Abstract: A reference standard and a method for manufacturing a reference standard for use in calibrating an eddy current probe is disclosed. The reference standard is produced from a block of metal that is deformed by an indentation tool to provide a notch of prescribed dimensions. The reference standard is compressed along an axis substantially transverse to the longitudinal axis of the notch to substantially close the notch. A family of reference standards formed in this manner can be produced to calibrate an eddy current probe prior to use of the probe in evaluating metal components such as aircraft framework for the presence of fatigue cracks and the like.

Abstract: A method and system (1) for adjusting the curvature of an electrical relay armature (4), and the energizing voltage level of the electrical relay (2) in which it is contained, is disclosed. The adjustment system (1) uses a rotatable carrier (16) from which an extendable cam (22) with a shaped bearing surface (23) directly communicates with, and provides necessary adjustment to, a curved armature section (8) of a misconfigured relay armature (4). The necessary adjustment is determined and controlled by a controller in combination with an energizing level determining device.

Abstract: A system for photoinductive imaging for flaw detection of materials and for calibrating eddy-current probes includes positioning an eddy-current probe adjacent to a specimen to be analyzed or to be used as a calibration fixture. A source of thermal energy is modulated and focused to a localized area on the specimen. Thermal energy is then scanned across at least a portion of the detection area of the eddy-probe. The resulting signal from the eddy-current probe is recorded and can depict either thermal-influenced components of the specimen or the response pattern of the eddy-current probe. The record can therefore be used to image flaws or physical holes or shapes of the specimen or calibrate the eddy-current probe.

Abstract: A method and apparatus for ascertaining internal stresses in a hardened region to be tested for a component made of a predetermined material includes measuring coercive field strength and amplitude of magnetic Barkhausen noise as a function of mechanical stress and hardness in calibration samples of a predetermined material of known hardness and known internal stress. Calibration functions are ascertained from the measured values indicating the dependency of the hardness and the amplitude of the magnetic Barkhausen noise as functions of the hardness and mechanical stress. The coercive field strength and the amplitude of the magnetic Barkhausen noise is measured in a location-dependent manner over the region of the component to be tested. The measured values of the coercive field strength and the amplitude of the magnetic Barkhausen noise are converted in the region to be tested into location-dependent hardness and into location-dependent mechanical stress using the ascertained calibration functions.

Abstract: A method and apparatus for testing and calibrating an electromagnetic logging tool are described. The tool includes a tansmitting antenna and a receiving antenna. A shielded receiving device is placed around the transmitting antenna and intercepts the transmitted signal. A shielded transmitting device is positioned around the tool's receiving antenna and transmits to the receiving antenna a signal which has a phase and/or an amplitude related to the signal transmitted by the tool's transmitting antenna in a known manner which simulates the effects that a geological formation would have on the signal if it were to travel from the tool's transmitting antenna to the tool's receiving antenna through the formation. Since the simulated effect is known, the output of the tool may be verified as being correct or corrected if erroneous.

Abstract: A proximity detector of the integrated electronic type which includes an oscillator, which detector detects the position of a target relative to a proximity zone limit by Eddy current changes. The detector is operated over a cycle having a first period during which its functioning is checked by alternately starting and stopping the oscillator and for a second period during which the position of the target is determined.

Abstract: The manufacture of digital magnetic recording discs for computer disc drives requires the monitoring and control of the M-H hysteresis loop properties of the magnetic film deposited on the disc substrate. Several methods exist for measuring this M-H hysteresis loop, but they all have serious disadvantages. One method consists of cutting samples and measuring them with a vibrating sample magnetometer. This is a destructive test and requires a lot of time per sample. Another method uses the Kerr-rotation of polarized light. However, it samples only the mangetization of the surface and cannot determine the magnetic thickness of the film. A third method magnetizes the entire disc and samples a large region along a diameter. This method cannot distinguish between the top and bottom films of the disc, and cannot resolve circumferential variations of th M-H loop properties.

Abstract: A diagnostic debris sensor operating on the inductive pulse is triggered by ferrous particles floating by or attracted to a permanent magnet within a pulse-sensing coil and the entire sensor at that, the pulse-sensing coil is equipped with a second winding for either continuous monitoring or an occasional push-to-test checking of the pulse-sensing coil.

Abstract: Reproducability in the manufacture of rotating shaft sensing encoders and similar devices employing Hall effect switching devices to sense changes in magnetic fields is achieved in the present invention by forming a frame of the encoder as a unitary or one piece arrangement for both supporting a shaft bearing and an angular behavior sensor, such as a Hall effect switch, thus controlling tolerances, air gaps and angular orientation of the sensor. Calibration of such a device to compensate for manufacturing variability in the Hall sensing device as well as any other variabilities in the encoder is then achieved by providing a reversable calibrating magnetic field close to the Hall effect switch and moving that magnetic field until the desired switch calibration is achieved.

Abstract: An apparatus and method for non-invasively sensing physiological changes in the brain is disclosed. The apparatus and method uses an electromagnetic field to measure localized impedance changes in brain matter and fluid. The apparatus and method has particular application in providing time-trend measurements of the process of brain edema associated with head trauma.

Abstract: A method and apparatus for the determination of thickness of plastic materials, as well as of bonding and coating materials, by high frequency electric and magnetic alternating fields. The method enables a simple test of components, as well as of coatings and bondings, even if the plastic parts to be tested or the coatings or bondings to be tested are not yet completely cured and the surfaces to be tested are located, so as to be concealed or are accessible only with difficulty. The method and apparatus consists in that electrically conductive or ferromagnetic particles are added to the materials to be measured and subsequently the electrical conductivity or magnetic permeability is measured at the completed or coated test specimen by high-frequency electrical and magnetic alternating fields, whose progression in space and time is adapted to the measuring task.

Abstract: A method and apparatus for calibrating a displacement probe, such as a Hall effect displacement probe, wherein a preassembled probe is clamped in a calibration fixture which includes a calibration target and facility for selectively varying displacement between the target and the probe measurement tip. Probe output is read and stored at each of a plurality of preselected target/probe displacements. The stored output v. displacement data set is then employed to generate a polynomial equation which approximates probe output as a function of displacement. A displacement v. output look-up table unique to that probe is then generated from the polynomial approximation for a multiplicity of discrete displacement increments.

Abstract: The disclosure illustrates a self calibrating control system for a variable area turbocharger incorporating a pneumatic actuator having a limiting position achieved at low actuating pressure levels. The calibration takes place by monitoring the demanded actuator signal. If it stays at a level reflecting a physically limiting position of the actuator for a predetermined time air pressure to the actuator is terminated to positively maintain the actuator in the no air position. A signal reflecting the actual position of the actuator is then substituted in the control system as a new zero pressure condition. This procedure is performed periodically and is aborted if normal control inputs are demanded thus resulting in a minimum disruption to normal control inputs. In addition the system provides for fault indications if the calibration procedure fails to result in a zero pressure calibration within predetermined limits.

Abstract: A method of measuring a characteristic, such as thickness, of a test part makes use of the variation in impedance of a coil in a senor caused by eddy currents generated as a result of the proximity of the test part. The sensor measures two orthogonal components of the complex impedance. In use the sensor is moved towards the test part until one component of the impedance reaches a predetermined value and the characteristic measured as the value of the other component. The first component is selected during calibration as that component which is most sensitive to variation in the distance between the sensor and the test part.

Abstract: The control specimen according to the invention consists of a metal basic body and artificial inclusions arranged in it, where the inclusions are suitably sintered, non-metallic configurations arranged according to size and distribution conforming to the purpose of the test. During production of the control specimens at least one layer is formed with metal melt, into which inclusion, inclusions is/are inserted conforming to the shape and arrangement of the required fault location or locations. It is practicable to form at least one further upper layer from the metal melt inclusions. Further inclusions may be arranged in the top layer and in given case further top layers are formed with or without inclusions. The artificial defects can be produced either by forming cavities into the layer after solidification and cooling, and inserting the inclusion(s) into the appropriate cavity or cavities, or spreading them into the layer-forming metal melt before solidification.

Abstract: A method for calibrating a device for non-contact position measurement wherein a movable part subject to positional identification is provided spatially proximate to a sensor carrier that includes a plurality of signal generators electrically and spatially separated from one another in order that the position of the moving part can be identified via voltage signals therefrom. To obtain an unequivocal characteristic of the positional voltage distribution, only defined signals such as a zero value signal or other characteristic value, have length values signed to them and neighboring voltage values are coemployed to obtain an unequivocal position identification.

Abstract: A method and apparatus for magnetically measuring the amount and location of magnetite (Fe.sub.3 O.sub.4) debris adhering to the exterior of heat exchanger tubes which can be made of Inconel. A probe containing one or more coils of electrical wire is used to traverse the interior of the subject tube. One of the probe coils is energized with direct electric current to magnetize the magnetite coating on the tube exterior as the probe traverses the tube. The thickness of the magnetized coating is deduced from measurement of the voltage generated across a second coil of wire on a probe which traverses the tube at constant velocity.

Abstract: A method of and apparatus for measuring the layer of coating thickness of non-magnetic substances on a ferromagnetic parent material by the magneto-inductive method or of non-metallic substances on a conductive parent material by the eddy current method. This is done with the use of a probe whose coil inductance is evaluated as a criterion for the thickness of the layer to be measured. An adjustment to the geometry and the magnetic properties of the specimen are made before the first measurement. In the adjustment, at least one non-magnetic or non-conductive foil is disposed or are consecutively disposed between the probe and the surface of the coated specimen and the measured data obtained then and in the subsequent measurements are fed to a microcomputer.

Abstract: An apparatus for testing current sensors employing an electromagnetic coil and one or more Hall Effect switches including a microprocessor controlling a constant current source and visual and audio indicating circuits. A parameter input circuit is provided to permit an operator to select device types and to select test only, or adjustment and test sequences to be executed. The constant current source is adapted to apply a threshold, must-not-operate, and a must-operate current values to the electromagnetic coil. The visual and audio indicating circuits are adapted to provide messages, pass/fail indications, and audio signals signaling test success or failure results to an operator.

Abstract: A method of adjusting and testing for proper operation a current sensor by applying a threshold current value to the current sensor and adjusting the current sensor to a point just past the threshold of operation. Proper operation of the current sensor is tested by applying a non-operate current value followed by an operate current value to the sensor and checking for respective non-operate and operate output signals from the sensor. Messages, pass/fail indication, and audio signals are provided to signal test results to an operator.

Abstract: Sensitivity of a walk-through metal detector is checked by providing a standard metal object simulating the mass, size and metal content of a weapon or other contraband, suspending the object in successive positions simulating where the contraband might be concealed on a person walking through the detector, and swinging the suspended object through each of said positions while operating the detector and observing its response.

Abstract: In order to be able to carry out accurate measurements with a V.sub.0 -measurement device, it is important that the desired distance between the two measurement coils of the measurement device be accurately maintained. It has been found that it does not suffice to accurately measure the distance between the end faces of the two measurement coils, since the magnetic field foci of individual measurement coils do not always have the same spacing from the end surfaces. The distance between the magnetic field foci of both measuring coils is measured and is employed for determining the muzzle or initial velocity V.sub.0.

Abstract: An oxygen sensor utilizes the paramagnetic property of oxygen to determing the relative concentration of oxygen in a test gas. The test gas is supplied to the core of an electromagnet or the gap of a permanent magnet. A known magnetic flux density for the electromagnet or permanent magnet are utilized in conjunction with a Hall effect sensor to determine a change in flux which is primarily due to the oxygen component of the test gas.

Abstract: The invention relates to a self-testing proximity switch, wherein the testing is carried out with the aid of bipolar double pulses which, independently of the switching state of the trigger stage, each time cause a short-timed triggering thereof. At the output of the trigger stage, the superimposed pulses can be evaluated by the test circuit in order to monitor proper functioning of the proximity switch.

Abstract: A device to be lowered into a string of well drilling pipe to the location of a non-magnetic section of the pipe near its lower end, with the device including a compass assembly or other instrument for making a photograph or other record at that location. The device includes a detector which responds to arrival of the device within the non-magnetic section of the drill pipe to automatically energize the instrument for making the photograph or other record. The present invention provides a test circuit for this type of device enabling it to be quickly and easily checked at the surface of the earth before being lowered into the drill string to make certain both that the detector which responds to arrival of the device in the non-magnetic section of pipe is in working condition and that the batteries which energize the device are at a sufficiently high voltage level to assure effective operation of the device in the well.

Abstract: A method of detecting the toner concentration of a two-component developer comprising a mixture of carrier particles and toner particles for use in an electrostatic copying apparatus or the like wherein a relationship between flow rate and the toner concentration of a two-component developer which passes through a container is obtained in advance, then the flow rate of the two-component developer whose toner concentration is unknown is measured by use of the container and developer flow rate detecting member. Thus, the toner concentration of the developer is determined from the measured flow rate and the relationship between the flow rate and the toner concentration which has been obtained in advance.

Abstract: A device for testing and calibrating treasure hunting metal detectors is provided. The device includes an enclosure which contains a quantity of background material of the type expected to be encountered in the search environment of the metal detector. Elongated cross members are positioned across the housing at varying distances from the top. Each cross member has an open interior region into which a slide containing a simulated metal treasure may be placed. When the search coil of a metal detector is placed on top of the device it senses the presence of the metal treasures in the slides within particular ones of the cross members. By varying the type of metal and the location of the simulated metal targets the capabilities of the treasure hunting metal detector can be tested and calibrated.

Abstract: The metal detector circuitry for a forage harvester is provided with a socket for receiving a pluggable unit, the arrangement being such that a resistor in the pluggable unit is connected into the detection circuitry of a metal detector whereby the sensitivity of the metal detector may be changed by inserting into the socket a pluggable unit containing a resistor of a different value. A metal detector test assembly connected to the metal detector through the socket, provides a means for testing the sensitivity of the metal detector and its associated circuitry. The test assembly includes a signal unit which is placed adjacent the metal detector sensing unit and generates a magnetic field that is sensed by the sensing unit, and a test box with circuitry, indicators and switches for selectively checking the sensitivity of the metal detector and correct operation of its associated circuitry.

Abstract: A method for measurement of distance using the curl-free vector potential radiation field. The system includes current-carrying apparatus for generating a predominantly curl-free vector potential field and apparatus for modulating the current applied to the generating apparatus. The receiving apparatus includes a detecting apparatus with observable properties that vary with the application of an applied curl-free vector potential field, a demodulation apparatus for determining the magnitude of the curl-free vector potential field. The magnitude of the detected curl-free magnetic vector potential field can determine the distance from apparatus generating predetermined periodic changes in the curl-free vector potential field. The vector potential field can be established in conducting and opaque materials which are not capable of transmitting typical electromagnetic radiation.

Abstract: Metal detector sensitivity is checked by holding its sensing means adjacent to a test unit containing a metal body mounted closer to one side than the other and calibrated to give a desired range of response when the sensing means moves from one of the said sides to the other.

Abstract: A method and apparatus for measuring precise distances between the turbine shaft and the inner cylinder is disclosed. A mandrel carrying proximity transducers is placed inside the inner cylinder and rotated to preselected points. A proximeter sends a voltage to the transducers and the voltage drop from the transducers to the preselected points on the inner surface of the inner cylinder is measured. Then, the top halves of the turbine are installed and voltage drop for the same points is recorded. A computer compares the voltages and converts the difference into engineering units to allow determination of the "sag" in the turbine spindle that will be introduced when the complete turbine is assembled.

Abstract: An apparatus for simulating and analyzing discontinuities in a tube using eddy current inspection techniques is disclosed. The simulation apparatus includes inner and outer tubular members arranged to define an annular chamber having a predetermined tubular configuration corresponding to the tubular configuration of a tube under investigation. The outer tubular member has an opening through the wall thereof and the inner tubular member defines an axially extending hollow interior. A supply of electrically conductive liquid material is provided in the annular chamber, the quantity of liquid material being such as to substantially and completely fill the annular chamber in the vicinity of the opening through the wall of the outer tubular member. A defect simulation member is supported in the opening in the outer tubular member for movement along a predetermined direction extending transverse to the axis of the inner tubular member.

Abstract: A method of detecting a flaw in a moving chain is disclosed in which two identical free-running oscillators are used, and through the inductive core of one a chain is passed. A comparator circuit monitors the oscillators' outputs so that changes in mass of the chain may be sensed.

Abstract: A magnetic thickness gauge is disclosed wherein a balance arm is pivotably mounted in a housing with a spring providing a bias force to counteract a magnetic attraction of the balance arm toward a base of a coating to be measured. The balance arm is provided with a probe assembly including a magnet selectively positionable with respect to a spherical contact member of either a particular alloy of aluminum, iron and silicon or of tungsten carbide. The housing is preferably provided with supports at either end of the gauge. A balance arm is moved by way of a protrusion provided between the probe assembly and an adjustment knob for the spring with a scale and pointer indicating the thickness of the coating to be measured.

Abstract: A system for measuring the cladding thickness on aluminum sheets which includes a cylindrical probe holder with four evenly spaced contact points surrounding a low temperature coefficient torroidal ferrite core which provides a signal to an aluminum cladding thickness signal processing circuit comprising a crystal oscillator, low drift detector, and push button calibration instrument portion thereby enabling drift free repeatable measurements.

Abstract: Eddy current non-destructive testing device comprising in per se known manner an exciting generator, a probe connected to the latter, means for sampling in the probe a measuring voltage, means for producing a reference voltage, a differential amplifier having a first and second input and an output, a first input receiving the measuring voltage and the second the reference voltage, digital signal processing means having an input connected to the output of the differential amplifier across an amplifier, said processing means successively comprising an analog--digital converter, a first random access memory and a digital processing circuit, wherein the means for producing a reference voltage comprise a second random access memory having an input and an output, the input being connected to the output of the first random access memory across a switching circuit and a digital--analog converter having an input connected to the output of the memory and an output connected to the second input of the differential ampli

Abstract: A test circuit which detects Hall effect device operate and release time failures. This circuit includes a magnetic field circuit, a comparison circuit, a storage circuit and a visual indication circuit. The magnetic field circuit causes a Hall effect device under test to periodically switch states. The operate and release times of such switching is compared to predetermined thresholds by the comparison circuit. Switching times within the allowable thresholds cause the storage circuit to operate the visual indication circuit.

Abstract: A simulated radiation source and a compatible detector system are disclos The combination is useful in training for detecting alpha radiation contamination. A flexible, soft iron plate or first permanent magnet in the detector system responds to a second magnet that is employed to represent an alpha radiation source. Where the first permanent magnet is used, an iron member may be adopted in lieu of the second magnet. The simulated source is affixed to the subject's clothing or body. When the detector system is brought into proximity with the simulated radiation source, the soft plate or first magnet responds and affects a strain gage which in turn provides an electronic indication.

Abstract: A Hall effect device test circuit which detects Hall effect device operate and release point failures. A magnetic field circuit, an analog-to-digital conversion circuit, a storage circuit, a comparison circuit and a visual indicator circuit are included. The magnetic field circuit causes the Hall effect device under test to switch between its operate and release states. The analog-to-digital conversion circuit provides a digital value, representative of the intensity of the magnetic field existing at the time of switching. These digital values are then stored in the storage circuit. The comparison circuit compares the stored switching values to predetermined thresholds and causes an appropriate visual pass/fail visual signal to be provided.

Abstract: A Hall effect device test circuit which detects Hall effect device operate and release point failures. A magnetic field circuit, a voltage switching circuit, a comparison circuit, a retriggerable monostable multivibrator circuit and a visual indicator circuit are included. The comparison circuit compares the Hall effect device switching voltage to a predetermined threshold and controls the multivibrator circuit which causes a visual pass/fail signal to be provided.

Abstract: Bodies of a ferrimagnetic material are disposed within small cavities provided in a magnetometer. The magnetometer is initially calibrated utilizing an electromagnet to produce an applied magnetic field of either known field strength, H.sub.DC, or known field distribution. Radio frequency energy is fed equally to each cavity and each material and results in resonance frequency output signals which may be coupled to a visual display. When the calibrating magnetic field is of known uniform strength, H.sub.DC, the orientation of the bodies is changed until each of the resonance signals have a frequency substantially given by f.sub.c =.gamma.H.sub.DC where .gamma.=2.8 MHz/oersted. When the calibrating magnetic field has a known field distribution the orientation of bodies is changed until such resonance signals have frequencies related to one another in accordance with the relative magnetic field strengths passing through the cavities.

Abstract: A device for measuring local electric conductivity of plasma, comprising a probe, which is kinematically coupled to a drive mechanism and has a series circuit including an inductive sensor, a measuring oscillator, and a detector having one output coupled, via an optoelectronic converter, to a differential stage having a switch and a memory member. An output of the differential stage is coupled to one input of a measurement recording unit having another input coupled to a unit for feeding commands which is electrically coupled to an electropneumatic control unit accommodating air valves of drive mechanisms of the probe and calibration crystal, the air valve being coupled to pneumatic cylinders of the drive mechanisms by means of flexible bases made of an insulating material.

Abstract: An eddy current probe calibration standard for calibrating eddy current probes and instruments utilizing calibration discs that provide a standard defect of known dimensions to produce a known repeatable signal. A plurality of round discs with different diameter holes through their centers are respectively provided to accommodate different size probes. Each disc has a defect in the wall of the hole in the form of a slot with known dimensions which will reproduce a known, repeatable signal. A flat, rectangular block which supports the discs, contains surface slots of known dimensions to produce known, repeatable signals for calibration when testing for surface defects.

Abstract: A method of effecting an examination by eddy current means (24) of the surface of a coated component (58) for cracks having at least a preset minimal dimension. The subject method can be used to detect such cracks in the surface of metal components (58) that are coated or covered with a nonmetallic material. Further, through the use of the subject method such cracks are detectable without necessitating the removal of the nonmetallic coating or covering from the surface of the metal component (58). The subject method encompasses the steps of establishing calibration readings for cracks of the desired dimension utilizing the eddy current means (24) with which the desired surface examination of the given component (58) is to be effected, performing a preexamination validation of the operativeness of the eddy current means (24), and conducting with the eddy current means (24) the surface examination of the given metal component (58) that is coated or covered with a nonmetallic material.

Abstract: A transducer having a field creating coil arrangement which produces a field having a field strength minimum, having a sensing coil positioned at that field strength minimum and responsive to changes in position of that minimum resulting from the proximity of an article to the field creating coil arrangement. By observing changes in the signal output of the sensing coil, information concerning the proximity of an article to the transducer is ascertained. Preferably the transducer includes a field disturbing means associated therewith for inducing a disturbance to the field created by the field creating coil so as to cause the sensing coil to operate by either simulating the disturbance of the field that would be caused by the proximity of an article or by changing the field while the article is present. Thus the transducer may be remotely checked as to its operation.

Abstract: Bodies of a ferrimagnetic material are disposed within small cavities provided in a magnetometer. The magnetometer is initially calibrated utilizing an electromagnet to produce an applied magnetic field of either known field strength, H.sub.DC, or known field distribution. Radio frequency energy is fed equally to each cavity and each material and results in resonance frequency output signals which may be coupled to a visual display. When the calibrating magnetic field is of known uniform strength, H.sub.DC, the orientation of the bodies is changed until each of the resonance signals have a frequency substantially given by f.sub.c =.gamma.H.sub.DC where .gamma.=2.8 MHz/oersted. When the calibrating magnetic field has a known field distribution the orientation of bodies is changed until such resonance signals have frequencies related to one another in accordance with the relative magnetic field strengths passing through the cavities.

Abstract: A method and apparatus are provided which are based upon a discovery that regardless of the type of ferromagnetic material of a part and its shape, there is a certain direct, uniform and constant relationship between the level of magnetization required for satisfactory testing by the magnetic particle method and the response which is obtained from an eddy current instrument which has been properly calibrated and which is used under proper conditions. After removal of scale from a surface portion of a part and after demagnetization of the part, a probe of the eddy current instrument is simply placed against such surface portion and the part is magnetized at a level which produces a certain target eddy current indication. The instrument may be readily calibrated through the use of a test block which has a milled slot of a certain size. Preferably, the probe is of a crossed coil type permitting a rapid scanning operation with respect to a plurality of surface areas of a part of irregular shape.

Abstract: An apparatus and method for testing low-power, low-band radio frequency metal detectors of the type employing a radio transmitter alone or a transmitter and a receiver. The apparatus is characterized by a variable voltage power supply, a transmitter, an antenna, a voltmeter, a rectifier connected to the voltmeter, a switch for connecting the rectifier to either the antenna or the power supply and for selectively energizing the transmitter, and a surface placed in a fixed position relative to the antenna and defining the proper position for placement of the equipment under test.

Abstract: A method and arrangement for testing the serviceability and for setting and calibrating a test apparatus for the non-destructive electrical and/or magnetic testing of metallic blanks, particularly steel slabs, for defects, such as surface or below-surface cracks, laps, shrinkholes, blowholes or the like, comprising inspecting means capable of detecting defects such as these and mounted for displacement relative to the surface of the blank to be tested, test plate simulating a defective metallic blank being brought up to the test apparatus in a position in which they are in substantial alignment with the surface of the blank to be tested, the inspecting means of the test apparatus being tested by the test plates for working order and calibrated.

Abstract: The present invention is an automatic sensitivity adjustment apparatus for calibration of a nondestructive inspection instrument with a reference standard. Calibration is performed by setting the gain of a variable gain amplifier while a reference standard containing a standard flaw is passed before the sensing means of the instrument. A discriminator circuit connected to the sensing means detects when the output of the sensing means exceeds a predeterminedlevel. A hold time controller sends a sampling enable signal to a peak hold circuit which is also connected to the sensing means to cause the peak hold circuit to sample the sensing means output. The hold time controller senses the peak in the response of the sensing means and causes the peak hold circuit to hold that peak value. The output of the peak hold circuit is applied to the input of a variable gain amplifier. A comparator compares the output of the variable gain amplifier with a reference voltage produced by a reference voltage setting means.