Ivan C. Getting (CIRES) and John L. Hall (JILA), University of Colorado at Boulder
NSLS-U2 (DAC)
Johnson noise thermometry offers a means to determine temperature accurately in high pressure environments. The thermal agitation of the charged particles in a resistor generates a minute, time varying voltage. This signal is essentially white noise with amplitudes in the sub-microvolt range. Temperature can be determined from the mean of the voltage squared if the resistance in also know. All affects of pressure, mechanical deformation, chemical reaction, etc. are cast into changes in the resistance itself. Measurement of the resistance each measurement accounts for all such affects leading to accurate temperature determination in virtually any environment. A sensitive, stable circuit has been developed to measure the requisite thermal voltage signal. The signals in question are smaller than the input noise of the best amplifier chips. This leads to the use of a dual amplifier and correlation technique to isolate the desired signal. Instrument control and data acquisition software has been developed. The type A relative standard uncertainty is 0.2 % for one measurement averaging the noise over 10 seconds. Details of the logic and results will be presented. Calibration of thermocouples in the hydrostatic environment of the gas piston cylinder apparatus is planned for next winter with calibration in multi-anvil devices to follow