• + LOC % LEL - The Ultima Gas Monitor has been
exposed to a high concentration of gas (above the
LEL) and there is a possibility that the over-range
condition may still exist.
• + 100 % LEL - The Ultima Gas Monitor has been
exposed to a high concentration of gas (above the
LEL) and the over-range condition definitely still exists.
"!
CAUTION
In either mode, correct the condition causing the excessive
gas level and vent or purge the area before attempting the
following.
In the + LOC % LEL mode, the output signal will also be
locked at full-scale. If this condition occurs, the
Ultima Gas Monitor must be unlocked by performing
a "Zero Function" with the Ultima Gas Monitor
Calibrator or Controller. (See the Ultima Gas Monitor
Calibrator or Controller manual for details of "Zero
Function"). The Ultima Gas Monitor will not revert to
a normal condition until a successful zero operation
has been performed. This is an exclusive safety
feature of the Ultima Gas Monitor which pre-empts
the possibility of ambiguous readings when the
sensor is exposed to concentration of gas above
100% LEL.
In the +100% LEL mode, the combustible gas is over the
100% LEL range. It will return to normal operation
when the gas concentration level falls below 100%
LEL.
Calibration
As with any type of gas monitor, the only true check of its
performance is to apply gas directly to the sensor. The frequency
of the calibration gas tests depends on the operating time and
chemical exposures of the sensors. New sensors should be
calibrated more often until the calibration records prove sensor
stability. The calibration frequency can then be reduced to the
schedule set by the safety officer or plant manager. Before
calibrating the sensors, it is good practice to apply power to the
unit to allow the sensor to adapt to the new environment.
Sensors should be powered at least one full hour before any
calibration attempt is made.
Chapter 2, Start-up
2-3
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