083730510A
DCN
Teledyne API T500U CAPS NO
2
Analyzer with NumaView™ Software
11
1.
INTRODUCTION, SPECIFICATIONS, APPROVALS, &
COMPLIANCE
Teledyne API’s Model T500U CAPS NO
2
Analyzer uses Cavity-Attenuated Phase-Shift
(CAPS) spectroscopy to render direct, true measurements of nitrogen dioxide (NO
2
). This
technology eliminates the need for catalytic conversion or reagents that then introduce
measurement artifacts from traditional heated metal converter-based chemiluminescence
instruments The T500U operates as an optical absorption spectrometer, wherein the
absorbance (lost light) is directly proportional to the path-length and the concentration of
the absorbing gas (Beer-Lambert law), providing direct measurement of NO
2
.
The T500U uses few components: an optical cell, a pair of highly reflective spherical
mirrors centered at 450nm (strong NO
2
absorbance band), a light emitting diode (LED),
and a vacuum photodiode detector. The LED is located behind a mirror at one end of the
cell, and the detector behind the other mirror at the opposite end of the cell. The LED emits
ultraviolet light (UV) into the cell; the light reflects back and forth between the two mirrors,
building intensity and running a very long path length. The long path length extends the
“time” or “life” of the photon, thus providing ample time to measure absorbance when NO
2
is present. Through the use of precisely timed data acquisition coupled with a proprietary
algorithm the measured absorption is translated into a phase shift, from which the NO
2
concentration is calculated. The phase shift decreases as the NO
2
signal increases.
The CAPS method is faster than the traditional chemiluminescence method since the
sample does not require cycling through a catalytic converter to calculate a difference
measurement. Its speed also makes measurement more precise due to the ability to capture
samples closer to “real time” before ventilation vortices (e.g., urban canyons and other
traffic-related forces) can scatter the concentration.
Economically, the Model T500U CAPS method is less costly to operate than traditional
analyzers in that it uses less power (~80W) and fewer components.
The section on Principles of Operation provides more detail on the behavior and technique
of the CAPS method for NO
2
measurement.
SPECIFICATIONS
Table 1-1. Specifications
Parameter
Description
Range
Min: 0-5 ppb Max: 0-1 ppm NO
2
(User-selectable)
Measurement Units
ppb, ppm, µg/m
3
, mg/m
3
(User-selectable)
Zero Noise
< 20 ppt
Span Noise
< 0.2% of r 20 ppt
Zero Drift
< 0.1 ppb / 24 hours
Span Drift
< 0.5% of reading / 24 hours
Lower Detectable Limit
< 40 ppt
Response Time
< 40 Seconds to 95%
Linearity
< 1% Full Scale
Precision
0.5% of reading above 5 ppb
Summary of Contents for T500U
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