Remote measuring telescope determining frequency of oscillating object - has twin antiphase detectors in image plane connected in arms of Wheatstone bridge

摘要

The remote-measuring telescope for determing the frequency of oscillation of swinging overhead cables comprises a standard field telescope in which the eyepiece is replaced by a photoelectric detector. The detector consists of a circular plate at right-angles to the longitudinal axis of the telescope (5). The plate carries two triangular photo-resistors (7-8), both of which are equal-sized right-angled triangles forming a parallelogram at the centre of the plate and in the image plane of the telescope. The anti-phase signals from the resistors due to the movement of the image, are fed to a Wheatstone bridge (10). A frequency-indicating instrument connected across bridge diagonal (15) displays the rate of swing of the image (9).