Patent GB-783524-A (GB)
Title: Means for measuring and/or recording the air gap between the parts of a machine
Inventor: BRAUNERSREUTHER EBERHARD
IPC: G01B11/14
Filed: 1954-05-21
Abstract: 783,524. Photo-electric apparatus. SIEMENS-SCHUCKERTWERKE AKT.-GES. May 21, 1954, No. 15101/54. Class 40 (3). [Also in Group XXXVIII] Apparatus for measuring the width of an air gap between parts of a machine comprises means for projecting radiation through the gap to form an optical image thereof, means for scanning the image along the width dimension and for generating an electric signal dependent on the duration of a scan, a parameter of which signal depends on the width of the air gap but is independent of the radiation intensity, and means for measuring either the value of said parameter or of some parameter of an electrical output from a converting arrangement to which the signal is applied. The air gap (Fig. 1) is illuminated by a beam of light formed by lens 5 and a image of the gap is projected by lens 7 and prism 8 on to a disc 12 provided with a radial slit or equal width slits, which is rotated at constant speed in front of photo-cell 10, the periods of illumination of which are therefore dependent on the width of the image. The output pulses from the cell which vary in amplitude due to non-uniformity of the image forming beam or to variation in the light source intensity and absorption of the light path, are applied to the input of a non-linear network, such as a thermionic valve amplifier driven to saturation by the pulses, so that its output consists of a series of voltage pulses of constant amplitude but of the same duration as the pulses from the photo-cell. Alternatively the pulses from the cell are fed to a non-linear network consisting of reverse-connected rectifiers in parallel. These voltage pulses are averaged at 17 (e.g. by an R.C. network) and the average voltage which is proportional to air gap width is indicated by meter 18. The saturated amplifier may be replaced by a relay operated by output pulses from the photo-cell to connect an R.C. averaging network periodically to a D.C. source, the mean condenser voltage representing the air gap width. In a further embodiment a modulated radiation source is used, the modulation frequency being much higher than the rotation frequency of the disc, to which it is preferably locked, so that the air gap image is periodically illuminated. The relative frequencies are suchthat during passage of the slit across the image the latter is illuminated a number of times proportional to the width of the inage and the number of consequent pulses from the photocell is counted, preferably by an electronic counter of the decade type driven directly by the photo-cell output. Alternatively as in the first embodiment the pulses may be used to produce further constant amplitude pulses, this time of uniform duration, which are integrated to give an output voltage proportional to the number thereof. The radiation used may be light as described, or penetrating radiation such as γ-rays, e.g. from isotope radiators, in which case no windows in the turbine or other machine casing would be necessary, appropriate image forming and radiation directing and detecting means replacing the prisms and lenses used with light.