Patent GB-1011673-A (GB)
Title: Improvements in or relating to the photography of moving particles
Inventor: DOMBROWSKI NORMAN
IPC: G03B15/16
Filed: 1962-08-15
Abstract: 1,011,673. Photographing moving particles. CENTRAL ELECTRICITY GENERATING BOARD. Sept. 11, 1963 [Aug. 15, 1962], No. 31364/62. Heading G2A. [Also in Divisions H4 and F4] To obtain a stationary image of a particle moving in a duct 10 in order to photograph it, a repetitive light source 12, e.g. a high voltage electrical discharge between steel electrodes 13, Fig. 2, is focussed on to the moving particle by means of an optical system comprising a double reflecting mirror system and a microscope objective 36 Fig. 3, and the optical image thus formed is focussed on to the photocathode of an image converter tube 37, the electron image caused thereby being focussed on to a phosphor screen 40 and the movement of the particle being cancelled by scanning means which apply a deflection to the electron beam thus forming a stationary electron image of the particle on the phosphor screen. In the embodiment, a cathode ray display tube 55 fed from a television camera 54 which scans the screen 40 is photographed, the image comprising a number of successive images superimposed one on another on a single frame with the particles as light images on a dark background. Control pulses from a generator 16 which pass through a pulse gate 17 having associated with it a timing unit 18, i.e. a chain of pulses of known length or a continuous series of pulses, are fed through a pulse amplifier 19 to a hydrogen thyratron spark control unit 15 which controls the initiation and duration of the discharge between the electrodes 13. The pulses are also fed to a delay line 21 which is adjusted so that the control pulses fed to the remainder of the equipment occur when the flashes reach maximum intensity. The light from source 12 passes through the optical system being brought to a focus at the location of the moving particles, e.g. water drops, in the duct 10, which has two parallel windows 11 formed of optical flats and forms an image magnified 25 times on the photocathode of tube 37. Tube 37 gives a further magnification of 4 times and has electromagnetic coils 38 energized from source 39 for focussing the electron image from the photo cathode on to the phosphor screen 40. The image of a moving particle is held stationary on screen 40 by applying a linear sawtooth scanning waveform synchronized with the repetitive frequency of the light source to electromagnetic deflection coils 41. This scanning waveform is produced in scan pulse amplifier 43 which is triggered by pulses from generator 20 to which is applied pulses which have passed through delay line 21. The duration of the scan fixed by generator 20 is held constant and the amplitude of the scan is adjusted by control unit 49. When the amplitude has been set to hold the image stationary the amplitude of the scanning waveform given by indicator 60 is a measure of the velocity of the particle. The output from the delay line 21 is also applied to a pulse amplifier 52 to give a brightening pulse which is applied to the grid of the tube 37. The television camera tube 54 is also synchronized by pulses from the delay line 21 and the output from the camera is displayed on three separate display tubes in display units 55, 56 and 57. The display unit 55 contains a photographic camera and the display tube has a short persistence phosphor or high luminous intensity. An imate inverting stage is provided so that the image on the film emulsion consists of white spots on a black background to enable a number of exposures to be superimposed on one frame of the film e.g. 25 exposures. The display unit 56 has a display tube similar to that being photographed and the display unit 57 has a long persistence phosphor which in effect integrates the display. Instead of using an image converter tube the image may be held stationary by a rotating mirror. The sizes of the particles can also be measured.