General Overview
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SafeCheck 200 Operator’s Manual
7
2.3 Backlight:
The unit features a backlight which illuminates the screen for 10 seconds
each time a key is pressed. Refer to Section 3.4.3 Setup under Display
Options on page 14 to enable/disable the backlight illumination feature.
The backlight also illuminates for 10 seconds any time the unit goes into
alarm.
2.4 Alarm and Level Definition:
All of the following levels and alarm levels are based on the measurement
of one sample per second. Refer to Section 3.6.3 Setup under Alarms Set
on page 13 to change any of the alarm activation levels.
2.4.1 Oxygen Alarms and Levels:
Both oxygen deficient atmospheres and oxygen rich atmospheres present
gravely hazardous work conditions.
• Low: The Low alarm level for oxygen is any level less than 19.5%.
Oxygen deficiency is the leading cause of worker fatality during confined
space entry, therefore the importance of monitoring the oxygen level
cannot be overstated.
• High: The High alarm level for oxygen is any level greater than 23.5%.
Oxygen rich atmospheres can lower the combustible range of some gases
and can cause them to burn violently.
2.4.2 Combustible Gas Alarms and Levels:
Combustible gas levels can be measured as a percent of the LEL or as a
percent by volume of CH
4
(methane). Refer to Section 3.4.3 Setup under
Display Options on page 14 to change the way that combustible gas levels
are measured.
• LEL: LEL stands for Lower Explosive Limit. An atmosphere which
contains less than the LEL, the value of which varies among the com-
bustibles is referred to as a lean atmosphere. An atmosphere which
exceeds the UEL, or Upper Explosive Limit, the value of which also varies
among the combustibles, is referred to as a rich atmosphere. The range
between the LEL and the UEL is the combustible (explosive) range.
General Overview
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SafeCheck 200 Operator’s Manual
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The default alarm level is set to 10% of the LEL. When this level is
reached or exceeded, the unit goes into alarm. If the measured level
exceeds 98% of the LEL, the alarm automatically latches on and the unit
will remain in alarm until the unit is taken out of the RUN mode. When
this occurs, a high probability exists that the gas concentration is above the
LEL, in the combustible range, and overloading the LEL sensor.
• CH
4
: This is a mode where the unit is set up to measure a specific com-
bustible gas, methane (CH
4
) in a percent by volume concentration rather
than a percent LEL concentration. This is just a different way of reporting
the concentration of one specific gas (CH
4
). When CH
4
is at 5.0% by vol-
ume, it is also at 100% of it's LEL point.
The default alarm level is set to 0.5% by volume CH
4
. When this level is
reached or exceeded, the unit goes into alarm. If the measured level
exceeds 4.9% of CH
4
, the alarm automatically latches on and the unit will
remain in alarm until the unit is taken out of the RUN mode. When this
occurs, a high probability exists that the gas concentration is above 5.0%
by volume, in the combustible range, and overloading the combustible gas
sensor.
ALTHOUGH A RICH ATMOSPHERE MAY NOT PRESENT
IMMINENT DANGER OF IGNITING AT THE TIME OF CURRENT
MEASUREMENT, ANY DILUTION OF THIS RICH ATMOSPHERE
COULD BRING THE CONCENTRATION DOWN INTO THE
COMBUSTIBLE RANGE.
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