GB968561A - Electro-acoustic measuring apparatus - Google Patents

Abstract

968,561. Ultrasonic analysis of materials. CHESAPEAKE INSTRUMENT CORPORATION. April 27, 1962 [June 12, 1961], No. 16095/62. Heading H4D. The velocity-temperature relationship of ultra-sonic waves in a medium is utilized to determine the amount of a particular substance forming part of the medium. The invention is described in connection with the determination of the butter fat (BF) content of milk, the velocity-temperature relationship for ultrasonic waves in which is shown in Fig. 1 for various proportions of BF, " solids-not-fat " (SNF) and water (H 2 0). By measuring the velocity of two (different) temperatures T 1 , T 2 , the slope of the characteristic and hence the BF content may be determined. In Fig. 2, which shows the arrangement employed for carrying out the invention, milk at temperature T 1 (monitored by device 32) flowing through a conduit 30 passes a first velocity measuring position comprising an electro-acoustic transducer 38 and an acoustic wave reflector 40 and then passes via a heating element 34, which raises the temperature to T 2 (monitored by device 36) to a second velocity measuring position comprising an electro-acoustic transducer 42 and an acoustic wave reflector 44. The two transducers are energized via respective blocking oscillators 46, 48, both preferably operating on the same frequency (> 500 kc./s.) and so arranged that after a burst of frequency has been produced the oscillators stop until triggered by a pulse derived by reflection of the transmitted energy by the reflectors 40, 44. The repetition frequencies f, f 1 of the oscillators is then a measure of the velocity of the acoustic waves at the two positions and by supplying the two frequencies to a mixing circuit 64 and selecting the difference frequency from the mixer output a signal is derived which is proportional to the slope of one of the curves (Fig. 1) and hence to the BF content of the milk. Such signal is supplied via a device 68 which produces a steady state signal for application to an indicator 72 and for measurement of the frequency f, a similar arrangement employing the elements 52, 56 is employed. The frequency f 1 on line 62 may also be indicated by a further similar arrangement. The acoustic reflectors 40, 44 may be replaced by receiving transducers, the outputs of which are arranged to trigger the oscillators 46, 48 and instead of making the two velocity measurements on a single milk sample two separate samples may be employed.