100 Ohm transfer standard
A new 100 /spl Omega/ transfer standard has been built and placed in service at VTT Automation. The temperature of the resistor is maintained at 30.72/spl deg/C where the temperature coefficient is zero. The daily variation in temperature is less than /spl plusmn/0.005/spl deg/C. The temperature during transportation is about 0.06/spl deg/C less than the nominal value and it can be hold for about 40 hours. The behavior of the standard was verified in the resistance comparison between VTT (Finland), PTB (Germany), BIPM (International) and BNM-LCIE (France) in November-December 1998. The result indicates that the variation of the standard during the transportation is less than 6.10/sup -9/.
Comparison of four QHR systems within one month using a temperature and pressure stabilized 100-Ω resistor
We have carried out a resistance comparison of four QHR systems using a 100-/spl Omega/ resistor in a temperature-controlled and hermetically sealed enclosure, the comparison was performed in November and December 1998, the participants were Bureau International des Poids et Mesures (BIPM), Bureau National de Metrology-Laboratoire Central des Industries Electroniques (BNM-LCIE) France, Physikalisch-Technische Bundesanstalt (PTB) Germany, and Valtion Teknillinen Tutkimuskeskus (VTT Automation) Finland, acting as a pilot laboratory. The comparison results agree within 3 parts in 10/sup 9/ with a relative combined standard uncertainty of /spl plusmn/1/spl times/10/sup -8/.
Multiple‐Bridge Circuits for Measurement of Small Changes in Resistance
In the multiple‐bridge circuit, first‐order effects of random resistance variations occurring at the junctions of a Wheatstone bridge are eliminated by an extension of Kelvin's method, which involves adding an auxiliary resistor pair at each bridge corner at which the variations occur. The remaining second‐order error, and the effects of thermals, are evaluated. The multiple‐bridge technique makes possible precise resistance comparisons, and the accurate measurement of small changes in resistance of an element that is connected through switch contacts, or brushes and sliprings. Some numerical design data are given. Elaborations of the basic circuit, and typical applications, including measurements with resistance strain gauges, are described.