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Abstract
A new densitometer, which has been constructed, could be used to provide a standard for density measurement or serve as the basis for an automatic densitometer.
The instrument does not employ servo mechanisms and has a minimum of moving parts. In principle it is an analogue computer which solves the equation, Density = log10 Io/I where Io is the incident intensity and I the transmitted intensity. The incident and transmitted intensities are measured in sequence by a photo-multiplier and the difference between their logarithms taken by a sample and hold circuit. Either an Analogue or a Binary Coded Decimal (BCD) output is available.
Its precision is better than 0.5% or 0.002 density whichever is the greater.
Its accuracy, as with all densitometers, depends on the efficiency of collection of the light, its spectral response and the definition of density. It is certainly no worse than existing densitometers and probably better. The agreement with the Ilford standard Visual Densitometer is very good.
It is calibrated by reference to an electrical standard which can be readily established and maintained. The calibration can be checked easily and rapidly at any time.
Notes
The work described in this paper was carried out before Mr. Hercock’s retirement. Regrettably, since the preparation of the paper he has died.Footnote