Campbell Scientific TGA100 Trace Gas Analyzer Manual - Manual (Page 21)

1.7 Specifications
1.7.1 Measurement Specifications
Sample Rate: 10 Hz
Averaging Period: 0.1 sec
Sample cell volume: 480 ml
Frequency Response (@ 4.8 liter/sec actual flow rate): 3 Hz
The TGA100 frequency response is determined by the averaging time (0.1 s) and the time for a new sample to fill the
sample cell. The frequency response was measured at 14.4 slpm flow rate and 50 mbar sample pressure (4.8 actual l/s)
by injecting 1 µl of N
2
O into the sample stream. The resulting time series and frequency response graphs are shown in
. Figure 1-9
Figure 1-9. TGA100 Impulse Response (left) and Frequency Response (right)
0.0 0.5 1.0 1.5 2.0
0
1
2
3
4
Concentration (ppmv)
Time (sec)
0.1 1 5
0.01
0.1
1
Frequency Response
Frequency (Hz)
The typical 10 Hz concentration measurement noise, given in , is calculated as the square root of the Allan
variance with no averaging (i.e. the two-sample standard deviation. This is comparable to the standard deviation of the
10 Hz samples calculated over a relatively short time (10 s). The typical 30-minute average gradient resolution is given
as the standard deviation of the difference between two intakes, averaged over 30 minutes, assuming typical valve
switching parameters.
Table 1
Table 1. Typical Concentration Measurement Noise
Gas Wave number
(cm -1 )
10 Hz Noise
(ppbv)
30-min Gradient
Resolution (pptv)
Nitrous Oxide N
2
O 2208.575 1.5 30
Methane CH
4
3017.711 7 140
Ammonia NH
3
1065.56 6 200
Carbon Monoxide CO 2176.284 3 60
Nitric Oxide NO 1900.08 13 260
Nitrogen Dioxide NO
2
1630.33 3 60
Sulfur Dioxide SO
2
1366.60 25 500
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