Abstract: A non-contacting electrostatic mark/sense length measurement gauge is used to place discrete areas of electrostatic charge at very accurately spaced intervals along a relatively moving material surface. Special construction of both the electrostatic marking and sensing transducers is employed. To compensate for expected unreliability of the mark/sense length gauge, a conventional highly reliable but less accurate contacting length gauge (such as a tachometer in rolling contact with the relatively moving material) is employed. The output from the electrostatic mark/sense length gauge and from the tachometer length gauge are combined by special electronic circuits to provide a length measurement of the passing material which is both highly accurate and reliable under all expected measurement conditions.

Abstract: An arrangement for monitoring the potential of a cathodically protected buried metallic structure. The apparatus includes a measuring electrode to be inserted into the soil and electrically coupled to the metallic structure to be measured, a reference electrode placed on or in the soil, and a measuring circuit for measuring the potential difference between the measuring and reference electrodes. The measuring circuit also generates a reference potential to generate a pulse signal having a frequency proportional to the amount by which the measured potential exceeds the reference potential. A counter counts the number of pulses during a measuring cycle that is measured by a timer. A computer computes from timer and counter output data, the average value of the amount by which the measured potential exceeds the reference potential during a measuring cycle.

Abstract: A tri-electrode probe consisting of a central electrode and a pair of measuring electrodes on the opposite sides of the central electrode disposed so as to symmetrically cover an immaginary surface having a plane of symmetry, is connected to a measuring system including minute current ammeters and a variable D.C. voltage source, the tri-electrode probe is positioned at a measuring point within an electric field where both positive and negative ions coexist as oriented in such direction that the plane of symmetry is directed in perpendicular to the direction of the electric field with one of the measuring electrodes opposed to a negative ion source and the other measuring electrode opposed to a positive ion source, a current flowing through the minute current ammeter connected to the central electrode is made substantially zero by varying the voltage of the variable D.C.

Abstract: A sensing element for measuring atmospheric electrical field comprising a fixed detection electrode and a rotating modulator. Between the detection electrode and the rotating modulator there is interposed a fixed apertured screen, conductive of electricity and connected to the sensing element mass. The screen has a peripheral portion protruding relative to the modulator. The sensing element measures both slow field variations and abrupt field variations.

Abstract: An instrument for monitoring the hazard arising from electro-magnetic (electric and/or magnetic) radio-frequency fields comprising an electric and/or magnetic field probe, a radio-frequency converter for converting the signals picked up by the probe into continuous current electric signals, a comparator for comparing the continuous current electric signals with predetermined reference values, and output indicators activated by the output signals of the comparator. Preferably the reference values divide the values of the field levels into three contiguous zones, respectively-of insignificant risk, of possible risk and of certain risk.

Abstract: An apparatus and method of detecting, tracking and displaying lightning activity is disclosed. A lightning stroke has associated therewith electric and magnetic field components characterized by maximum rise times and minimum power levels. The field signals comprise a plurality of sub pulses also. An electric field antenna and a pair of magnetic field antennas are disposed to receive the field components associated with lightning activity. Control circuitry cooperating with rise time and threshold measuring which operates on the field signals received by the antennas generates control signals including integration and sampling control signals for integrating the electric and magnetic field signals over a predetermined time interval (preferable one hundred microseconds) and for sampling and holding the field signals at each of the sub pulse peaks.

Abstract: In a monitoring system for protecting a metal pipe against corrosion, transmission of monitoring signals is carried out by the use of the pipe itself as a transmission line between a center station and a substation, which are coupled to the pipe at center and subordinate locations, respectively. The substation sends data signals over the pipe to the center station. These data signals represent the degree of corrosion that is measured at the subordinate location and are monitored by the center station. When a plurality of substations are coupled to the pipe, the center station selects a substation by transmitting through the pipe an address assigned to the substation. Each substation returns the assigned address to the center station in combination with the signals representing the measured degree of corrosion at the addressed substation. Preferably, the center station produces the selected address twice while each substation produces the assigned address and the measured corrosion signal, twice.

Abstract: A storm mapping system detects electrical activity caused by weather phenomona such as lightning strokes, and the like and displays information related to the electrical activity indicative of storm location in a frame of reference in which the observation location is taken as the origin. In order to give the observer good spatial understanding, signals detected from a relatively close disturbance (which produces relatively large signals) are displayed relatively close to the observation location as compared to display of signals generated from a relatively further disturbance which produces relatively smaller signals which are displayed relatively far from the observation location. The limited resolution display is effectively driven by signals read from digital storage wherein mapping between the different display segments and digital storage is maintained.

Abstract: An apparatus and method of conducting continuous or closely spaced buried structure-to-soil electrical surveys uses a soil contact cell adapted to be worn on the bottom of the walking field boots of a surveyor walking over the right-of-way of the buried structure such as an underground pipeline. The cell is in the form of a sandal which may readily be secured to and removed from the bottom of the boot. The cell includes an impervious upper plate and a pervious lower ground contacting flexible sole plate forming with the upper plate a flat chamber which may be filled with a loose silica sand fill or sponge material. A copper rod or strap is imbedded in the material and electrically connected through a meter carried by the surveyor to the structure through a length of economically disposable wire.

Abstract: Apparatus for detecting electric fields and providing an indication of their magnitude includes a glass bulb containing a gas such as neon. When the bulb is placed in a time varying electric field, pulses of electromagnetic radiation are generated within the bulb. The number of pulses is proportional to the magnitude of the variation in the electric field. The pulses are transmitted by a fibre optic bundle to detection and recording apparatus to provide an indication of the magnitude.

Abstract: An electrostatic detector comprising a detector electrode sensitive to electrostatic quantities such as fields, voltages, charges and the like, means for varying the capacitive coupling between the electrode and an electrostatic quantity to which the electrode is exposed, and an operational amplifier having an output and a pair of inputs, one of which is operatively associated with the amplifier summing node. A resistive feedback path is defined between the amplifier output and the summing node, the detector electrode is connected to the one amplifier input so that the detector electrode is operated directly into the amplifier summing node, and the other amplifier input is connected to an electrical reference, such as ground. As a result, the detector electrode is held at virtual ground and the amplifier is operated as a current to voltage converter to cause an output voltage to be generated equal to the product of the input current and the resistance of the feedback path.

Abstract: The surface potential electrometer includes a reciprocating chopper, a measuring electrode on which a voltage is induced which is associated with the surface potential of a member to be measured, a shield member for shielding the measuring electrode and the chopper from electric field emanating from the member to be measured, and a driver for driving the chopper, thereby detecting the surface potential of the member in the form of an AC signal. The shield member is provided with an aperture for guiding the electric field emanating from the member to the measuring electrode.

Abstract: A monitor for measuring the field strength of RF radiation is disclosed. A set of three mutually orthogonal antennas sense the total field strength. Digital linearizing and scaling circuits provide an output equal to the sum of the square of the field components. In the preferred embodiment, the digital circuitry includes a control or zero channel which provides a zero level control signal which is processed to provide a correction signal to the analog to digital conversion circuitry to remove the effects of noise, pickup and drift on both the transmission line, which connects the antenna and the monitor, and on the analog electronic circuits of the monitor.

Abstract: This invention relates to monitoring the condition of sheathings which electrically insulate a submarine structure brought to an electrical potential differing from that of the sea water, or to monitoring the operation of the anodes if said pipeline is under cathodic protection.According to the invention one or more sets of three electrodes, which are spaced apart and aligned parallel to said pipeline, is/are displaced longitudinally above said pipeline, and the difference between the potential of the central one of said electrodes of the or each set and the algebraic sum of the potentials of the other two of said electrodes of the or each set, is measured in continuous fashion.

Abstract: An apparatus for testing the pipe-to-soil potential of a buried pipeline having a plurality of rectifiers electrically connected to it in spaced-apart intervals for applying an electrical potential to the pipe includes a plurality of interrupter units electrically connected to the rectifiers for turning them on and off at intervals. A clock reference unit is electrically connectable to each of the interrupters for synchronizing them for turning all of the rectifiers on and off in unison. A portable sensing device produces signals indicative of the pipe-to-soil potential of the pipe and directs these signals to a demultiplexer unit which is also synchronized with the clock reference unit for separating the signals corresponding to the ON and OFF potentials which are then separately recorded.

Abstract: Precisely positionable apparatus for collecting corona-generated current. A conductive sheet or coating is affixed to one side of an insulative sheet material. A low residue of nonresidue adhesive alone or carried by a tape is affixed to the other side of the insulative sheet. The sheet is then placed on a copier photoconductor or photoconductor carrier such as a drum, adhesive side to the carrier. The adhesive keeps the sheet flat against the surface at which the measurement is to be made. A shock protection line including front-to-back parallel diodes is connected between the conductive surface and ground. With the corona on, and the carrier in position, a current measuring device is connected between the conductive surface on a tab of the sheet and ground.

Abstract: A discharge counter and arrester current meter employs a zinc oxide disk in combination with a pair of bridge rectifiers to accurately determine surge arrester steady state current and to count the number of discharges occurring through a voltage surge arrester. The discharge counter and meter circuit, connected between the surge arrester and ground, monitors the steady state current by means of an ammeter and records the number of discharges by means of a capacitor, cyclometer coil, and a recorder. The meter circuit and the discharge counter are uniquely protected by a single zinc oxide disk during the discharge of high current surges.

Abstract: A method for checking for electrical frit breakdown in kinescopes uses a novel probe which is dimensioned to enter into the neck of the kinescopes without contacting the interior of the neck. A movable electrical contact is actuated to a position against the conductive coating on the inside of the tube. A high voltage supply is connected between the movable contact and the frit seal and current flow indicates an electrical frit seal breakdown.

Abstract: Apparatus for measuring a high voltage electric field, such as may be used in simulating lightning strikes or the like on a test specimen, is disclosed. In general, a capacitive electric field sensor is disclosed which utilizes a pair of spaced conductors or electrodes and which is placed in the field to be measured. The conductors shield a device within the sensor which generates a signal responsive to the intensity of the electric field. This signal is transmitted to a remote data acquisition system by means of non-electrically conductive data transmission lines (e.g., fiber optic transmission lines) so as to electrically isolate the sensor and the data acquisition system whereby the sensor only minimally distorts or affects the field being measured thereby. A method for measuring high voltage electric fields is also disclosed.

Abstract: An apparatus for making electrical surveys of structures contained in an electrolyte by measuring potential difference therebetween includes an electrode to contact the electrolyte proximate the structure, a wire electrically and mechanically connecting the apparatus with the structure, and an electronic system for automatically electrically sensing and storing the potential difference values taken at a plurality of locations along such structure. In the method for making structure-to-electrolyte potential difference surveys a supply of elongate electrical conductor is electrically and mechanically connected to the structure; the conductor is played out along the structure, and the electrolyte is contacted at plural test locations proximate the structure; and the potential difference at such test location is automatically sensed and stored.

Abstract: The invention relates to a combined current and voltage converter for metal-enclosed high-voltage installations with compressed-gas filling. In order to be able to avoid any passages for the connecting leads through the housing (1, 2), the electrode of the capacitive voltage converter part consists of an intermediate element (3) inserted into the housing in an insulated and gas pressure-tight manner. The intermediate element (3) has on its outside a layer of insulating material (9) and on top of this a metal layer (10). The whole (3, 9, 10) forms a support body for current converter cores (11) surrounded by secondary windings. The low-voltage capacity between the intermediate element (3) and the metal layer (10) is fed to an electronic measuring amplifier (14) via a screened measuring cable (12/12a). The current converter cores (11) are protected mechanically by a sheath tube (16), the latter simultaneously conducting housing currents. FIG. 1.

Abstract: An electromagnetic system for determining the orientation including position of a helmet worn by a pilot is disclosed, having a transmitting antenna for transmitting electromagnetic field vectors, a receiving antenna for sensing the electromagnetic field vectors, a control apparatus responsive to the sensed electromagnetic field vectors and the transmitted electromagnetic field vectors for determining the orientation including location of the helmet, the control apparatus having a first output for supplying the orientation to a utilization apparatus and a second output, a driver for supplying driving energy to the transmitting antenna coils, and a selector switch connected to the second output of the control apparatus and to the driver for sequentially energizing the coils of the transmitting antenna.

Abstract: Measuring apparatus for providing a reading representing a magnetic field component or the electric field component of incident radio frequency electromagnetic radiation comprises a set of magnetic field sensors and a set of electric field sensors interchangeably connectable to a measuring device which has an indicator instrument and an optical output to which can be connected a repeater device by means of an optical fibre cable which thus does not exert a perturbing influence on the field being measured. The sensors are omnidirectional balanced devices in which the detector elements are constituted by suitably shaped metallic film deposits on dielectric substrates, and can be interchanged by a simple plug-in connection which also holds the sensor physically in position on the measuring device.

Abstract: A low frequency electric field exposure monitor integrates personal exposure to an electric field into intervals of electric field intensity.

Abstract: In a gas-insulated electric apparatus, such as a gas-insulated switchgear and a gas-insulated bus, having an insulating-gas-filled metallic container or sheath within which an electric conductor carrying a high-voltage current is supported by an insulating supporter, a potential detected by a first potential detector through at least a portion of the insulating supporter and another potential detected as a reference value by a second potential detector through an electro-static capacity disposed between the metallic container and the second potential detector are fed to the inputs of a differential amplifier of a partial discharge detecting device to thereby detect possible partial discharges along the insulating supporter with high sensitivity.

Abstract: An input signal from an antenna is level-adjusted by a first level adjuster and then frequency-converted by a frequency converter. The frequency-converted signal is further level-adjusted by a second level adjuster and then detected by a detector, and the detected output is displayed on a first display. A control signal for controlling the frequency of a local oscillation signal of a local oscillator, which is applied to the frequency converter, is adjusted to select the input signal to be measured. The control signal is applied to a compensating signal generator to derive therefrom a compensating signal for compensating for the frequency characteristic of the antenna. The compensating signal, a first set signal representing the set value of the first level adjuster, and a second set signal representing the set value of the second level adjuster are added together.

Abstract: A system for differentiating between cloud-to-cloud and cloud-to-ground lightning discharges which include an electric field antenna that senses the rate of change of an electric field produced by a lightning discharge. When the signal produced by the electric field exceeds a predetermined threshold, it is fed to a coincidence detector. A VHF antenna it also provided and generates a video signal responsive to a cloud-to-cloud lightning discharge, and this signal is fed through a level sensor, an inverter, to the coincidence detector simultaneously with the signal from the field detector. When signals from the electric field antenna and the VHF antenna appear at the coincidence detector simultaneously, such indicates that there is a cloud-to-cloud lightning discharge; whereas, when there is not a signal produced on the VHF antenna simultaneously with a signal produced by the field sensor, then a strike indicator connected to the coincidence detector indicates a cloud-to-ground lightning discharge.

Abstract: An electrostatic voltmeter including a probe having a detector which is resistively coupled into a region bearing ionized air and an electrostatic field or potential to be measured. An ionization source in the form of a radioactive material is carried by the probe housing and ionizes the air in the region of the detector to provide an ionic current flow into the detector in response to the measured electrostatic field or potential. The electrostatic voltmeter further comprises an amplifier having an input and an output and connected for unity gain, the amplifier input being coupled to the detector. The amplifier has a feedback path connected as a voltage reference for the detector to cause the ionic current flow to change in a manner which will drive the amplifier and feedback to reduce the electrostatic field in the vicinity of the detector to zero.

Abstract: A voltage driven corona current sensing probe, utilized to sense electrostatic charge (such as on aircraft), is provided with higher positive operating voltage than negative operating voltage to compensate for the different electron emission threshold and mobility of electrons compared to positive ions. In an AC embodiment, the voltage difference is achieved by a polarity-asymmetric voltage divider on a high voltage AC source feeding a single probe. In another embodiment, separate DC power supplies drive respective probes with different voltages.

Abstract: In an arrester comprising a characteristic element made up of a stack of a plurality of metal oxide resistors, parallelly connected capacitor and a linear resistor are connected between the characteristic element and ground, and voltage drop across the linear resistor is used to light a neon lamp or to operate an alarm device for detecting deterioration of the characteristic element. To protect the capacitor and the linear resistor at the time when the arrester operates, a nonlinear resistor may be connected in parallel with the capacitor and the linear resistor.

Abstract: A lightning detection system utilizes a plurality of remotely located lightning detectors that provide information defining the azimuth of a lightning discharge to ground as well as information defining the strength of the electric and/or magnetic field produced by the lightning discharge to a central office. The central office includes a position analyzer for processing the data to determine the position of the discharge. The position analyzer utilizes either the received angle information and triangulation techniques, or the relative amplitudes of the fields to determine position, depending on whether or not the discharge occurs along or near a line joining two of the remotely located detectors.

Abstract: A method and apparatus for determining the presence of partial discharge ivity (corona) which makes use of corona current signals in the 20 MHz to 50 MHz frequency range and provides for identification of the corona source in a capacitor matrix. A current probe coupled to the high potential side of the capacitor detects corona discharge current signals that are fed to a bandpass filter which passes signals in the frequency range of 20 MHz to 50 MHz. The signals from the bandpass filter are amplified and integrated to provide a d.c. level proportional to the corona activity. The d.c. level signal is encoded by a voltage controlled oscillator and then converted to light. A fiber optic link transmits the converted signal to a remote console where the encoded light is reconverted to a d.c. level signal which can be displayed as an analog signal as well as activating an audio or visual alarm.

Abstract: The signal generator produces an output comprised of a periodic signal and a precision amplitude pulse. A periodic waveform source is fed to the center tap of a transformer. The instantaneous amplitude of the waveform is sensed and, when it reaches a predetermined level, one free end of the transformer is grounded thereby producing a predetermined amplitude pulse, superimposed on the periodic waveform, at the remaining free end.

Abstract: The disclosed device is an electromechanical parametric amplifier. It utilizes, as the required nonlinear mixing element, the square law force of an electric field on the surface of a conductor. In an exemplary device, a wire grid (10) is placed adjacent to a conducting diaphragm (11). The diaphragm (11) is mechanically resonant at the local oscillator (LO) frequency. When a signal from the local oscillator (15) is applied to the grid (10), the diaphragm (11) experiences both the electrostatic force from the grid (10) and electrostatic force from the electric field to be measured. The amplitude of the vibration of the diaphragm (11) at the LO frequency is a measure of the electric field of interest. In an exemplary embodiment the vibration was measured by an electret microphone (12) and a lock-in amplifier (14). The measurement of electric field is important, for example, in industrial environments in which the buildup of static electricity is a problem.

Abstract: The sensor system senses a drop in the flow of impressed cathodic protection current to a minimum threshold level. A potential difference is developed which is a sample of the cathodic protection current. A comparator receives the sample potential difference and normally produces an output control signal which drops to substantially zero when the cathodic protection current drops to a predetermined threshold level. A relay responsive to the control signal then switches a signaling device to its signaling condition. A standby battery is also coupled to the signaling device through the relay. In the event of any failure in the sensor system or in the primary source of power energizing the sensor system, the standby battery becomes connected to the signaling device to cause it to change to its signaling condition.

Abstract: An electromagnetic noise source locator is comprised of an audio amplifier which is connected to drive a speaker and to which is connected at the input a series circuit that includes a very small antenna loop of area less than 1 in.sup.2, a diode and a capacitor. This apparatus responds only to bursts of radiated energy and furthermore responds only to such bursts having frequency components over about 1 GHz. It is therefore particularly suitable for the selective sensing and location of sparking gaps as may occur on power lines.

Abstract: A large bandwidth non-contacting voltage follower for detecting and following both static or d.c. and dynamic or a.c. data of an electrical field or potential being measured. A probe or sensor includes a pair of voltage sensitive electrodes which are vibrated or oscillated within a housing to vary the capacitive coupling between the electrodes and external field or potential in an inverse manner to induce signals on the electrodes having static and dynamic data from the field or potential. The signals are processed and applied to the input of a voltage follower amplifier, the output of which is coupled to the probe housing as a reference, so that the follower output follows the static and dynamic characteristics of the external field or potential.

Abstract: The present invention relates to a method and apparatus for detecting the earth's static electric field and determining the contour of its equipotential lines and surfaces and for utilizing the detected field as a reference for other measurements. In particular, the contour of the field can be determined by sensing the potential at a plurality of points and measuring the differences in potential at the points with a differential static amplifier. Alternatively, a fluxmeter for measuring the electric field vector directly can be used to sense changes in the magnitude and direction of the field. A line defined between two points or a plane defined by three noncolinear points in space can be made to coincide with an equipotential line or surface in space, respectively, by adjusting the relative positions of the points such that either the potential differences between the points or the field components sensed along the defined line or in the defined plane are zero.

Abstract: A lightning detection system utilizes a gated magnetic direction finder for determining the range and direction of lightning discharges to ground. The magnetic direction finder is controlled by an electric field detector that includes logic circuitry for analyzing the waveforms of the detected electric field to determine whether the discharge is a ground stroke or other type of discharge, or background noise. The magnetic direction finder is gated by the electric field control logic circuitry so that a direction measurement may be made for a few microseconds after it has been determined from the electric field waveform analysis that a ground stroke has occurred. Different criteria are used for determining whether or not a stroke is a ground stroke depending on whether the stroke being analyzed is the first stroke in a flash or a subsequent stroke.

Abstract: An electrostatic voltmeter for measuring the electrostatic potential on a photosensitive drum has a detector capacitively coupled to the drum for providing an output signal in response to the potential on the drum. An AC voltage source is coupled in circuit with the drum and the detector for applying an AC signal across the surface-to-detector capacitance. Circuitry coupled to the detector determines the detector gain in response to the value of the AC component of the output signal and the value of the applied AC signal. The product of the reciprocal of the detector gain and the value of the DC component of the output signal is representative of the electrostatic potential on the surface.

Abstract: A corona discharge detection apparatus particularly suited for use in detecting corona signals mixed with noise which is in synchronism with a cycle of a power supply such as corona discharge which occurs in a flyback transformer of a television receiver. The noise and the corona signals are converted to a digital signal and the digital signals in two cycles are subtracted one from the other and the resulting digital signal is converted to an analog signal for observation. In this manner, a corona signal which has not been detected by a phase technique can now be detected.

Abstract: An auto-bias developing process for developing an electrostatic latent image formed on a photosensitive member which includes the step of storing a detected potential in order to apply a fixed bias potential to a developing electrode plate wherein the surface potential of a photosensitive member is detected through a developing solution by a sensor electrode, and is stored in a memory circuit for subsequent conversion to a fixed bias potential which corresponds to the detected potential and is applied to the developing electrode. The process also includes the step of removing any toner which attaches to the developing electrode plate, by the application of a reverse bias potential thereto when the developing process is not taking place and the step of rendering the developing electrode plate electrically floating for removing toner from the plate and preventing deposition of toner onto the surface of the photosensitive member.

Abstract: An acoustic output electrical tester has externally accessible test terminals and internal test switches. The tester includes a multivibrator circuit which provides an output tone, the pitch of the tone, and its presence or absence, providing an indication with respect to the impedance, or transistor being tested. The externally accessible terminals can be selectively connected to a transistor, with the switching function replacing the externally connected transistor in the circuit of the multivibrator. A conductivity type reversal switch is provided to place the externally connected transistor in an internal circuit appropriate to the two conductivity types of the transistor.

Abstract: Process and test generator for simulating the operation requirements of a protection device for an AC low, high or very high voltage power network. The generator comprises a voltage branch connected to the protection device for producing a sparkover voltage and an injection branch in parallel with this voltage branch for producing across the device under test a follow current of a value corresponding to the value of the current injected by the power network through this protection device when the latter is in operation. A resonant branch is connected to the injection branch for producing across the terminals of the protection device an alternating voltage corresponding to the voltage of the power network. The generator can also stimulate a long power transmission line and repetitive sparkovers of the device under test. Furthermore, a sparkover of the device can be performed at any phase angle of the power network voltage. The process and the generator are particularly useful for the testing surge arresters.

Abstract: An apparatus is provided for the detection and counting of the number of lightning discharges on the skin of an aircraft. The apparatus comprises a sensor electrode for the detection of such discharge, an electronic circuit for generating and shaping a pulse at each detection interval, and a circuit for counting and displaying such pulses.

Abstract: A method and apparatus for making relatively closely spaced pipe-to-soil potential difference measurements, the method and apparatus being characterized by a dual function economically disposable, relatively lightweight, flexible electrical wire that provides for the necessary electrical connection to a pipeline and also for accurate distance measurement at the test end of the wire along the pipeline. The wire is electrically connected at a test station or lead to the pipeline and is played out from a supply thereof carried by the surveyor along the length of the pipeline through distance measuring means. At each selected test location, the potential between the wire connected to the pipe and a reference electrode contacting the soil proximate the pipe are measured by a high resistance input meter. The wire is economically disposable and may be discarded when no longer used eliminating the need to rewind the wire.

Abstract: A conductive housing includes a needle for contacting the object whose potential is desired to be sensed. The housing supports an electrometer probe within its confines. In such manner the probe measures the charge on the housing and provides a reading indicative of the potential on the test object without loading it down.

Abstract: Test apparatus which indicates the peak potential to which copy paper is charged, the surface potential remaining after a dark decay interval, and the potential remaining after a light exposure interval.

Abstract: A novel method for detecting charge on large bodies such as the earth is accomplished by means of disclosed apparatus which includes a vertical column of mercury having an associated electrode which is capacitively coupled to the mercury column when the mercury level is above the position of the electrode. By establishing an initial unipotential state for the apparatus by short circuit connection of the electrode and mercury column to the earth and an electrometer connected between the electrode and the earth which is initially short-circuited across its terminals the apparatus is conditioned to sense the charge of the large body to which it is connected (the earth) by moving the mercury column up and down past the position of the electrode with the electrometer open-circuited and thus connected between the electrode and earth during the passage of the mercury in one direction past the electrode.

Abstract: An electrometer having reduced spacing sensitivity, with the electrometer including a probe with a charge receiving sensor element and a surrounding shield. A voltage equivalent to that sensed by the probe element is fed back to the shield to render the electrometer substantially spacing insensitive. A duty cycle control regulates the width of electrical pulses to a power transformer whose output is fed back to the probe shield to maintain the spacing insensitivity. Means are also provided to automatically test and calibrate the electrometer prior to use.