GB617897A - A new or improved pyrometer - Google Patents

Abstract

617,897. Pyrometers. STOKES, C., and ROBERTS, M. H. Feb. 14, 1946, No. 4722. [Class 40 (iii)] In a pyrometer a pencil of radiation from a hot body is directed on a photo-cell, the output of which is varied at a predetermined frequency, amplified and used to operate indicating, recording, or automatic control means responsive to the amplifier output. Fig. 1 of the drawings accompanying the Complete Specification shows a hot body 1, the radiation from which is focused by lens 2 on the screen 5 having a circular hole 4 behind which a motor-driven rotating shutter 6 interrupts the radiation passing to photocell 9, at about 200 c.p.s. Suitable filters may be inserted to pass only the required range of radiation wavelengths, which may be confined to the infra-red, The photo-cell VO output is applied to the input of a resistance - coupled negative-feedback amplifier V1-V4 (Fig. 2) having a variable attenuator R17-27 and supplied with stabilized H.T., the amplified signal being rectified by a double diode V5, the output of one section biassing the grid of a valve V6 having a measuring instrument 16 connected in the cathode circuit. The other diode section rectifies only a signal exceeding its variable positive cathode bias, and its output supplies the grid of a valve V7 in the anode circuit of which is connected a relay L2, operating at a given temperature, to switch off a H.F. furnace, or to change a workpiece, the radiation from which falls upon the measuring photo-cell. The instrument may operate a pen recorder, and the indicating means may have an expanded scale covering a small temperature range, or a logarithmic scale. The Provisional Specification and accompanying drawings (not shown) describe an amplifier differing in detail from the above, and furnace control by means of a gas-filled triode operated by the amplified alternating photo-cell signal.