Spectrophotometer using plural filters

Claim 2

Apparatus for automatically determining the concentration of an unknown substance that absorbs radiant energy within a predetermined band of wavelengths in the presence of other interfering substances that absorb radiant energy in the region of the predetermined band, comprising in combination: a source of radiant energy; optical means for transmitting a beam of radiant energy along a single path through the substances; first filter means for transmitting a first radiant energy pulse at a first wavelength at which the absorption coefficients of the unknown substance and the interfering substances are substantially different; second filter means identical to the first filter means; third filter means for transmitting a second radiant energy pulse at a second wavelength at which the absorption coefficients of the unknown substance and at least one of the interfering substances are substantially The same; fourth filter means identical to the third filter means; rotational means for simultaneously rotating the first, second, third and fourth filter means so that at a first instant in time the beam is intersected by the first filter means at a first point along the path, by the second filter means at a second point along the path, and by the substances at a third point along the path between the first and second points and so that at a second instant in time the beam is intersected by the third filter means at the first point, by the fourth filter means at the second point and by the substances at the third point; transducer means for producing a plurality of electrical pulse signals, each of the electrical pulse signals corresponding to a predetermined one of the radiant energy pulses transmitted through the substances; synchronous detection means for separating the electrical pulse signals that correspond to radiant energy pulses having different wavelengths; means for periodically preventing the transmission of radiant energy through the substances so that a reference level is established; and electronic comparison means for comparing the electrical pulse signals to produce an analysis signal having a value that is proportional to a property of the predetermined substance.

Claim 3

Apparatus, as claimed in claim 1, wherein the transducer means produces a first electrical pulse signal having a first value proportional to the intensity of said first radiant energy pulse received by a transducer means and a second electrical pulse signal having a second value proportional to the intensity of said second radiant energy pulse received by the transducer means, and wherein the electronic comparison means produces an analysis signal having a value proportional to the logarithm of the ratio of the first value and the second value.

Claim 4

Apparatus, as claimed in claim 1, and further comprising: a disk rotatable around an axis for rotation; means for locating the first and second filter means on opposite sides of the disk along a first radian of the disk; means for locating the third and fourth filter means on opposite sides of the disk along a second radian of the disk; and means for rotating the disk.

Claim 5

Apparatus, as claimed in claim 3, wherein the means for periodically preventing comprises opaque segments of the disk separating the first, second, third and fourth filter means.

Claim 6

Apparatus for automatically determining the concentration of an unknown substance that absorbs radiant energy within a predetermined band of wavelengths in the presence of other interfering substances that absorb radiant energy in the region of the predetermined band, comprising in combination: generating means for generating and transmitting along a single path through the substances a first radiant energy pulse having a first wavelength substantially in the center of the energy absorption band of the predetermined substance, a second radiant energy pulse having a second wavelength that is less than the first wavelength and that is substantially outside the energy absorption band of the predetermined substance, and a third radiant energy pulse having a third wavelength that is greater than the first wavelength and that is substantially outside the energy absorption band of the predetermined substance; transducer means for producing first, second, and third electrical pulse signals corresponding respectively to said first, second, and third radiant energy pulses; first synchronous detection means for producing on a first conductor a first detected signal corresponding to said first electrical pulse signal; second synchronous detection means for producing on a second conductor a second detected signal corresponding to said second electrical pulse signal; third synchronous detection means for producing on a third conductor a third detected signal corresponding to the third electrical pulse signal; means for periodically preventing the transmission of radiant energy through the substances so that a reference level is established; first electrical filtering means for producing a first D.C. signal having a magnitude proportional to the amplitude of the first detected signal; second electrical filtering means for producing a second D.C. signal having a magnitude proportional to the amplitude of the second detected signal; third electrical filtering means for producing a third D.C. signal having a magnitude proportional to the amplitude of the third detected signal; summing means for producing a summed signal proportional to the sum of the second and third D.C. signals; timing means for generating a timing signal that varies monotomically; first comparator means for producing a first resultant signal when the first D.C. signal and the timing signal have a predetermined relationship; second comparator means for producing a second resultant signal when the summed signal and the timing signal have a predetermined relationship; and gate means for initiating the production of the analysis signal upon receipt of one of the resultant signals and for terminating production of the analysis signal upon receipt of the other resultant signal, said analysis signal having a value proportional to the logarithm of the ratio of the first D.C. signal and the summed signal.

Claim 7

Apparatus for automatically determining the concentration of an unknown substance that absorbs radiant energy within a predetermined band of wavelengths in the presence of other interfering substances that absorb radiant energy in the region of the predetermined band, comprising in combination: generating means for generating and transmitting along a single path through the substances a first radiant energy pulse having a first wavelength substantially in the center of the energy absorption band of the predetermined substance, a second radiant energy pulse having a second wavelength that is less than the first wavelength and that is substantially outside the energy absorption band of the predetermined substance, and a third radiant energy pulse having a third wavelength that is greater than the first wavelength and that is substantially outside the energy absorption band of the predetermined substance; transducer means for producing first, second, and third electrical pulse signals corresponding respectively to said first, second, and third radiant energy pulses; first synchronous detection means for producing on a first conductor a first detected signal corresponding to said first electrical pulse signal; second synchronous detection means for producing on a second conductor a second detected signal corresponding to said second electrical pulse signal; third synchronous detection means for producing on a third conductor a third detected signal corresponding to the third electrical pulse signal; means for periodically preventing the transmission of radiant energy through the substances so that a reference level is established; first electrical filtering means for producing a first D.C. signal having a magnitude proportional to the amplitude of the first detected signal; second electrical filtering means for producing a second D.C. signal having a magnitude proportional to the amplitude of the second detected signal; third electrical filtering means for producing a third D.C. signal having a magnitude proportional to the amplitude of the third detected signal; summing means for producing a summed signal proportional to the sum of the second and third D.C. signals; timing means for generating a timing signal that varies monotomically; first comparator means for producing a first resultant signal when the first D.C. signal and the timing signal have a predetermined relationship; second comparator means for producing a second resultant signal when the summed signal and the timing signal have a predetermined relationship; and gate means for initiating the production of the analysis signal upon receipt of one of the resultant signals and for terminating production of the analysis signal upon receipt of the other resultant signal, said analysis signal having a value proportional to the logarithm of the ratio of the first D.C. signal and the summed signal.

Claim 8

Apparatus, as claimed in claim 5, wherein said first detection means comprises: a gate circuit for shunting the signal appearing on the first conductor in response to a gate signal; and commutator means for producing a gate signal except during the generation of the first pulse.

Claim 9

Apparatus, as claimed in claim 5, wherein said first, second and third filtering means each comprise a low pass filter.

Claim 10

Apparatus, as claimed in claim 5, wherein said timing means comprises a resistive, capacitive circuit that generates a signal which varies exponentially.

Claim 11

Apparatus, as claimed in claim 5, wherein said first comparator means produces a resultant signal when the sum of the timing signal and the first D.C. signal equals zero.

Claim 12

Apparatus, as claimed in claim 5, wherein said gate means comprises: first flip-flop means connected to the first comparator means; second flip-flop means connected to the second comparator means; and an exclusive OR gate connected to the first and second flip-flop means.