Thermistor controller with microkelvin stability (for strainmeter testbase temperature control)

Abstract

A DC excited thermistor bridge, and a thyristor controller have been used to provide enhanced temperature stability in a 10 m long strainmeter testbase. Short term temperature variations are held within 40 mu K standard deviation. Drift over 800 h is less than 130 mu K h-1 indicating that thermistor sensors can provide extreme stability in fixed point applications. The relative bimetallic length change occurring between the steel base, and the monitoring vitreous silica catenary strainmeter has been maintained at a stability varying between approximately 10-10 to approximately 10-12/h, being limited by ambient influences rather than by testbase temperature changes.