Héctor Laiz

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 todays 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.

Comparison of three accurate methods to measure AC voltage at low frequencies

Three methods for the determination of the RMS value of AC voltage at low frequencies are compared: the step calibration of a digitally synthesized source, the optimized sampling method, and the AC-DC voltage transfer with a multifunction thermal converter. The three methods agree within 1/spl times/10/sup -6/ with an uncertainty of 2.5/spl times/10/sup -6/ in the frequency range from 10 Hz to 100 Hz.

Low-frequency AC-DC voltage transfer standards with new high-sensitivity and low-power-coefficient thin-film multijunction thermal converters

New Planar Multijunction Thermal Converters (PMJTC) with low power coefficient and high dynamic range using CuNi44/BiSbTe-thermocouples were developed. Together with carefully evaluated range resistors for voltages up to 1000 V they resulted in ac-dc transfer standards with negligible ac-dc voltage transfer difference at low frequencies. The measuring system was improved with a new highly stable low frequency voltage source.

AC-DC current transfer step-up and step-down calibration and uncertainty calculation

New AC-DC current transfer standards are built for the current range from 0.3 mA to 20 A and the frequency range from 10 Hz to 100 kHz. A three-dimensional PTB-multijunction thermal converter (MJTC) with a heater resistance of 27 /spl Omega/ is the basic standard for the AC-DC current transfer at currents from 20 to 50 mA. At lower currents, planar MJTCs (PMJTCs) with heater resistances from 90 to 960 /spl Omega/ are used in a step-down procedure. Coaxial current shunts in parallel with PMJTCs extend the current range up to 20 A. The standard measurement uncertainties are in the range from 0.2 /spl mu/A/A at 25 mA and 1 kHz to 50 /spl mu/A/A at 20 A and 100 kHz. The high sensitivity of the PMJTC allows bigger steps in the step-up calibration and some smaller steps between these steps. Calibration of all these steps leads to an overdetermined system to check for the validity of the assumptions made in the step-up procedure. This results in reduced uncertainties at the different current levels compared to the old method.

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 chip results in improved performance for frequencies higher than 100 kHz 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. The temperature of the heater is radiometrically sensed with a thin-film infrared sensor. 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.

New thin-film multijunction thermal converters with negligible low frequency ac-dc transfer differences

The ac-dc transfer differences of thin-film thermal converters at low frequencies are caused by nonlinearities of the heat transport mechanisms and of the thermal-to-electric conversion. A compensation circuit has been designed which results in converters with ac-dc transfer differences below 0.3/spl middot/10/sup -6/ at 10 Hz. The standard uncertainty of the ac-dc transfer difference measurement was reduced to 0.3/spl middot/10/sup -6/ at 10 Hz.

An international comparison of 50/60 Hz power (1996-1999)

An international comparison of 50/60 Hz power is described. The traveling standard was an electronic power transducer which was tested at 120 V, 5 A, 53 Hz, at five power factors (1.0, 0.5 lead, 0.5 lag, 0.0 lead, and 0.0 lag). Fifteen national metrology institutes from six metrology regions participated in the comparison.

Determination of the AC-DC voltage transfer difference of high-voltage transfer standards at low frequencies

The ac-dc transfer difference at low frequencies of thermal converters for higher voltages with planar multijunction thermal converters (PMJTCs) and series resistors has been determined by using only the established linear change of the low-frequency ac-dc current transfer difference of the PMJTC with input power. Uncertainties of less than 1 muV/V are achieved up to 1000V

A simulation tool for the AC-DC transfer difference of thermal converters at low frequencies

To find the reason for the AC-DC transfer differences of the planar multijunction thermal converter (PMJTC) at low frequencies, where temperature oscillation is present due to the lack of integration of the oscillating Joule heat, the coupled electro-thermal mathematical problem has been solved. The dynamic nonlinear model includes the temperature dependence of all material parameters, of heat conduction through the air and radiation losses. The results of the simulation are compared with those of measurements using a sampling voltmeter with special software as a reference. A new design is proposed to improve the performance of the PMJTC at low frequencies.

A 1000 V resistor for AC-DC voltage transfer

The new design of a thin-film 100 k/spl Omega//1000 V resistor on a thick AlN substrate with very high heat conductance results in a small resistor temperature of less than 4 K increase above ambient. As all the Joule heat is conducted through the substrate to the outside heat sinks, the inside electrostatic shield as well as the outer cylinder remain at ambient temperature. This design reduces the voltage coefficient of the AC-DC voltage transfer standard for the step-up from 300 V to 1000 V and frequencies from 1 kHz to 100 kHz.