Patent GB-600467-A (GB)
Title: Electrical apparatus for testing metals
IPC: G01N27/90
Filed: 1944-11-09
Abstract: 600,467. Determining physical qualities of materials ; cathode-ray oscillographs. STANDARD TELEPHONES & CABLES, Ltd. Nov. 9, 1944, No. 22063. Convention date, Nov. 9, 1943. [Class 37] Metals are tested by passing them through an inductance coil and observing the effects produced upon a high-frequency oscillatory wave that is modulated by low-frequency oscillations. The high-frequency oscillations are amplified after the low-frequency components have been removed, and the amplified signal is applied to the vertical deflection plates of an oscillograph, the signals on the horizontal deflection plates being synchronized with respect to the vertical signals. The specimen to be tested is inserted into an inductance coil 10 of large diameter and short axial length which forms part of a high-frequency oscillator 1-12. The oscillations produced by this are modulated by low-frequency oscillations produced by an oscillator 67-79 and an amplifier 81-86. The modulated output from the oscillator 1-12 is passed through a push-pull amplifier 20, low-frequency remover 29, 30 and balanced phase inverter 33, 34 to the vertical deflection plates of a cathode-ray oscillograph 45. The output of the low-frequency oscillator 67-79 is passed through an amplifier 103, phase-shifter 99-102, and balanced phase inverter 106-112, to the horizontal deflection plates of the oscillograph 45. The output of the amplifier 20 is passed by a lead 118 through a low-frequency remover 122, H.F. amplifier 120, detector 128, high-frequency filter 130 and low-frequency amplifiers 131, 135, the output being the low-frequency sinusoidal envelope of the modulated high-frequency signal fed to the amplifier 120. A low-frequency signal of the modulating frequency is fed from the amplifier 103 by a lead 119 through a lowfrequency amplifier 141 and phase-shifter 145- 148 to a mixer 151-153 where it is mixed with the envelope voltage from the amplifiers 131, 135. The output of the mixer is passed through an amplifier 158, network 161 for rejecting the second harmonic and push-pull amplifier 103-4, to the vertical deflection plates of a second cathode-ray oscillograph 167, the horizontal deflection plates of which are supplied with a frequency of 2000 cycles from an oscillator 180-184 and push-pull amplifier 188-9. The output of the amplifier 158 is also coupled to the grid of a grid-controlled gas discharge tube 172, the anode of which is connected to the grid of a triode 173. This operates relays 176, 177 when the output voltage of the mixer is above a predetermined value. The relays may control a circuit for operating a sorting device for the specimens passed through the coil 10. With an unwanted specimen in the coil 10 the oscillator 1-12 is adjusted until the oscillations are almost quenched, as shown on the oscillograph 45. The specimen is then removed, a good specimen substituted, and the gain control adjusted until full scale deflection is shown on the oscillograph 45. With no specimen in the coil 10, the phase-shifter 145-148 is adjusted until the pattern on the oscillograph is a straight line along the X-axis, indicating that the inputs to the mixer 161-153 are balanced. A sample is then inserted in the coil 10, thereby altering the circuit loss with a change in amplitude of the high-frequency oscillations. The modulated signal fed to the mixer 151-153 no longer balances the output from the phaseshifter 145-148, so that an output signal due to this unbalance is applied to the oscillograph 167 and produces a rectangular pattern thereon.