Abstract: A method and apparatus for determining the inert content of a coal dust and rock dust mixture uses a transparent window pressed against the mixture. An infrared light beam is directed through the window such that a portion of the infrared light beam is reflected from the mixture. The concentration of the reflected light is detected and a signal indicative of the reflected light is generated. A normalized value for the generated signal is determined according to the relationship.phi.=(log i.sub.c `log i.sub.co) / (log i.sub.c100 -log i.sub.co)wherei.sub.co =measured signal at 0% rock dusti.sub.c100 =measured signal at 100% rock dusti.sub.c =measured signal of the mixture.This normalized value is then correlated to a predetermined relationship of .phi. to rock dust percentage to determine the rock dust content of the mixture. The rock dust content is displayed where the percentage is between 30 and 100%, and an indication of out-of-range is displayed where the rock dust percent is less than 30%.

Abstract: A method for determining the surface density of coal dust on top of rock dust or rock dust on top of coal dust is disclosed which comprises directing a light source at either a coal or rock dust layer overlaying a substratum of the other, detecting the amount of light reflected from the deposit, generating a signal from the reflected light which is converted into a normalized output (V), and calculating the surface density from the normalized output. The surface density S.sub.c of coal dust on top of rock dust is calculated according to the equation:S.sub.c =1/-a.sub.c ln(V)wherein a.sub.c is a constant for the coal dust particles, and the surface density S.sub.r of rock dust on top of coal dust is determined by the equation: ##EQU1## wherein a.sub.r is a constant based on the properties of the rock dust particles. An apparatus is also disclosed for carrying out the method of the present invention.

Abstract: A spectrophotometer (10) is provided having the capability to accurately measure spectral reflectance at relatively long sample distances. A first illumination optics arrangement (14) assures uniform illumination to a portion of the sample and a second optical arrangement (20) focuses the reflected image of part of the illuminated sample onto a polychromator (22). Reference beam means are provided so that the polychromator sequentially measures the spectral characteristics of the reference beam and the sample. Continuous monitoring of the illumination at select wavelengths provides illumination normalization data so that a microprocessor (40) can normalize the illumination and compare the reference beam and sample measurements to accurately determine the spectral reflectance characteristics of the sample. Angular and raster scanning capability is also provided.

Abstract: In a method of identifying or comparing compositions of material, the reflectivity of a material to be identified or compared is measured at index points distributed through the near infrared spectrum. A similar measurement is made for at least one standard or known material. From the reflectivity measurements, sets of values representing the first or higher order derivative curves are determined. These values mathematically define vectors by representing the coordinates of the end points of the vectors and multiple dimensional space. An index of a similarity between the composition of a test sample and a standard material is calculated by determining the cosine of the angle between the corresponding vectors.

Abstract: An optical measuring system for measuring in situ by means of one or more fiber-optic probes reflection absorption fluorescence, phosphorescence and turbidity of a fluid or (for all but the last measurement) of a fluid-solid interface. High intensity pulsed light is conveyed to the measurement site by a fiber-optic cable and is given a specific direction at the site by means of the geometry of the probe, reaction light resulting from the stimulating light pulse is discriminated by the geometry of the probe, or another probe, and is returned via a further fiber-optic cable to a measurement system which is enabled to sense the returning light only for the duration of the light pulse. The measurement system comprises means for sensing the relative intensity of the stimulating light pulse and for deriving a signal at least representative of the ratio of the magnitude of the quality sensed, by means of the probe, and the relative intensity of the stimulating light pulse.

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: Method and apparatus for measuring a distance to an object includes directing first and second laser beams having frequencies .omega..sub.11 and .omega..sub.12 toward the object. A first reference signal is derived having a beat frequency .omega..sub.1 =.omega..sub.11 -.omega..sub.12. A first reflected light beam reflected from the object is detected and has the beat frequency .omega..sub.1 and a first phase difference with respect to the first reference signal. The first phase difference is then extracted from the first reference signal and the first reflected light beam and a first plurality of distance nodes is calculated from the first phase difference. Then, the frequency of the second laser beam is changed to .omega..sub.13. A second reference signal having a beat frequency of .omega..sub.2 =.omega..sub.11 -.omega..sub.13 is then derived. A second reflected light beam reflected from the target is detected and has the beat frequency of .omega..sub.

Abstract: A control system for discriminating the occurrence of fogging of the windscreen of a vehicle due to the deposition of water drops or the like from the degree of optical scattering and automatically starting and stopping the operation of a defogging apparatus according to the result of the discrimination. To prevent the defogging apparatus from being stopped undesirably due to an optical system being subjected to the effect of a disturbance light, the disturbance light is detected so that when the disturbance light exceeds a predetermined value, the defogging apparatus is maintained in operation.

Abstract: An uneven-surface data detection apparatus, includes a transparent plate having an uneven-surface contact portion against which an uneven surface to be detected is pressed. A light source illuminates the uneven-surface contact portion through the transparent plate. An uneven-surface image drawing out optical element draws out the light reflected on the uneven-surface contact portion of the transparent plate. A detector detects the light drawn out from the transparent plate by the optical element.Light reflected by a projection-facing portion of the uneven surface contact portion to be introduced into the detector diverges from a propagation direction of light reflected by a recess-facing portion of the uneven surface contact portion. The optical element is arranged to guide the light reflected by the projection-facing portion into the detector.

Abstract: Road surface condition detection system comprising light projector means for projecting light including the infrared region of the spectrum to a road surface to sense the condition thereof, the infrared having wavelengths at which the reflectance of snow is smaller than that of the road surface in a dry condition, light receiving means for receiving light reflected from the road surface, comparisons means for comparing the output signals generated from the light receiving means with reference signal levels corresponding to dry, wet, snowy and frozen conditions, and judging means for judging the road surface to be one of the conditions in accordance with results of comparison.

Abstract: An apparatus for detecting defects in a laser mirror by using a laser beam in order to detect any possible changes in reflectivity over the surface of the mirror. A laser beam is split by a beam splitter into one portion for scanning the mirror to be inspected and which is reflected therefrom to produce a reflection signal, the remaining portion of the beam providing a reference signal. A computer receives both signals and on the basis of comparison thereof determines the condition of the mirror because there will be incorrect reflection of the laser beam from any region of the mirror which is defective.

Abstract: A measuring device which is equipped with a number of sensors determines the area coverage of a printing original or printing plate for printing presses. Each individual sensor of the measuring device is calibrated with the air of calibration strips. By means of an additional sensor of the measuring device, a printing-plate and/or printing-original-specific correction calibration and an adjustment to identical values of all sensors are provided. The correction calibration and adjustment are performed by way of a calibration field and a calibration area on the printing plate and/or printing original.

Abstract: An analyzer for analyzing the surface of an object which is substantially opaque to ultraviolet light. The analyzer includes a substantially light-tight housing having an aperture therein for viewing the surface of the object to be analyzed. An illuminator is carried by the housing and includes a source of ultraviolet light and an optical imaging device for directing light from the source through the aperture and onto the surface of the object to illuminate the surface of the object. A collector is carried by the housing including a sensor responsive to ultraviolet light and an optical imaging device for receiving ultraviolet light from the surface through the aperture and directing it onto the sensor.

Abstract: A road surface is scanned with a laser beam in a direction transverse to the road surface to pick up the scanning locus of the laser beam on the road surface in a direction inclined to a beam scanning surface so as to obtain transverse profile data. The laser light reflected from the road surface is received in a direction inclined to the beam scanning surface for obtaining crack data. The distances to the road at three points in the longitudinal direction of a measuring car are measured. The running distance of the car is measured and the measured distance data are recorded in a recording device together with crack data, transverse profile data and longitudinal profile data.

Abstract: Automatic material identification is achieved using infrared thermometry. A focused beam of high flux energy is passed through a dichroic beam-splitter to remove visible UV with the remaining infrared directed to the surface of the material to be identified. An infrared thermometer sensor is positioned to sense the magnitude of the energy received from the material surface with the magnitude of the energy being indicative of the type of material scattering such energy. Control apparatus are employed to provide control signals as a function of the type of material identified such that automatic process operations may be effected in accordance therewith.

Abstract: A novel apparatus is provided for inspecting defects in cigarette bundles layered in buckets which are fixed to a bucket conveyor. The defects include tip fall state where the top content of cigarette piece is dropped off, loss of filter and shortage in the number of cigarette pieces. The apparatus consists of a gate time measuring device, a dark time measuring device, a computing device and a comparison device. The gate time measuring device measures gate time showing the passing time of the internal length of buckets, and the dark time measuring device measures dark time showing the passing time of a defective part of cigarette and of spaces between cigarette pieces. The computing device selects the maximum value of the dark time and computes a percentage of the gate time to the maximum value. The comparison device then compares the computed value with a predetermined value so as to determine whether or not there are defects in cigarette piece bundles.

Abstract: In a fog detecting apparatus with optoelectronic system, comprising infrared-emitting means and infrared-receiving means, is provided means for adjusting a reference which is compared with a voltage value of a detecting signal generated according to an electrical signal produced by the infrared-receiving means in order to distinguish whether a windshield of a vehicle is in the fogging condition or not. The reference is changed according to the detecting signal which is produced when the windshield is in good condition against the fogging after a fog removing apparatus has been actuated to remove the fog attached on the windshield, so that the fogging condition is detected in accuracy independently of the contamination of the optoelectronic system or the like.

Abstract: The total optical loss caused by laser induced damage to an optical component is measured by monitoring the phase shift during mirror reflectance or transmission. The phase shift is directly proportional to the amount of loss. A secondary laser illuminates the area under test with a coherent light beam well below the component's damage threshold. This reference beam is modulated. The reflected or transmitted reference beam is monitored by a photomultiplier tube whose output is fed to a lock-in circuit. The lock-in circuit compares the phase of the received light to the induced modulation.

Abstract: A color-sensitive currency verifier operating with a plurality of narrowband light sources optically coupled to a single broadband photodetector and including means for automatically balancing the color outputs of the various light sources. Color balancing is accomplished just prior to the examination of a specimen bill. The data samples are taken under the control of a microprocessor and used to authenticate the specimen bill both on the basis of pattern and color information stored in memory. Multiple data samples from a single target area are divided to compensate for soiling condition of the bill, and further compensation for condition of the bill is provided by adjusting the conversion scale factor of an A/D converter on the basis of data samples taken from a reference target area on the surface of the specimen bill before test or data samples are taken.

Abstract: A method of ore sorting includes distinguishing ore objects or ore containing objects by the light reflected from a laser beam arranged to scan across each of the objects to be sorted. Where the surface of the object is transmitting to the light a halo is produced by certain objects caused by internal scattered reflections of the light. By monitoring the occurrence or degree of occurrences of halos clean distinction of respective objects can be made. In a particular application, the identification of the presence of quartz pebbles in rock specimens can be used for detecting and sorting gold containing objects.

Abstract: A parallel light beam having a predetermined diameter is projected onto an aluminum deposition film formed on a semiconductor wafer in a direction normal to the wafer surface. Light reflected by the aluminum deposition film is converted into reflected light intensity data by a plurality of photoelectric conversion elements arranged in a spherical surface with the center thereof at the center of the parallel light beam incidence spot. The reflected light intensity data are stored in a RAM in a microprocessor. The data stored in the RAM are displayed as a reflected light intensity distribution plot on a display unit for comparison with a standard reflected light intensity distribution plot, whereby the bonding property of the aluminum deposition film is judged.

Abstract: A method is disclosed for calibrating a reflectometer using black and white references observed in locations optically different from the sample location. Dark and light standards are selected to have reflectance values, while examined in the detection location of the test elements, that are within .+-.0.005 and .+-.0.05 of the values of the black and white references, respectively, when examined in a location displaced from the detection location of the test elements. Such standards are then read on a referee reflectometer having "ideal" black and white references, and the reflectances so read on the referee reflectometer are recorded for use as calibrating factors in making reflectance readings for the test elements.

Abstract: An apparatus for automatically detecting and evaluating print characteristics comprising an optical detection and comparison means. In particular comparison is made using reflector means which is at the same time a background area for a print in its test position.

Abstract: The quality of a product, for example the degree of filling of cigarette papers, is non-destructively tested using reflectivity measurement. Compensation is provided for the effects of stray light in the measuring zone and the signals commensurate with the measurements performed on individual units of the object being tested are compared with the average of signals obtained through measurements performed on a preselected number of units of acceptable quality. The state of operability of the test apparatus may be self-checked during incremental periods between the testing of units.

Abstract: A method and device for detecting and evaluating the optical properties of a specimen, utilizing a light source that has alternating light and dark phases, a detector that picks up light from the light source by way of the specimen being examined, and a circuit that integrates and digitalizes the signals received from the detector, that includes an integrator, and that can be connected to the detector. The signals emitted from the detector are integrated both during at least part of the light phase and during at least part of the dark phase. The integral obtained during the dark phase is subtracted from that obtained during the light phase in order to determine the results. The integrator that is used to integrate the signals is used like an analog-to-digital converter of the double-integration type to convert the integral into a digital signal.

Abstract: A device and method for measuring the reflectivity of the tungsten oxide surface coating on cathode ray tube heaters are described, in which selected small areas of an illuminated heater wire turns are scanned by a microscope, and the collected reflected light converted to voltage values by a photomultiplier tube and compared to a standard value.

Abstract: The invention relates to a method of checking the coating of a metal surface, in which the surface to be checked is exposed to electro-magnetic radiation and the amount of reflected radiation is measured and compared with the amount incident to the surface exposed.The invention also relates to a device for carrying out such method.

Abstract: Spectrophotometer apparatus and method is disclosed which utilizes a totally unobstructed test light flux channel in combination with a periodically occluded reference light flux channel. The outputs of the test and reference channels are mixed and presented to a common light analyzing device from which successive timed-multiplexed measurements can be used to provide spectrophotometric data automatically corrected for drift in critical parameter values associated with the common source and/or light analyzing device. For example, by subtracting light flux measurements obtained during occluded periods from those obtained when the reference channel is not occluded, a measurement can be derived for the light flux passing through the reference channel alone. This derived measurement can then be used to drift-correct measurements made on the light flux coming through the test channel alone when the reference channel is occluded. Comparison of successive light flux measurements made under similar conditions (i.e.

Abstract: A device for reflected-light photometry, that determines the reflectivity of a specimen area which is part of an objective area specifically dedicated for the determination of certain properties, especially those of the reaction area of a medical-laboratory test strip. The device has a light source for illuminating the specimen area, preferably with diffuse light, and a photodetector that picks up light reflected from the specimen area. There is, in accordance with the invention, an opaque diaphragm with a particular shape, position, and mounting in the path of light between the specimen area and the detector.

Abstract: In a reflectance measuring instrument, an integrating sphere is provided to illuminate the sample of which the reflectance is to be measured. A first fiber optic cable is provided to receive a light beam reflected by the sample and a second fiber optic cable is positioned to receive a light beam reflected from the wall of the integrating sphere. The transmitting ends of the fiber optic cables are mounted in a pivoted plate to selectively position the transmitting ends to emit light into the entrance slit of a monochromator.

Abstract: Filter cigarettes which are grouped in the form of one or more rows on their way to the draping station or stations of a packing machine are transported sideways past a testing station between two testing units each of which has a discrete detector for each row of cigarettes in a group. Each detector has a source of light, a photoelectric transducer, and a bundle of fiber optics which convey light beams from the source against the respective end faces of cigarettes advancing between the two testing units and which convey reflected light to the respective transducer so that the latter generates signals denoting the characteristics, the presence or absence of cigarettes. Such signals are compared with a reference signal denoting the characteristics of satisfactory cigarettes, and the groups wherein one or more cigarettes have caused the generation of signals deviating excessively from the reference signal are expelled from the conveyor prior to reaching the first draping station of the packing machine.

Abstract: In order to avoid the encumbrance of a rotary mirror scanner by large calating radiation sources for intermittently illuminating the detector element of the scanner, a supplementary radiometer responsive to the same scene as is scanned is absolutely calibrated by intermittent illumination from calibrating sources that are conveniently small. The calibrated radiometer signal is compared to portions of the scanner output responding to the same object field, for calibration of the scanner output. The radiometer may be scanned at right angles to the direction of scan of the scanner in order to provide calibration of both the forward cross lines and rear cross lines alternately scanned by a stereoscopic scanner, for stereoscopic observation of cloud formations, land masses, air traffic distribution or the like from a space craft.

Abstract: The clearing point of photoresist development is detected automatically by illuminating the developing photoresist surface with intense monochromatic light. Interfering reflection from the resist-substrate interface and the fast eroding and slow eroding resist surfaces produces fast and slow oscillatory signals. These signals are processed to produce a logical output indicative of the cessation of the fast oscillations in the presence of the continuing slow oscillations signaling the clearing point of development.

Abstract: For indication of the amount of a constituent in a substance, for example the proportion of moisture in hay, a pair of light-emitting diodes 1 and 2 have their emissions reflected from the substance being analyzed. The diodes emit radiation in narrow bands selected so that there is differential reflection depending on the proportion of the constituent in the substance. The supply currents to the diodes are switched in alternate sequence and their relative magnitudes adjusted to give minimum output at the switching frequency. For determining the proportion of moisture in hay suitable wavelengths are 1450 nm and 1300 nm. The diodes may be constructed as InGaAsP/InP diodes with the proportions of the constituents adjusted to give emission at the required wavelengths.

Abstract: An instrument for measuring surface characteristics based on the opacity of a material has an optical projection system for illuminating a sample and photocell arrangement for measuring light reflected from the sample. The instrument contains standard black and white surfaces with reference to which the sample opacity is measured. The photocell signal is digitized and the results processed and calculations made by a microprocessor system enabling sets of results to be stored and mean and standard deviations to be calculated. The instrument is particularly intended for testing paper and, in connection with carbonless copy paper, enables a measure to be made of the density of an imprint relative to the background that is called calender intensity.

Abstract: A scanning apparatus periodically sweeps a beam of light across a printed circuit board in a plurality of sweep paths. An associated detector is responsive to radiation from the printed circuit board for producing first and second signals indicating whether a conductor portion or substrate portion of the board is being swept. An associated automatic level control is responsive to the first and second signals for providing level adjusted output signals. The levels of the adjusted output signals are substantially the same for all printed circuit boards swept in the scanning apparatus.

Abstract: A scanning apparatus which periodically sweeps a beam of light across a printed circuit board along a plurality of sweep paths, includes a detector responsive to radiation from the printed circuit board as the board is swept by the beam of light. The detector is also responsive to first and second adjustment signals indicating whether a conductor portion or substrate portion of the board is being swept. An automatic level control is responsive to the first and second signals for providing level adjusted output signals via an adjustor coupled to the detector. The levels of the output signals form a ratio R substantially the same for all boards swept in the scanning apparatus.

Abstract: A detector for use in optical measuring instruments such as a double-beam spectrophotometer, comprising a photoelectric element having a photosensitive surface and a beam mixer disposed adjacent the photosensitive surface for causing each of two alternate light beams to be projected evenly and uniformly onto the photosensitive surface of the photoelectric element thereby to eliminate errors which would otherwise be caused in the result of measurement due to local difference in sensitivity of the photosensitive surface of the photoelectric element. The beam mixer comprises a symmetrical pair of light diffusing plates so arranged as to form a roof-shaped configuration and a tublar body having one end opening closed by the pair of light diffusing plates and the opposite end opening closed by the photosensitive surface of the photoelectric element.

Abstract: An apparatus for determining the sex of a chick which includes a sensor for sensing certain characteristics of the chick and for producing output values corresponding to each of the sensed characteristics, a comparator for comparing the output values with preset characteristic values and for producing affirmative signals whenever each of the output values correspond to the preset characteristic values and an indicator for indicating the sex of the chick in response to the affirmative signals.

Abstract: A method and apparatus for monitoring the average cell size of a plastic foam structure continuously emerging from a production extrusion source which include means and process steps for magnifying an image of an area of a cross-section of said foam structure, developing said image and comparing the cell size of the image with a known standard and controlling production process parameters to obtain a foam structure of predetermined average cell size.

Abstract: A method and apparatus for photogoniometric analysis of surfaces is disclosed. A photogoniometric instrument includes a light source (12) for providing a collimated beam of light illuminating a test surface (18). A light detector (20) is mounted for rotation about the point of intersection of the illuminating beam on the test surface. A motor (44) drives the detector through a range of reflectance angles, and a microcomputer (52) digitizes the detector output periodically, storing the digitized data words in its memory (68). These stored words define a photogoniometric curve (FIG. 2A) including a specular portion (FIG. 2D) and a nonspecular, or diffuse, portion (FIG. 2C). A host computer (62) receives the photogoniometric data from the microcomputer, deconvolutes the data into spectral and diffuse portions, and analyzes the two portions separately from one another.

Abstract: Apparatus for determining the reflectivity of the surface of a measured object, and, in particular, for determining properties of the measured object which are connected with its reflectivity. A light source emits light along a light path so that a wide-band light beam impinges on the surface of the measured object. The light reflected by the surface of the measured object goes through a pair of narrowband light filters which pass, respectively, light beams of different narrow bands of wave-lengths effective for evaluation by a photo-detection device. The photo-detection device comprises two separate photo-detectors each covered by one of the narrow-band filters. The filters are fixed in their positions relative to the photo-detectors and transmit their different wave-lengths of light to their respective photo-detectors.

Abstract: A portable instrument quantitatively determining the distinctness of image of a sample paint film by providing comparison of the film with several standard films of known distinctness of image is provided. The instrument displays the sample and one of the standards within an enclosed casing while an image forming pattern is projected simultaneously on both by a light source within the instrument. By changing the standard which is displayed, an observer compares the distinctness of image of the sample with the known values of several standards until a match is found.

Abstract: Surface roughness is tested by an optical probing method which involves scanning a beam of light from a laser over a specimen workpiece via a semi-reflecting mirror and a cylindrical lens and detecting the specular component of the light reflected back through the lens and the semi-reflecting mirror to a photomultiplier the output from which is fed to an electronic processor circuit which derive a numerical value representing the mean intensity of the reflected radiation. A workpiece to be tested is then substituted for the specimen workpiece and a new numerical value derived. The two numerical values are compared, as by division or subtraction to obtain an output signal representing the relative surface roughness of the workpiece under test with respect to that of the specimen.

Abstract: A light source is arranged with a light sensing device in such a way that the sensing device receives transmitted light for a translucent medium or reflected light for an opaque medium. The reading of the sensor is stored, then the same source and sensing device are moved over a reference medium whose absorptivity varies unidirectionally. A comparator compares the reading of the sensor with the stored reading and indicates when they are equal. The relative position of the reference and sensor indicates the absorptivity of the medium. One embodiment uses multiple devices and filters to determine composite color.

Abstract: Gold plated surfaces are inspected by means of reflected light in the wavelength range of 450 to 575 nanometers to give a sensitive indication of surface conditions. This test automates the visual inspection for "brown gold" and is advantageously used in continuous strip gold plating operations. The technique may be used as a quality control check or as a process control to correct non-optimum process parameters that lead to degradation of gold surface conditions. In a preferred embodiment, the reflected light from the surface being inspected is compared with light reflected from a reference surface. Alternately, a separate wavelength band, typically 700 to 800 nanometers, is reflected from the surface being inspected and compared to the reflected light in the 450 to 575 nanometer wavelength band.

Abstract: Labelled bottles are inspected by illuminating the labelled surface and generating brightness or intensity level signals for a plurality of points on the surface with a photo-sensitive diode array. Each intensity level signal is compared with a stored maximum intensity level and a stored minimum intensity level for the corresponding point. A difference signal is generated if the intensity level is greater than the maximum or less than the minimum intensity level. The difference signals are then weighted and summed to generate a figure of merit for the bottle being inspected. The figure of merit is compared with a predetermined value representing a "good" bottle in order to reject "bad" bottles. The maximum and minimum intensity levels can be generated by passing a plurality of known "good" bottles through the apparatus with labels distributed about the edges of the desired label area.

Abstract: An improved grain quality analyzer, for analyzing the percentage concentration of various constituents, e.g. protein and water, in a grain sample, photo-optically measures the change in the optical density of the sample, .DELTA. OD, in a range of characteristic wavelengths and, for protein, in a range of neutral wavelengths and uses these measured values to compute the percentage concentration of the constituents.A grain sample is irradiated with light, the wavelength of which sweeps across the infrared light-spectrum including a range of wavelengths termed characteristic wavelengths, and, for protein, a range of wavelengths termed neutral wavelengths.

Abstract: Process and apparatus for measurement of brightness of milled products, especially flour, are disclosed. The process is of the general type in which the surface of a layer of flour is illuminated, and the returned quantity of light is taken to an optical electrical transducer. A light source is used for illumination, and the light beam is optically decomposed into at least two part-beams (reference beam and measurement beam) for transmission to the transducer. At least one of the part-beams is cyclicly interrupted or broken into two essentially time-shifted measurement phases in such a way that of the two part-beams, only one of the two-part beams will strike the transducer during a first measurement phase, and during a second measurement phase at least the other part-beam will be applied to the transducer.

Abstract: Retrodirective optical prisms are tested for light reflection and efficiency by generating two substantially co-axial beams of light, a signal beam and a reference beam. The beams are passed through an optical beam splitter arranged at a predetermined angle to the axis of the beams, thereby separating them. The separated signal beam is passed into the prism to be tested, reflected back along its initial path, and back through the beam splitter. The intensity of the reflected beam is measured and compared with the intensity of the reference beam. It thus gives an indication of the light reflective efficiency of the prism.