Date of Award

Fall 1970

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Ocean & Earth Sciences

Program/Concentration

Oceanography

Committee Director

Ronald E. Johnson

Committee Member

Donald J. P. Swift

Committee Member

William J. Hanna

Committee Member

Rudolf P. Savage

Call Number for Print

Special Collections LD4331.O35H43

Abstract

A new sophisticated electromagnetic current meter was laboratory and field tested in a wide variety of applications, ranging from measurement of net bottom currents (primarily tidal origin) on the continental shelf, to horizontal and vertical components of wave induced orbital motion of waves with periods as small as one second.

These tests indicate that this instrument is capable of performing to at least the following specifications, subject to the comments which follow:

Speed range: Accuracy: Threshold: 0 to + 5 knots + 0.2 knots + 0.02 knots Response time: 0.25 sec. Direction: -+ 7 degrees Depth: '0 to 42 feet

A single check of 7.5 knots was made in the 0 to 10 knot range. This was within specifications.

The sensing probe has no moving parts. It senses two orthogonal components of the average instantaneous current (in a plane perpendicular to the axis of the probe) in an area approximately 4.5 inches in radius. Each of the two pairs of sensing plates will give an essentially undistorted cosine response of flow not parallel to the plane of the plates.

Because of the great sensitivity and rapid response of the meter, the design of the mount must minimize structural responant frequencies (in situ) within the spectrum of interest. When this is not possible, on site observations can be made to record natural resonant frequencies of the mounting system.

The output level of the equipment. is virtually independent of temperature and salinity, although when employed in fresh water the signal to noise ratio decreases noticeably. There is no noticeable effect of the presence of local electrolytic potentials, but there is an indication that some factor in the local environment can create a zero offset. that must be detected and measured by 180 rotation of the sensor. A computer program easily normalizes such data.

Measurements made less than three feet from a sharp magnetic discontinuity will be unreliable. However measurements within one foot of the surface and one-half foot of a sand bottom remain within specified accuracy.

Input power variations of ± 20 volts or less do not affect the output. Minor (5%) variations from 60 cycles similarly cause no problem except perhaps in ancillary recording equipment.

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DOI

10.25777/s0r8-4a28

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