Abstract: A method of photometric in vitro determination of the content of an analyte in a sample is disclosed. The sample is located in a measuring chamber which has a radiation path length and has at least one at least partially transparent wall part. The measuring chamber is in optical communication with an optical system adapted for the analyte which includes a radiation source and a radiation detector. The measuring chamber is adjustable in shape which enables the radiation path length across the measuring chamber to be changed. In a first measuring step an unknown first radiation path length across the measuring chamber is set and radiation at at least two wavelengths is transmitted from the radiation source through the measuring chamber and to the radiation detector. In a second step, the measuring chamber is adjusted in shape thereby setting a second unknown path length across the measuring chamber.

Abstract: A sampling device for photometric determination of the content of an analyte in a sample of whole blood has at least one measuring chamber having two wall parts, at least one wall part being locally transparent, at least one wall part being sufficiently deformable to facilitate displacement of the whole blood sample from the measuring chamber. The measuring chamber also contains a transparent body having a radiation transmission characteristic dependent upon the concentration of a predetermined analyte in the whole blood sample. The sample device is employed in an analyzer for photometric determination of the content of an analyte in a sample of whole blood and in a method of photometric in vitro determination of the content of an analyte in a sample of whole blood.

Abstract: The purpose of the invention is to properly determine the replacement time of a guard window of an arc sensor using an original function of the arc sensor.The apparatus for monitoring a guard window of an arc sensor according to the present invention is provided with an arc sensor guard window (28) mounted on an arc sensor unit (20) and a standard reflecting plate (30) located at a position a determined distance from the front surface of the guard window (28). And the apparatus detects the reflected light (27) from the standard reflecting plate (30) when a laser beam (26) scans the standard reflecting plate (30), before the guard window (28) is used for an arc welding operation. The apparatus memorizes the quantity of detected light reception as the first quantity. The apparatus then detects the reflected light (27) from the standard reflecting plate (30) in the same way as before, after the guard window (28) is used for an arc welding operation.

Abstract: A dual wavelength optical sensor for measuring chemical properties of a particular quantity, the optical sensor including a sensor probe having a thin sensing film whose optical characteristics are responsive to the chemical properties of the measured quantityThe United States Government has certain rights in this invention pursuant to Contract No. ITA87-02 between the U.S. Department of Commerce and Iowa State University.

Abstract: The invention is a media positioning system for determining the position of the media relative to reference positions thereof in a media transporter in which media having opposed faces is transported along a path of a track including a spatially varying pattern on the media, the alignment system including a light sensor having a light-sensitive surface facing one face of the media in at least approximate registration with the track, the light-sensitive surface including plural sections, the sensor producing plural signals at an output thereof proportional to the intensity of light impinging on respective ones of the plural sections of the light-sensitive surface, a light source facing the other face of the media and directing a beam of light through the media onto the light-sensitive surface, whereby the plural signals vary as a function of the spatially varying pattern of the track as the media is transported along the path of the track, and signal detection and logic apparatus for converting the plural sign

Abstract: A sampling device for photometric determination of the content of an analyte in a sample of whole blood has at least one measuring chamber having locally transparent wall parts, at least one wall part being sufficiently deformable to facilitate displacement of the whole blood sample from the measuring chamber, with a transparent body having a radiation transmission characteristic dependent upon the concentration of a predetermined analyte in the whole blood sample disposed between the wall parts. The sampling device is employed in an analyzer for photometric determination of the content of analyte in a sample of whole blood and in a method of photometric in vitro determination of the content of an analyte in a sample of whole blood.

Abstract: Method and apparatus for monitoring film formers in an opaque process stream by immersing a segment of a transparent eccentrically mounted rotatable disc in the fluid stream, allowing time to accumulate film formers, then rotating the disc to expose the previously immersed section to optical monitoring by which a sample transmittance may be compared to a reference transmittance; the disc may have a segment presenting a hydrophilic surface and another segment presenting a hydrophobic surface so that different kinds of film formers may be monitored.

Abstract: A method and apparatus for analyzing fluid by a multi-fluid modulation mode is characterized by subjecting a plurality of sample fluids (which may be different or a single sample fluid divided into a plurality of systems) to a fluid modulation by reference fluids at various frequencies, respectively. An analytical portion provided with only one sensor is simultaneously and continuously supplied with the respective sample fluids. An output signal from the sensor in the analytical portion is divided into signal components of the respective modulation frequencies for the respective sample fluids to rectify and level, whereby obtaining analyzed values about the respective sample fluids is achieved.

Abstract: Particle pattern images of the sample are optically measured by an image reader of a particle agglutination pattern judgment apparatus, and the measured particle pattern images are retrieved by a data processing controller to be able to execute pattern judgment processing. The data processing controller obtains predetermined parameters on the basis of the particle pattern images read by the image reader, and automatically judges an agglutination, non-agglutination, or unidentified attribute of each particle pattern on the basis of the obtained parameters. An operator visually observes the particle pattern images of the sample to visually determine an agglutination, non-agglutination, or unidentified attribute of each particle pattern of the sample. The operator inputs the visual judgment results in the particle agglutination pattern judgment apparatus using an input unit.

Abstract: In a media transporter which positions media, a method and apparatus is provided for positioning the media for accurate alignment. The method includes the steps of sensing a spatial pattern of densities in the media along a scanned strip, saving the spatial pattern of densities during the initial pass to create a path map from the start position to an end point, comparing subsequently sensed spatial patterns of densities to the path map, and following the path map to repeatedly and accurately position the media at any point along the scanned path. The spatial pattern of densities in the media is sensed by shining a light through the media and sensing the transmitted light intensity.

Abstract: Automatic particle pattern judging method, in which particles to be tested, such as blood cell particles, are delivered into not only a reaction vessel but also a reference vessel, and an amount of the particles delivered into the reference vessel is measured and a judgement whether the particle pattern formed in the reaction vessel is agglutinated or not is conducted by correcting values of a reaction liquid contained in the reaction vessel concerning parameters for the judgement or correcting threshold values, with which the values of the test liquid concerning the parameters should be compared in accordance with the amount of the particles delivered into the reference vessel. Therefore, by the method according to the invention, even when the amount of particles to be tested delivered into the reaction vessel is varied for some reason, it is possible to judge correctly whether the particle pattern is agglutinated or not.

Abstract: A system for analysis of specific binding complexes. A reaction surface is treated with a specific receptor chemical (SRC) having specific binding properties and is allowed to bind with an unknown reactant to form specific binding complexes (SRC) on the reaction surface. The output of a laser is directed through the reaction surface to a detection mechanism. Shadows in the detected light may be interpreted to detect the presence of the unknown reactant. The unknown reactant may also be quantified. Preferred embodiments of apparatus, and methods of their use, are disclosed for detecting the presence of the unknown reactant within a system for interpreting the results, including interactive system components by which the bases for interpretation may be updated.

Abstract: Analyzing the level of a treating agent and/or stress metals in a body of water containing an inert transition metal tracer added to the water proportionally with the treating agent by determining the absorbance (first absorbance value) of a reagent dye added to water, said dye producing a second absorbance value when reacted at the same concentration with the tracer and stress metals in a measure of said body of water, and said dye producing a third absorbance value when reacted at the same concentration with only the transition metal contained in a measure of said body of water; determining the second and third absorbance values and resolving their differences to determine the concentration of the tracer and, separately, the concentration of said stress metals.

Abstract: A photomultiplier (10) with an elongated rectangular, cathode (20) tilted with respect to the inlet opening (14) is alternately illuminated by a measuring light beam (36) and a reference light beam (40). The measuring light beam (36) and the reference light beam (40) extend in a plane parallel to the longitudinal sides of the cathode (20) and impinge upon the cothode (20), such that they illuminate the same areas of the cathode (20).

Abstract: An apparatus for detecting overlapped paper sheet feed in a paper sheet feed path. The apparatus includes a photosensor and a load resistor located in the paper sheet feed path for detecting a voltage representing a light transmittivity of paper sheet(s) fed through the paper sheet feed path.

Abstract: A method for analyzing fluid by a multi-fluid modulation mode is characterized by subjecting a plurality of sample fluids (which may be different or a single sample fluid divided into a plurality of systems) to a fluid modulation by reference fluids at various frequencies, respectively. An analytical portion provided with only one sensor is simultaneously and continuously supplied with the respective sample fluids. An output signal from the sensor in the analytical portion is divided into signal components of the respective modulation frequencies for the respective sample fluids to rectify and level, whereby obtaining analyzed values about the respective sample fluids is achieved.

Abstract: A luminometer for assaying bioluminescence and chemiluminescence reactions characterized by sample wells having transparent bottom walls, a light detector positioned beneath the sample wells and a reagent injector above the wells.

Abstract: There is provided a gas analyzer, including a radiation source, an analytical space through which passes the gas to be analyzed, at least one detector for detecting the intensity of radiation passing through the space, apparatus for facilitating the alternating introduction, into the space, of the gas to be analyzed and a reference gas having a concentration located at least in the upper half of the range of concentrations to be measured by the gas analyzer. The analyzer further includes processing apparatus, having a memory device, to process signals originating in the detector, the memory device adapted to store in a first mode of operation, signals representing instantaneous intensity values of the detected source and, in a second mode of operation, to store signals representing intensity values obtained when the analytical space is filled with the reference gas, a circuit for comparing the instantaneous values with the reference value, and an indicator device for indicating concentration.

Abstract: A probe for remote spectrometric measurements of fluid samples having a hollow probe body with a sliding reflective plug therein and a lens at one end, ports for admitting and expelling the fluid sample and a means for moving the reflector so that reference measurement can be made with the reflector in a first position near the lens and a sample measurement can be made with the reflector away from the lens and the fluid sample between the reflector and the lens. Comparison of the two measurements will yield the composition of the fluid sample. The probe is preferably used for remote measurements and light is carried to and from the probe via fiber optic cables.

Abstract: A portable hand held instrument is capable of making accurate colorimetric measurements in the field. The instrument has a body which houses the electronic circuitry and a door which allows a vial having a solution to be measured to be placed therein. The vial is illuminated lengthwise by a light beam of two wavelengths, one of which serves as a reference. The light emerging from the top of the vial is spatially integrated and directed to a detector. The detector measures the intensity of the transmitted light, and the electronic circuit determines the difference between the logarithms of the detected signals. This difference is multiplied by a constant to produce a signal representative of the concentration and is displayed. The resolution of the measurement is automatically increased when the processor senses that the signals are too small.

Abstract: A system to apply a bar-code label or the like upon a product or to apply a protective laminate strip or the like upon a bar-code label or the like which is already in place upon a product. The label or the protective laminate strip first is removed from a moving carrier and applied to an applicator head which, in turn, applies the label on the product or the protective laminate strip very precisely onto the label. The relative positions of the applicator head and the label, for example, are predetermined. It remains to establish the moving forward edge of the bar-code label or the protective laminate strip to be stripped from the moving carrier so that the either can be accurately placed on the applicator head, a particularly vexing problem in view of the fact that transmissivity, usually, or reflectivity of all the films involved, typically, have closely related optical characteristics.

Abstract: An adaptor for holding a micropipette in a spectrophotometer includes a base member for holding the micropipette and an optical system for linearly focusing visible or ultraviolet light onto the micropipette. Specifically, the optical system includes a cylindrical lens which focuses collimated light from a light source into a line along the axis of the micropipette. The optical system also includes a cylindrical quartz lens which recollimates the light that has passed through the micropipette sample holder. A detector is provided to receive the recollimated light for measuring the absorptivity of the sample material held in the micropipette.

Abstract: Apparatus (10) and methods for measuring dark and bright reflectances of translucent sheet material (2) are disclosed. The apparatus (10) comprises first optical means for illuminating one side of the sheet material (2) with a source of electromagnetic radiation. A portion of the radiation is transmitted through the sheet material (2) and another portion of the radiation is reflected by the sheet material. The apparatus (10) also comprises optical gating means (30) that is positioned adjacent the other side of the sheet material (2) in a fixed position relative to the first optical means. The optical gating means (30) absorbs substantially all of the transmitted portion of the radiation when switched to a dark state and reflects substantially all of the transmitted portion of the radiation back through the sheet material (2) when switched to a bright state.

Abstract: A variable optical attenuator includes incoming and outgoing surfaces which are inclined relative to each other so that light reflected at an attenuating coating on one or both surfaces is reflected away from the optical path to avoid interference effects. The attenuating coating varies in density depending upon the angle of rotation of the attenuator. Variable attenuation may be achieved by rotating the attenuator a predetermined amount under microprocessor control.

Abstract: In a method and a device for determining the optical transmission factor of a glass panel by identification transmits an incident electromagnetic radiation towards the glass panel and the intensity of the reflected radiation is detected and measured. The reflection coefficient of the panel is compared with reflection coefficient reference values representing the transmission factor of tinted glass reference panels to determine the optical transmission factor of the panel examined.

Abstract: An examination apparatus measures the oxygenation in body organs by the near infrared light transmission spectrophotometry. To inspect the examination apparatus itself before the oxygenation measurement, an illumination-side fixture and a detection-side fixture have such structures that these fixtures can be assembled together in such a manner that near infrared light is directly made incident on the detection-side fixture from the illumination-side fixture. In the midst of the measurement, the examination apparatus is regularly inspected and a photomultiplier tube can be separately inspected by employing a separate light source for inspection.

Abstract: An improved aethalometer (10) having a single light source (18) and a single light detector (20) and two light paths (21, 22) from the light source (18) to the light detector (20). A quartz fiber filter (13) is inserted in the device, the filter (13) having a collection area (23) in one light path (21) and a reference area (24) in the other light path (22). A gas flow path (46) through the aethalometer housing (11) allows ambient air to flow through the collection area (23) of the filter (13) so that aerosol particles can be collected on the filter. A rotating disk (31) with an opening (33) therethrough allows light for the light source (18) to pass alternately through the two light paths (21, 22). The voltage output of the detector (20) is applied to a VCO (52) and the VCO pulses for light transmission separately through the two light paths (21, 22 ) are counted and compared to determine the absorption coefficient of the collected aerosol particles.

Abstract: An apparatus for the calibration and quality assurance of a multichannel spectrophotometer, particularly an ELISA spectrophotometer, comprises a series of filters having a known first color and linearly increasing optical density. The response of the spectrophotometer is measured against the known color and linearly increasing optical density. Additional filters of at least one additional color permit checking the color response of the spectrophotmeter. An algorithm determines whether the response conforms to predetermined conditions. An output is produced to provide a record of the calibration and quality assurance of the spectrophotometer. The invention has particular utility for conducting calibration and quality assurance of ELISA spectrophotometers used in clinical laboratory screening for infectious diseases, such as Hepatitis B and the AIDS viruses.

Abstract: An apparatus and method for spectrophotometric analysis of material in a moving process stream wherein the material is directed into an observation chamber within a sample cell and exposed to a radiation beam suitable for spectrophotometric purposes. A radiation source and a radiation detector are contained within a first compartment and a second compartment environmentally isolated from the first compartment and within which the sample cell is contained. Reflectors are positioned within the second compartment for receiving the radiation beam from the first compartment, directing the radiation beam through the sample cell and the material to be analyzed contained therein, and directing the radiation beam back into the second compartment and the radiation detector positioned therein. The second compartment maintains the environment therein within a range acceptable for radiation analysis of the material within the sample cell.

Abstract: The invention relates to a method of taking measurements along an optical transmission path by means of an optical sensor. The optical sensor includes an optical converter whose optical attenuation properties can be influenced according to the value to be measured and through which a first beam portion of a high-frequency amplitude-modulated optical transmission beam is passed. A second beam portion of this transmission beam is conveyed via a delay element. The second beam portion is applied together with the first beam portion outputted by the optical converter, via the transmission path as a receive beam to the receiver arrangement. In this way the modulation change produced by the sensor is processed and evaluated as an information about the measure value. Measuring a value at the transmitter end is possible with any optical transmission path of an undefined length, without recalibration of the receiver arrangement, because the optical transmitter beam is additionally subjected to low-frequency modulation.

Abstract: A photometer in which a measuring phase, a reference phase and a dark phase are produced by means of a chopper. These phases are staggered in time, so that a single detector can be provided for all phases. In the photometer the object to be measured is situated between two light conductors, the one light conductor leading to the detector and the other light conductor leading to the chopper input. The chopper output is carried by an additional light conductor to the detector.

Abstract: A device for detecting a thickness variation of a piece of fabric passing under the presser foot of a sewing machine. The device includes a transmitter and receiver between which the fabric passes. The receiver stores maximum and minimum signals in memory units generated when the fabric passes between the transmitter and receiver. A computing unit calibrates the thresholds as a function of the stored maximum and minimum signals. A comparator compares the incoming signals with the calibrated thresholds and sends a signal to a logic unit to control the sewing operations accordingly.

Abstract: An optoelectric circuit for measuring the different optical densities of an image carrier, a toned test patch in an otherwise untoned imaging area of a photoconductor surface in a xerographic apparatus, wherein a LED (46) irradiates a test area of the surface, a phototransistor (47) receives radiation reflected from the text area, an amplifier (51) amplifies the output signal of the phototransistor, the LED is driven by the amplified output current of the phototransistor, and the current through the LED is used as a measure of the optical density.

Abstract: A method of detecting the feeding of doubles in a high speed document counter is disclosed. Also, a method of detecting the feeding of a chain of documents as a batch of documents are fed through a feed path is disclosed.

Abstract: A photometric measuring apparatus having a measuring chamber which can be cut off from extraneous light when a sample vessel is inserted and removed from the open end of the measurement chamber. A plunger, having a light-tight seal, movable vertically and horizontally on a pivotable arm driven by a drive mechanism for sealing the measuring chamber after a sample vessel is inserted in the measuring chamber. A guide means comprising a cylindrical guide tube having a guide groove on its surface which acts as cam means for controlling the vertical and horizontal movement of the plunger. The drive mechanism includes a drive motor and photocells for controlling the drive of the motor and vertical movement of the plunger and drive of the motor until the sample vessel upon which measurements have been completed are removed. The drive motor is spring mounted and actuates a microswitch to interrupt the motor drive when the drive is obstructed by the operator.

Abstract: A method and apparatus for monitoring the passage of sheets past at least one sensing assembly (48,49). The sensing assembly (48,49) generates an output signal whose level varies in accordance with a characteristic of the sheets, for example the thickness of the sheets. The method comprises for the or each sensing assembly, presetting a first threshold (62) spaced by a predetermined amount from a datum output signal level (57) when no sheet is sensed, the predetermined amount being such that the first threshold (62) is not passed as a result of random noise variations in the output signal but is passed during the passage past the sensing means of all sheets which it is desired to monitor. The size of the output signal from the sensing means (48, 49) relative to the datum level is monitored when the output signal first passes the first threshold (62) corresponding to the passage of a first sheet.

Abstract: A color photosensitive device includes a transparent base plate and a lamination of alternate layers of transparent conductive films and photoelectric conversion layers. The photoelectric conversion layers are sensitive to light of increasing wavelength as the distance from the base plate increases. The photoelectric conversion layers comprise amorphous silicone and the transparent conductive films comprise an oxide of indium, tin, or the like.

Abstract: Double sheet detection method and apparatus of a sheet-fed rotary press, wherein a theoretical reference value is set as an intermediate value between a first theoretical amount of light transmitted through one sheet and a second theoretical amount of light transmitted through two sheets, respectively; the theoretical reference value is subtracted from the first amount of light to obtain a theoretical subtracted value; the theoretical subtracted value is subtracted from an actual amount of light transmitted through one sheet to obtain an actual reference value; and an actual amount of light transmitted through a current sheet is compared with the actual reference value to perform double sheet detection.

Abstract: A transmissometer includes electronic shutters for interrupting the transmitted and reference light beams at selected locations and at selected time intervals for establishing the various modes of operation of the transmissometer. The electronic shutters take the form of liquid crystal displays that are selectively energizable to either a clear or an opaque condition. The transmissometer also includes an electronic stepwise light attenuator located in the path of the light beams. The attenuator includes a body and multiple liquid crystal display segments uniformly distributed throughout the body, with the segments being independently energizable to provide stepwise opacity.

Abstract: The object of this invention is a double multichromatic photometer including a single light-source and a single detector, particularly for the determination of chemical and clinical analyses, in which the photometer light comes from a single light-source which radiates along three distinct optical paths that converge onto a single detector; two of the optical paths are the first and the second measuring channels, which are alternatively excluded whereas the third optical path is for reference purposes. An optical collimation assembly and a measurement cuvette are inserted into each of the two measuring optical paths or channels. Within said three optical paths is inserted a rotating drum, said drum holds a number of interference filters, allowing the third reference optical path to pass freely, and inserts one filter at a time into one or the other of the two measuring optical paths.

Abstract: An apparatus to evaluate objectively the concentration and motility of particles suspended in a sample of liquid, and particularly to an apparatus to solve objectively the problem of evaluating these important characteristics in a very simple manner and in a short time by exploiting the Doppler effect. The sample to be examined is subjected to one of the two sub-beams resulting from the suitable division of a coherent monochromatic light beam emitted by a polarized LASER, while the other sub-beam is considered as a reference light sub-beam. Because of the very little difference between the frequencies of the original and scattered light a beat is originated in the rejoined two sub-beams which is dependent on the characteristics of the examined sample.

Abstract: Method for the measurement of the difference in the optical properties dependent on the light direction of two samples (1,2), in which method one or several sources of light (3 to 6) as well as one light detector (7) are used. According to the invention, both of the samples (1, 2) are illuminated simultaneously and from both samples (1, 2) the light is passed simultaneously to the light detector (7). The lights to be measured from the samples (1, 2) have different directions in relation to the sample. The directions of the lights to be measured from the samples (1, 2) are alternated with each other at an appropriate frequency, such as a frequency within the range of 1 c/s to 10,000 c/s. The AC signal given by the light detector (7) is used as a measure of the difference in some optical property dependent on the direction of light between the samples, such as, e.g.

Abstract: Apparatus for controllably admitting a sample volume of engine exhaust into a bifurcated, closed-loop opacity chamber and wherein the exhaust sample is controllably directed away from the internal optics via symmetric flow inducing air guides. A pulsed light source is controllably directed through the opacity chamber and exhaust sample and the detected light is compared to a reference level so as to determine a relative measure of the sample's opacity. Attendant control circuitry permits the selected display of corresponding sample opacity and density values.

Abstract: In a method of analyzing chemical substances in sample liquids, reagent blank absorbances with respect to a light amount transmitted through air or water are measured previously at a plurality of photometering positions and are stored in a memory. Then sample absorbances are measured at respective photometering positions and the reagent blank absorbances are substrated from the sample absorbances at the respective photometering positions, so that a required absorbance variation of the sample liquid with respect to time is calculated from the sample absorbances thus corrected. Therefore, even if a calibration curve linearity is not perfectly identical with each other at the respective photometering positions, it is possible to obtain accurate analyzing results.

Abstract: Liquid hydrocarbon samples from a mainstream are diverted through a sample cell in cooling chamber. An optical cloud point detector signals a microprocessor-based control system which controls the charging and cooling of the cell. Cloud point reference level is continuously updated. After each measurement cycle, the control system readjusts the cooling power so that the time interval between the end of the flush cycle and cloud point detection is brought within a predetermined range. The control system switches between several distinct modes of operation automatically.

Abstract: Method and apparatus to measure the quantity of sebum secreted by the skin, by passing light through the specimen. The light passed through the specimen is modulated at a predetermined frequency, and only light of the same modulated frequency is measured by a receiver. The apparatus includes automatic zero calibration, and several embodiments of stabilized phototransistor circuits.

Abstract: Method and apparatus to measure the quantity of sebum secreted by the skin, by passing light through the specimen. The light passed through the specimen is modulated at a predetermined frequency, and only light of the same modulated frequency is measured by a receiver. The apparatus includes automatic zero calibration, and several embodiments of stabilized phototransistor circuits.

Abstract: A correlation spectrometer permanently incorporates a reference cell (12) and an electro-optical phase modulator (EOPM) (50) in the light path between a sample cell (30) and a detector (20). The effect of the EOPM is such that its frequency modulates all of the monochromatic component of the incoherent radiation passing through it. The EOPM is adjusted so that when it is ON all of the energy in the monochromatic components is thrown into sidebands (55) differing from the original frequencies by integral multiples of the modulation frequency, with the total amount of energy absorbed from the original radiation remaining constant. When there is no coincidence between the constituents in the two cells, the detector's output is the same when the EOPM is ON and when it is OFF. However, when there is coincidence the detector's output changes when the EOPM is switched between its two states. The change in the detector's output is related to the quantity of the constituents in the sample cell.

Abstract: An apparatus and method is described for separately measuring the optical tensities of the following: a sample beam having traversed a sample medium; a backscattered beam having been backscattered by the sample medium; a composite beam composed of the sample beam plus a reference beam having traversed a reference medium; and a second composite beam composed of the backscattered beam plus the reference beam. Measurements of these parameters is accomplished through the use of a linearly polarized source beam whose plane of polarization may be rotated between two orthogonal planes. The source beam is split into the sample and reference beams. The plane of polarization of the sample beam is caused to be rotated 90.degree. from the plane of polarization of the backscattered beam after interaction with the sample medium.

Abstract: A method for measuring a halftone dot area rate or a halftone picture density in a densitometer or half-tone dot area rate measuring means. A light beam is emitted by a light source and impinges upon an object to be measured. The light beam passes through or is reflected from the object to be measured and is received by a photoelectric element. A weighting of the light beam is performed by a weighting means so that the assigned weigth is substantially large at its central part and is reduced radially to its periphery, the reduction depending upon a transmittance or a reflectance of the object.