The precision and accuracy of interferometers using quadrature fringe detection are often limited not by the interferometer itself but by the detector system. There are three typical errors: unequal gain in the two channels; quadrature phase shift error; and zero offsets. This paper describes a simple method for determining the quadrature errors from experimental data obtained in the interferometer and correcting for them. A numerical example demonstrating the significant improvement in the precision of interferometer data is given.
The first part of this paper describes the use of ultrasonic interferometry for the measurement of the lengths of manometer columns. The major known sources of errors of manometers are then analyzed, and design criteria are developed which reduce these errors below set limits. Finally, two ultrasonic manometers now being developed at the National Bureau of Standards for measurements in the low and medium vacuum ranges are described. The ultrasonic mercury manometer, with a range of 13 kPa, has been operated with a resolution of 1.4 mPa.
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