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This paper presents a non-contact approach to obtain simultaneous current-voltage (I-V) curves of photovoltaic (PV) substrings and modules in a string without the need of disconnecting the individual modules from the string. There are two types of I-V curve tracers currently available in the marketplace, capacitor-based and electronic load-based. The primary requirement of these conventional I-V tracers is the disconnection of individual modules in the string so that the individual modules can be connected through the connectors of the individual modules. These conventional contact-tracers have three major limitations in the utility scale power plants: safety during disconnecting and reconnecting field-aged module connectors, extensive time and hardship of test personnel and limited availability of clear sunny hours/days to obtain I-V curves of 1000s of modules in the field. To mitigate all these three limitations, we experimented with a non-contact I-V (NCIV) tracer approach. In this approach, we utilized an electrostatic voltmeter (ESV) in combination with a voltage probe and a hall sensor to obtain I-V curves. A major application of the NCIV tracer is that it can instantaneously identify the underperforming modules in a string without the need of disconnecting the individual modules and translating the measured I-V curves to standard reporting conditions such as STC (standard testing conditions) because all the modules in the string are simultaneously measured at a single prevailing weather condition of irradiance, temperature, wind speed and wind direction.

The ability of polymers to acquire and retain electrostatic charges is valued in designing new equipment like electrostatic separators, electret filters, and powder coating devices. Several recent studies have pointed out the beneficial effect of electric charges on the lubricated contacts. The aim of this paper is to compare two physical mechanisms of electric charging of polymers: 1) triboelectric effect; and 2) corona discharge. The experiments are performed with 5-mm-thick samples of Acrylonitrile-butadiene-styrene, poly-vinyl-chloride, and polypropylene. The cartography of the electric potential is made using the induction probe of an electrostatic voltmeter. The tribocharging is done by back and forth movement of two polymer plates in conformal contact with each other (speed: 7 to 30 mm/s; constant normal force: 10 N). Uniform corona charging is performed by moving the sample in the space charge zone generated by a wire-type high-voltage electrode used in a triode configuration with the potential of the grid electrode set at 1 and 2 kV. The electric potential at the surface of tribocharged polymers is less uniform, but decays slower than that of corona-charged samples.

Epoxy resin is widely used in disc-type spacers of gas insulated switchgear (GIS). Surface flashover related to the existence of surface charge often occurs on the spacer, which is a great threat to the application of GIS and the safety of entire grid. Moreover, the influences on surface charge under pulse voltage produced by switch overvoltage, accompanying with the AC voltage, are still unclear. In order to research the comprehensive effect of AC and pulse voltage on surface charge, in this paper, epoxy resin sample was charged by a corona discharge system and the charge distribution was measured by an electrostatic voltmeter. The results are obtained from the research of different pulse amplitudes, pulse numbers and pulse polarities. The surface potential is a negative value after AC voltage applied for a period of time. When AC and negative pulse voltage are applied, smaller pulse voltage would push the original negative charges away. As a result, initial negative surface potential decreases. But bigger pulse voltage could increase the charge accumulation. When the pulse polarity becomes positive, surface potential at the sample center will be positive value at the beginning and then it gradually changes from positive to negative potential. In addition, the influence on surface charge decay rate will be enhanced with the increase of pulse number under the same pulse voltage. Trap energy distributions were used to analyze charge decay process in the last section.

Electrostatically induced voltage generated on printed circuit boards in a grounded metal box occasionally causes a malfunction and failure of the electronic equipment. A person who walks into a room that has an air conditioner can be electrified up to −10 kV or more. However, a microelectronics device malfunctions by an occurrence of induced voltage of less than 10 V. In the present paper, the induced voltages on an ungrounded one of two conductors that are contained in the metal box are measured and calculated when a charged body moves away from a partially opened metal box. The induced voltages are measured by the use of a spark gap and an electromagnetic wave sensor and are compared with the results from an electrostatic voltmeter. The induced voltages are calculated, moreover, by the use of q=cv, with the capacitances and charges. The results show that the induced voltages of −42% of the voltages of the charged body are generated in the metal box when a charged body moves away from the metal box. The results will be helpful in considering preventive measures of the malfunction and failure of electronic equipment.

As one kind of the basic insulating materials, polyimide has been widely used in turn to turn insulation and turn to ground insulation in inverter-fed motors. However, the pulse voltage from the converter often causes overvoltage and localized high electrical field in the insulation system. During applying the pulse voltage, charges accumulate on the surface of the insulator, which could affect the dielectric property and cause the breakdown of insulation. Direct fluorination is a method to modify the surface layer of the polymers without changing the bulk properties. As a result of the fluorination, hydrogen atoms are replaced by the fluorine atoms and the component of the polymer surface is changed, which can influence the surface charge accumulation and affect the electrical properties. The experiment in this paper was focused on the effect of pulse duration and pulse number on surface charge of the polyimide films. The polyimide films with the fluorination time of 0, 15, 45 and 60 min were prepared. Surface charging was performed by corona discharging using repetitive pulse power at the temperature of 20 °C with the relative humidity of ~15%. The repetition frequency was 1 kHz and the pulse duration was 50, 110 and 210 μs, respectively. The surface charge decay was measured using a specific probe coupled with an electrostatic voltmeter. The results showed that the surface charge increases with increasing the pulse number and the duration of the microsecond pulse.

The most widely used techniques for neutralizing the static charge at the surface of insulating bodies make use of the bipolar ions generated in an ac corona discharge. The aim of the present work is to evaluate the efficiency of the neutralization achieved with a corona electrode energized from a generator of sinusoidal, triangular and square ac voltages of various amplitudes and frequencies. The experiments were performed on 120 mm $\times$ 90 mm samples that were cut from the same nonwoven polypropylene (PP) fabric. The samples were charged for 10 s, in ambient air, using a triode-type corona electrode system of positive polarity. The neutralization was performed 300 s after the charging process, with the samples moving at constant speed (3 cm/s) in the ac corona discharge zone. The electric potential distribution at the surface of the samples was measured with an electrostatic voltmeter (model 3450, Trek Inc., Medina, NY). The efficiency of the neutralization was evaluated by calculating the inverse ratio between the maximum absolute values of the potential before and just after the neutralization. The amount and the polarity of the residual charge after neutralization depend on the frequency, amplitude, and type of ac voltage. The results show that an excellent neutralization can be obtained for any of the three wave shapes of ac voltage, at industrial frequency (i.e., 50 Hz) by varying the amplitude of the offset.

Triboelectric charging is used in many applications including electricity nanogeneration, safety or electrostatic separation of insulating materials. Insulating granules charge must be the highest in electrostatic separators so that the electric field forces allow their separation. Dielectric Barrier Discharge (DBD), used for ozone production, depollution or surface treatment, is able to change the triboelectric properties of insulating materials. The aim of this study is to improve the triboelectric charging of Polyethylene (PE) particles by exposing them to an atmospheric Dielectric Barrier Discharge. Signal shape, exposure duration, voltage amplitude and frequency, which rule the DBD, are studied. After exposing the particles to DBD, they are charged in a vibratory device during 5 min. Then, particles are put in a Faraday pail connected to an electrostatic voltmeter to measure the acquired charge. Results show that the square waveform has the best effect and that the duration of the DBD treatment should not exceed 10 s, for the amplitude of the applied voltage of 21 kV.

Polyimide film, as a special type of engineering plastic film, is a kind of basic insulating material and is widely applied in the aerial, nuclear, microelectronic industry, turn to turn insulation and turn to ground insulation of inverter-fed motors. However, premature insulation failures occur frequently in motors with the disadvantage of pure PI inherent in all organic materials. The existence of surface charge has a great effect on breakdown characteristic and is the main reason leading to dielectric breakdown. Fluorination as change the chemical component in surface layer of polymers should give rise to the corresponding change in electrical properties of the surface layer thus influence the charge injection from electrodes when they are used as an insulator. This paper presents a study aimed at clarifying the effect of fluorination time on surface charge accumulation and decay behaviors of fluorinated polyimide film. Samples were surface fluorinated in a laboratory vessel at about 328 K (55 °C) using a F2/N2 mixture with 20% F2 by volume and 0.05 MPa (500 mbar) for respectively 15, 30, 45 and 60 minutes. Corona charging tests were performed at room temperature with a relative humidity of ~ 40%. The charge distribution was measured by means of an electrostatic voltmeter. Obtained results show the dependence of the charge density as well as the charge decay rate upon the fluorination time of samples, varying as a function of the charge polarity and charging time. It is suggested that the fluorination can significantly improve the decay rate of the surface charge in polyimide films.

In order to overcome the drawback that the measurement uncertainty of the ultra-high resistance over 1014 Ω may be deteriorated severely due to insufficient resolution of the electrometer in conventional scheme, a novel method based on the dual sources high resistance bridge and non-contact voltage measurement is presented. The measurement uncertainty is largely dependent on the standard resistance and determined by the resolution of the electrostatic voltmeter. It is shown by the experimental results that the measurement uncertainty for the resistance of 100 TΩ to 1000 TΩ is better than 0.2%, k = 2.

The features of the measurement of a high-frequency ac voltage with electronic voltmeters are considered for cases when the measured ac voltage is normalized at the input of the electronic-voltmeter probe or at the input of a special connector to which the voltmeter probe is connected.

Fibrous polymers with extremely low electrical conductivity such as polypropylene (PP), polycarbonate, polyurethane, and polyethylene are commonly employed as air-filter materials. The charge accumulated on such materials due to tribocharging effects inherent to the manufacturing process might be harmful either to the operator or to the electronic equipment of the production line. Whenever charge buildup cannot be avoided, it is important to have an effective method available in order to rapidly discharge the materials. The present work aims to evaluate the efficiency of active neutralization of charged nonwoven fabrics. The experiments have been carried out on 0.4-mm-thick PP and polyester fibrous media, with the average diameter of the two types of fibers being 28 and 19 , respectively. The nonwoven fabrics were charged by exposing them to a negative corona discharge generated by a wire-grid-plate electrode system. The samples, laid on the surface of the grounded electrode or suspended at a small distance (4.6 mm) above it, were then subjected to the action of the bipolar ions generated by a commercial neutralizer (model 6430, Ion Systems Inc., Berkeley, CA). The monitored variable was the surface potential detected by the probe of an electrostatic voltmeter. The controlled variables were the potential of the grid electrode, the neutralization time, and the distance between the neutralizer and the media. The results of the experiments enabled a crude evaluation of each factor effect. Research should continue, using the experimental design methodology, in order to establish the optimum conditions for charge neutralization.

Measurements of surface charge and potential became very common in industrial applications and academic research. In this paper authors present use of a contacting ultra-high input impedance voltmeter in the areas where traditionally the non-contacting measurement methods were used. With very low input capacitance of the order of 10−15 F, and very high input resistance of the order of tens of teraohms, there is practically no charge transfer from the measured object to or from the instrument. Experiment presented in this paper explains a correlation between the non-contacting and contacting measurement techniques using a finite element analysis model.

Field mill instruments are often employed for the measurement of electric fields, electric charges, voltage potentials, and atmospheric effects. This paper discusses in more detail the application of a field mill for measuring dc voltages in high-voltage laboratories. Some specific problems, which arise when voltages in the kilovolt or megavolt range have to be measured, are emphasized. Safety, signal transmission, and electrode design are dealt with. Field meter theory is summarized and generalized in the function of this application. The design of a practical field-mill-based electrostatic voltmeter is described along with some useful enhancements. Finally, test results of the voltmeter are presented.

The charge accumulation on the surface of dielectric materials is a long-term academic research focus. As part of an effort to understand the origins of this behavior, surface charge distribution on silicon rubber under DC high voltage before and after flashover in atmosphere was measured by an electrostatic voltmeter with a vibrating Kelvin probe. Three types of electrode systems were employed in the study, i.e. circle-circle electrodes, ellipse-circle electrodes and tip-circle electrodes. The results showed that surface charging processes are close related with uniformity of electric field and voltage polarities. Once flashover happens, there exists a channel linking HV and grounded electrodes, which presents a low potential.

International audience; This work presents an improved method for measuring the direct piezoelectric voltage and energy of flexible polymers. Well-controlled stress is applied with a four-point bending system and voltage is measured in real open-circuit conditions. The presented method separates the piezoelectric part from the measurement part by introducing a mechanical switch, allowing instantaneous post-deformation discharge measurements. Oscilloscope and contactless electrostatic voltmeter are compared. Direct piezoelectric measurements under open-circuit conditions have been performed on commercial PVDF (polyvinylidene fluoride) and its copolymers. Significant differences to data sheet values (close-circuit conditions) are reported and commented.

Renewable energy penetration is on the rise in the Ontario distribution network. Renewable energy sources such as wind farms and solar PV system have poor power quality, therefore, it is expected that it will hamper the power quality of the grid. The insulation system is vulnerable to the steady state power quality issues. Poor power quality can have adverse effects on cable accessories such as cable joints and terminations. The impact of poor power quality on the SG layer of cable termination and electric field concentration on the surface of cable termination is identified in this paper. In particular, the effect of distorted voltage waveforms on cable termination is studied considering the penetration of odd harmonics from 3rd to 15th harmonic at 10%, 20%, and 30% level. The cable termination is diagnosed with electrostatic voltmeter (ESV) that measures potential on the surface of the cable termination.

In the future development of smart grid, wind power generation will be widely used as clean energy. Addition of nanoparticles into epoxy can improve the insulating properties compared with undoped material. However, due to the change of the material structure, trap characteristics and charge behaviors are altered as a consequence. This may cause electric field distortion and partial discharge which would lead to insulation breakdown. In this paper, the effect of nano-filler content on surface charge accumulation and decay behaviors of epoxy nanocomposites with BN particles is studied. Samples were prepared by dispersing nano-scale BN into epoxy by mixing with shear force. Corona charging tests were performed at room temperature with a relative humidity of ∼ 40%. The charge distribution was measured by means of an electrostatic voltmeter. Obtained results show that the concentration of BN has a great effect on charge accumulation and decay. The charge polarity, charging time and charging voltage also play an important role on charge behaviors.

Electric charge accumulation on fibrous dielectric media during manufacturing processes can easily attain high levels of electrostatic hazard. In a previous paper, the authors addressed the problem of the accelerated discharge of such materials using a commercial ion generator. The aim of the present work is to evaluate the various factors that influence the efficiency of charge neutralization performed using a wire-type corona electrode energized from either a sinusoidal or a triangular AC high-voltage supply. The experiments were performed on 400 µm-thick non-weaved sheets of polypropylene and polyester, in ambient air. The samples were charged for 10 seconds using a triode - type corona electrode system of negative polarity. The surface potential on the charged media, which was in contact with the grounded electrode, was then measured with an electrostatic voltmeter. After 10 minutes, the media was moved beneath a neutralizing electrode, connected to a high-voltage amplifier. The efficiency of the neutralization was quantified by the ratio between the surface potential after and prior the charged sample exposure to AC corona discharge. The experimental design methodology was employed for evaluating the effects of two factors: amplitude (range: 16 to 24 kV) and frequency (range: 20 to 400 Hz) of the neutralizing voltage. The potential at the surface of the non-woven fabrics after neutralization was found to vary insignificantly with thermal conditioning and signal waveform, but was significantly lower for higher frequencies and amplitudes.

The relative residual charge distribution (RCD) on a dielectric surface due to the discharge created by a single high-voltage pulse was measured using an electrostatic voltmeter equipped with a 2-D scanning system. This distribution was compared with the discharge image recorded with an intensified charge-coupled device camera. The comparison confirmed that the relative RCD reflects the discharge morphology composed of a main discharge channel and branching, while the discharge image provided the relative residual charge distribution on the dielectric surface.

A method for determining the amount and the mean spatial depth of charge in electret-semiconductor systems is presented. It consists of two nondestructive measurements, from which the internal and external electric fields can be calculated independently. First, the surface potential at the electret-air interface is measured by an electrostatic voltmeter. Second, using a contacting front electrode, a metal-insulator-semiconductor structure is formed, on which capacitance or conductance voltage measurements are carried out. With these results, one obtains the surface potential at the electret-semiconductor interface. The charge centroid and the charge density can now be calculated. For SiO/sub 2/-silicon structures, where the 1- mu m-thick thermally wet-grown SiO/sub 2/ layer acts as an electret, it was found that the charge centroid can be influenced strongly by temperature treatment prior to charging. >

A standard voltmeter designed for measuring up to ± 2 MV in vacuum was modified to operate at −4 to −6 MV, appropriate levels for measuring the convolute voltage during z-pinch experiments on Z. Field shaping structures are used to eliminate electron emission from the voltmeter grading rings. The voltmeter operated as expected during tests at −4 MV on the Mercury generator, indicating this voltmeter could work for the lower voltage range expected on Z. At −6 MV on Mercury, the voltmeter did not operate correctly, probably because of electron emission. Particle-in-cell modeling is consistent with the observed voltmeter response. An improved field shaper could extend the voltmeter operation to −6 MV.

Practical assessment of risks for Electrostatic Discharge (ESD) failures of semiconductor devices, due to charges induced on devices in a manufacturing or repair environment of electronics has been difficult, because easily measurable parameters such as the electrostatic field and the potential of a charged surface do not directly quantify the risk. In this paper a new method of assessing the risks with induction charging of a sensitive device is presented by introducing a well-defined dummy device, which is a simple modification of the probe of DC type non-contacting electrostatic voltmeter. By placing the modified potential probe (mimicking large sensitive device) in front of charged surface, risks of ESD failure for a device due to induction charging can be assessed. The electrostatic response of the probe at different distances between charged surface and the probe has been verified by numerical model calculations. (6 refs.)

The integration of MEMS sensors and interface circuitry has yielded low-cost, high-performance instruments with excellent reliability. In inertial sensing, deterministic electrical waveforms are applied to a MEMS capacitive element to determine an unknown deflection. The inverse of this measurement method can also be exploited: the MEMS element can be deterministically modulated to measure an unknown electrical variable. This paper presents the design of a non-contact electrostatic voltmeter using a MEMS-based electrostatic field meter.

This paper reports the results of a series of fundamental studies on streaming electrification of liquid nitrogen flowing through an electrical insulating or a metal pipe by using a so-called Faraday cage. Streaming electrification of liquid nitrogen flowing through mesh(es) installed in a pipe is also discussed. Furthermore, potentials measured with an electrostatic voltmeter of the inner surface of a pipe and on the surface of a solid insulating materials placed in the pipe are also reported after flowing liquid nitrogen in the pipe.

This work presents results of measurements of voltages induced by electric charges flowing through a pipe. The materials used to conduct the study were an electrophotographic toner, glass microspheres, and aluminum oxide powder (Al/sub 2/O/sub 3/). These materials were transported pneumatically through the tube under investigation. Voltages induced on the pipe by the flow of charges were recorded with an electrostatic voltmeter (ESVM). A total charge of each powder was measured before and after it passed through the pipe. The ESVM was measuring the voltage induced by charges carried by the flux of solid particles and by the charges generated on the tube. Author was looking for a correlation between the initial and final charge of the toner and the ESVM voltage. As a result, method of flowing charges measurement with the ESVM is proposed.

The problem of using a noncontacting electrostatic voltmeter to measure surface charge is addressed. By design a noncontacting voltmeter enforces a zero-field condition at its probe by adjusting its own probe potential. When an isolated charge distribution is measured, the field around the probe is shown to consist of two superimposed components, one equal to the field caused by the measured charge distribution and a grounded probe, and the other equal to the field of the energized probe with the charge distribution absent. The resulting probe potential is shown to depend on the magnitude of the measured charge, its physical geometry, the geometry of the probe, and the position of the probe relative to the charge distribution. A method for interpreting the reading of a noncontacting voltmeter based on these factors is presented and experimentally verified. >

The prototype for a microminiature, noncontacting electrostatic voltmeter (ESV) is discussed. The ESV works on the principle of intermittent shuttering and exposing a sensing electrode to an electric field between a remote electrode at a different potential from the sensing electrode. The resultant time-varying field at the electrode produces an electrical signal which can be used to monitor the remote voltage. The prototype ESVs hat have been made and tested have electrostatic-comb drives and shutters with areas ranging from 0.022 to 0.067 mm/sup 2/ that are suspended roughly 2 mu m above the surface of the silicon substrate. Initial tests on ESVs showed them to respond to voltages above 20 V for electrodes spaced 0.2 mm away. Sensitivity is expected to be greatly improved by redesigns that are already being investigated. >

The standards for testing the ESD sensitivity of electronic components according to the HBM (MIL, JEDEC, ESDA) require a specific switch in the HBM ESD waveform generator to ensure that the socket and the DUT is not left in a charged state after the stress. The absence of this switch may result in the wrong ESD threshold levels. For two different waveform generators, the charging effect was measured by using an electrostatic voltmeter. An unexpected experimental result, showing that the HBM ESD threshold voltage strongly depends on the number of stress pulses, could be explained by the measured charging of these components. Consequences for other types of components and corrective actions are discussed.

The purpose of this paper is to provide information on the use of electrostatic fieldmeters and electrostatic voltmeters to make field and voltage measurements on GMR recording heads. Charge is often impractical to measure directly, requiring that the charged object be transferred into a Faraday enclosure and then measured using a coulombmeter. When this transfer method cannot be used, charge is often evaluated indirectly by detecting the electrostatic field associated with the charge using an electrostatic fieldmeter or an electrostatic voltmeter. However, electrostatic fieldmeter and electrostatic voltmeter measurements are often difficult to interpret. The goal of this paper is to introduce several types of electrostatic fieldmeters and electrostatic voltmeters, explain the operating principles of each type of instrument, and to describe some of the capabilities and limitations of each type for making measurements on small objects such as GMR recording heads.

A method for measurement of triboelectric charging is described. Triboelectric charges are produced by a cylinder, rolling on the surface of the test object. The rolling is performed at controlled speed and pressure. The voltage produced on the test object is continuously measured by an electrostatic voltmeter and the final value is taken as the result of the measurement. The only manual operation of the test, which is the removal of the cylinder from the test equipment, can easily be automated. The cylinder materials used in this evaluation are quartz and PTFE ("Teflon") respectively. Use of other materials should be possible but is not yet verified. The process of cleaning the cylinders is of the utmost importance. The developed process includes a heat treatment of the cylinders at 150/spl deg/C. The test method is shown to give a repeatability better than /spl plusmn/10% (1 /spl sigma/) in measurements of electrostatic conductive foils. This figure includes spread in the test object itself. Tests have been performed on different types of foil materials and the method discriminates well between them. Tests on hard materials are probably not suitable if the cylinder is made of hard, plane material. The method has to be further evaluated. Comparative measurements ("Round Robin tests") should be performed by other laboratories to evaluate the reproducibility of the method.

Charge generating source on an integrated circuit (IC) lead scanner was identified using a fast response electrostatic voltmeter in conjunction with storage oscilloscope and plotter. Alternative low tribo-charging material was used in this pick and place equipment to provide an ESD safe handling environment for the IC.

Both electrostatic and toner concentration (TC) electrophotographic process control systems can beconstructed with the proper use of bias current measurements of the development subsystem. A TC Idevelopability controller can be made by measuring the development bias current for each print or copy, summing the measurements, subtracting offset currents and dispensing toner proportionally to this developed charge measurement. If certain constraints are fulfilled, the system will operate at a constant developed toner mass. Similarly, a photoconductor electrostatic measurement I control system can be made by utilizing bias currents. This is accomplished by choosing a stable portion on the developed charge vsdevelopment voltage relationship of the development subsystem. This setpoint is then used to measurephotoconductor test patch voltages by monitoring the bias current. In some cases this provides the samefunction as an electrostatic voltmeter. These low cost techniques enable the practical process control

A digital voltmeter is shown to successfully capture the voltage decay signal during eddy current decay (ECD) measurements at cryogenic temperatures on low-resistivity specimens. The use of a voltmeter simplifies ECD measurements, typically made using a digital oscilloscope. An added benefit of using a voltmeter is that under certain circumstances, measurement precision exceeds that which is normally obtained with a preamplifier-digital oscilloscope combination. Results indicate that the best combination of instruments for capturing extremely weak signals (i.e., those with long exponential time constants) is a preamplifier-voltmeter configuration. Results of a comparative study using a preamplifier-digital oscilloscope configuration, a digital voltmeter alone and a preamplifier-digital voltmeter arrangement are presented and discussed.

Results of electron beam charging of pure Kapton and mesh-covered Kapton used to control charge buildup on spacecraft are presented. The electron beam energy was varied from 200 eV to over 10,000 eV. The sample with the aluminum grid had about 10% of its total exposed surface area covered with a hexagonal-shap ed aluminum grid. The addition of the aluminum grid limits the area involved in arcing. It is able to bleed off some, but not all, of the deposited charge. Experimental data are presented, and a qualitative explanation is suggested.

An improved loaded voltmeter test (ILVT) was developed based on the preparation of a table of voltage measurements of the tested battery with a constant resistor load as a function of the state of charge. The function is stored in the memory of the microcomputer; when a certain value of the charge is then needed, it can be found using the ILVT and the stored function. The action of the power system is not disturbed. A circuit based on this method was built and tested at Tel Aviv University, Israel. Half as many errors occurred when the ILVT was used as when the conventional loaded voltmeter test was used. Although the system consists of only lead-acid batteries, the ILVT is also suitable for testing other types of batteries.

Various means have been available for many years to measure electrostatic potentials with ever increasing sensitivity and with decreasing current requirements. Instruments such as the electroscope or the common laboratory electrostatic voltmeter have been developed to the point where they operate reliably, with an input resistance of the order of 1016 ohms and higher, but in general these extremely sensitive instruments cannot conveniently be used to record potential over a period of time, thus requiring the continuous presence of an operator. A type of electrostatic voltmeter is described which is designed to record potentials as low as 1 volt d-c with an input resistance of 1014 ohms using an electrostatic generator to provide an a-c signal proportional to voltage, and a simple audio amplifier requiring only a commercial 1-milliampere recording meter in the way of auxiliary equipment.

In a paper by Mr. R.S.J. Spilsbury and the present author, † apparatus for providing a voltage-drop of about 2 volts propotional to and in time phase with an alternating current is described. The 2 volts is obtained from a “non-inductive” resistance connected either in the main-current circuit or in the secondary circuit of a high-precision current transformer, the primary winding of which is connected in the maincurrent circuit. The problem is to measure this 2 volts to a high degree of accuracy. Voltages of the order of 100 volts may be measured to an accuracy of about 1 part in 10 000 by means of a suitable electrostatic voltmeter, and this paper describes the performance of a transformer for transforming 2 volts up to 100 volts. The core is of mumetal, and the ratio of transformation is shown to be constant to 1 part in 10 000 over a wide range of frequency and applied voltage. The phase displacement between secondary and primary voltage is less than 2 minutes at rated voltage.The testing of the transformer necessitated the development of a special bridge and apparatus, which is described.

That the current-voltage characteristics of vacuum tubes obey an exponential law near cutoff is pointed out. The larger the coefficient ? appearing in the exponent, the steeper will be the current-voltage curve, and the better suited the tube will be for use in a slide-back voltmeter. The problem of obtaining high values of ? is considered, and a simple theory of rectification by an exponential conductor is given. The error inherent in slide-back voltmeters of the ordinary type is discussed, and a correction factor applicable to sine waves is derived. The circuit of a slide-back vacuum-tube voltmeter which includes means for measuring the ? of the tube is shown.

The paper summarizes briefly the main precautions which should be adopted in the purchase, installation and use of electrical instruments which in a test department serve for calibrating instruments of a lower order of accuracy.The errors to which the potentiometer, dynamometer wattmeter, electrostatic voltmeter and moving-coil indicator are liable are considered, and means for eliminating or reducing such errors are pointed out.The author emphasizes the advantage of the method of discovering how errors may be produced, with the object of securing control of such errors.The conclusion is reached that, although preliminary investigations may be somewhat tedious, the result of due precautionary measures is increased all-round efficiency.

A direct-current, degenerative, slide-back, vacuumtube voltmeter employing standard potentiometer design principles is described. The voltmeter is completely self-calibrated upon construction. By adjusting the voltmeter to the same reference balance condition for all voltage measurements, the grid current is readily reduced to less than 10-9ampere. Voltages in the range from 1 to 100 volts are read to four significant figures in the experimental model of the voltmeter.

A new design of a generating voltmeter with a rotating measuring electrode system is described. It is based on an arrangement of eccentric circular cylinder electrodes. Hence an essential advantage of the voltmeter is a calculable voltage-current ratio provided the rotation frequency is known. Moreover the electrode arrangement is self-shielding. For these reasons, in principle, no calibration is necessary. The properties of the voltmeter are discussed theoretically. Two practical laboratory devices are presented. Prospects for future development are discussed.

The conditions for the correct operation of an electrostatic peak voltmeter are given and the correct method of making the return circuit to the filament or heater shown, together with the correction for filament voltage, when required. The use of a metal rectifier is discussed and test results show that its reverse resistance is too low and its forward resistance too high to be of service. Means of increasing and decreasing the range of an electrostatic voltmeter for D.C. and a peak voltmeter for A.C. are shown. Circuit diagrams illustrate each case.

The paper reviews the methods by which the mean, r.m.s., or peak values of voltages ranging from 10 kV upwards may be measured by indicating or recording instruments to an accuracy within about 1%. Most of the methods use either a low-range high-impedance voltmeter or cathode-ray oscillograph in conjunction with a voltage divider or a milliammeter in series with a high impedance. Voltage dividers suitable for use with direct, alternating and impulse voltages are considered, and, amongst the measuring instruments, the diode peak voltmeter is discussed in some detail. High-range electrostatic voltmeters are also considered. It is concluded that there are always at least two different methods by which a particular type of voltage may be measured.

The paper discusses the electrical characteristics and performance in service of porcelain insulators for outdoor high-voltage apparatus. It is emphasized that if large power systems are to be operated with a minimum of breakdowns a carefully planned scheme of field testing, supplemented by laboratory investigation, is essential.Part 1 describes the laboratory apparatus and the field testing equipment used by the Central Electricity Board. For laboratory investigations, two outdoor high-voltage testing sets are installed, having maximum voltages of 85 kV and 250 kV. A test tower and rack are associated with each equipment, and continuous pollution tests can be made simultaneously on 60 insulators. Counters are installed on all the insulators to record the leakage-current “surges.”Field tests are made with the lines in service, with an apparatus consisting of a capacitance potential-divider and electrostatic voltmeter. The potential distribution on the insulator is measured, and faulty units are detected by the abnormally low potential-drop across them. The surge counter is also applied to equipment in service in order to indicate when insulator cleaning is necessary.Part 2 gives some of the results of investigations made with the apparatus and technique described in Part 1. Information is given regarding the performance of line insulators, post insulators and bushing porcelains. The behaviour of insulators in fog, and similar weather conditions, is discussed, and examples are given of the highly irregular potential distributions and leakage-current surge records obtained under such conditions. Comparative results are given for “normal” and “anti-fog” insulators. The mechanism of insulator flashover in fog is described in detail. The requirements of a good anti-fog insulator are discussed, and for an insulator for use in highly polluted and humid atmospheres a leakage path of 2 in. per kV of applied voltage is recommended. A new design of insulator unit is described in which the potential distribution is stabilized by resistors.Information, based on service experience, is given on the deterioration of insulators. With high-quality modern insulators, the rate of deterioration should not exceed 0.1% per year, but it is nevertheless essential to make field tests, as a single faulty unit may lead to the complete failure of the insulator string. Confirmatory tests made in the laboratory show that in most cases (approximately 90%) the field diagnosis of faulty insulators is correct. Deterioration takes the form of cracks in the porcelain head, and the mechanism of insulator failure due to cracking is described.The cause and characteristics of radio interference due to power lines are discussed, and data are given of the interfering field strength due to high-voltage lines operating in various weather conditions. Under the worst condition—fog—the interference increases by 40 db. above the fine-weather value. The attenuation of the interfering field is very rapid at right angles to the line, and a decrease of 25 db. occurs in 50 yd.; at this distance from the line, local broadcasting stations may be received virtually free from interference even under the worst weather conditions.

A digital voltmeter for two digits is described. The principle of operation is the comparison of the input voltage with a known voltage generated in the instrument. The internal voltage is generated by a photoconductive potentiometer which is optically scanned by ring counters. The voltmeter is a continuously indicating instrument. The maximum delay time between the application of the input voltage and the indication is less than a second.