The problem of noise in precision bridge measurement.

In this thesis an investigation is made into thelimitations to the accuracy of balance of bridge measuringcircuits as a result of noise. Particular attention isfocused on the capacitance bridge.The sources of noise considered arise in the bridgecircuit and the detector amplifier. Noise from the sourceoscillator, particularly in the case of a frequencysensitive bridge is also of consequence.A survey of preamplifier types suitable for usewith a capacitance bridge is made to find the one contributingthe least noise. These preamplifiers comprise untuned, tunedand parametric amplifiers.Theoretical consideration of a mechanically drivencapacitor in a parametric up-converter amplifier indicatesits usefulness as a low frequency amplifier.Investigations were made to determine the sourcesof noise in a vacuum tube preamplifier and relatively simplemethods evolved for the determination of vacuum tube noiseperformance at low frequencies.The indicator displaying the bridge unbalance wasconsidered in regard to its performance at small signal tonoise ratios. A particular indicator is considered and theperformance of the human operator in balancing a bridgeusing this unit is studied.For comparison an ideal detector comprising aphase sensitive detector followed by a resistance capacitancefilter and perfect integrator is considered. A determinationis made of the ultimate sensitivity of a bridge measuringsystem when using this type of indicator.The sources which contribute to the noise of theoscillator driving the bridge are discussed and a methodfor the reduction of the harmonic frequencies of the sourceat the output of a frequency sensitive bridge is described.Included as portion of this thesis are severalpapers by the author, the titles of which are listed onpage 194