EP0067574A2 — Spectrophotometer

Claim 1

Independent Claim 242 words

A spectrophotometer having a light source (3), a scanning type monochromator (4) having an entrance slit (5) and an exit slit (11) for a light beam from the light source and containing a light dispersing or selection element (6a, 6b) and a wavelength drive mechanism (7) to provide light beams of different wavelengths over a light spectrum being scanned, beam-shaping optics (12) at the exit slit of said monochromator and an object photometer (17) for measuring the intensity of reflected or transmitted light from an object being tested (13) and generating an electrical signal proportional to the intensity of the light measured and electrically connected to means (18) for recording said electrical signal as a function of wavelength measured, characterised in that the spectrophotometer includes: (a) a beam splitter (14), positioned between said beam-shaping optics and said object, for dividing the beam exiting from the monochromator into first and second light beams, whereby the first beam is incident upon the object; (b) a reference photometer (16) measuring the flux of the second light beam and generating an output electrical signal proportional to the intensity of the light measured; and (c) a light source control (2), connecting said reference photometer with said light source, which receives the electrical signal from the reference photometer and generates a feedback electrical signal to adjust the intensity of the light source to maintain the reference photometer output electrical signal level constant across the light spectrum being scanned.

Claim 2

Dependent Claim 242 words

A spectrophotometer having a light source (3), a scanning type monochromator (4) having an entrance slit (5) and an exit slit (11) for a light beam from the light source and containing a light dispersing or selection element (6a, 6b) and a wavelength drive mechanism (7) to provide light beams of different wavelengths over a light spectrum being scanned, beam-shaping optics (12) at the exit slit of said monochromator and an object photometer (17) for measuring the intensity of reflected or transmitted light from an object being tested (13) and generating an electrical signal proportional to the intensity of the light measured and electrically connected to means (18) for recording said electrical signal as a function of wavelength measured, characterised in that the spectrophotometer includes: (a) a beam splitter (14), positioned between said beam-shaping optics and said object, for dividing the beam exiting from the monochromator into first and second light beams, whereby the first beam is incident upon the object; (b) a reference photometer (16) measuring the flux of the second light beam and generating an output electrical signal proportional to the intensity of the light measured; and (c) a light source control (2), connecting said reference photometer with said light source, which receives the electrical signal from the reference photometer and generates a feedback electrical signal to adjust the intensity of the light source to maintain the reference photometer output electrical signal level constant across the light spectrum being scanned.

Claim 3

Dependent Claim 46 words

2, A spectrophotometer as claimed in Claim 1 in which the electrical signal from the object photometer (17) and reference photometer (16) are separately amplified by two-stage amplifiers (20, 21) in which the voltage level at the output of the first stage is at virtual ground.

Claim 4

Dependent Claim 23 words

A spectrophotometer as claimed in Claim 2 in which the feedback resistance of the two-stage amplifier for the object photometer is electrically guarded.

Claim 5

Dependent Claim 27 words

A spectrophotometer as claimed in any one of the preceding claims in which the object photometer (17) and the reference photometer (16) have similar spectral response characteristics.

Claim 6

Dependent Claim 49 words

A spectrophotometer as claimed in any one of the preceding claims in which the recording means comprise a voltage to frequency converter (18) and said converter is electrically connected to an internal processor (9) which is connected to a computer (10) to provide a readout in standard colour values.

Claim 7

Dependent Claim 34 words

A spectrophotometer as claimed in Claim 5 in which the monochromator (4) is a double-grating type monochromator being continuously driven and wherein measurements are taken at different wavelengths selected by the internal processor (9).

Claim 8

Dependent Claim 24 words

A spectrophotometer as claimed in any one of the preceding claims in which the object photometer (17) and reference photometer (16) comprise vacuum diodes.

Claim 9

Dependent Claim 28 words

A spectrophotoseter as claimed in any one of the preceding claims in which the object photometer signal is measured at wavelength intervals provided by the shaft encoder (8).

Claim 10

Dependent Claim 17 words

. A spectrophotometer as claimed in Claim 1 in which the recording means comprises an A/D converter.

Claim 11

Dependent Claim 31 words

A spectrophotometer as claimed in Claim 1 in which the recording means comprises a voltage to frequency converter electrically connected to a microprocessor which provides a readout in standard colour values

Claim 12

Dependent Claim 137 words

/ 11. A method of measuring the colour of a sample wherein a beam of light from a monochromator, including a light source, is directed onto the sample and the light reflected by or transmitted through said sample is measured with an object photometer, characterised in that said beam of light is split into first and second beams, the first beam being directed at the sample while the second beam is directed to a reference photometer so as to measure the flux thereof and generate an output electrical signal proportioned to the intensity of said second beam and maintaining constant the intensity of light perceived by the reference photometer over the spectrum being scanned by utilizing said output electrical signals to generate feedback electrical signals arranged to effect appropriate adjustments in the intensity of the light source.

Claim 13

Dependent Claim 137 words

/ 11. A method of measuring the colour of a sample wherein a beam of light from a monochromator, including a light source, is directed onto the sample and the light reflected by or transmitted through said sample is measured with an object photometer, characterised in that said beam of light is split into first and second beams, the first beam being directed at the sample while the second beam is directed to a reference photometer so as to measure the flux thereof and generate an output electrical signal proportioned to the intensity of said second beam and maintaining constant the intensity of light perceived by the reference photometer over the spectrum being scanned by utilizing said output electrical signals to generate feedback electrical signals arranged to effect appropriate adjustments in the intensity of the light source.

Spectrophotometer

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