Method and apparatus for measurement of sheet opacity

Claim 3

Apparatus for measuring sheet opacity in combination with another optical measurement of the same sheet comprising an optical measurement gauge including means for impinging upon said sheet infrared radiations of one spectral band which is characterized by it lying outside any absorption band of the sheet material being measured or radiations in the visible band, means for impinging upon said sheet infrared radiations of a second spectral band which is characterized by it lying within a resonant absorption band of the sheet material being measured, detector means that are responsive to the intensities of the first and second spectral bands after they have impinged upon said sheet and producing a first electric signal which varies with the intensity of said first spectral band emerging from said sheet and a second electric signal which varies with the intensity of said second spectral band emerging from said sheet, means taking the ratio of said first and second electric signals and producing a resultant signal that depends on the amount of the material in said sheet which is being measured, and an opacity indicator means which is responsive to said first electric signal for indicating the opacity of said sheet.

Claim 4

Apparatus for measuring sheet opacity in combination with another optical measurement of the same sheet comprising an optical measurement gauge including means for impinging upon said sheet infrared radiations of one spectral band which is characterized by it lying outside any absorption band of the sheet material being measured or radiations in the visible band, means for impinging upon said sheet infrared radiations of a second spectral band which is characterized by it lying within a resonant absorption band of the sheet material being measured, detector means that are responsive to the intensities of the first and second spectral bands after they have impinged upon said sheet and producing a first electric signal which varies with the intensity of said first spectral band emerging from said sheet and a second electric signal which varies with the intensity of said second spectral band emerging from said sheet, means taking the ratio of said first and second electric signals and producing a resultant signal that depends on the amount of the material in said sheet which is being measured, and an opacity indicator means which is responsive to said first electric signal for indicating the opacity of said sheet.

Claim 5

The apparatus set forth in claim 2 wherein said first and second spectral bands are transmitted through said sheet and said detector means is responsive to the transmitted intensities of said spectral bands emerging from said sheet.

Claim 6

The apparatus set forth in claim 2 wherein said first and second spectral bands are reflected from said sheet and said detector means is responsive to the reflected intensities of said spectral bands emerging from said sheet.

Claim 7

The apparatus set forth in claim 2 wherein said sheet is a continuously moving web and said apparatus includes cyclically scanning means whereupon said gauge is mounted for transversely scanning said moving web and periodically moving to an off-web position, and automatic means for standardizing said gauge in said off-web position.

Claim 8

A gauge for measuring the opacity of a sheet of material in combInation with another optical measurement of the same sheet comprising a source of infrared radiations including at least infrared radiations to a first spectral band which lies outside of any absorption band of the sheet material being measured or radiations in the visible band, and infrared radiations of a second spectral band which lies within a resonant absorption band of the sheet material being measured, means for collimating the radiations from said source into a collimated beam passing through said sheet, a first filter for transmitting only the radiations in said first spectral band, a second filter for transmitting only the radiations in said second spectral band, chopper means intersecting said beam in which said first and second filters are mounted, said chopper means cyclically passing at a preselected frequency said filters in alternate succession through said beam and at all other times blocking said beam, a photoelectric detector means for sensing the radiations of said first and second spectral bands after the radiations in said band have passed through said sheet and alternately producing a first electric pulse signal which varies with the intensity of the radiations in said first spectral band, and a second electric pulse signal which varies with the intensity of the radiations in said second spectral band, a variable gain amplifier connected to said detector means for amplifying said first and second electric pulse signals, signal demultiplexer means connected to said variable gain amplifier for separately collecting said first and second electric pulse signals and producing a scatter reference signal output which is an average voltage value of said first electric pulse signal, and producing an absorption signal output which is an average voltage value of said second electric pulse signal, timing means for sensing the frequency of said chopper means and sending timing pulses to said signal demultiplexer means, a reference voltage source, comparing means for comparing the voltage from said reference voltage source with said scatter reference signal and producing an error signal which is the difference between said first reference voltage and said scatter reference signal, an error integrator responsive to said error signal, said error integrator being an integrating amplifier for producing an integrated voltage output, means feeding said integrated voltage output back to said variable gain amplifier to vary the gain of said variable gain amplifier in a manner such that said absorption signal output is equal to the ratio of said second electric pulse signal to said first electric pulse signal, readout means for said absorption signal, a zero and span amplifier connected to said error amplifier for amplifying said integrated voltage output, and an opacity readout means responsive to the amplified voltage output from said zero and span amplifier means for reading out an indication of the opacity of said sheet.

Claim 9

A gauge for measuring the opacity of a sheet of material in combInation with another optical measurement of the same sheet comprising a source of infrared radiations including at least infrared radiations to a first spectral band which lies outside of any absorption band of the sheet material being measured or radiations in the visible band, and infrared radiations of a second spectral band which lies within a resonant absorption band of the sheet material being measured, means for collimating the radiations from said source into a collimated beam passing through said sheet, a first filter for transmitting only the radiations in said first spectral band, a second filter for transmitting only the radiations in said second spectral band, chopper means intersecting said beam in which said first and second filters are mounted, said chopper means cyclically passing at a preselected frequency said filters in alternate succession through said beam and at all other times blocking said beam, a photoelectric detector means for sensing the radiations of said first and second spectral bands after the radiations in said band have passed through said sheet and alternately producing a first electric pulse signal which varies with the intensity of the radiations in said first spectral band, and a second electric pulse signal which varies with the intensity of the radiations in said second spectral band, a variable gain amplifier connected to said detector means for amplifying said first and second electric pulse signals, signal demultiplexer means connected to said variable gain amplifier for separately collecting said first and second electric pulse signals and producing a scatter reference signal output which is an average voltage value of said first electric pulse signal, and producing an absorption signal output which is an average voltage value of said second electric pulse signal, timing means for sensing the frequency of said chopper means and sending timing pulses to said signal demultiplexer means, a reference voltage source, comparing means for comparing the voltage from said reference voltage source with said scatter reference signal and producing an error signal which is the difference between said first reference voltage and said scatter reference signal, an error integrator responsive to said error signal, said error integrator being an integrating amplifier for producing an integrated voltage output, means feeding said integrated voltage output back to said variable gain amplifier to vary the gain of said variable gain amplifier in a manner such that said absorption signal output is equal to the ratio of said second electric pulse signal to said first electric pulse signal, readout means for said absorption signal, a zero and span amplifier connected to said error amplifier for amplifying said integrated voltage output, and an opacity readout means responsive to the amplified voltage output from said zero and span amplifier means for reading out an indication of the opacity of said sheet.

Claim 10

The apparatus set forth in claim 6 together with means whereupon said gauge is mounted for cyclically scanning said sheet and moving to an off-sheet position at periodic intervals, and automatic means for standardizing said gauge in said off-sheet position.

Claim 11

The apparatus set forth in claim 6 wherein said automatic standardizing means includes circuit interrupting means for sensing said off-sheet position and an auto-standardizing circuit controlled by said circuit interrupting means, said standardizing circuit being connected from the output of said error integrator to said comparing means and providing said reference voltage for said comparing means, said standardizing circuit including a differential amplifier receiving said integrated output signal as one input, and a preset reference voltage applied on the second input to said differential amplifier, an error integrator for integrating the output of said differential amplifier, and a holding amplifier for holding the error output voltage from said error integrator and applying said error voltage to said comparing means, said circuit interrupting means being connected in said standardizing circuit between said error integrator and said holding amplifier to close said standardizing circuit when the gauge is in the off-sheet position and to open said standardizing circuit when the gauge is moved away from said off-sheet position.

Claim 12

The apparatus set forth in claim 2 further comprising a reference voltage source, means for comparing the voltage from said reference voltage source with said first electric signal and producing an error signal which is the difference between said reference voltage and said first electric signal, means for integrating said error signal to provide an integrated voltage output, and means responsive to the output of said integrating means for controlling the level of said first and second electric signals, said opacity indicator means connected to be responsive to the output of said integrating means.