Patent GB-1046443-A (GB)
Title: A method of and apparatus for assessing the quantity of inclusions of foreign material in solid specimens
Inventor: MELFORD DAVID AUSTIN
IPC: G01N23/203
Filed: 1962-04-24
Abstract: 1,046,443. Local viewing systems using scanning. T.I. (GROUP SERVICES) Ltd. April 23, 1963 [April 24, 1962], No. 15481/62. Heading H4F. [Also in Divisions G1 and G4] To assess the quantity of inclusions of foreign material in a solid specimen, a beam of electrons is generated and focused on to the surface of the specimen and caused to scan the surface, and an electrical signal is produced in response to the back scatter of electrons from the surface as the surface is scanned. In addition or alternatively an electrical signal or signals is or are produced by an X-ray spectrometer responsive to X-rays produced when the beam strikes the specimen and an output signal is produced which is a measure of the quantity of inclusions of foreign material in the area scanned by the beam. As shown in Fig. 1 a beam of electrons 3 from a gun 1 and an electromagnetic condenser lens 2, is focused by a lens 4 on to the flat surface of one of a number of specimens 5 supported on a rotatable table 7, and scans a region on the specimen under the action of scanning coils 6. Back scatter from the surface is detected by a scintillation counter and photomultiplier 8 and X-rays of different wavelengths are detected by a number of X-ray spectrometers 9 of the crystal type each producing an electrical pulse as the beam passes over an inclusion containing an element of which the characteristic wavelength is that to which that particular spectrometer is adjusted. A corresponding pulse is produced by the scintillation counter and photomultiplier 8 as an inclusion or a hole in the surface is scanned. Simultaneous pulses produced by combinations of the X-ray spectrometers are used to identify the composition of the inclusion causing the X-ray emission. When steel is examined, a pulse received from the scintillator alone without any corresponding simultaneous signal from any of the spectrometers indicates either the presence of ferrous oxide or a hole and not an inclusion. In the arrangement shown in Fig. 2 a pre-recorded sine wave signal on a track D1 of a magnetic drum store D rotated at constant speed by a motor M is picked up by a head H, amplified and used to generate a saw-tooth signal which controls the line scanning coils L for the electron beam. The saw-tooth signal is differentiated to produce a pulse at the end of each revolution of the drum D and these pulses actuate a monostable multivibrator MV of which the output is integrated to form a signal increasing stepwise to feed the frame scanning coils. These pulses are also counted by a counter and after 300 pulses the stepwise signal is returned to zero and the motor M driving the drum is switched off and in addition an electric motor (not shown) is switched on to turn the table 7 bringing another specimen under the path of the beam. The pulses from the scintillator 8 are fed to a pair of pulse height discriminators T in the form of Schmitt trigger circuits set respectively to different levels to provide the necessary discrimination between for example sulphides and silicates when steel is examined. The outputs of the trigger circuits together with the outputs from the X-ray spectrometers which are fed through pulse-shaping Schmitt triggers (not shown) are fed to a known logic circuit system E which includes coincidence circuits to determine from the combination of signals from the spectrometers what the composition of the inclusions is, and it has seven output channels the output signals of each being in the form of pulses, each pulse occurring when the beam passes over an inclusion of the kind associated with that output channel. The length of each pulse is dependent on the width of the inclusion in the direction of the scanning lines. The outputs are fed through a multi-pole multi-way selector switch S to an analysis circuit A which utilizes further tracks on the drum D to (1) count the total number of inclusions present in the scanned area, (2) count the number of inclusions in each of a number of size ranges by means of pulse height discriminators, (3) count the number of inclusions greater than a certain size, (4) count the number of inclusions (also, if required, by size) of a selected composition, (5) obtain an indication of the average size of inclusion of a given type or any type, (6) determine roughly the shape of inclusion by measuring their aspect ratio. The circuit can alternatively indicate the total quantity of inclusions present as a percentage of the total area scanned. The magnetic drum may be replaced by an electromechanical or electronic delay line or an endless loop of magnetic tape. The circuit A may include binary stores so tha t at the end of a scanning operation the informat ion stored may be read out sequentially by means of a multiway switch so that it can be viewed on an illuminated display or printed out on paper tape P. In addition, a monitoring cathode-ray tube screen CR carrying a raster representing the area scanned may be provided, the brightness of the spot being controlled selectively by any of the signals from the circuit A, so that it may display the distribution of inclusions of any selected type or size. The information produced by the circuit A may be shown in other manners such as on magnetic tape, punched cards or on punched tape for analysis in further machines or displayed as histograms on cathode-ray tubes.