Patent GB-644983-A (GB)
Title: Improvements in and relating to supersonic testing apparatus
IPC: G01N29/11
Filed: 1945-07-23
Abstract: 644,983. Feeding, drafting, and testing textile laps. BRITISH THOMSONHOUSTON CO., Ltd. July 23, 1945, No. 18792. Convention date, July 27, 1944. [Classes 120(i), 120(ii) and 120(iii)] [Also in Groups XXXV and XXXVIII] In a testing device comprising means for transmitting supersonic waves through a test body and receiving the waves, means is provided for conveying across the path of the waves a test body comprising a plurality of fibrous particles bound together or suspended in a carrier, such as textile fabric or paper pulp, and the receiving means are adapted to determine the intensity or magnitude of the received waves, the arrangement being such that the test body is not contacted by the transmission and receiving means during the test, and that the waves are either passed directly through the body to a receiver, or are reflected by a backing plate in which the body lies before being passed to the receiver. As shown, a continuous length of paper pulp or matted cotton fibres 10 is fed by rollers 11, 12 between a mutiple crystal transducer 3 and receiver 5. An oscillator 1 vibrates the crystal 3 to produce supersonic vibrations which are passed through the fabric &c. and received by crystal 5. The detector circuit includes an amplifier 7, a battery 9, and a d.c. instrument 8, such as a valve voltmeter, which indicates the amount of energy received by the crystal 5. The roller 11 is driven by a motor 13 the speed of which is manually controlled and the roller 12 is driven by a motor 14 having a speed-adjusting device 17 controlled by a reversible motor 18 which is controlled by the instrument 8. The thickness of the fabric 10 thus controls the amount of energy reaching the instrument 8, and the latter controls the speed of the roller 12 which stretches the fabric to vary the thickness thereof. Since vibrations in the supersonic range are unaffected by the moisture content of the material to be tested, if moisture content is to be accounted for, a second arrangement utilizing vibrations of 1000 cycles per second can be used in combination with the apparatus described, a single instrument giving a differential measurement of the two detector outputs in terms of moisture content. A cotton flannel diffuser may be arranged between the transmitter 3 and material 10. In a modification, the fabric 10 to be tested is compared with a stationary sample length of standard fabric, means being provided for directing the supersonic vibrations first on the sample and then on the fabric 10, and the difference in energy absorption is used to control the speed of the stretching roller. The vibrations pass through the fabric and sample and are reflected by glass or metal backing-plates on to the receiver crystal, which is moved into receiving position in unison with the movement of the transmitter crystal. Several transmitters and receivers may be used, arranged on an endless chain reciprocated by a solenoid arrangement controlled by motor-driven control disc. A rectifying detector, to which current is supplied alternately by the receiver for the sample and the fabric, supplies each current to an integrating condenser, these condensers being connected to a balancing, control bridge and an indicating control instrument. The control instrument operates a reversible motor to balance the bridge and to regulate the speed of a stretching roller for the fabric. The thicknesses of the sample and fabric are thus compared, and the fabric thickness is regulated to the thickness of the sample. The balancing control device may include a recording means comprising a pen which records on a moving chart the vibrations in thickness of the fabric 10 as compared with that of the standard sample. Limit switches are embodied in the recording-device to stop the machine if variation between fabric 10 and sample is too great.