US 4,398,821 A · Instrument for measuring angles

Abstract

An instrument for measuring sun elevation which includes a structure rotating at a controlled, constant speed. By means of a magnet on said structure a pulse is produced once per revolution. This pulse forms a datum point and can coincide with the horizon. A further pulse is produced by sunlight reflected onto a photo-sensitive device by a mirror rotating with said structure. An oscillator and divider produces a train of pulses, and there is a counter which counts the number of pulses of the train between the datum pulse and the further pulse. As the number of pulses counted is a measure of the time between the further and datum pulses, and this time is a measure of the angle through which said structure has rotated, and this in turn is a measure of the angle between the sun and the horizon, the number of pulses counted can be converted electronically into a read-out of the sun angle. In another form, specifically intended to measure the elevation of a star, the datum and other pulses are produced by rotation of discs, each having a slot therein. A light is shone on each disc and there are photo-sensitive devices normally blocked-off from the sources by the discs. As the discs rotate, the photo-sensitive devices produce pulses. One light source and photo-sensitive device produces the datum pulse and are maintained in a fixed position. The other light source and device move as the instrument is tilted upwardly. This causes the spacing between the two pulses to vary in dependence on the tilt of the instrument.

Claims5

Dependent claims

A navigational instrument for determining the angle of elevation of the sun, the instrument comprising a rotatable structure including means for producing a reference signal each time that a specific part of the rotatable structure passes a reference point;

photo-sensitive means for generating an indicator signal when light from the sun falls on it;
image-forming means, forming part of said rotatable structure, for causing a succession of images of the sun to fall onto the photo-sensitive means, thus causing a succession of indicator signals to be generated by said photo-sensitive means;
means for detecting the time interval between an indicator signal and a reference signal and for generating a signal proportional to said interval;
a telescope through which the horizon and the image produced by said image-forming means can be viewed to enable a user to place the axis of the telescope, the sun and the point on the horizon at which he is looking in the same vertical plane;
and manually operable switch means for causing said signal proportional to said time interval to be generated.

2 more elements

Dependencies are inferred from the claim text.

Instrument for measuring angles

Life of this patent

Instrument for measuring angles

Life of this patent

Abstract

Claims5