Jay Dratler

A proportional thermostat with 10 microdegree stability

The general problem of designing active proportional thermostats is discussed, and a design philosophy is deduced. The application of this philosophy to the construction and operation of a precision proportional thermostat for geophysical accelerometers in boreholes is described in detail. The thermostat discussed is of small size and weight, is simple to operate, and requires less than 5 W of power. It maintains the temperature of an instrument and its vacuum enclosure of 1688 cm3 total volume and 7 kg mass constant within 10 μ°C over periods of days in the presence of fluctuations in the ambient temperature of several degrees. Various models of the thermostat, with several different configurations of thermal insulation, have been tested extensively in both laboratory and borehole environments. Stable proportional operation has been achieved with setpoint temperatures ranging from 15 to 35 °C and with the difference between the setpoint and mean ambient temperatures varying from 4 to 10 °C. The electroni...

Inexpensive linear displacement transducer using a low power lock‐in amplifier

Differential capacitance displacement transducers (DCDTs) using audo frequency excitation and phase‐sensitive detection are discussed, and their sensitivities are calculated. An inexpensive, low‐power DCDT using a miniature lock‐in amplifier made of integrated circuits is described. The lock‐in amplifier has a digitally controlled phase shift between drive and reference signals, a full‐scale output of ±10 V, and total noise and drift of about 1 mV peak to peak. The DCDT system has a detection limit of 0.01 nm/√H√z, a dynamic range between 60 and 80 dB, and a power consumption of less than 0.75 W. Parts cost for the system is about

Quartz Fibre Accelerometers

200. A simplified DCDT not requiring the full lock‐in amplifier is outlined, and improvements possible in the DCDT design are mentioned where appropriate.

High‐Q Overtone Modes of the Earth

New vertical and horizontal accelerometers based on torsion fibres of fused quartz and differential capacitance position sensors are discussed. The instruments have low drift, flat response from d.c. to nearly 1 Hz, and gain sufficient to measure tidal and seismic accelerations. They are small, weigh less than 9 kg, and have strict control of internal temperature and pressure. Tidal, free oscillation, and seismic data from the accelerometers are presented. Records of earthquakes of surface wave magnitude 6.5 to 7.5 yield free oscillation spectra with greater than 20 dB signal-to-noise ratio. Records of distant teleseisms provide a detection threshold of surface wave magnitude 2.5 at a distance of 30°. A record of the San Fernando earthquake of February 1971 gives an upper bound of 1mm for a vertical displacement step 190 km from the source.