Abstract: Corrosion of a metal member under heat transfer condition is monitored by using a test coupon made of the same material as that of the metal member. The test coupon may have a welded portion and a crevice. One substantial surface of the test coupon is heated by a sheet shaped heating element, and at least one portion of the other surface of the test coupon is contacted with the corrosive fluid. After detecting a status of corrosion of the test coupon, the corrosion of the metal member is monitored based on the results of the detection. In case a counter electrode or reference electrode is used, the electrode is immersed in the corrosive fluid, and electrical signals between the test coupon and the electrode are measured. Then, the corrosion of the metal member is monitored.

Abstract: A method to minimize corrosion in aqueous systems while maintaining microbiological control in such systems is disclosed. This is achieved by regulating the feed of oxidizers with an oxidation-reduction potential (ORP) signal, while incorporating corrosion information provided by an on-line corrosion meter.

Abstract: A hand-held and flexible corrosion sensor is described that uses electrochemical impedance spectroscopy (EIS, also known as AC impedance) to detect coating degradation and corrosion of coated and uncoated metals. The hand-held and flexible corrosion sensor is pressed against the surface of the structure of specimen to be inspected, and may be either straight in structural configuration in the form of a pen or bent in a curved or angled manner to achieve better access to the structure. An EIS spectrum can than be obtained in the field or under arbitrary conditions and the degree of coating or material degradation can be determined from the resultant spectrum. There are no restrictions on the configuration of the structure being inspected. The area of detection is controlled by moderating the extent and degree of wetness of the surface. A dry surface will provide a localized measurement; a wet surface will allow inspection of the wetted area.

Abstract: The present invention is directed to a system for continuous physical integrity monitoring of large civil structures such as bridges and high-rise buildings . . . wherein the relevant sensor data stream is generated continuously and transmitted to the data gathering location without the need for an incoming triggering signal of any kind; i.e., it is a one way transmission system. Specifically, it is a concept for an interlinked multi-parameter Early Warning Sensor system with a full time data management capability for structures. The invention is also directed to both the system construction, with its communication capability, and also designs of specific sensors applicable to the system as a whole. As a practical example of application of the present invention to a structure, the description in this application is directed primarily towards system applications for bridge integrity early warning systems.

Abstract: A sensor is provided with a conductive sensing element that has a composition adapted to provide a resistance large enough that predetermined magnitudes of voltage noise do not create a false indication of removal, e.g. by abrasion or corrosion. Also, the sensing element composition is adapted to provide a temperature coefficient of resistivity small enough that measurements are substantially independent of temperature. Resistance is preferably greater than 10 ohms and the absolute value of TCR is preferably less than 1000 parts per million per .degree. C. The conductive sensing element may be formed from several materials, including alloys of palladium or lead, particularly palladium-gold, lead-bismuth, or lead-palladium. A combination sensor is provided that includes an abrasion sensing element and a corrosion sensing element on the same substrate.

Abstract: It is an object of the present invention to provide a corrosion resistance test process, wherein the estimation of the corrosion resistance of an article formed of a metal material and a coating can be carried out synthetically and in a short time. In carrying out a corrosion resistance test, the article is immersed into an electrolytic solution and then, a voltage is applied to the metal material to carry out a metal material corroding step and a coating peeling-off step alternatively and repeatedly. The voltage applied to the metal material is a superimposed voltage Vd+Va resulting from superimposition of a DC voltage Vd and an AC voltage Va. A voltage condition of Vd<0 and Vd+Va>0 is established at the metal material corroding step, while a voltage condition of Vd<0 and Vd+Va<0 is established at the coating peeling-off step.

Abstract: A method and apparatus for examining the electrochemical kinetics occurring at the surface of a galvanized steel cable undergoing fatigue in the presence of a corrosive environment allows the prediction of the corrosion life of the cable. In one embodiment, an apparatus for detecting localized corrosion in a cable is provided undergoing mechanical fatigue, comprising a weir cell containing an electrolyte and a reference electrode, one or more pulleys, and a motion control device. In other embodiments, methods for detecting and monitoring the electrochemical response of corrosion coupled to fatigue in a galvanized steel cable are provided wherein the potential between a reference electrode and a moveable cable under tension and undergoing fatigue are recorded and/or monitored. In further embodiments, a method and apparatus are provided for inspecting entire runs of cable for localized corrosion, zinc porosity, and corrosion inhibition efficiency.

Abstract: An environmental test apparatus has a thermal chamber for stress testing electronic products and a wall separating the thermal chamber from ambient air around the apparatus. In the improvement, the wall comprises a pair of barrier walls having a flexible partition interposed between them. The barrier walls and the flexible partition substantially isolate the ambient air from the thermal chamber. The apparatus also includes a platform in the ambient air and a feedthrough card extending from the platform through the flexible partition into the thermal chamber.In one, more specific embodiment, the barrier walls are below the thermal chamber and the platform is below the barrier walls. In other embodiments, the barrier walls are lateral to the thermal chamber and the apparatus includes one or two racks, also lateral to such chamber. One or respective platforms are supported on the rack(s).

Abstract: An in situ sensor for monitoring the degree of corrosion of rebar in a concrete structure relies on a four-point resistance measure of a test wire embedded in the concrete structure. The resistance across the wire is compared with the resistance of a reference wire, which is corrosion resistant. As corrosion advances, the cross-sectional area of the wire decreases, effectively increasing the resistance measured. The sensor may be used to measure corrosion inhibitor performance, and the effect of dilution.

Abstract: Corrosion is monitored by making a resistance measurement between a contact and an uncorroded or relatively uncorroded portion of the article to be monitored. Changes in the resistance measured are a result of the presence of a corrosion product, or the breakdown of protective coatings by corrosion. The contact may be a sensor washer which is held in place around a threaded stud 6 by nut 12. The washer comprises a steel ring 14 and an electrically conducting ring 18 which is insulated from ring 14 and contacted by circling 21 and conductor wire 23 in resin jacket 22. The measurement may be made on magnesium alloy gearboxes in helicopter. The alloy may be protected by a paint film so that the initial resistance measured is very high.

Abstract: A method for the early detection of electrochemical corrosion and coating degradation utilizing an inexpensive, in situ electrochemical metallic sensor for sensing coating and material degradation, particularly for materials such as aluminum 2024-T3, 7075, 6061, cold rolled steel samples, and coated metal structures such as automobiles, bridges, aircraft, and ships has been developed. The sensor utilizes AC Impedance or Electrochemical impedance spectroscopy (EIS) to acquire a precise, low-frequency impedance signature and is comprised of conductive ink deposited on a coating in the shape of the outline of a quadrilateral or other configuration. The resulting apparatus is comprised of a coated, metallic coupon used as a sensor, while a metallic grid electrode is deposited onto the steel coupon, thereby eliminating the need for a remote or counter electrode (i.e., reduction from a traditional, three-electrode system to a two-electrode system).

Abstract: A method of determining the position and condition of reinforcing steel embedded in concrete is described. The method is non-invasive. Electrodes are use to carry out the method by contacting the outer surface of the concrete. The method measures the impedance of selected regions of the concrete by measuring the voltage generated across said selected regions by a current flowing through the concrete.

Abstract: An improved corrosion measurement system for determining the rate of corrosion of a fluid medium. The system is comprised of a highly sensitive excitation and amplification electronic circuitry for registering and displaying the stable and accurate measurement results. A unique unitized measurement probe is temperature stabilized using thermally inertially balanced metallic probes; the first reference element being coated with an impermeable insulating coating, the second, the corroding element, being fully exposed to the corrosive fluid medium.

Abstract: A switching device including a measuring means for monitoring contact erosion, which is provided between a contact element and an associated contact support. The switching device includes an electrically insulated signal line, which is usable in individual and/or multiple contacts, is used as the measuring means, the signal line being integrated into a single monitoring circuit. In the switching device, there is arranged, between at least one of the contact elements and the associated contact support or in the contact material, an electrical conductor with insulator as the signal line, damage to or destruction of the insulator and/or the conductor being utilized to generate an external signal as an indication of the end of the service life of the contact element.

Abstract: A method and apparatus for sensing corrosion are provided in which an interrogation unit (14) transmits interrogation pulses and receives responses. A plurality of corrosion sensors (12) are disposed in the structure to be monitored (10), each of the sensors (12) generating an output. A plurality of responders (16) are powered from the interrogation pulses, one each of the responders (16) associated with one each of the sensors (12). The responders (16) are operable to transmit responses to the interrogation pulses based on the corrosion sensors' (12) output.

Abstract: Switching components with contact parts that are mounted on a contact carrier in a switch housing may include devices for monitoring the contact erosion. The contact carrier may be split (sub-divided) and contact parts can be slotted at the rear and mounted on the sub-divided contact carrier. Thus, the oscillation response (vibration response) of the contact carrier in particular can be used as a measure of the erosion of the contact parts.

Abstract: A method and system for detecting and preventing Stress Corrosion Cracking (SCC) in buried pipelines or other structures is presented. The basic principle of the invention is to use a plurality of test coupons which are placed in the same environment as a pipeline or other structure of interest as indicators of the development of SCC in the structure of interest. Loading and temperature of the test coupons are controlled. The test coupons are given a range of different Cathodic Protection (CP) levels, with the range of CP levels selected so as to encompass the CP level at which SCC would be expected to occur. The occurrence of cracking in a test coupon indicates levels of CP which will sustain SCC. SCC is prevented in the structure by application of a level of CP which did not sustain SCC.

Abstract: A combination and unitary corrosion monitor and reference cell for cathodic protection systems includes an elongated tubular metal element of the same material as the structure to be protected and a reference cell on one end of the tubular element, adapted to be buried or submerged in an electrolyte. The tubular element includes resistance connections along its length and a reference resistance element sealed inside. Ratiometric resistance measurements enable the extent of corrosion and corrosion rates to be determined with automatic compensation for temperature changes. Both the resistance measurements and the potential measurements from the cell may be taken from the same test station or location.

Abstract: A fault detecting circuit for use with an electromagnetic acoustic transducer having an electrostatic shield and a wear surface for determining when the wear surface for contacting test surfaces has developed holes.

Abstract: A method for detecting the presence or absence of corrosion of cathodically protected steel structures in soil and concrete in which the cathodic protection circuit is subjected to an electrochemical impedance spectroscopic analysis and the presence of corrosion is indicated by the presence of a Warburg impedance.

Abstract: A method to estimate the thickness of a brake lining based on the periodic sampling of the output of a temperature sensor embedded in the brake lining. A temperature histogram is created which is compared to calibration histograms stored in an electronic processing unit to yield an estimated brake lining thickness which is transmitted to the vehicle cab or to another on-board electronics unit. A brake wear factor is calculated from the temperature histogram by multiplying the average value of each temperature range by the frequency of occurrence and then summing the results.

Abstract: A method for monitoring cracks in a sample of materials by applying the theory that the phase angle increases in the sample of materials being tested where cracks have formed. The method is performed by preparing a solution capable of forming cracks in the sample, preparing an auxiliary electrode, then making the sample and the auxiliary electrode contact with the solution, preparing a frequency generator connecting the sample and the auxiliary electrode respectively, choosing a frequency, and turning on the frequency generator with an alternating current of the frequency, monitoring the phase angle measured in the sample, and determining the formation of cracks in the sample by checking whether the phase angle measured in the sample increases with time.

Abstract: A method of detecting microbiological fouling in an aqueous system. The method includes determining a baseline corrosion rate. A corrosion rate is continuously monitored. A change in the corrosion rate is measured. A maximum corrosion rate is measured. A baseline fouling factor is determined by measuring and monitoring parameters of a fluid in the aqueous system. An increase in fouling factor over the baseline is determined. A change in the corrosion rate is integrated with respect to time over an interval of from a time of the determination of the baseline corrosion rate to a time that the maximum corrosion rate occurs. A change in the fouling factor is integrated with respect to time over an interval from a time of the determination of the baseline fouling factor to a time of the determination of the increase in fouling factor. The fouling factor and the corrosion rate are compared to determine if the fouling is microbiological.

Abstract: A corrosion degree measuring method capable of field measurement for intergranular corrosion, particularly the sensitization degree, of the plant's structural materials in a narrow space. The metal electrode made of a material being measured and the counter electrode to the metal electrode are immersed in an electrolytic solution. A voltage is applied to the metal electrode in the anodic direction so as to raise the potential of the metal electrode up to the passive state potential and to keep the metal electrode at the passive state potential. The passive state potential is used as a reference potential, and a pulse-like potential signal is applied to the metal electrode in the cathodic direction. At the time of the application of the pulse potential signal, a current between the metal electrode and the counter electrode is measured, and the corrosion degree of the material being measured is determined from the intensity of the current.

Abstract: A method for determining whether a metallic path (such as a wire) under test carrying an undetermined load current is so corroded as to require replacement applies a test current to the metallic path under test and a total current passing through the metallic path, equal to the sum of the undetermined load current and the test current, is measured. A voltage between two selected points, separated by a known length, on the metallic path is also measured. Resistance of the metallic path is then calculated by measuring an angular phase difference between the voltage and the total current, calculating an impedance of the metallic path from the values of the voltage and the total current then multiplying the impedance by the cosine of the angular phase difference. The resistance of the metallic path under test is correlated to the resistance of metallic paths of known corrosion to determine the degree of corrosion on the metallic path under test.

Abstract: An apparatus and a method are provided for determining solution resistance and corrosion rate of a metal surface contained in a solution such as an electrode. The signal is applied to the metal surface of interest and the current response is monitored from the applied signal. A peak detector is provided for detecting the peak of the current response. From the peak, the resistance of the solution is ascertained. Following independent determination of the solution resistance, polarization resistance of the metal surface in the solution may be determined. The corrosion rate of the metal surface may be calculated from the polarization resistance.

Abstract: The corrosion monitor system facilitates the detection and monitoring of material corrosion in remote areas. Sensors, which react to a corrosive environment similar to the material to be monitored, are placed in isolated areas and connected to a central control system via shielded cables. The system consists of a controller board, multiple dual preamp boards, a battery pack, sensors, and corresponding cables. The controller board consists of a microcontroller, memory, data conversion, and other control circuits. The dual preamp boards contain multiple precision instrumentation amplifiers, filtering, and voltage conversion circuits. The system operates on the principal that corrosion of a metallic conductor will cause a corresponding increase in the cross-sectional electrical resistance of that conductor. This change in resistance can be detected and monitored by passing a known constant current through the conductor and comparing the voltage across the conductor with that of a controlled reference conductor.

Abstract: Electric bus bar insulating coatings are calibrated to withstand long term outdoor exposure without failure. Manufacturing samples of the coating material are evaluated at the coating manufacturing site prior to shipment to the bus bar manufacturer. Bus bar samples coated with the material are suspended within a heated water bath and subjected to several hundred volt-amperes. The thickness of the coating is predetermined to provide accurate qualifying data for each coating sample within a reasonable time frame. Coating compositions that qualify are then applied to electric bus bar conductors by the bus bar manufacturer.

Abstract: An electrode for determining corrosion of metal reinforcement in concrete includes a wire surrounded by insulation and made of a metal which is more electro-positive than a metal reinforcement. An electrically active part of the wire is in electrolytic contact with moisture in concrete surrounding the reinforcement. The insulation is disposed along the whole of the electrically active part of the wire in such a way that the insulation keeps this part of the wire separated from the reinforcement and galvanically insulated therefrom.

Abstract: A simple, expedient method for measuring the effectiveness of a corrosion inhibitor provided to a metallic surface by a surface layer, wherein the layer is formed by use of the corrosion inhibitor is a corrosive fluid. The method employs the measuring of a high frequency phase angle as an indicator of inhibitor effectiveness.

Abstract: An on-board oil quality sensor for use in an internal combustion engine formed of a pair of resisitve elements mounted on a common substrate, wherein one of the resistive elements is exposed to the oil for corrosion as the oil contaminants increase and the other resistive element is protectively sealed from the oil contaminants. Both resistive elements are exposed to the oil temperature and are suitable for monitoring by a bridge type circuit to determine the level of corrosive contaminants in the oil.

Abstract: A lightweight corrosivity sensor is provided which is thin enough to be edded between the layers of a composite structure or placed on a surface beneath a coating. It comprises a thin non-conductive base and two electrically isolated conductive elements fixed to the surface thereof. Each conductive element comprises a bus bar and a plurality of strips extending from the bus bar and interdigitated with the strips of the other conductive element. The corrosivity sensor is connectable to a current measuring means for measuring the current across the two conductive elements as an indicator of the presence of a corrosive environment. A masking method of manufacturing such a sensor is also provided.

Abstract: A corrosion sensor (1), apparatus for detecting corrosion of a surface incorporating the sensor, a structural assembly (1,21) incorporating the sensor and method for detecting corrosion of a surface employing the sensor are provided. The sensor comprises a thin flexible non-conducting substrate (18) for attachment to a surface subject to corrosive influence and an array of at least two thin flexible metallic electrodes (2,3,4) carried on the substrate wherein the electrodes are disposed closely adjacent one another so as to permit the generation of electric current by electrochemical action therebetween upon corrosion of the electrodes.

Abstract: An electrical resistance corrosion probe incorporates a temperature sensitive resistor (RTD) that directly measures temperature of the probe and therefore of its environment as corrosion measurements are being made. The temperature sensitive resistor has one end connected to the common junction between the test and reference elements of the corrosion probe and has its other end connected in the common line to the several corrosion measuring circuits, including the test, reference and check circuits.

Abstract: A corrosion monitoring system having one or more anode elements made of a suitable anodic material that corrodes preferentially with respect to the structure being protected. The resistance of each anode wire is continuously or periodically monitored. The presence of moisture between an anode and the structure being monitored creates a current path and causes galvanic corrosion. The anode wire will begin to corrode, but the structural members will remain uncorroded until the anode has been completely consumed. The monitoring system uses the rate of change in anode resistance to extrapolate a prediction of the time remaining before the structure being protected begins to corrode.

Abstract: In a method of diagnosing deterioration of a paint film, a probe is applied to the surface of a paint film. A voltage having a predetermined waveform is applied by a preamplifier across the probe and a base metal on which the paint film is formed. A current flowing through the paint film is measured by the preamplifier. An analog signal indicative of a measured current value is converted to a corresponding digital signal by an analog-to-digital converter. A personal computer operates to analyze the digital signal in accordance with a predetermined analyzing procedure so that the degree of deterioration of the paint film is determined. The resultant determination is displayed on the display.

Abstract: The electrolytic resistivity leak detector comprises the method of electrical resistivity to measure the gradual intrusion of aggressive chemicals into the wall of a plastic or fiber reinforced plastic vessel. This device and method includes the use of electric sensors within the wall of the vessel. The sensors provide an electrical circuit as the chemicals permeate through the wall and make contact with the sensors. A microammeter is included as an instrument to monitor and register the degree of electrical resistivity caused by the chemical intrusion.

Abstract: A method and apparatus for carrying out the checking of the state of wear of a covering fabric in a driving belt (2) mounted on a plurality of pulleys (3, 4, 5) by measuring the electric resistance variations of the belt fabric. The apparatus provides that at least two of the pulleys (3, 4, 5) should be electrically insulated with respect to each other and connected to an electric circuit (20) designed to apply an electric voltage to said pulleys in order to carry out the measuring of the electric resistance of the fabric exhibited by belt stretches (A, B) comprised between the pulleys themselves. The electric resistance thus found lends itself to be compared with predetermined resistance values corresponding to different states of wear of the belt (2) fabric. The work surface of the belt (2) is coated with an electrically conductive fabric (12) acting by contact on the pulleys (3, 4, 5) and having characteristics of tensile strength.

Abstract: The invention relates to a device for measuring the electrode potential of the reinforcement in underwater concrete. The device is of the type comprising a reference electrode placed against the facing of the concrete and a voltmeter connected to the reference electrode and to the reinforcement. The reference electrode is disposed in a bell suitable for pressing in watertight manner against a facing of the concrete, thereby delimiting an enclosure. The device further includes means for injecting compressed air into the enclosure and means for enabling the water imprisoned therein to escape.

Abstract: In combination with a steam generator having a plurality of generator tube support plates, each generator tube support plate having a plurality of openings and a plurality of generator tubes, each tube passing through aligned openings in the support plates, a corrosion monitoring system is provided including a mockup probe, comprising a probe tube support plate having an upper side and a lower side and having substantially the same thickness and being constructed of substantially the same material as the generator tube support plates, having at least one opening of substantially the same size and shape as the openings of the generator tube support plates; at least one probe tube having an upper end and a lower end and having substantially the same diameter as the generator tubes and being constructed of substantially the same material as the generator tubes, the probe tube passing through the opening of the probe tube support plate; and wherein the mockup probe is adapted such that it may be inserted and seal

Abstract: An apparatus and method for monitoring corrosion to members within the core of a nuclear reactor, particularly fuel rod cladding. A sensor means is submerged inside the core of a nuclear reactor near the member or fuel rods. The sensor means is comprised of a generally cylindrical section having an outer surface that is subject to corrosion and radiation, and has a cross-sectional area A.sub.1. The sensor means additionally has a reference section subjected to radiation but not to corrosion, and having a cross-sectional area A.sub.2. At least one pair of first probes, separated by a length L.sub.1, is placed in electrical contact with the cylindrical section. At least one pair of second probes separated by a length L.sub.2, is placed in electrical contact with the reference section. A current is passed throughout the sensor means to produce a potential gradient in the cylindrical section and reference section.

Abstract: A technique is disclosed for using electrochemical noise (ECN) to charactze halide pitting reactions on a high strength aluminum alloy. ECN signals resulting from the pitting interaction of an aqueous halide solution with the oxide film on the aluminum alloy sample are measured. The signals are amplified, digitized, and then transferred to a digital computer where they are transformed from the time domain to the frequency domain by a fast Fourier transform function. Frequency spectrum amplitude data is then converted to a log-log scale thereby revealing a pattern of spectrum amplitudes indicative of pit initiation rates.

Abstract: An apparatus for holding a corrosion-testing coupon within a processing system. The apparatus includes a flexible member having a first end and a second end, the first end of which is adapted for holding the apparatus within the processing system; and an electrically insulative member which is attached to the second end of the flexible member. The electrically insulative member is adapted to hold a corrosion-detecting coupon. Preferably, the flexible member is a flexible corrugated metallic conduit. The apparatus advantageously includes an attachment member, such as a shaft, which is connected to the first end of the flexible member and which is adapted to attach to the processing system; and a sleeve which connects the electrically insulative member to the flexible member.

Abstract: An apparatus and method for monitoring corrosion to members within the core of a nuclear reactor, particularly fuel rod cladding. A sensor means is submerged inside the core of a nuclear reactor near the member of fuel rods. The sensor means is comprised of a generally cylindrical section having an outer surface that is subject to corrosion and radiation, and has a cross-sectional area A.sub.1. The sensor means additionally has a reference section subjected to radiation but not to corrosion, and having a cross-sectional area A.sub.2. At least one pair of first probes, separated by a length L.sub.1, is placed in electrical contact with the cylindrical section. At least one pair of second probes separated by a length L.sub.2, is placed in electrical contact with the reference section. A current is passed throughout the sensor means to produce a potential gradient in the cylindrical section and reference section.

Abstract: A system for monitoring and measuring the corrosion reaction of metals in an environment. The system includes a sample corrosion element of substantially the same material as the structure to be monitored, a galvanic cell for generating an electric signal indicative of the corrosion on the corrosion element, and a monitor for receiving and storing the generated signal. Moreover, the system is designed to incorporate corrosion products and environmental contaminants in order to simulate actual, localized conditions on a particular area of a structure.

Abstract: A procedure and a device for determining corrosion of preferably insulated structural parts (2) assures in a simple way early detection of corrosion. For this purpose an electric conducting resistance wire (4) exposed to the same corrosive medium, e.g. condensation water, as the structural part (2) to be examined for corrosion is placed outside the structural part (2) and the electrical resistance of the resistance wire is measured. The effective cross-section of the resistance wire (4) and its electrical resistance change with the corrosion of the resistance wire (4) so that the resistance change of the resistance wire (4) registers the effect of the corrosive medium.

Abstract: A sensor for electrochemical measurement is disclosed which includes a chamber made of an electrically insulative material and having an open end portion, a super absorbent polymer material filled in the chamber and absorbing at a selected rate a liquid electrolyte, an electrode disposed in the chamber, and a screen which covers the open end portion of the chamber and which prevents the super absorbent polymer material from dropping out from the chamber but permits the liquid electrolyte to transmit through the screen. A method is also disclosed which uses the sensor to measure the degree of degradation of a coating film on metal or the corrosion protective properties of a rust film created on the surface of steel.

Abstract: An evaluation method of corrosion of a steel material in a concrete. The evaluation is made by use of three parameters, i.e., the corrosion potential, the polarization resistance and the concrete resistance measured for plurality of measuring points on the concrete over the steel material. The values of polarization resistance and the concrete resistance are used after converting them to the value per unit area and unit length, thereby quantitative absolute evaluation being made without depending on the ambient conditions. The measured values of each parameter are classified to several zones by threshold value, and the results thereof are collectively took into consideration for the evaluation. The parameters and/or the threshold values are compensated in connection with temperature in view of accuracy.

Abstract: The method is based on the exploitation of the "skin effect" occuring in any current-conducting material as a function of the current frequency going through said material. A transformer (5) is supplied from a generator (2) and an amplifier (4) to produce the current intended to supply the tube (T) and to measure the voltage at the terminals of a shunt (6). This voltage which is characteristical of the energization current is amplified by an amplifier (8) and brought to the reference input of a phase correlation amplifier (1). The resistive component of the signal on the tube is then measured by said amplifier (1) by just measuring the signal phase component.

Abstract: Apparatus that detects the presence and condition of precipitation on the surface of a pathway. The apparatus has a block of electrically insulative material adapted to be embedded in the pathway with a top surface exposed to precipitation. A sensor is embedded in the block for sensing a physical property of the precipitation to produce a sensor output which is also influenced by a depth of the precipitation. Part of the top surface of the block has a well that is generally curved in outline above the sensor for gathering precipitation for the sensor. Advantageously, the influence of precipitation depth on the sensor is diminished. Other apparatus and methods are also disclosed.