Experimental Applications of Hall-Effect Wattmeters at 50 Hz

Since Hall effect is the result of multiplying together a magnetic and an electric field, taking into account any phase difference between them, a wattmeter employing a semiconductor device of this kind is a logical development. The paper describes three experimental applications in the United Kingdom, including single- and three-phase instruments metering the power input to 132 kV grid lines and also to 240 volt ac cables, with a record of their performance under practical operating conditions on Central Electricity Generating Board installations. Experience showed that using indium arsenide as the semiconductor element, temperature errors were reduced to an insignificant level and an overall accuracy of about ±2 percent was readily obtainable. It is claimed that this type of instrument applicable to high-voltage lines without the need for special current and voltage transformers is much cheaper than the conventional dynamometer equipment for the same purpose and quite as reliable.     

Wideband wattmeter based on RMS voltage measurements

A wideband wattmeter for measuring active power over a frequency range of dc to 500 kHz is described. The wattmeter is based on the three-voltmeter method in which three rms voltage measurements are used to calculate power. The wattmeter active power uncertainty is estimated to be within 0.03% from dc to 20 kHz and within 1.5% to 500 kHz     

High Power CW Wattmeter Calibration at NIST

The National Institute of Standards and Technology has established a measurement capability to support high power systems and devices. The automated wattmeter calibration system operates at power levels of 1 to 1000 W for frequencies from 1 to 30 MHz and 1 to 500 W from 30 to 400 MHz. A cascaded coupler technique is used to extend power measurements to high levels which are traccable to a 10 mW standard thermistor mount. This technique uses an arrangement of nominal 10, 20, 30, 40, and 50 dB couplers with sidearm power meters. The initial step transfers the calibration of the 10 mW standard to the 10 dB coupler/power meter. The standard is then replaced with a wattmeter to be calibrated. RF power is increased 10 dB and the calibration is transferred to the adjacent 20 dB eoupler/power meter. This sequence is repeated with the remaining coupler/power meters until the wattmeter is calibrated at the desired power levels and frequencies. Power ratios calculated from simultaneous power measurements made at each transfer are used to calculate the incident power at the wattmeter. Due to nonideal components, corrections are made for nonlinearities, mismatch, and other errors. Two types of wattmeters have been evaluated at selected frequencies and power levels. Total uncertainties are based on the random and systematic components.     

An Automatic Data Acquisition System for Semiconductor Device Testing

An automatic data acquisition system was designed and fabricated from both commercially available and proprietary special-purpose equipment to obtain the large quantities of accurate voltage versus current data needed to define and study the voltage-current characteristics of semiconductor devices exposed to neutron bombardment. The operation of the system in tracing out the entire current-voltage characteristic, per preprogrammed instructions, requires only a start command from the operator. The system is capable of measuring currents in the range of 10-10 to 2×10-1 amperes with an absolute accuracy of ±1 percent of reading and a precision (repeatability) of ±0.3 percent of reading, with a maximum voltage drop across the current sampling element of only 5 mV. This low value of voltage drop across the sampling element is made possible by the use of an autoranging technique, which selects discrete values of resistance for sampling the current being measured. The system is capable of programming input voltages from 0 to 50 V in 0.1-mV increments, or input currents from 0 to 2 amperes in increments of 0.01 to 10 ?A, depending on current range. The currents are sampled by the current sampler, whose output voltage is amplified by low-noise amplifiers, and measured by a Dymec 2401C-M31 digital voltmeter. The voltmeter readings, along with resistor identification information in digital form from the current sampler, are serialized by a Dymec 2540B coupler and recorded on a Friden Model SFD Flexowriter in both typewritten form and on punched paper tape.     

A Simple Transistorized Linear Scale Ohmmeter

The detailed design and the analysis of a simple, accurate, and inexpensive linear scale ohmmeter are presented. The accuracy of measurement by the new ohmmeter is within ±1 percent in the range 10-1-106 ?, ±2 percent at 10 M?, and ±10 percent at 100 M?. Unlike most other conventional megohmmeters, this operates with low voltage across the sample and does not require the use of a high input impedance voltmeter. The new circuit exhibits good operational stability.     

A Programmable Precision Voltage-Step Generator for Testing Waveform Recorders

A pulse generator for testing the approximate step-response of waveform recorders is described. The initial and final levels of voltage steps are each programmable within the range of ±1 V for a 50-? termination and within ±5 V for a high-impedance load. Voltage steps within these ranges settle to within ±0.02 percent of full-scale range (FSR) in less than 30 and 40 ns, respectively, for a load capacitance ?30 pF. The corresponding 10-90-percent transition durations are approximately 7 and 12 ns.     

10-kY 10-mA DC Supply with 0.1-ppm Stability

A 10-kV stabilized supply with a dc capacity of 10 mA has been constructed. Its drift rate measured over time intervals greater than about 1 minute and extending to times of more than 10 hours is about 1 part in 107 per hour. For shorter times from 1 second to 1 minute the peak-to-peak deviation from the mean is about 2 mV at 9.2 kV or ±1 part in 107. This performance has been achieved by the use of an initially well regulated commercial 10-kV supply in a closed-loop control system. High dc loop gain has been achieved by the use of a chopper-stabilized amplifier, and a guarded resistive divider of special design. The reference voltage is made up of a bank of unsaturated standard cells enclosed in a temperature-controlled air bath whose short term temperature stability is ±0.001°C. The control resistive divider, together with a measuring divider and a guard divider, are enclosed in an oil bath whose temperature is controlled near ambient to within ±0.01°C.     

Wide-Range Low Current Measurements of Diode Reverse Currents with Automatic Ranging Features

This paper describes a method used successfully by the author in measuring silicon diode reverse leakage currents. The technique used is straightforward and provides wide-range, low current measurements with improved accuracies and automatic ranging features. The full-scale indications extend from 10-3 through 10-10 amperes in eight decade ranges. The full-scale accuracies achieved are better than ±0.5 per cent on ranges 10-3 through 10-8 amperes, ±1 per cent on the 10-9 ampere range, and ±10 per cent on the 10-10 ampere range. The automatic ranging feature exhibits a response of 10 msec per range. The method used is based on sensing the voltage drop (ES) across a sensing resistor (RS). This sensing resistor is in series with the reverse biased diode, as shown in Fig. 1. The sensing voltage is then amplified to an appropriate level (Eo) which can be more easily and accurately measured and/or digitized, depending upon the type of output display and storage method used.     

A Method of Increasing the Accuracy of Active Power Measurements by Inverting the Current or Voltage

A current or voltage inversion method is proposed for increasing the accuracy of active power measurements. The combined use of the inversion method and the method of equal output signals is considered. A wattmeter circuit is proposed, and its errors are analyzed.     

A New High-Frequency Current Standard

A short-circuited-ring electrodynamic ammeter is described. The short-circuited ring is supported by a fine quartz fiber and is suspended midway between the inner and outer conductors of a coaxial transmission line. The current on the line is found by measuring the torque exerted against the ring by the current on the coaxial line. A new technique is given for determining the relationship between the torque on the ring and the current on the transmission line, and is compared with the technique used in the past. The new method is an application of the resonator action theorem used by Cullen for calibrating a torque-operated microwave wattmeter. The major weakness in the previous evaluations of the torque-current relation is discussed. The ammeter is useful for measuring current from 1 to 100 amperes over the frequency range 1 MHz to 1 GHz, with an uncertainty of the order of 0.5 percent.     

An Automatic RMS/DC Comparator

The design of an instrument for the automatic comparison of an ac voltage with a stable dc source is described. A differential multijunction thermal converter is used as an rms/dc converter with an FET-switched input amplifier for ac/dc substitution. The output voltages of the rms/dc converter with ac and dc input voltages are sampled and stored, and the difference amplified and displayed on a panel meter or chart recorder. Accuracy is ±20 ppm of input ranges of 10-200 V at frequencies of 50 Hz-1 kHz, and maximum full scale deflection sensitivity is 0.01 percent of input range. The instrument may be used either as an rms comparator with a linear voltage scale or as a mean-square comparator with a linear power scale.     

A Low-Cost Digital Psychrometer and Humidity Controller

The digital psychrometer presented in this paper is a general type of humidity meter with an accuracy of ±1 percent with 8-bit resolution and the humidity controller has an accuracy of ±0.5 percent. It is optimized by using the fewest possible number of components in order to increase the reliability and to reduce the cost. The speed of operation of this circuit is on the order of 500 ns. This circuit is used for measurement and control of humidity in the temperature range of 0-31°C with an accuracy of ±1°C for temperature with 5-bit resolution and 1-kbyte memory space is used for storing humidity values. This circuit is provided with wide flexibility to change its measurement range according to the users' specifications. This circuit is used for measurement and control of humidity in cold-storage process applications, textile industrial applications, etc.     

Measurement of the energy loss in superconducting magnets

A device is described which measures the energy losses in superconducting magnets. It is excited by alternating current, and is based on the use of a Hall probe as a wattmeter. The signal from the probe, proportional to the power of the losses, integrated over a cycle of current change, corresponds to the losses in the magnet. A feature of the device consists in the use of a special measuring magnet and a system for balancing the reactive voltage, so that the losses can be measured in high-power superconducting magnets.     

An Active Frequency Technique for Precise Measurements on Dynamic Microwave Cavity Perturbations

A new method for the dynamic measurement of the passive parameters of a microwave cavity is described. Both the resonant frequency (f0s) and the loaded Q factor (QLs,) are measured simultaneously from active frequency signals generated by a closedloop circuit containing the test cavity. Resonant frequency deviations of up to 20 MHz are measured with an accuracy of better than ±0.25 percent, and loaded Q-factor variations (from 500 to 7000) are measured with an accuracy of better than ±1.2 percent. The unperturbed cavity resonance was at 2452.0249 MHz, and the time of measurement of each cavity parameter was < 1 s.     

High-Accuracy Settling Time Measurements

Methods are described for measuring the settling times and other dynamic characteristics of voltage and current output D/A converters (DAC's), operational amplifiers, and precision voltage step generators. Circuits are described for measuring voltage-output device settling times as short as 1?s to within a settling error of ±2 ppm, and current-output device settling times as short as 40 ns to within a settling error of ±0.012 percent.     

An Evaluation of the Three-Voltmeter Method for AC Power Measurement

The accuracy and frequency response limitations in the present square-law responding laboratory wattmeters have promoted the search for alternate methods of ac power measurement using electronic instrumentation. The three-voltmeter method is based on an old principle of operation implemented by new analog circuitry. Results of the tests reported here show a precision of power calculation with 0.01 percent error at frequencies below 5 kHz. A unique test procedure is described for the comparison of the three-voltmeter device and a time-division multiplier wattmeter operating at zero power factor.     

Simple Time-Delay Circuit with Very High Duty Cycle

A voltage-controlled time-delay arrangement with a duty cycle equal to unity is described. This performance of the circuit is based on the use of a new monostable switch with complementary transistors. The monostable switch, derived from a free-running multivibrator with very small mark/space ratio is employed as the trigger time base generator, the recovery time of which is very short. Such a time base generator is suitable for various applications in the measurement instruments. Connected to the Schmitt trigger, this timing circuit is very useful in the design of wide-range time-delay arrangements. The experimental performance of the presented time-delay arrangement is as follows: the delay-time variation in one range from about one microsecond to several milliseconds; the delay time/control voltage linearity better than ± 0.15 percent for the control voltage greater than 0.5 volt; the temperature stability of about 0.2 percent in the temperature range from 25-100°C.     

An RC Discharge Digital Capacitance Meter

A simple digital capacitance meter which utilizes the RC discharge is proposed and the wide range capability from 0.1 pF to 10 mF and the excellent linearity to ± (0.02 percent of reading + 1 digit) are shown. The RC discharge capacitance meter provides the capacitance to be measured at a frequency which is reciprocal to the product of the discharge resistance and the measured capacitance. Therefore, the meter can be used to test the frequency dependence of the capacitor even though the test signal is a dc voltage. The proposed RC Discharge Capacitance Meter can also be used in applications such as the measurement of the deviation from the preset value, or the torellance check of capacitance to make the GO or NO-GO decision by adding a few logic gates.     

Thermal Instrument for Measurement of Voltage, Current, Power, and Energy at Power Frequencies

The design of an instrument for precision measurement of ac voltage, current, power, and energy is described. It has been developed as a standard for evaluating the performance of instrumentation used in the power frequency range (45-65 Hz). Its accuracy relies on a continuous ac/dc transfer which is achieved by automatically balancing the alternating current derived from the quantity to be measured against the equivalent direct current, both passing alternately through the heater of a thermal converter. Since the instrument can be calibrated with direct voltage and current, its total systematic error is limited by the ac/dc transfer to ±0.0005 percent of full scale for voltage and current, and ±0.001 percent of full scale for power and energy measurements.     

一种脉宽调制的高稳定连续可调直流电压源

介绍了一种以深埋齐纳电压基准元件LTZ1000A主电路为基础,结合脉宽调制技术实现的在0～10 V范围内连续可调的高稳定直流电压源。选用精密电阻并采用适当的保温与隔离措施,实现了电压基准主电路输出高稳定7 V电压,其短期稳定性达到1.7×10^-8。利用具有相同温度系数和阻值的精密电阻组成比例升压电阻网络,使输出10 V电压的短期稳定性为2.4×10^-8。同时利用脉宽调制并经DC-DC转换电路及滤波电路得到0～10 V的电压输出,短期稳定性可在10^-7量级左右。