Third Body Quenching; Light Leaks; Reaction Cell Temperature Control - Teledyne T200 User Manual

THIRD BODY QUENCHING

As described by Equation 6-3, other molecules in the reaction cell can collide with the
excited NO
photon of light. This is known as third party quenching.
Quenching is an unwanted phenomenon and the extent to which it occurs depends on the
properties of the collision partner.
• Larger, more polarized molecules such as H
quenching interferents of NO chemiluminescence.
• The influence of water vapor on the analyzer's measurement can be eliminated with
an optional, internal sample gas dryer (see Section 2.3.2.6).
• The interference of varying CO
negligible.
• In cases with excessively high CO
be calibrated out by using calibration gases with a CO
air.
Only very high and highly variable CO
•
interference. For those applications, it is recommended to use other analyzer models.
Please consult Teledyne API's Sales Department or our website (front cover, this
manual).
Smaller less polar and electronically "harder" molecules such as N
•
interference of this type as well, however, the concentrations of N
constant in ambient air measurements, hence provide a constant amount of
quenching that is accounted for in the calibration of the instrument .

LIGHT LEAKS

The sensitivity curve includes a small portion of the visible light spectrum (see Figure 6-2),
therefore it is important to ensure that the reaction cell is completely sealed with respect to
light. To ensure this:
All pneumatic tubing leading into the reaction cell is opaque in order to prevent light
•
from entering the cell.
• Light penetration is prevented by stainless steel filters and orifices.

REACTION CELL TEMPERATURE CONTROL

The stability of the chemiluminescence reaction between NO and O
changes in the temperature and pressure of the O
order to reduce temperature effects, the reaction cell is maintained at a constant 50° C, just
above the high end of the instrument's operation temperature range.
Two AC heaters, one embedded into the bottom of the reaction cell, the other embedded
directly above the chamber's exhaust fitting, provide the heat source. These heaters operate
off of the instrument's main AC power and are controlled by the CPU through a power
relay on the relay board (see Section 6.3.4.4).
A thermistor, also embedded in the bottom of the reaction cell, reports the cell's
temperature to the CPU through the thermistor interface circuitry of the motherboard (see
Section 6.3.3.3).
083730200A DCN7962
, causing the excited NO
*
2
amounts at low concentrations (less than 0.5%) is
2
Teledyne API T200 NO/NO
to return to its ground state without releasing a
*
2
O and CO are the most significant
2 2
concentrations (larger than 0.5%), the effect can
2
content equal to the measured
2
concentrations will then cause a measurable
2
and sample gases in the reaction cell. In
3
/NO Analyzer with NumaView™ Software
2 x
and O can cause
2 2
and O are virtually
2 2
can be affected by
3
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