The Development of a Laser-Operated Scanning Rod Gauge

Abstract

Unsatisfactory tests on a rod gauge using bar radiation led to the adoption of a scanning gauge using back illumination. The chosen design employs a helium-neon laser and a multi-face mirror rotated by a synchronous motor driven by a crystal-controlled oscillator. Digital counting techniques are employed to determine bar diameter to better than ± 0.001 in. (±0.025 mm) over a range from 0.2 in. (5 mm) to 1.0 in. (25 mm). In the course of laboratory and on-site testing improved techniques were developed to overcome errors due to rod movement and interference by dirt and water. Results better than required by the specification were obtained. Experience has led to the adoption of an instrument giving a digital output updated every 0.4 to 0.8 s. for indication and a fast (0.01 s. response time) instrument giving an analogue deviation signal for control.