AC-DC comparators for audio-frequency current and voltage measurements of high accuracy

Hermach, F. L.

doi:10.1109/tim.1976.6312271

Cited by 28 publications

(24 citation statements)

References 24 publications

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“…When a low-frequency sinewave is applied to a TC, the ratio m of peak ripple to average output EMF ranges (approximately) from 1 at very low frequencies to zero at high frequencies. Lack of square-law response has no effect on the ac/dc difference 3 (Fig. 2).…”

Section: Rms Voltmeter Designmentioning

confidence: 95%

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An RMS Digital Voltmeter/Calibrator for Very-Low Frequencies

Schoenwetter

1978

IEEE Trans. Instrum. Meas.

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A portable rms digital voltmeter (DVM) has been developed at NBS to support vibration measurements over the ranges of 0.1 to 50 Hz and 2 mV to 10 V. A self-contained calibrator provides for self-calibration and may be used for calibrating other VLF voltmeters. The calibrator basically consists of a Kelvin-Varley divider fed by a reference voltage (either dc or sinewave generated by a ROM-DAC combination) A multijunction thermal converter (MJTC) was selected as the sensing device in the rms/dc converter of the DVM since its low ac/dc difference facilitates calibration of the ac calibrator. Factors Manuscript received February 20, 1978. This work was supported in part by the Calibration Coordination Group of the Department of Defense.The author is with the Electricity Division, National Bureau of Standards, Washington, DC 20234. ' The design was later modified to extend the range to 0. for the calibration of other voltmeters. In addition, the calibrator facilitates transfer measurements. The accuracy objective for the voltmeter was 0.1 percent of reading above 2 Hz and 5 mV and 0.25 percent of reading for lower frequencies and voltages. As explained in the next section, the minimum response time obtainable in rms voltmeters is directly proportional to the period of the input voltage. Commercial rms DVM's require 15-20 periods for a response to within + 0.1 percent of the input change. This extrapolates to 150-200 s for 0.1 Hz. Since slow response limits an instrument's usefulness, the design objective also was to decrease the response time below these figures as much as was practicable. II. RMS VOLTMETER DESIGNA. Design ConsiderationsThe rms voltmeter designed for this instrument follows the conventional approach shown in Fig. 1 IM-27, NO. 3, SEPTEMBER 1978 Thus ripple filtering is required in the converter to limit this rms/dc conversion error to an acceptable level. This constraint still allows a relatively large peak-to-peak C. Detailed Design 1) Input Amplifier: The input amplifier is direct-coupled and has gains from 0.5 to 2500, selectable in 12 ranges of 1-2-5 gain sequence. The amplifier consists oftwo cascaded low-noise low-drift operational amplifiers with buffering to provide high-input impedance and power capability with low distortion at its output. The sequence of voltage ranges limits the nominal input range over which the rms/dc converter must operate from 2 to 5 V. Reed relays in DIP configuration are used for range switching. The frequency response for all gain ranges is flat from dc to 50 Hz to within 0.01 percent or better.2) RMS/DC Converter:4 a) General description: The rms/dc converter in this instrument (Fig. 2) allocated error budget. At 1 Hz, 6(5 < 10 ppm and decreases to zero below 10 Hz. The ac/dc difference from other causes (such as Thompson and Peltier effects) is less than 1 ppm up to 10 kHz [10], [11], and is expected to be constant over the voltmeter's frequency range.The rms/dc converter has essentially the same ac/dc difference as the MJTC if its output ripp...

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Section: Rms Voltmeter Designmentioning

confidence: 95%

“…Therefore, it is seen from (1) 2) RMS/DC Converter:4 a) General description: The rms/dc converter in this instrument (Fig. 2) is a feedback type, employing a differen- 4 Bibliographies on rms/dc converters may be found in [3] and [4]. [7], [8].…”

Section: Rms Voltmeter Designmentioning

confidence: 99%

An RMS Digital Voltmeter/Calibrator for Very-Low Frequencies

Schoenwetter

1978

IEEE Trans. Instrum. Meas.

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“…The quantities of EDC and EAC represent the output EMFs of the thermocouple when the DC voltage (VDC) and AC voltage (VAC) are applied to the thermal converter. In this case, VAC is required to produce an output EMF that is equal or nearly equal to the VDC (Hermach, 1976). In the above condition, the n variable needs to be included as the exponent of the thermal converter ,…”

Section: Mathematical Model and Uncertainty Of The Ac-dc Difference Mmentioning

confidence: 99%

“…The Electrical Metrology Laboratory (EML) maintains its AC (Alternating Current) voltage standards at 1-1000 V using three single junction-type Thermal Voltage Converter (TVC) standard units (Hermach, 1976;Syahadi et al, 2015). The accuracy levels of these standards are maintained via measurement processes based on the intercomparison method.…”

Section: Introductionmentioning

confidence: 99%

Calibration Process Quantity Reduction of the Thermal Voltage Converter Standard using a Three-stage Build-up and Build-down Method

Sardjono¹,

Wijonarko²

2018

IJTech

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Currently, three single junction-type Thermal Voltage Converter (TVC) standard units represent the highest standard of AC (Alternating Current) voltages owned by the Electrical Metrology Laboratory, Research Centre for Metrology-Indonesian Institute of Sciences. The accuracy of the single junction-type TVC is maintained regularly via intercomparison processes using a one-step build-up and build-down method. To reduce the calibration process quantity, three steps of build-up and build-down measurements that refer to the 4 V measurement point of a HOLT production single junction-type TVC were carried out. The dissemination processes with the best measurement accuracy up to 20 ppm were successfully obtained from measurement points between 1 V and 20 V via 4-1V, 4-2V, 4-3V, 4-6V, 4-10V, and 4-20V formations.

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“…Specific objectives for the new system included: 1) use of commercially available, programmable instruments whenever possible; 2) elimination of the need for manual data entry into a computer for reduction; 3) elimination of the frequent data checks and cross-checks required in manual tests; 4) elimination of as much operator intervention as possible during the test procedure; 5) simplification of necessary remaining interaction by providing displayed operator instruction via computer control; 6) close control of the time interval between application of both ac and dc voltages to the test circuit in order to minimize drift effects; and 7) achievement of the same level of uncertainty as is presently possible with manual testing methods.…”

Section: Objectivesmentioning

confidence: 99%

A semiautomatic ACDC thermal voltage converter calibration system

Lentner¹,

Tremaine²

1982

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AC-DC comparators for audio-frequency current and voltage measurements of high accuracy

Cited by 28 publications

References 24 publications

An RMS Digital Voltmeter/Calibrator for Very-Low Frequencies

An RMS Digital Voltmeter/Calibrator for Very-Low Frequencies

Calibration Process Quantity Reduction of the Thermal Voltage Converter Standard using a Three-stage Build-up and Build-down Method

A semiautomatic ACDC thermal voltage converter calibration system

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