A TDM wattmeter with a 0.5-MHz carrier frequency

The author describes a standard time-division-multiplexing (TDM) wattmeter with a constant average carrier frequency, no inherent phase error, and known systematic magnitude frequency error, as well as efforts to increase frequency bandwidth. The residual error of the wattmeter, after corrections, is below 100 p.p.m. up to 5 kHz. The meter is expected to find application in accurate power measurements under distorted and low power factor conditions, and as a transfer standard for interlaboratory comparisons     

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 Electronic Multiplier for Accurate Power Measurements

The time division multiplier-type wattmeter is based on a new principle of operation. An operational amplifier operates as an integrator of the sum of Ez (one of the two inputs) and either +E8, or -E8, E8 being an internal standardized voltage. A pulse-width modulation in the form of switch reversals is obtained which differs from balance condition by an amount proportional to Ex. Instantaneous multiplication provides a wattmeter with dc accuracy of ± 0.1 percent up to at least 10 kHz. The output voltage is ± 1 volt for a ± 1-volt input from Ex and Ey. To obtain the required flat frequency characteristics, a coupling transformer and an adjustable resistor are provided. A time constant of 6.8 X 10-9 seconds has been achieved. The voltage signal is readily provided by a precision ratiotran. Errors of ± 0.0001 percent in magnitude and 50 microradians in phase angle are reasonable.     

Precision Measuring Equipment for Electrical Power in the Range of Audio Frequencies

The design and construction of an electrodynamic wattmeter for precise measurement in the range of direct current to 20 kHz is discussed. The method of operation, construction, and compensation for effects and errors is described. Calculations, test results, and several test methods are described and show that the instrument is capable of high accuracy and resolution in the power and audio frequency range.     

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.     

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.     

Analysis and implementation of an active snubber dc/dc converter with series?parallel connection in primary and secondary sides

An active snubber dc/dc converter to achieve zero voltage switching (ZVS) on power switch is presented. In the proposed converter, the primary windings of two transformers are connected in series so that the primary currents of the two transformers are equal. The secondary sides of the isolated zeta converters are connected in the parallel to share the load current and reduce the current stresses on the secondary windings of the two transformers. A boost type of active snubber is connected in parallel with the main switch to recycle the energy stored in transformer leakage and magnetizing inductors and to limit voltage stress of the main switch. During the transition interval between the active switch and the auxiliary switch, the resonance based on the resonant inductor and the output capacitor of the power switch will allow the switch to turn on at ZVS. The principle of operation, steady-state analysis and design consideration of the proposed converter are provided. Finally, experimental results for a 360 W (12 V/30 A) prototype circuit with 150 kHz switching frequency were given to demonstrate the circuit performance and verify the feasibility of the proposed converter.     

Characterization of Core Materials for Microscale Magnetic Components Operating in the Megahertz Frequency Range

Suitable materials forming the core of microscale magnetic components have been characterized for the application of magnetic passive components in the 0.5-10 MHz frequency range. The performance of electrodeposited nickel-iron, cobalt-iron-copper alloys and the commercial alloy Vitrovac 6025 have been assessed through their inclusion within a custom-made solenoid microinductor. Inductance values ranging from 0.3 to 120 H with component power efficiency above 90% have been measured. Although the present inductor, at 500 kHz, achieves 77% power efficiency for 24.7W/cm³ power density, an optimized process predicts a power efficiency of 97% for 30.83 W/cm³ power density.     

Measurement of the Transfer Function of Hot-Wire and Hot-Film Turbulence Transducers

A microwave simulator for controlled variation of air-flow velocity in the dc to 500 kHz frequency range is described. The simulator serves for measurement of the transfer function of hot-wire and hot-film transducers used in turbulence research. The microwave simulator consists of an X-band power modulated klystron which delivers electromagnetic energy to the transducer, mounted in a small-size calibration wind-tunnel supplying the transducer mean flow velocity (in the 0 to 80 m/s range). Experimental results are given for the absolute value of the transfer function in a 60 dB range, of a hot-wire tungsten transducer (5 micron diameter X 1 mm long) and of a platinum-plated quartz hot-film transducer (25 micron diameter × 0.5 mm long).     

Measurement of FM Noise Spectra of Low-Noise VHF Crystal Controlled Oscillators

The design and characterization of stable, low-noise crystal controlled VHF oscillators are described. Operating in the 60 MHz to 80 MHz frequency range, these oscillators have shown total rms frequency deviations of less than 4 parts per 1010 in a 5 kHz band. Noise characteristics have been determined from power spectra measurements, FM noise measurements, and phase noise measurements. The equivalent noise sideband power spectra corresponding to each method of measurement were calculated and compared to the spectra predicted by a very simple model of the oscillator circuit. Agreement within a few dB was found for the region within about 500 Hz of carrier frequency, but measured noise power was found to be considerably higher than predicted for higher baseband frequencies in the range from 800 Hz to 5 kHz. Measurement techniques and evaluation of data are presented.     

An Automatic System for AC/DC Calibration

An automatic ac/dc difference calibration system using direct measurement of thermoelement EMFs is described. The system operates over a frequency range from 20 Hz to 100 kHz, covering the voltage range from 0.5 V to 1 kV. For all voltages, the total uncertainty (including the uncertainty of the specific reference thermal converters used) is 50 ppm at frequencies from 20 Hz to 20 kHz, inclusive, and 100 ppm at higher frequencies up to 100 kHz. In addition to ac/dc difference testing, the system can be used to measure some important characteristics of thermoelements, as well as to calibrate ac voltage calibrators and precision voltmeters. Results of intercomparisons between the new system and the manual NBS calibration system, using single-range, coaxial-type, thermal voltage converters as transfer standards, are reported. The results indicate that the ac/dc differences measured are accurate to well within the combined total uncertainty limits of the two systems.     

Simultaneous alternating and direct current readout of protein ion channel blocking events using glass nanopore membranes

Alternating current (ac) phase-sensitive detection is used to measure the conductance of the ion channel alpha-hemolysin (alphaHL), while simultaneously applying a direct current (dc) bias to electrostatically control the binding affinity and kinetics of charged molecules within the protein lumen. Ion channel conductance was recorded while applying a 10-20 mV rms, 1-2 kHz bias across a single alphaHL protein inserted in a 1,2-diphytanoyl-sn-glycero-3-phosphocholine lipid bilayer that is suspended across the orifice (100-500 nm radius) of a glass nanopore membrane. Step changes in the ac ion channel conductance with a temporal response (t(10-90)) of 1.5 ms and noise amplitude of approximately 2 pA were obtained using a low-noise potentiostat and a lock-in amplifier. These conditions were used to monitor the reversible and stochastic binding of heptakis-(6-O-sulfo)-beta-cyclodextrin and a nine base pair DNA hairpin molecule to the ion channel. Alternating current methodology allows the binding kinetics and affinity between the protein ion channel and analyte to be investigated as a function of the dc bias, including ion channel conductance measurements in the absence of a dc bias.     

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.     

Tunable and frequency-stabilized diode laser with a Doppler-free two-photon zeeman lock

We describe frequency locking of a diode laser to a two-photon transition of rubidium using the Zeeman modulation technique. We locked and tuned the laser frequency by modulating and shifting the two-photon transition frequency with ac and dc magnetic fields. We achieved a linewidth of 500 kHz and continuous tunability over 280 MHz with no laser frequency modulation.     

Compact inductance standard

A portable Maxwell-Wien bridge as a part of the Korea Research Institute of Standards and Science (KRISS) inductance standard has been developed. Two auxiliary resistive-capacitive networks (analogous to a "Wagner ground") provide excellent stability of the bridge balance and impose less strict requirements on the components of the networks. Removable capacitance and ac/dc resistance standards used in the bridge arms make it possible to realize the inductance unit in terms of capacitance and resistance in the frequency range 500 Hz to 3 kHz. Investigations of the standard and results of preliminary (trial) comparison with the Mendeleyev Institute for Metrology demonstrate that the bridge can be used for measurement of 10 and 100 mH inductance standards with an uncertainty within (1-3) /spl mu/H/H at frequencies of 1 and 1.6 kHz. The use of this bridge as a constituent part of a transportable standard gives an opportunity to eliminate any uncertainty arising from instability of the standard inductors.     

End-of-Line Waveguide Thermistor Power Meters in the Frequency Range 16.7–37.5 GHz

Measurement Techniques - In this study, a multiprobe end-of-line converter, which is a part of a waveguide thermistor wattmeter, was developed. This converter functions to improve the power...     

Ponderomotive power meter

Conclusions The testing of the above ponderomotive wattmeter leads to the conclusion that it is advisable to use such instruments in UHF measurements. The fact that these instruments measure transmitted power, and that they can be calibrated by an absolute method and are relatively accurate makes them particularly suitable for use as reference instruments for calibrating power meters of other systems.     

A 1000 A/20 kV/25 kHz-500 kHz Volt-Ampere-Wattmeter for loads withpower factors from 0.001 to 1.00

Many industrial processes and scientific experiments utilize large amounts of ac power at frequencies from 3 kHz to 500 kHz. The phase angle and the impedances of these loads often vary over a wide range. This paper describes an instrument to provide an accurate measurement of currents (1 A to 1000 A), voltages (100 V to 20 kV), and powers (100 W to 20 MW) over the frequency range from 25 kHz to 500 kHz. It deals with loads having power factors down to nearly zero and with load impedances from 10 Ω to 20 kΩ. The paper contains practical details of both the design and the calibration of the front-end voltage and current transducers. The characteristics of a nearly ideal broadband current transducer are presented. Overall instrument calibration, verification and traceability problems are considered in detail     

Audio frequency magnetoresistive watt-converter

A new audio frequency magnetoresistive watt-converter is designed. It has less than 0.5% nonlinearity in the power range up to 40 W and less than 0.5% change in sensitivity in the frequency band 20 Hz-20 kHz. This type of watt-converter may be used for measurement of active power in industrial circuits with highly distorted sinusoidal signals and reasonably large reactance     

Hall transducer as an UHF power indicator

Conclusions Hall transducers made of n-type germanium can be used as sufficiently efficient power indicators in the long-wave portion of the UHF range for medium power. A wattmeter of that type using a Hall transducer described above in conjunction with high quality resonators has a linear scale and a sensitivity of 1 V per 4 m W. The error in measuring power evaluated by deviations from the mean does not exceed ±5%.