Abstract

The derivative spectrometer, developed for monitoring environmental air pollutants, employs signal processing to subtract the mean value of the minima of second derivative from the maximum, and to average the subtracted values. The signal processing leads to compensation of the long-term drift and hence to improvement of the sensitivity, i.e., the detection limit is 2–3 ppb or less for such gases as SO2, NO, and NO2, under circumstances where the ambient temperature fluctuates between 0 and 40°C.

© 1983 Optical Society of America

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References

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  1. R. N. Hager, Anal. Chem. 45, 1131A (1973).
  2. T. Izumi, K. Nakamura, J. Phys. E 14, 105 (1981).
    [CrossRef]
  3. T. Izumi, K. Nakamura, Anal. Chem. 53, 782 (1981).
    [CrossRef]
  4. D. T. Williams, R. N. Hager, Appl. Opt. 9, 1597 (1970).
    [CrossRef] [PubMed]
  5. A. R. Hawthorne, J. H. Thorngate, Appl. Opt. 17, 724 (1978).
    [CrossRef] [PubMed]
  6. J. W. Strojek, D. Yates, T. Kuwana, Anal. Chem. 47, 1050 (1975).
    [CrossRef]

1981

T. Izumi, K. Nakamura, J. Phys. E 14, 105 (1981).
[CrossRef]

T. Izumi, K. Nakamura, Anal. Chem. 53, 782 (1981).
[CrossRef]

1978

1975

J. W. Strojek, D. Yates, T. Kuwana, Anal. Chem. 47, 1050 (1975).
[CrossRef]

1973

R. N. Hager, Anal. Chem. 45, 1131A (1973).

1970

Hager, R. N.

Hawthorne, A. R.

Izumi, T.

T. Izumi, K. Nakamura, J. Phys. E 14, 105 (1981).
[CrossRef]

T. Izumi, K. Nakamura, Anal. Chem. 53, 782 (1981).
[CrossRef]

Kuwana, T.

J. W. Strojek, D. Yates, T. Kuwana, Anal. Chem. 47, 1050 (1975).
[CrossRef]

Nakamura, K.

T. Izumi, K. Nakamura, Anal. Chem. 53, 782 (1981).
[CrossRef]

T. Izumi, K. Nakamura, J. Phys. E 14, 105 (1981).
[CrossRef]

Strojek, J. W.

J. W. Strojek, D. Yates, T. Kuwana, Anal. Chem. 47, 1050 (1975).
[CrossRef]

Thorngate, J. H.

Williams, D. T.

Yates, D.

J. W. Strojek, D. Yates, T. Kuwana, Anal. Chem. 47, 1050 (1975).
[CrossRef]

Anal. Chem.

R. N. Hager, Anal. Chem. 45, 1131A (1973).

T. Izumi, K. Nakamura, Anal. Chem. 53, 782 (1981).
[CrossRef]

J. W. Strojek, D. Yates, T. Kuwana, Anal. Chem. 47, 1050 (1975).
[CrossRef]

Appl. Opt.

J. Phys. E

T. Izumi, K. Nakamura, J. Phys. E 14, 105 (1981).
[CrossRef]

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Figures (5)

Fig. 1
Fig. 1

Half-duration of a sample function (second-derivative signal), jf(t), obtained under the jth wavelength-scanning duration; t0 is a sampling period around the maximum and minima, and τA is an averaging time (τA = mt0).

Fig. 2
Fig. 2

Block diagram of the repetitive-scanning type derivative spectrometer: CM1, collimation mirror; CM2, condenser mirror; G, grating; S2, exit slit; PMT, photomultiplier tube; C, capacitor.

Fig. 3
Fig. 3

Relationship between the full width of electronic noise and the number of samples, m, for various time constants of the lock-in amplifier (τL). The spectrometer was adjusted for NO2 (i.e., center wavelength 448 nm) and the number of samples for the moving average 2n is 400. The unit in the vertical axis is in ppbNO2 gas concentration.

Fig. 4
Fig. 4

Relationships between the full width of electronic noise and the number of samples for the moving average, 2n, for various gases. The unit in the vertical axis is in ppb gas concentration.

Fig. 5
Fig. 5

Record of the output of the microcomputer-driven electronics MEE.

Tables (1)

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Table I Conditions of Optics and Electronics; (v + w), Total Number of Maxima (v) and Minima (w) in a Half-Period of Scanning

Equations (1)

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S j = 1 2 n p = j 2 n + 1 j d p ,

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