GB814072A - Improvements in and relating to electrical apparatus - Google Patents

Abstract

814,072. Infra-red testing arrangements. MERVYN SOUND & VISION CO. Ltd. Sept. 30, 1955 [July 1, 1954], No. 19305/54. Class 40 (3). An infra-red testing device for determining the ability of a test sample 15 to pass radiations of varying wavelengths includes means compensating for variations in source output and response device sensitivity. The source 10 is mounted inside a chopper drum 11 driven by motor 12 and having a castellated interrupting part (see Fig. 1A). Radiation passing out of the drum is directed by mirrors 13 and 14 through the sample 15 and a correcting filter 16 to a slit 17. The energy from slit 17 is collimated by mirror 18 and directed to diffraction grating 19. Energy of a selected requency reflected by the grating is directed by mirror 20 through slit 21 on to mirror 22 and thence to radiation responsive device 23. The device 23 is also responsive to energy from the source 10 passing through slits 25 in the drum 11 and reflected by mirror 26 through adjustable slit 27. The slots 25 are so positioned that " reference " illumination through them only reaches device 23 when the beam through sample 15 is obstructed. The electrical output of the device 23 is amplified at 24 and fed to two output devices 32, 33 through a commutator switch 28 driven synchronously with the drum 11 by motor 12. This switch directs output pulses corresponding to radiation passing through sample 15 to output device 32 and those corresponding to radiation passing through slots 25 to device 33. Device 33 incorporates an integrator and is used to control the gain of amplifier 24 to compensate for any variation in response due to any variation in the output of the source or the sensitivity of the device 23. Output device 32 also includes an integrator and feeds an indicating instrument 36 and recorder 37 through an isolating stage 35. The recorder may co-operate with a drive rotating grating 19 so that a record of response over a waveband can be made. In a modification (Fig. 2, not shown) alternate half-cycles of the output of amplifier 24 are applied across a load resistor and the output across the whole resistor taken during reference pulses and integrated. The output from an adjustable tapping point on the resistor is taken during the times that radiation is received through the sample and is also integrated. The output of the two integrators are compared and used to control the positioning of the tapping point to obtain equal outputs and also an indicator and/or recorder.