Patent GB-890447-A (GB)
Title: Improvements in and relating to the testing of materials by spark-testing
IPC: G01N33/20
Filed: 1960-08-11
Abstract: 890,447. Photo-electric spark-testing of materials. HUTTENWERK OBERHAUSEN A.G. Aug. 11, 1960 [Aug. 12, 1959], No. 27813/60. Class 40(3). In a method of testing material, the material is ground superficially and the light emitted by the sparks flying off is evaluated photoelectrically. The invention is described as applied to the testing of steel and has particular application in the determination of the carbon content. The hot steel particles flying off react with the oxygen in the air to cause the particles to be destroyed in a series of bursts, the repetition frequency of which is a measure of the carbon content. By applying the output of the photo-electric cell to a counter through a circuit which passes only short duration impulses due to the bursts an indication of the carbon content is furnished. The arrangement is of application only where a specimen under test is compared with a standard. Where an absolute measurement is required, it is also necessary to make a measure of the total amount of material ground off in a test period. This may be effected by integrating the overall light emitted in the test period. This permits the ratio of the number of impulses to the total amount of material to be determined. A suitable arrangement is illustrated in Fig. 1 where the light from the sparks 3 is detected by a photo-electric cell and the cell output is applied to a circuit consisting of a transformer 6 and a capacitor 7. The transformer 6 passes only the short duration impulses which are applied through an amplifier 8 to a counter 9. The capacitor 7 provides a voltage representative of the integrated light which is applied through a D.C. amplifier to an indicator 11. Where greater accuracy is required an arrangement is described, Fig. 4 (not shown), in which the amount of material ground off is determined only from the light due to the smooth spark tracks, the light due to the bursts being ignored. This is effected by frequency selective amplifiers which allow impulses in the range 3-60 kc./s. to pass to the counter and impulses in the range 180-600 c./s. to pass to the integrator. An arrangement is also referred to (without giving details) in which the results are made independent of the absolute sensitivity of the measuring apparatus by determining the amount of material ground off by counting the smooth spark tracks. The arrangement may operate so that count of the counter for the short duration impulses due to the bursts is terminated when a predetermined number of spark tracks has been counted. It is stated that the influence of magnesium, silicon, chromium and tungsten may be determined by making light intensity measurements at various distances from the point of grinding. Reference is also made to the use of the colour of the emitted light. Differences in brightness levels may be determined by the use of amplitude filters. A portable photo-electric apparatus for mounting on a grinder is described, Fig. 3 (not shown), light from the emitted sparks being directed to the photo-electric cell by a concave mirror. A filter restricted to the red end of the spectrum may be used to eliminate the effects of daylight.