at or below 2.00%. We then arbitrarily choose a value to mix. The MGD
is then allowed to siphon this test mixture, and the display should read
the amount within 25ppm. To test the higher numbers, a tank of premixed
scientific grade 15.00% tracer gas is used. The MGD should display the
correct value within 0.2%.
HUMIDITY vs. ACCURACY:
As stated earlier water vapor or H
2
O is a normal component of air.
The unit of measure of humidity is known as %RH, or percent relative
humidity. An average value of humidity on a normal dry day is 20%,
whereas on a very humid day can reach into the nineties or 100% when
raining (misting). The MGD can correctly function with RH levels as
high as 50%, any value above 50 results in what is seen as negative
gas. Another way to state this is when the humidity goes up, the accuracy
goes down. Humidity and accuracy are inverses of each other. This
doesn’t mean that the MGD-2002 cannot be used when the humidity
goes above 20%. The wand section contains three independant filters,
one removes water vapor, one removes chloroflourocarbons, and the
last removes large particulates.
MOISTURE FILTER:
Dielectric’s revolutionary (Patent Pending) replacement filter car-
tridge system removes almost 100% of the moisture from the sample
air before entering the sensing compartment. Our revolutionary new
procedure allows the user to quickly assess the daily life-span of the
filter by simple visual cues. A new dry cartridge will be vividly bright
blue in color, and is shown in figure #1 on page 9. The moisture car-
tridge will turn pink as it removes moisture from the air (Figure #1 on
page 9). The filter cartridge is still within it’s useful life, but will de-
grade further to a clear white color if continually used in high humidity
environment or if water is present.
The useful life of these filters depends the relative humidity (%RH)
of the working environment. For example, on an average dry day, the
%RH is roughly 20%, in this case the filter should last between 4-6
hours. If the relative humidity climbs to 50% RH, the single cartridge
might last only 2-3 hours. If the humidity climbs to between 50-90%
RH, the filter may only last one hour.
8
