A method to determine the calorimetric equivalence correction for a coaxial microwave microcalorimeter

A way is presented to obtain the microcalorimeter correction factor by direct measurement rather than by an indirect estimate or modeling. The microcalorimeter is used to measure the effective efficiency of a reference standard thermistor mount. The correction factor accounts for the different thermal paths and losses in the microcalorimeter reference standard combination. The uncertainty in the measurement depends primarily on an accurate determination of the correction factor. This has been an especially difficult problem in the coaxial case because of the center conductor. The method requires the fabrication of components that duplicate the thermal and RF loss in the microcalorimeter and reference standard. Using the technique with the new National Institute of Standards and Technology (NIST) type N coaxial microcalorimeter has substantially reduced the systematic uncertainty. The total uncertainty is about one-half the uncertainty of the prior NIST standard at frequencies above 1 GHz