Electrometer Circuit Research Articles

Wire-free method of measurements of weak electrostatic values under stationary and dynamic conditions

Usage of a developed and updated electrometer (EM) allows one, first, to obtain new information on physical properties of materials (glasses and other solids) as well as on the manifestation of the properties in the field of mechanical forces. Second, the applicational significance of such researches could be also important when designing new nondestructive methods of material defects controlling and procedures of their removal. The EM is up to measure both slowly and rapidly varying electric potentials at some distance from a target. EM allows one measure relaxation times of charges in dielectrics, which do not exceed the time constant of discharge time of the amplifier under stationary conditions. Owing to the developed scheme of the EM input circuit, the input capacity of amplifier was decreased with a corresponded increase of its sensitivity.

Fast high-resolution nanoDMA measurements with a 25 ms response time electrometer

Two fast electrometer circuits (1011 and 1012 V/A) are installed in a Faraday cage having a relatively small residence time. Removing readily distinguishable occasional spikes, the root mean square (r.m.s.) noise level at 1012 V/A is 0.11 fA when acquiring data at 1 Hz. This value is close to the expected thermal resistor noise at room temperature (0.09 mV). Both electrometers exhibit a 20 ms flow-related delay, followed by respective half-height rise-times of ∼4 and 25 ms. Fast high-resolution mobility spectra in the 1–2 nm size range are acquired with electrosprayed tetraheptylammonium ions by combining these electrometers with a high-speed DMA. At 1012 V/A, there is no ion mobility peak distortion when acquiring data with discrete voltage steps and dwelling 100 ms at each voltage. With the 1011 V/A electrometer, the DMA voltage VDMA is continuously swept up and down over 600 V in a triangular wave, at up to 1200 V/s. A shift ΔVDMA in the peak center is apparent, with little peak shape distortion. ΔVDMA is symmetric with respect to up or down sweep, and linear with sweep frequency, corresponding approximately to a pure delay Δt = 25 ms. This peak displacement may be offset by adding the correction ΔVDMA = Δt (dVDMA/dt) to the measured peak voltage. Extrapolating the measurements made here over a mobility range Zmax/Zmin of 4 to a much wider mobility range of 300 typical of aerosol studies, we conclude that almost undistorted high-resolution mobility spectra may be acquired in 1.3 s.Copyright © 2017 American Association for Aerosol Research

Development and Evaluation of a Faraday Cup Electrometer for Measuring and Sampling Atmospheric Ions and Charged Aerosols

A simple and inexpensive Faraday cup electrometer for measuring and sampling ion and aerosol charge was developed and evaluated. It consists of a Faraday housing, a filter holder, a high efficiency particulate air (HEPA) filter, Teflon® insulator, and electrometer housing. In the Faraday cup, the ion and aerosol charge entered the electrometer and then collected on the filter. All ion and aerosol charges were induced and generated an ultra-low current of less than 10 pA corresponding to the number concentration of ion and aerosol. The performance of the prototype electrometer circuit was calibrated with a current injection circuit, high-impedance current source and compared with theoretically and numerically predictions. Good agreement was found from the comparison. Experimental testing of ion and aerosol charge measurements were carried out for different operating air-flow rates for both positive and negative ions. Ion and aerosol charge measurements were also performed. Finally, this Faraday cup electrometer proved particularly useful as an ion and aerosol charge sampler and detector for both positive and negative ions.

HVDC Corona Space Charge Modeling and Measurement

An electrometer circuit is designed and developed to measure the ion-space charge created during HVDC corona events. The interpretation of the electrometer output and visualization of various discharge processes are facilitated by a particle-in-cell computational code. The time it takes for the space charge to be created during a single monopolar corona event to reach the ground electrode in a corona test method is computed for a small corona cage, a short test line, as well as a large corona cage. This complements results obtained by the authors in another paper where it is shown that a small corona test cage cannot be used to predict the RI performance of HVDC conductors due to the space charge buildup in the small electrode gap.

Universal Tritium Transmitter

At the Savannah River Site and throughout the National Nuclear Security Agency (NNSA) tritium is measured using Ion or Kanne Chambers. Tritium flowing through an Ion Chamber emits beta particles generating current flow proportional to tritium radioactivity. Currents in the 1x 10-15 A to 1x 10-6 A are measured. The distance between the Ion Chamber and the electrometer in NNSA facilities can be over 100 feet. Currents greater than a few microamperes can be measured with a simple modification. Typical operating voltages of 500 to 1000 Volts and piping designs require that the Ion Chamber be connected to earth ground. This grounding combined with long cable lengths and low currents requires a very specialized preamplifier circuit. In addition, the electrometer must be able to supply “fail safe” alarm signals which are used to alert personnel of a tritium leak, trigger divert systems preventing tritium releases to the environment and monitor stack emissions as required by the United States federal Government and state governments. Ideally the electrometer would be “self monitoring”. Self monitoring would reduce the need for constant checks by maintenance personnel. For example at some DOE facilities monthly calibration and alarm checks must be performed to ensure operation. NNSA presently uses commercially available electrometers designed specifically for this critical application. The problems with these commercial units include: ground loops, high background currents, inflexibility and susceptibility to Electromagnetic Interference (EMI) which includes RF and Magnetic fields. Existing commercial electrometers lack the flexibility to accommodate different Ion Chamber designs required by the gas pressure, type of gas and range. Ideally the electrometer could be programmed for any expected gas, range and high voltage output. Commercially available units do not have “fail safe” self monitoring capability. Electronics used to measure extremely low current must have sufficient time to thermally equilibrate. Amplifiers, transistors, resistors all need time to stabilize before the electrometer circuit will measure accurately in the 10-15 and 10-14 ampere range. Existing electrometers give the user no indication when the unit has stabilized and is acceptable for low level measurements. Savannah River National Laboratory (SRNL) funded through the NNSA Plant Directed Research and Development (PDRD) program, has developed a truly Universal Tritium Transmitter (UTT) capable of solving many known problems with existing commercial electrometers. This UTT pushes the state-of-the-art in electrometer design and incorporates solutions to deficiencies found in commercial electrometers.

Transfer and Detection of Single Electrons Using Metal-Oxide-Semiconductor Field-Effect Transistors

A single-electron turnstile and electrometer circuit was fabricated on a silicon-on-insulator substrate. The turnstile, which is operated by opening and closing two metal-oxide-semiconductor field-effect transistors (MOSFETs) alternately, allows current quantization at 20 K due to single-electron transfer. Another MOSFET is placed at the drain side of the turnstile to form an electron storage island. Therefore, one-by-one electron entrance into the storage island from the turnstile can be detected as an abrupt change in the current of the electrometer, which is placed near the storage island and electrically coupled to it. The correspondence between the quantized current and the single-electron counting was confirmed.

A quasilinear wide-range radiometer amplifier implemented with correlated phase-sensitive detection

A radiometer amplifier capable of wide-range optical measurement is described. Based on a novel automatically ranged electrometer and amplifier circuit, the radiometer provides a quasilinear analog output for the measurement of input radiation over ten orders of magnitude. Together with the scheme of phase-sensitive detection of modulated optical signals, the circuit resulted in an output voltage of low noise and offset drift. It can be applied directly to various kinds of photodetectors. The application of standard integrated circuits and lock-in amplifiers makes the whole system low cost and it can be readily built.

Remodeling light emitting diode in low current region

A general expression is proposed for the current-voltage (I-V) characteristics of junction diode by which it is possible to determine forward voltage across diode at actual current and temperature. Expressions fur the band gap and temperature coefficient of junction voltage based on the experimental measurements are also presented. The expressions include only experimentally obtained and derived values. These expressions have been used to check the performance of logarithmic amplifier using light emitting diode (LED) as a feedback clement, at different temperatures. Further, it has been shown that it is possible to predict the behavior of a logarithmic amplifier without temperature compensation techniques within 5% accuracy for the current range 10/sup -12/-10/sup -5/ A and for the temperature range -5/spl deg/-60/spl deg/C. The alternative could be the use of temperature compensation circuitry which may make electrometer circuit more complex. The proposed scheme is useful in applications where it is difficult to incorporate temperature compensation technique and space and power are at premium.

Floating electrometer for scanning tunneling microscope applications in the femtoampere range

In this work, a floating, high precision current–voltage converter, applicable to scanning tunneling microscopy (STM) and ballistic electron emission microscopy (BEEM) measurements, is described. The electrometer circuit presented shows a bias independent output offset, adds low noise, and has low thermal drift. The amplifier is useful for any floating applications where an ultrasmall current has to be measured with high resolution (±20 fA). The circuit is fast enough for typical sampling rates required for BEEM or STM image measurements and can also be used for fA measurements related to ground.

An antenna electrometer system for atmospheric electrical measurements

A ±300 V dynamic range, battery-powered, and inexpensive electrometer system is described that has been used with passive horizontal wire antennas to measure the atmospheric electric potential at 1 and 2 m above the earth’s surface. Input currents drawn by the electrometer circuit are of order femtoamperes, and a guard drive output is provided to minimize leakage. The implementation of the passive wire antenna is described, using rigorous insulation and signal guarding, together with results obtained in fair weather conditions. Linearity of the portable electrometer over the input range is demonstrated to be comparable with a commercial laboratory electrometer, and the antenna potential can be determined to within a few volts in the fair weather electric field. Several such portable systems can be cheaply combined, sharing a common high tension supply, to measure the profile of the atmospheric electrical potential above the surface, at a remote site. Damage to the electrometer sustained in electrical storms can be cheaply repaired.

Analytical correction of temperature in a logarithmic electrometer using light-emitting diodes

The current–voltage characteristics of logarithmic amplifiers depend considerably on the ambient temperature. A theoretical correction has been estimated considering the temperature dependence of various parameters in the diode equation. A log electrometer using light-emitting diodes has been fabricated and its I–V characteristics are obtained experimentally for calibration and also to determine the device constant. If a measurement is obtained at a temperature other than the one for which calibration has been done, the theoretical correction can be applied to get the correct value. It has been shown that the theoretically corrected readings lie within ±4% of the experimentally obtained data in the temperature range of 5–60 °C for the operating current range of 10−12–10−4 A. The alternative can be to introduce temperature compensation circuitry into the logarithmic amplifier. However, this makes the electrometer circuit more complex. The proposed theoretical correction method may find applications where space and power are at a premium and the accuracy requirement is not very stringent.

The dc volume resistivity of plasticized PVC

A study has been made of the dc volume resistivity of plasticized PVC using a guarded-electrode system in a sensitive vibrating capacitor–electrometer circuit. Transient effects were found to be pronounced in all but the least plasticized compositions, and the behavior in general was non-Ohmic. The resistivity decreases with plasticizer concentration and with temperature; an Arrhenius-type relationship is observed and resistivity undergoes an inflection at the glass transition temperature. The mechanism of conduction appears to be electrolytic rather than charge injection or semiconduction.

Signal/noise ratio in the opticoacoustical channel of gas analyzers with the microphone in an electrometer circuit

Signal/noise ratio in the opticoacoustical channel of gas analyzers with the microphone in an electrometer circuit

Method of measuring an electrostatic field in air

The input signal falls on the anode and is modulated with an ac voltage fed to the control grid of the tube from a generator M. The modulated signal is selected by a resonance circuit formed by the primary winding of the transformer Tr and the condenser C. The resonance circuit is tuned to the generator frequency. From the secondary winding of the transformer the signal passes to the amplifier A. After amplification, the ac signal is converted into a steady voltage by the demodulator D, this voltage being proportional to the input. The resistors R1-R 5 and the stabilitron St are provided to establish the initial mode of the tube. The circuit is fed from a stabilized voltage source SVS. A special feature of the electrometer circuit is the use of special negative feedback, as a result of which any change in the input voltage leads to a similar change in the voltage on all the tube electrodes, including the auxiLiary screen. Thus, the potential differences between the tube electrodes remain practically constant, and this has a beneficial effect on the stability of operation of the instrument. On the other hand, the auxiliary screen within which the measuring electrode is placed is all the time held at a potential approximately equal to the potential being measured. Hence the expected distortion of the field due to the in~oduction of the probe at the point of measurement is minimal The negative feedback voltage on the auxiliary grid is taken from the resistor P~.

Ion Emission Regulator for the Surface Ionization Ion Source

This article describes a simple ion emission regulator for a surface ionization ion source in the current range of 10-7-10-9A. The principle of regulation is quite similar to that of an electron emission regulation for an ionization vacuum gauge, except that the regulator has a simple electrometer circuit. The stability is about 1% after running of 1 hour, if a stabilized a. c. power supply is used. The regulator has been successfully employed in an ion beam experiment using hydrogen as a target gas.

Air capacitors of constant and variable capacitance and capacitor box for electrometer circuits

Air capacitors of constant and variable capacitance and capacitor box for electrometer circuits

A Logarithmic Electrometer for Space Flight Application

A very simple logarithmic response dc electrometer circuit is described which makes use of a novel connection for developing the log feedback signal. The resulting improvement in bandwidth over familiar circuits is discussed.

A ten-channel secundary emission monitor for electron beam analyzing purposes

To facilitate proper operation of a 60 MeV linear electron accelerator a grid-type secundary emission monitor has been installed perpendicularly to the deflected beam for energy spectrum analyzing purposes. The monitor consists of ten aluminium strips in a geometry and location covering a 5% energy band. The ten strips are scanned with reed relais connected with an electrometer circuit. The energy spectrum is directly shown on an oscilloscope. The electronic equipment is discussed and a transfer function analysis of the electrometer circuit is presented.

Thickness measurements in the electron microscope

A probe unit and a simple electrometer circuit are described for the measurement of the electron beam currents in an electron microscope. These measurements are used to calculate the thickness of the sample in the microscope.

A simple tandel electrometer circuit part II

The properties of a simple electrometer circuit using a tandel are described in detail. The influence of changes in the external conditions (frequency and amplitude of heating voltage and ambient temperature) and in some important parameters of the circuit (load resistance and series capacity) on the properties of the circuit is shown as well as the influence of feedback which was introduced to decrease the input capacity of the circuit. It is shown how to form a bridge connection from two basic simple circuits and the advantages of such a connection are pointed out. The circuit described has a d-c input resistance of about 1013 Ω for an input capacity of approx. 250 μμF. It can work with a symmetrical or asymmetrical input signal while the output may also be symmetrical or asymmetrical.