Abstract: An ozone detector in the form of two basic embodiments which can measure ozone concentration in ambient air at 0.001-1 ppm. The first embodiment includes a stretched elastic material and a standard which can give ozone concentration in response to degree of microcracking or frosting of the elastic material. The second embodiment includes a chamber containing a long strip of elastic material wound on a spool, a small amount of manganese dioxide in the chamber to neutralize any ozone therein so that the ozone does not attack and frost the elastic material, a take-up spool mounted away from the chamber and adapted to wind the material from the chamber, a component for stretching the material, a light source for generating a light beam and illuminating the film between the chamber and the take-up spool and a detector for the light beam after the light beam passes through the material.

Abstract: The present invention provides methods and devices for measuring radiation absorption by a sample. The invention enables one to determine whether the sample scatters the radiation of interest and, if so, to factor out the effects of such scattering and ore accurately determine the true absorption of the sample. The invention may employ a selectively controllable occluder which is moved between three or more different positions to yield three or more different radiation measurements. These measurements can then be compared to one another to determine the nature of any radiation scattering and factor out its effects, enabling more accurate absorption determinations.

Abstract: According to an embodiment of the invention, the device comprises a unique optical path and a movable means providing for the selective passage of a light beam respectively through a transparent cell (4) containing a substance to be studied, at least one reference filter (6). The light reflected successively by one and the other of said two components is selectively applied to three filters (F 1-F3) which filter three wavelenghts selected as a function of the substance to be analyzed. Three detectors (D1-D3) are used to measure the successive light intensities which have gone through each of the filters, and from the measures obtained, it is possible to determine a correction coefficient before calculating a characteristic of the substance contained in the transparent cell.

Abstract: Apparatus for sampling a laser beam used in an analytical instrument, e.g., a clinical hematology or flow cytometer instrument, for measuring absorption by particles suspended in a stream moving through a flow cell. The laser beam is typically passed through a mask, e.g., a beam shaping aperture, to shape the beam. The shaped beam is then passed through a beam splitter, located downstream of the beam shaping aperture, so that one part of the shaped beam strikes the flow cell (e.g., is focused onto the moving stream of particles), and a second part is diverted to obtain a reference measurement of the beam about to strike the flow cell. An absorption measurement is obtained of the light passing through the flow cell, and a difference circuit is used to obtain a difference signal relating the differences between the measured absorption and the unabsorbed reference sample of the initial beam intensity.

Abstract: A photomask defect inspection method is provided by which defects of pin holes with the diameter equal to or less than 0.35 .mu.m can be detected with certainty. According to the inspection method, a pattern whose image is projected onto an imaging position by the use of illumination light (P1) for exposure consists of light transmitting portions (41) formed on a glass base (2) and light intercepting portions (42) which transmit part of the illumination light (P1) in such a way that a phase of the part of the illumination light (P1) passing through the light intercepting portions (42) is delayed with respect to a phase of the illumination light (P1) passing through the light transmitting portions (41).

Abstract: A silicon wafer measuring method includes: (a) a first step of measuring a light transmission characteristic (I.sub.OBS) of the pulled silicon wafer by utilizing parallel polarized light incident at the Brewster angle into the pulled silicon wafer, (b) a second step of measuring a light transmission characteristic (I.sub.O) of a floating zone silicon wafer functioning as a reference silicon wafer by utilizing parallel polarized light incident at the Brewster angle into the floating zone silicon wafer, and (c) a third step of calculating a substitutional carbon concentration ?C.sub.SC ! on the basis of the light transmission characteristic (I.sub.OBS) of the pulled silicon wafer measured during the first step and the light transmission characteristic (I.sub.O) of the floating zone silicon wafer measured during the second step, (d) a fourth step of comparing the substitutional carbon concentration ?C.sub.

Abstract: In order to diagnose non-distructively the deterioration degree of such as insulation oil and insulation paper during operation of an oil filled electrical machine and apparatus without stopping the operation thereof, a deterioration degree disgnosis method for the oil filled electrical machine and apparatus makes use of optical fibers (6, 7) and oil immersed probe (5) and diagnoses the deterioration degree of an insulation paper non-distructively based on reflection absorbance difference between those for any two wavelengths of the insulation paper.

Abstract: A device and method for quantitative determination of an analyte in a biological sample utilizes a non-transparent support medium for retaining a chromatogenic reaction product with the medium being exposed to a source of light for transmitting therethrough a scattered, uniform response light signal which is collected at a photosensitive device whereby the amount of the analyte is correlated to the intensity of the response light signal. The response light signal may be converted to a time-duration signal proportional to light intensity to facilitate the quantitative determination.

Abstract: Method of assay of enzymatic activity, comprising projecting excitation light to a sample containing an enzyme, a substrate which forms a product by action of the enzyme, and a reference substance which is insensitive to the action of the enzyme but emits fluorescence; obtaining a first measured value of fluorescence intensity of the sample at a first wavelength region which includes fluorescence emitted by the substrate or the product at least, obtaining a second measured value of fluorescence intensity at a second wavelength region which is different from the first wavelength region for the first measured value and includes fluorescence emitted by the reference substance; and assaying the enzymatic activity from the ratio of the first measured value to the second measured value and apparatus for performing the method. The method assures high accuracy and high sensitivity of measurement in enzyme labeled immunoassay and enzyme labeled DNA hybridization.

Abstract: A process and apparatus for preparing blood for analysis of white blood cells involves:preparing a mixture made up of blood and a lysing agent,emitting luminous radiation in the direction of the mixture,receiving the light emitted through the mixture,comparing the quantity of light received at a pre-determined threshold, the process of erythrolysis, being complete when the quantity of light corresponds to the threshold and,neutralizing the action of the lysing agent when erythrolysis is completed by the addition of an appropriate reagent.

Abstract: A spectrometric technique is described for quantitatively determining the change in concentration of a substance which is contained in a medium which both absorbs and scatters spectroscopically interrogated radiation, and in particular to the specific case in which the change in concentration of the substance occurs in one spatially distinct region of the medium. The medium includes a plurality of such regions displaying potentially different absorption and scattering properties to the radiation. Specific applications are disclosed involving the noninvasive determination of changes in concentration of the substances oxyhemoglobin and deoxyhemoglobin and/or changes in the redox state of the substance cytochrome oxidase within the brain or skeletal muscle, and in cases where the brain or skeletal muscle is interrogated by radiation in the near-infrared part of the electromagnetic spectrum through intervening surface tissues, i.e.

Abstract: A fire detecting apparatus is designed to have improved reliability by reducing the possibility that the apparatus is influenced by an environmental change, external noise or the like which would otherwise cause erroneous fire information to be sent to a receiving unit to generate a false alarm.

Abstract: A multi-purpose on-line or field-portable system and method for monitoring the presence and concentration of selected antigen-antibody reactions singly or in combination that result from the presence of specific microorganisms or free antigens present or suspended in aqueous solutions, during a given time period. The detection system comprises a detection column and two sensors mounted around the detection column. Each sensor consists of an electromagnetic radiation source and an appropriate detector for the electromagnetic radiation. The reacted analyte tends to accumulate at the sensor located at the bottom detection column. The lower sensor continually nulls against the upper sensor to subtract any optical effects due to non-reactants in the aqueous process or environmental stream. The response from the detector sensors drive an electric circuit, which provides an output signal. In the on-line automatic version, the signal can drive elements of a process system by switching automated valves.

Abstract: An assay for photometrically detecting and/or quantitating the presence of an analyte in a sample in which the signal generated by a label associated with the analyte is photometrically detected in the presence of a suspended solid support.

Abstract: In a stained particle analyzing method and apparatus for staining a test sample containing suspended particles, shooting an image of the stained sample, and classifying the particles and computing the density from the shot image of the sample, the sample, which may not be analyzed precisely, is detected before the start of an image analyzing process. Only the sample, which will be analyzed precisely, is stained and subjected to the image analysis. Color information of the sample before the staining is detected and stored. Color information of an image of the sample shot after the staining is compensated based on the color information of the sample detected before the staining. The sort and density of the particles are classified and computed on the basis of the image after the color compensation.

Abstract: A rewriteable card of the invention is composed of a thermally reversible thermosensitive recording material which changes reversibly between a slightly opaque state and a transparent state depending on a given heating condition wherein the rewriteable card includes a reference slightly opaque portion at the part thereof having the reflectance equivalent to a slight opacity state of the thermally reversible thermosensitive recording material in an early stage or a last stage of use of the rewriteable card. A method of judging the life of the rewriteable card is based on the result of detection of the reflectance on a printing slightly opaque portion and that on the reference slightly opaque portion, and a printing apparatus is provided with a card life judging device employing the judging method.

Abstract: An assay for photometrically detecting and/or quantitating the presence of an analyte in a sample in which the signal generated by a label associated with the analyte is photometrically detected in the presence of a suspended solid support.

Abstract: A method for measuring or detecting halogenated organic compound content. For example, the method can be used to identify polychlorinated biphenyls ("PCB's"), contaminating soil or oil. The method is based on a light induced color producing reaction between a photodonor reagent and a halogenated organic compound. This reaction produces change in the optical absorption of the light exposed photodonor. Reversing the role of reagent and halogenated organic compound provides a method for identifying polyaromatic organic compounds such as pyrenes.

Abstract: A determination of optimal energy insertion, or input, results from a measurement of opacity at various heights in a fluid coagulating system and at the same time from measuring a deviation width of the opacity at a lower measuring point. Simultaneously, a continuous comparison takes place of the opacity measured at the various measuring points, which changes with time, and a comparison of the deviation width of opacity. The optimal energy insertion in the fluid coagulating system is achieved if, at each point in time, the opacity at all measuring points is maintained approximately the same and the deviation width of the opacity is maintained at or near a maximum.

Abstract: An instrument for measuring sperm concentration and calculating dose value and having an optical assembly with a light source, a specimen holder and a photodetector, a computation unit, a display, and a storage unit for storing a concentration calculation equation. The computation unit provides for calculating sperm concentration using the stored concentration calibration equation and a sample transmittance value, the optical assembly provides for measuring transmission of the specimen holder while empty with the light source energized, sample transmission of the specimen holder with a semen specimen with the light source energized, and dark cell output of said photodetector with said light source unenergized, and dark cell output of said photodetector with said light source unenergized, and said computation unit further provides for calculating actual sample percent transmission.

Abstract: The invention related to a method for determining a silicon wafer in which the interstitial oxygen concentration of a pulled silicon wafer is calculated on the basis of a light transmission characteristic measured by utilizing parallel polarized light incident at the brewster angle into the pulled silicon wafer and a further light transmission characteristic measured by utilizing parallel polarized light incident at the brewster angle into the floating zone silicon wafer function as a reference silicon wafer. The interstitial oxygen concentration value of the pulled silicon wafer is compared with a reference value to determine a defect in pulled silicon wafer.

Abstract: Apparatus and method for determination of concentrations of a substance in solution in a sample by determining the time between when the substance first appears and when it disappears. The time between the appearance and the disappearance of the substance is used to determine the concentrations of the substance in a sample. The apparatus includes many elements of a flow injection analysis system but also includes a very important stirred dilution chamber that enables the apparatus to use a simplified detection system that is capable of being used over a wide range of sample concentrations. The apparatus can include a microwave digestion system and in one embodiment a continuous flow microwave digestion system.

Abstract: Method and apparatus for spectroscopic measurement of the concentration of a gas in a sample where you detect the intensity of light from a light source (1) passed through the sample (4) and through a reference cell (5) and generates a signal which represents the concentration of the gas. A laser diode (1) constitutes the light source which is locked to the absorption line of the gas at known concentration and pressure contained in a reference cell (5). The laser light with the properly selected wavelength is distributed via optical fibres (2, 3, 6) and/or glass prisms (19, 20) to the reference cell (5) and the sample (4). Non-gas-related transmission variations in the measurement path or in the optics is automatically compensated for by a special laser modulation which generates a time multiplexed reference.

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: In a method wherein sets of measured values of the intensity of electromagnetic radiation, which has been subject to optical interference, absorption or scatter by a sample, are correlated with different sets of known values derived from either a model of the optical properties of the sample, or from an analogue technique, correlation is by means of either a zero dependent correlation function, or a normalized residual function. Both functions are unaffected by gain factors, thereby avoiding any need to determine and to maintain absolute sensitivities of optical detectors; provide greater variation of correlation than with techniques employing a conventional correlation coefficient, thereby increasing the precision with which the optimum correlation can be determined, especially when either the measured value, or known values are subject to error; enable the method to be carried out with only two radiation components; and can enable a reduction in computing time.

Abstract: The present invention comprises a simple multi-purpose on-line system for monitoring the concentration and/or the total amount of an organic analyte species or inorganic analyte species in an aqueous solution. The on-line detection system comprises a detection column and a sensor mounted around the detection column. The sensor consists of an electromagnetic radiation source (typically a light source) and an appropriate detector for the electromagnetic radiation. The response from the detector drives an electric circuit, which provides a signal to a recorder as well as a means to trip an alarm system and/or a process system.

Abstract: Disclosed is a technique for probing dynamic sheet charge density variations in integrated semiconductor devices. Using a specially designed non-invasive Nomarski phase contrast interferometer a sheet charge density sensitivity of 2.6.times.10.sup.8 e/cm.sup.2 / .sqroot.Hz is extracted from experimental data for 1 mA of detected photocurrent. The charge density sensitivity makes possible .mu.V signal level detection in an active device, and with digital signals the corresponding signal/noise level is sufficiently high that multi-mega-baud data can be captured in real time.

Abstract: Optical apparatus which compares the transmittance of radiation through a coated product with the transmittance of radiation through only the base material of the coated product to measure the coating weight of the coating on the coated product. A dichroic filter or similar device is included to minimize or even eliminate radiation losses, due to reflections from the coated product, which affect the accuracy of the apparatus. The apparatus can be modified to measure selected characteristics of the base material instead of the coating.

Abstract: The specification discloses apparatus and methodology for calibrating optical-response tissue-examination apparatus of the type having an optical probe with at least one light-sending terminal portion adapted for introducing light into a test subject and a terminal portion for receiving resulting light from such subject. The calibration apparatus includes a body having outer walls which enclose an internal area and define an inlet aperture and an outlet aperture adapted to receive the terminal portions of the optical probe in a manner to substantially preclude entry or exit of ambient light. Means are included within said body for conveying inlet light from the test probe along a tortuous path communicating with the outlet aperture.

Abstract: For controlling the dye receptivity or color absorption capacity of a running web of textile goods, a monitoring method by means of electromagnetic waves penetrating through the web of goods is used (FIG. 2).

Abstract: The attenuation of an optical waveguide is measured by comparing the light power input into the waveguide with the light power output from the waveguide. The input power is encoded on the light signal by pulse frequency modulation. The output power is measured by a light receiver.

Abstract: An automatic analyzing apparatus for automatically effecting chemical analysis on a sample of blood, urea or the like dependent on measurement items by measuring the light absorption degree of a reaction liquid through a reaction vessel, comprising a reaction liquid photometric unit, a photometric unit independent of the reaction light photometric unit and operative to measure beforehand the light absorption degree of the reaction vessel per se or the reaction vessel containing a reagent or dilute liquid, and means for correcting the light absorption degree of the reaction liquid measured at the reaction liquid photometric unit on the basis of the light absorption degree of the reaction vessel per se or the light absorption degree of the reaction vessel containing the reagent or dilute liquid measured at the independent photometric unit.

Abstract: An apparatus for continuously measuring the concentration of particulates in a sample gas by using an optoacoustic effect. Identical laser rays are directed along two optical paths, and a chopper and an optoacoustic cell are position in the recited order in each of the optical paths. Sample gas containing particulates is introduced into one optoacoustic cell and sample gas from which the particulates have been removed is introduced into the other optoacoustic cell. The respective choppers are driven for producing a chopping action on the respective laser rays at a frequency corresponding to the resonant frequency of the corresponding optoacoustic cells, and the outputs from the cells can be compared for providing an indication of the concentration of the particulates in the sample gas.

Abstract: The optical densities of both the background and the image areas of an original are measured so as to obtain a control signal useful in photocopying the original, by a system which includes a detector for generating a measuring signal representing optical densities detected on the original; a detector for deriving from the measuring signal a peak signal level representing the background density; first and second detection circuits for producing respective output signals representing numbers of measuring signal portions detected at first and second reference signal levels, which levels differ from each other and each from the peak signal level; a control rendering the reference signal levels dependent in magnitude on the derived peak or background signal level, and preferably proportional to it; and a comparison circuit for deriving from the output signals a control signal indicating in relation to the background density the relative amounts on the original of image information items that have optical densitie

Abstract: A method and apparatus for illuminating a surface to provide a desired light intensity. The light intensity at discrete points along the illuminated surface is measured through a light transparent material, and opaque materials are applied to the transparent material to block out some of the light and thereby produce a light filter such that the desired intensity at each of the discrete points along the surface is obtained. An oscilliscope, or alternatively, a computer display to indicate light intensity are used.

Abstract: Apparatus for controlling output signals from two light detectors in a photometer. The sensitivities of the light detectors, or the gains in amplifiers for amplifying output signals from the light detectors are controlled in such a manner that the sensitivity characteristics and output characteristics of the two light detectors are in agreement with one another, to thereby improve the measuring accuracy thereof.

Abstract: An automatic analyzing apparatus for automatically effecting chemical analysis on a sample of blood, urea or the like dependent on measurement items by measuring the light absorption degree of a reaction liquid through a reaction vessel, comprising a reaction liquid photometric unit, a photometric unit independent of the reaction light photometric unit and operative to measure beforehand the light absorption degree of the reaction vessel per se or the reaction vessel containing a reagent or dilute liquid, and means for correcting the light absorption degree of the reaction liquid measured at the reaction liquid photometric unit on the basis of the light absorption degree of the reaction vessel per se or the light absorption degree of the reaction vessel containing the reagent or dilute liquid measured at the independent photometric unit.

Abstract: A photometric detection method and apparatus employ a variable beam modulation device, such as a planar oscillating disk whose reflectance and transmittance with respect an incident beam of electromagnetic radiation vary with disk angular position, to form, from an incident beam of radiation, two amplitude modulated correlated component beams. Preferably the amplitudes of the component beams vary sinusoidally, 180.degree. out of phase. In one illustrative embodiment, one of the component beams passes through a sample fluid, which absorbs a portion of the radiation at a wavelength characteristic of a selected component. The second component beam passes through a reference path and provides a reference signal relative to which changes in the sample fluid are measured. A feedback mechanism is provided to automatically adjust for variations which can occur while the apparatus is operating.

Abstract: Coke guide and coke oven infrared pyrometer degrading is minimized to continuously permit better accuracy and reliability in hostile environment of coke mass and heat, dust and/or dirt present in many coke plant areas. These benefits are obtained using production-worthy pyrometer equipment having a purged pyrometer with any of three window cleanliness monitors to determine errors and automatically correcting for same through self-calibration.

Abstract: In a method for identifying one or more botanical component parts from plants, a sample of the component parts is irradiated with electromagnetic radiation within the visible and/or ultra-violet and/or X-ray range for excitation of the component parts to fluorescence which is analyzed for determining characteristic fluorescence from the component parts. For determining the relative contents of the component parts in the sample, intensity measurements are carried out on the characteristic fluorescences or the number of emitters of characteristic fluorescence is counted.

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: The highly sensitive spectrophone assembly of the subject invention simultaneously and continuously provides an accurate measure of the absorption of electromagnetic radiation by atmospheric gases and particulate matter by providing successive flow through chambers. The gases and particulate matter pass through the first chamber, are directed through a filter where the particulate matter is removed, leaving the gases to flow through the second chamber. The signal representative of the absorption of energy is generated in each chamber and fed into a differential amplifier, to provide an accurate indication of the particulate matter in the atmosphere being monitored. Grounding one side yields a signal attributable to the gaseous absorption.

Abstract: By autocorrelating the sample photoacoustic response signal and the reference photoacoustic response signal, respectively, obtained from the sample and reference cells, of a photoacoustic spectrometer, and cross-correlating the autocorrelated signals to produce a third signal, simple mathematical operations upon the resulting three signals will produce accurate sample analysis free from the effects of the noise arising from sample illumination intensity variations and other random phenomena.

Abstract: A method for the measurement of minority carrier lifetime in semiconductor wafers, sheets and ribbons by purely optical means. The method does not require electrical or MOS contacts to the wafer, nor does it require any specific processing to facilitate measurement. The technique is non-destructive, and is applicable to any semiconductor wafer, with or without surface dielectric films (e.g., SiO.sub.2, Si.sub.3 N.sub.4, Ta.sub.2 O.sub.5) as long as it has no metal films. This technique is fast, accurate, and of reasonable high resolution, so that it may be applied to evaluate the effects of specific process steps (e.g., ribbon growth, diffusion, oxidation, ion implantation, delectric deposition, annealing) in real time and hence serve as a production control technique as well as a research tool. By utilizing reasonable equipment sophistication, this technique should enable the measurement of lifetime over a wide range of values, covering the scale from high-speed bipolar devices and integrated circuits (.

Abstract: An optoacoustic analyzer which allows the light from a laser resonator to enter a differential cell assembly can not provide accurate measurement of a specific component of ultralow concentration because the laser light, as it passes through the sample chamber and reference chamber, is absorbed to cause significant attenuation and the adverse effect of a low concentration of an inhibitory component in the fluid sample can not be effectively eliminated. Further, this type of anaylzer receives the laser light at the detector after it has passed through mirrors, and therefore, only few percents of the light within the resonator reaches the detector, thus providing only low sensitivity. To solve these problems, the differential cell type, light transmitting, optoacoustic analyzer of this invention has the sample chamber and reference chamber disposed on the beam path between the resonating mirrors in the gas laser resonator.

Abstract: A system and method for monitoring and maintaining a predetermined concentration of material in a fluid body or carrier includes a control arrangement for detecting the transmissivity of a flow cell in each of two states. One of the states during which the flow cell is observed contains substantially no fluid present therein but provides a basis for determining the degree of existence of external factors affecting measurements made via the flow cell. The measurements for one state are subtracted from the measurements for the other in order to determine the transmissivity of the fluid body itself as distinguished from the combination of fluid body and flow cell.

Abstract: An analyzer such as a two beam infrared analyzer is assembled in building block fashion and includes a radiation source module and a detection module tied together by rods and in optical alignment with each other. Intermediate or "cell"-modules are hung on the rods and all adjacent, interfacing faces of the several modules are constructed for indexing, preventing lateral deflection when the fastened rods hold all parts together.

Abstract: An immunoassay wherein the sample containing an immunologic substance is added to a suspension of particles coated with a second immunologic substance which is specific to the immunologic substance of the sample. The change in percentage of light transmission through the suspension undergoing the resulting agglutination is measured for a predetermined period of time and compared to a standard graph. The suspension is under constant agitation during the measurement.

Abstract: A method of determining the need for post-addition of antigen or antibody to an antigen-antibody reaction to ascertain whether the reaction is in an antigen excess or an antibody excess condition. The time rate of change of a nephelometric signal developed from the reaction is monitored to generate a rate signal having a peak value providing a measure of antigen concentration. The post-addition step is performed only if the peak rate value is ambiguous--, i.e. if it indicates one antigen concentration value for a reaction in antigen excess but another value for a reaction in antibody excess. The need for the post-addition step is determined from measured qualities of the rate signal including one or more of (1) the peak rate value, (2) the elapsed time from the start of the reaction to the peak rate, and (3) the product of the peak rate and the elapsed time. When required, the post-addition step may be performed during progress of the antigen-antibody reaction after measurement of the peak rate value.

Abstract: The composition of etchant solution withdrawn from an etcher is monitored to diagnose a component deficiency. A light sensor is responsive to the color density of light rays passing through the etchant. A meter relay is responsive to the light sensor and if the color density of the etchant falls outside preset levels a pump is energized causing addition of a constituent component into the etchant. A second light sensor senses the color density of the light rays passing through the etchant after the addition of the constituent component. A second meter relay is responsive to the second light sensor. If no improvement of the etchant color is detected, the second meter relay causes the discontinuance of the constituent component addition and switches to the addition of another constituent component.