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/.
An analytical approach to the design of electrodes in high-power, fast-transverse-flow CO2 lasers
Abstract Usually, the design of the electrodes of fast-transverse-flow CO 2 lasers relies more on experimental data than on theoretical analysis. Traditional systems sustain a stable, high-power discharge but the current distribution generates a peaked, non-uniform small-signal-gain pattern. We present a theoretical model suitable for the design of electrodes that achieves a quasi uniform gain distribution. The analysis, based on a two-temperature model and the gas-transport equations, computes the electron density that supports a flat gain pattern. Combining the desired electron density with the electron-balance equations, the model determines the required electric field. The results were used to design a new set of electrodes for a home-made fast transverse flow CO 2 laser. A stable, large volume discharge ( 4 × 8 × 90 cm 3 ) with very good uniformity was obtained. The resulting gain distribution was registered in a bi-dimensional map. The peak gain rose from 1.2 m - 1 , attained with the old electrode set, to 1.6 m - 1 with the new one and the gain showed a homogeneous profile.