Patent GB-912546-A (GB)
Title: Improvements in radiation pyrometers
IPC: G01J5/54
Filed: 1959-08-21
Abstract: 912,546. Radiation pyrometers. BODENSEEWERK PERKIN-ELMER & CO. G.m.b.H. Aug. 21, 1959 [Sept. 23, 1958 (2)], No. 28619/59. Class 40 (3). In a radiation pyrometer a sharply focused real image of the source of the radiation to be measured is formed on a diaphragm through a small aperture in which a portion of the radiant energy passes to a radiation detector. With this arrangement the calibration of the instrument is independent of the distance from the source since variation of the energy from the source according to the inverse square-law is compensated by a variation in the proportion of energy in the real image which passes through the aperture due to the variation in area of the real image with variation in distance of the source. As shown in Fig. 1, a lens 1 forms a real image of the source of radiation on an operatured diaphragm 2 and a second lens 9 forms an image of the aperture, via a beam splitter 6 producing two beams 7 and 8 on photo-electric cells 10 and 11 respectively. An adjustable wedge filter 14 for initial adjustment and a filter 13 having a transmission range appropriate to the black temperature of the source are included in beam 8 whilst beam 7 includes a filter 12 appropriate to the colour temperature of the source. Both beams are alternately interrupted by a semicircular rotating mirror 18 (see Fig. 2) which reflects radiation from a reference source 15 on to the cells 10, 11 during the periods of interruption of the beams 7 and 8 respectively. Any difference between the intensity of the source and reference radiation beams then produces a pulsating signal in the photo-electric cells 10, 11 and such signals are employed via servo control devices 25, 26 to adjust the positions of comb-shaped diaphragms 23, 24 in the reference beams to equalize such intensities. The amounts of such adjustments are then measures of the colour and black temperatures of the source. The latter temperature is recorded by a device 27 and a " quotient " forming circuit 28 supplied with signals related to the adjustments of the diaphragms 23, 27 feeds a recording device 29 for the colour temperature. In operation, if the distance between the source and lens 1 varies, the proportion of the energy in the real image (which should be sharply focused) on diaphragm 2 which passes through the (constant size) aperture varies in an inverse manner so that, since the total energy in the real image varies inversely as the distance of the source from lens 1 and the area of such image also varies inversely as this distance, the energy in the beams 7 and 8 is independent of such distance. For initial adjustment of the apparatus some of the energy is directed by a beam splitter 4 on to a ground glass viewing screen 3. Alternatively, the diaphragm 2 may be slightly inclined to the axis of lens 1 and energy scattered from its surface directed via a suitable optical system on to a viewing screen (Fig. 4, not shown). The filters 12, 13 are preferably of the interference type and the beam splitters 4 and 6 preferably consist of surfaces provided with uniformly distributed zones of totally reflecting and totally transmitting layers.