ABSTRACT

A brief survey around the basement of Clark Hall shows that there are about four bridges associated with each cryostat. Bridges for resistance thermometers, capacitative level detectors, strain gauges (pressure and temperature measurement), and susceptibility bridges for paramagnetic salt thermometers are typical examples. Bridges allow accurate measurement of component values with short time constants and very low power dissipation. The excitation level which may be used in a resistance bridge is a trade-off between power dissipation and noise. The dot-dash line is the voltage noise in the preamp divided by the voltage drop across the resistor which is an estimate of the precision of the measurement. Low temperature torsional oscillators were first used by Andronikashvilli for his classic experiments on the density of the normal component of helium II. Torsional oscillators are home-brewed devices. Torsional oscillators are somewhat delicate devices and reasonable care must be excerised during their construction.