Brasch GSE Generation 2 - Maintenance; Testing the Response to the Target Gas

Maintenance
Testing the Response to the Target Gas
Carbon Monoxide and/or Nitrogen Dioxide Detectors
Testing these detectors requires that the target gas be applied to the sensor using one of two
methods. Gas can be applied from a tank of air containing a known concentration of the target
gas or from the exhaust of an operating engine to produce a level of target gas sufficient to
activate the detector. For the latter method, use a gasoline or petrol engine to produce CO
and a diesel engine to produce NO
2
.
Of the two methods of obtaining test gas, the simplest is operating an engine in the vicinity of
the detector under test. The engine should be placed about 10 feet away from the detector so
that exhaust gases will not contact the detector directly.
The engine should be allowed to operate until a level of the target gas is displayed on the
detector that is sufficient to activate the ventilation system. Depending upon the Low Alert and
delay switch settings, and the volume of the area where the detector is located, this may take
from 10 to 30 minutes.
Using test gas applied from a tank has the advantage of speed as well as assurance that the
detector is responding accurately to the target gas. However, the gas must be applied directly
to the sensor if the response is to be close to the value present in the tank. The test gas can
not be allowed to become diluted by the air in the room before it comes in contact with the
sensor. This reduces the concentration to a level too low to give the desired result.
While test gas is readily available for CO, gas containing low PPM levels of NO
2
is not as easy
to find. Check with your local environmental or chemical supply store for more information.
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CAUTION
Allowing the detector to come in direct contact with undiluted exhaust gases will decrease
the expected useful lifetime of the sensor. The high concentration of acids and other
components in the exhaust gas will overload the activated carbon filter inside the sensor and
will increase the effects of interfering gases on the accuracy of the sensor.
If the sensor becomes damaged, it must be replaced with a new sensor calibrated at the
factory.