AC-DC Voltage Transfer Difference Research Articles

High-frequency thin-film multijunction thermal converter on a quartz crystal chip

The design of a new planar or thin-film multijunction thermal converter (PMJTC) on a quartz membrane and a quartz crystal chip results in a calculable standard for AC-DC voltage transfer for frequencies from 100 kHz to 100 MHz with improved uncertainties. This is due to smaller dielectric losses and higher insulation resistance in the quartz membrane and the quartz chip. The window with the membrane is anisotropically etched into the quartz crystal chip. For the first measurements, the temperature of the heater was radiometrically sensed with a thin-film infrared sensor and later with an array of 100 Cu-CuNi thermocouples. At frequencies higher than 100 kHz, the AC-DC voltage transfer differences are one order smaller than with the standard PMJTC with the Si/sub 3/N/sub 4//SiO/sub 2//Si/sub 3/N/sub 4/ sandwich membrane on a silicon chip.

High performance millivolt-amplifier for the planar multijunction thermal converter

A new amplifier concept combining two amplifiers in the master-slave configuration and the flying supply technique is proposed as the input stage for the planar multijunction thermal converter for AC-DC voltage transfer in the millivolt-range. High input impedance >2 M/spl Omega//spl par/<4 pF and small AC-DC voltage transfer differences from 10 Hz up to 1 MHz are the main features.

Development of thin-film multijunction thermal converters at PTB/IPHT

The thin-film multijunction thermal converter (PMJTC) developed in cooperation between Physikalisch-Technische Bundesanstalt (PTB) and Institut fur Physikalische Hochtechnologie e.V. (IPHT) is today's most sensitive and accurate standard for the precise measurement of electrical AC quantities in the frequency range of 10 Hz-1 MHz. Thin-film technology and micromechanics in silicon were essential for this success. The thin-film heater and bismuth/antimony thermocouples with high Seebeck effect deposited on a thin membrane of low heat conductance result in the attractively high sensitivity of the PMJTC which allows voltage measurements down to 100 mV to be performed. The statistics of the mass production of the PMJTCs show that PMJTCs built into a housing with an N-connector at the input can be reproducebly manufactured with an AC-DC voltage transfer difference smaller than 0.1 /spl mu/V/V at 1 kHz, 8 /spl mu/V/V up to 100 kHz, and below 40 /spl mu/V/V up to 1 MHz for a heater resistance of 90 /spl Omega/. A compensation circuit has been added on the chip which results in low-frequency PMJTCs (LF-PMJTCs) with AC-DC transfer differences below 0.3 /spl mu/V/V at 10 Hz.

AC-DC voltage transfer difference due to Seebeck effect in thermal converters

The thermoelectric transfer difference of Thermal Converters (TCs) can be evaluated in both current mode and voltage mode, using a fast-reversed dc (FRDC) source. Some types of TCs show differences in the thermoelectric transfer difference between voltage and current mode as large as some parts in 10/sup 6/. In order to investigate the origin of the discrepancy, the change of the thermoelectric transfer difference with the value of a resistor in series with the thermal converter has been measured. The result was in good agreement with an assumption that the Seebeck effect in the heater/heater support junction is the main source of the voltage transfer difference.

Thermal converter with quartz crystal temperature sensor for ac-dc transfer

The design and features of an experimental thermal ac-dc converter with frequency output are presented. A bulk acoustic wave LC-cut quartz resonator with linear frequency versus temperature characteristic is used as a temperature sensor. The resonator is excited through an inductively-coupled Butler oscillator. The sensitivity of this device is about 1 kHz/spl middot/K/sup -1/. In order to reduce the electromechanical coupling between the heater and the vibrating area, a thin-film Ni-Cr heater was sputtered at a location where the convex surface of the resonator intersects the nodal plane of the vibrations. The overall temperature coefficient of the output frequency is about -0.3%/spl times/K/sup -1/. The responsivity of the device is 300 kHz/spl times/W/sup -1/. The short-term stability of the output frequency permits an ac-dc transfer at the 10/sup -6/ level. The ac-dc voltage transfer difference of the converter is less than 10/spl times/10/sup -6/ at an input voltage of 3 V in the frequency range from (1-5) kHz. Below 1 kHz, the ac-dc transfer difference increases proportionally to the input power and doubles with a decade decrease of the input frequency. No resonances of the quartz plate were detected between 5 kHz and the frequency of the strongest fundamental thickness shear mode (9.5 MHz). Hence the converter can be probably used up to 1 MHz.

An accurate AC-Dc voltage transfer standard test system using the differential and the dual-channel method

In the Electrotechnical Laboratory (ETL) the accuracy of the AC-DC voltage transfer difference was improved for the voltage range of 1-20 V in the frequency range from 10 Hz to 100 kHz. At the same time, the AC-Dc transfer standards and the measurement system which is used in the Japan Electric Meter Inspection Corporation (JEMIC) were also improved. The system is realized by applying an improved differential and a dual-channel method. The test repeatability is better than 1 ppm for nominal test voltages. The voltage and frequency measurement ranges are extended up to 200 V and up to 1 MHz. The whole system is controlled by a desktop computer with an optically isolated GP-IB bus system. >