ELECTRICAL SYSTEM FOR USE IN OPTICAL DENSITOMETRY

• US 3,704,950 A
• Filed: 02/22/1971
• Issued: 12/05/1972
• Est. Priority Date: 02/22/1971
• Status: Expired due to Term

• Current Assignee: VWR Corp. (Avantor, Inc.)
• Original Assignee: Robert Rosencranz
• Inventors: Rosencranz, Robert
• Primary Examiner(s): Wibert, Ronald L.
• Assistant Examiner(s): McGraw, V. P.
• Application Number:
  US05/117,541
• Time in Patent Office: 652 Days
• Field of Search: 356/72,73,201,204,206,223,224,226,229,96,97,202,209 324/115,140
• US Class Current: 356/73
• CPC Class Codes: G01N 21/27 using photo-electric detection G01N21/31 takes precedence; circuits for computing concentration logarithmic circuits G06G7/24; photometric circuits in general G01J
• CPC Class Codes: G06G 7/28 for synthesising functions by piecewise approximation

Abstract

An electrical system for use in optical densitometry. The system includes a plurality of separately operable electrical circuits contained in a single unit, and each circuit is adapted to produce response characteristics in a single voltmeter or other associated readable instrument which characterize one selected property or characteristic of the specimen being analyzed. In use, with the electrical system operatively associated with a photometer and a voltmeter or the like, the user, by merely manipulating a single control, may select a circuit which will produce a readable signal indicative of the characteristic he wishes to measure, and such indication or measurement may then be read directly from the voltmeter, for example, while moving the switch to other positions will select other circuits and cause the voltmeter reading to indicate measurements of other characteristics of the same sample. All these operations may be carried out without the necessity of changing the sample, the photometer, the connections thereto, or the character of the voltmeter or other instrument providing the reading. The characteristics typically able to be read include (a) percent dot area of a half tone specimen, (b) the percent of light transmitted through or reflected from the specimen, and (c) the optical density of the specimen. The electrical circuits are arranged so that the signal furnished to the meter for indicating percent dot area is inversely proportional to the strength of the incident light, so that for indicating light transmission percentage, the signal furnished to the meter is directly proportional to the strength of the incident light, and so that for indicating optical density, the signal furnished to the meter is inversely proportional to the logarithm of the strength of the incident light.

Claims

1. An electrical system for use in optical densitometry, said system having means for detecting incident light transmitted through or reflected from a specimen, and an electrical indicator for indicating the magnitude of said incident light, Means for converting said incident light to an electrical input signal of a given polarity, a summing network adapted to produce a resultant signal for amplification, said network including means for combining said input signal and a signal having an opposite polarity and a fixed intensity greater than that of said input signal, means for amplifying said resultant signal, and means for feeding said amplified resultant signal to said electrical indicator for display thereon of a reading which is inversely proportional to the intensity of said incident light.

2. An electrical system for use in optical densitometry and adapted to provide, on a single associated instrument, readings indicative of plural optical characteristics of specimens exposed to light and having light transmitted through or reflected from said specimens for detection and measurement, said system including a photometer for detecting incident light and for convering said incident light to an input electrical signal, the magnitude of said input electrical signal emitted from said photometer being proportional to both the intensity of said incident light and to a biasing potential applied to said photometer, a first amplifier having a first input terminal for receiving signals of a first polarity and a second input terminal for receiving signals of a second and opposite polarity, and providing at an output terminal amplified signals of said second polarity;

means for controlling said photometer biasing potential, a source of unidirectional current of said first polarity, plural position selector means adapted to provide selected conductive paths through the elements of said system, said selector means being adapted, in a first position thereof, to provide an operative connection between said photometer and said second amplifier terminal for feeding said input signal to said second terminal and between the output of said amplifier and said instrument, whereby said instrument will display a reading directly proportional to the intensity of incident light received by said photometer, said selector means being adapted, in a second position thereof, to provide an operative connection between said photometer and said first amplifier terminal, between said means for supplying said unidirectional current and said first terminal and between said amplifier output and said instrument, whereby said instrument will display a reading which is inversely proportional to the intensity of light incident upon said photometer, and said selector means being adapted, in a third position thereof, to provide an operative connection between said photometer and said first amplifier terminal, between said means for supplying said unidirectional current and said first terminal, between said amplifier output and said instrument, and between said amplifier output and said means for controlling said photometer biasing potential, whereby said instrument will provide a reading which is inversely proportional to the logarithm of the intensity of the light incident upon said photometer.

3. A system as defined in claim 2 which further includes an impedance connected between said output terminal and said first input terminal, said impedance forming in conjunction with the impedance of said unidirectional current source a feedback loop for said amplifier.

4. An optical densitometry system including an electrical circuit adapted to produce for application to an associated electrical indicating instrument of the type directly responsive to the magnitude of an applied signal an output signal having a magnitude which is substantially inversely proportional to the magnitude of an input signal received by a portion of said system from an associated photometer, said system including an amplifier having an input terminal for receiving a signal of predetermined polarity, and an output terminal, and means for feeding the amplified output signal from said output terminal of said amplifier to said electrical indicating instrument, and means for feeding a sigNal of said predetermined polarity and of a predeterminable, variable magnitude to said input terminal, and means adapted to receive from said associated photometer an input signal of an opposite polarity to said predetermined polarity and of a magnitude which is directly proportional to the intensity of the incident light on said associated photometer, said magnitude being lesser than said predeterminable, variable magnitude, whereby said input terminal will receive a signal having a magnitude equal to the difference between said predeterminable, variable magnitude and said lesser magnitude, and whereby said output signal from said amplifier will bear an inversely proportional relation to the intensity of said input signal.

5. An optical densitometer of the type providing an output indication inversely proportional to the intensity of an incident light, comprising:

means comprising a photometer for producing an output signal of predetermined polarity and of an amplitude directly related up to a predetermined maximum level to the intensity of said incident light;

an amplifier having an input terminal and an output terminal and adapted to provide polarity inversion between said terminals;

means for applying said output signal from said photometer to said amplifier input terminal;

a source of unidirectional current of opposite polarity to the predetermined polarity of said photometer output signal;

means for applying said unidirectional current to said amplifier input terminal at an absolute voltage level greater than said predetermined maximum output voltage level of said photometer to develop on said output terminal an electrical signal inversely proportional to the output signal level of said photometer;

an output indicator directly responsive to an applied electrical signal; and

means for applying the output signal from said amplifier to said output indicator to provide an output indication inversely proportional to the intensity of said incident light.

6. An optical densitometer as described in claim 5, wherein said means for applying said unidirectional current to said input terminal comprise an adjustable voltage divider.

7. An optical densitometer as described in claim 6, wherein said densitometer further comprises an impedance element coupled between the input and output terminals of said amplifier, said element providing in conjunction with said voltage divider a feedback loop for determining the effective gain of said amplifier.

8. An optical densitometer for producing an output indication inversely proportional to the logarithm of the intensity of incident light comprising:

a photometer for detecting said incident light and for producing an output electrical signal of a given polarity and of a magnitude proportional to both the intensity of said incident light and to the magnitude of an applied bias;

a summing network for combining said output electrical signal from said photometer with a second signal of opposite polarity and of a fixed magnitude greater than that of said output signal to produce a resultant signal;

an amplifier having input and output terminals;

means for applying said resultant signal to said input terminal;

an output indicator responsive to an applied electrical signal;

means for applying a bias proportional to the amplified resultant signal on said amplifier output terminal to said photometer to achieve a logarithmic output characteristic therefrom; and

means for applying the amplified resultant signal from said amplifier output terminal to said indicating instrument to provide an output indication inversely proportional to the logarithm of the intensity of said incident light.