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SRI 6002 Multi-Junction Thermal Converter

Technical Contact: stefan.cular [at] (Stefan Cular)

SRI 6002a and 6002b are restricted from sale.

The most accurate ac voltage measurements are made by comparing the heating effect of an unknown ac signal to that of a dc reference using devices known as thermal converters. In its most basic form, thermal converters consist of a thermocouple placed at the midpoint of a heater structure, commonly a thin wire. These devices are extremely broadband, with a frequency range from 10 Hz to more than 100 MHz, and generally have input voltages limited to a few volts. The quantity of interest, called the ac-dc difference, can be nearly zero at audio frequency, but may be as large as several percent at 100 MHz.

The most accurate thermal converters, called multijunction thermal converters (MJTCs) consist of multiple thermocouples arrayed along a heater structure. Modern MJTCs are made using semiconductor fabrication techniques, resulting in thin-film MJTCs. These devices form the international basis of ac voltage and current metrology. Thin-film MJTCs fabricated on glassy substrates have the same broadband characteristics as traditional thermal converters, but have larger dynamic ranges and smaller ac-dc differences at varying input voltages or currents (voltage coefficients). MJTCs are also expected to have smaller ac-dc differences than traditional thermal converters because their design results in smaller thermoelectric errors.

The MJTCs developed as Standard Reference Instruments are of the bifilar type, fabricated on substrates of fused silica, and bonded to AL2O3 carriers. Each device is equipped with a cover to protect the die and wire bonds. They are identical to standards used in the AC-DC Difference Project at NIST.

Specifications Certificate (PDF format)

Standard Configurations

The prices listed below are for the individual instrument and do not include costs related to the final measurement calibration performed before delivery or post-delivery installation and training.  The related Calibration Service ID for the SRI are  53350C, 53351C, and 53352C.  To obtain a quote for the instrument and calibration services, please contact Sales and Customer Service by phone at 301-975-2200 or email at srminfo [at] 


Multi-Junction Thermal Converter - Nominal input resistance 600 Ω ± 15 Ω


6002b Multi-Junction Thermal Converter - Nominal input resistance 1040 Ω ± 20 Ω




Created September 28, 2016, Updated January 23, 2024