Auto Zero - Teledyne T200 User Manual

The heated molybdenum reacts with NO in the sample gas and produces a NO gas and a
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variety of molybdenum.
Equation 6-4
( 315 )
xNO + yMo → xNO + M O at ° C
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y z
Once the NO in the sample gas has been converted to NO, it is routed to the reaction cell
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where it undergoes the chemiluminescence reaction described in Equation 6-1 and
Equation 6-2.
By converting the NO in the sample gas into NO, the analyzer can measure the total NO
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content of the sample gas (i.e. the NO present + the converted NO present). By switching
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the sample gas stream in and out of the "moly" converter every 6 - 10 seconds, the T200
analyzer is able to quasi-continuously measure both the NO and the total NO content.
X
Finally, the NO concentration is not directly measured but calculated by subtracting the
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known NO content of the sample gas from the known NO content.
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A Z
UTO ERO
Inherent in the operation of any PMT is a certain amount of noise. This is due to a variety
of factors such as black body infrared radiation given off by the metal components of the
reaction cell, unit to unit variations in the PMT units and even the constant universal
background radiation that surrounds us at all times. In order to reduce this amount of noise
and offset, the PMT is kept at a constant 7° C (45° F) by a Thermo-Electric Cooler (TEC).
While this intrinsic noise and offset is significantly reduced by cooling the PMT, it is not
eradicated. To determine how much noise remains, once every minute for a short period
the analyzer diverts the sample gas flow directly to the vacuum manifold, bypassing the
reaction cell. During this period, only O is present in the reaction cell, effectively turning
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off the chemiluminescence reaction. Once the cell is completely dark ("zero" light), the
analyzer records the output of the PMT and keeps a running average of these Auto Zero
(Azero) values. This average offset value is subtracted from the raw PMT readings while
the instrument is measuring NO and NO to arrive at an Auto Zero corrected reading.
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180 Teledyne API T200 NO/NO /NO Analyzer with NumaView™ Software 083730200A DCN7962
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