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Journal of the Optical Society of America

Journal of the Optical Society of America

  • Vol. 50, Iss. 1 — Jan. 1, 1960
  • pp: 40–43

New Class of Wide-Range Logarithmic Circuit for a Light-Intensity Meter

DAVID S. GREY, PETER MARK, and STANLEY HASKELL  »View Author Affiliations

JOSA, Vol. 50, Issue 1, pp. 40-43 (1960)

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A new wide-range logarithmic circuit for a light-intensity meter is described. The circuit, consisting only of photoconductors and constant resistor, takes advantage of the inverse power law that the photo conductors obey. The indicator (miocroammeter) used is of simple linear type: the deflection is proportional to the current. Accordingly, the over-all response is logarithmic in light intensity. An experimental unit covering more than four decades of intensity is described. The same principle may be applied to nuclear radiation meters.

DAVID S. GREY, PETER MARK, and STANLEY HASKELL, "New Class of Wide-Range Logarithmic Circuit for a Light-Intensity Meter," J. Opt. Soc. Am. 50, 40-43 (1960)

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  1. Photoconductors are particularly desirable for use in compact light-intensity measuring devices because of their high responsivity.
  2. For a discussion of the physics of photoconductors see, for example: A. Rose, RCA Rev. 12, 350 (1951); H. Kallmann and B. Kramer, Phys. Rev. 87, 91 (1952); Proc. IRE 43, (1955); G. F. J. Garlick, Handbuch der Physik (Springer-Verlag, Berlin, 1956) Vol. XIX, p. 316.
  3. Superlinear photoconductors are excluded.
  4. Such photoconductors were supplied by the Clairex Company, New York, and from the Physikalische-Technische Werkstätten, Wiesbaden, Germany.
  5. Supplied by the Clairex Company, New York. The Clairex cells are particularly appropriate for compact exposure meters. The average photosensitive area of these cells is about 1 mm×5 mm. Measurements on these Clairex cells indicate that n≃0.5 and is nearly constant from 0.01 to 50 ft-c, that k≃4×104 and that the contacts are ohmic throughout the operating voltage range.
  6. Supplied by the P. Gossen Company, Erlangen, Germany.
  7. The ammeter's esistance, being in series with the parallel network, will affect the response. If C [in Eq. (9)] is the conductance of the two-element network and Rm is the meter resitance, the total conductance CT is C(1+CRm)-1. Consequently, so long as Rm is small compared with 1/C at high intensities, the logarithmic character of the response is not appreciably changed.
  8. Supplied by the Physikalische-Technische Werkstätten, Wiesbaden, Germany.
  9. R. Frerichs, J. Appl. Phys. 21, 312 (1950).
  10. H. Kallmann and R. Warminsky, Ann. Physik 4, 69 (1948).
  11. R. Frerichs and R. Warminsky, Naturwissenschaften 33, 251 (1946).
  12. F. Lappe. Z. Physik 154, 267 (1959).
  13. H. Kallmann and R. Warminsky, Research 2, 389 (1949).
  14. R. Hofstadter, Proc. IRE 38, 726 (1950); S. M. Ryvkin, J. Tech. Phys. (U.S.S.R.) 26, 2667 (1956); S. M. Ryvkin and A. V. Airapetyants, J. Tech. Phys. (U.S.S.R.) 27, 106 (1957).
  15. Ryvkin, Bogomazov, Konovalenko, and Mateyev, J. Tech. Phys. (U.S.S.R.) 27, 1601 (1957).
  16. Klick, Peake, Cole, Rabin, and Lambe, Nucleonics, 13, 48 (1955).

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