on / off “MODE”
button is used to enter “Auto-Calibration”
mode, and to automatically make all
calibration adjustments.
It is also possible to manually calibrate the
instrument by using simple push-button
controls located on the instrument keypad.
“One-Button Auto-Cal” procedures are
discussed in Section 3.4. Manual
calibration procedures are discussed in
Section 3.5.
3.1
Verification of accuracy
The accuracy of Ex
Chek instruments should be checked
periodically with known concentration
calibration gas. Failure to check
accuracy can lead to inaccurate and
potentially dangerous readings.
Verification of accuracy is a two step
procedure. In the first step the Ex Chek is
taken to an area where the atmosphere is
fresh and the readings are checked. If the
readings differ from those expected in fresh
air a "zero" adjustment must be made. The
second step is to make sure the sensor is
accurate by exposing it to known
concentration test gas and noting the
response. LEL readings are considered
accurate when they are within ±10% of the
expected concentration as given on the
calibration gas cylinder. If readings are
accurate, there is no need to adjust your gas
detector. If the readings are inaccurate, the
instrument must be span calibrated before
further use.
Always check the
expiration date on calibration gas
cylinder(s) prior to use. Expired
calibration gas can lead to inaccurate
and potentially dangerous readings.