An investigation of multijunction thermal converters

Hermach, F. L.; Flach, D. R.

doi:10.1109/tim.1976.6312280

Cited by 24 publications

(32 citation statements)

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Section: Rms Voltmeter Designmentioning

confidence: 99%

“…The second term of (8) The attenuation factor of the LP filter (sections R7-C2 and R8-C3) is'0 4co2 + a2 a2 (11) 8 The second term of (8) and (10) corresponds to the second term of (1). 9 A long-range program is underway at NBS to develop an all-digital system for measuring and analyzing VLF waveforms in time periods approaching the theoretical minimum.…”

Section: Rms Voltmeter Designmentioning

confidence: 99%

“…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 ripple is negligible (maximum filtering used). Consequently, the ac/dc difference of the rms voltmeter (input applied to the TC DIRECT terminals) changes less than 10 ppm from 1 to 10 Hz and is negligible above 10 Hz.…”

mentioning

confidence: 99%

“…The response of the critically damped circuit to an input (Fig. 3), matched to the resistance of heater H1, reduces bm in two ways: 1) It minimizes the dependence of input power on small cyclic resistance changes [10] which decreases b', and 2) it reduces 6m by decreasing I to a full-scale value of 2.5 mA (rated current for the MJTC is 5 mA). The value of b' should be specified so that 6m < 0.1 percent for m = 1.…”

mentioning

confidence: 99%

“…At very-low frequencies (VLF's), particularly below 10 Hz, the major source of error in calibrating these transducers (both reference standards and test items) has been the error in measuring the output voltage from the transducer [1], [2]. This is because the measurement error of the few commercial voltmeters (that measure VLF's) ranges from a few tenths of a percent to over 1 percent, depending upon the voltage and frequency.…”

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confidence: 99%

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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: 99%