GB1459825A - Device and method for detecting the degree of vacuum in container for products such as food products - Google Patents

Abstract

1459825 Gauging vacuum PLASMON SpA 4 Nov 1974 [5 Nov 1973] 47579/74 Heading G1G The degree of vacuum in a container is checked by electromagnetically inducing vibrations of a wall of the container, receiving sound waves resulting from the vibration, analyzing them to determine whether or not the air-pressure in the container exceeds a given value, sensing the presence of the container at the checking point, and producing a container rejection signal if the given pressure is exceeded or if the sensed presence is not accompanied by a received sound wave signal. In the Fig. 2 embodiment the caps of jars on a conveyer are caused to resonate by electromagnet TD 1 energized with frequency-modulated pulses. The resulting sounds pass up conduit 11 to transducer H1 whose output is filtered to pass only those frequencies characteristic of jars having insufficient vacuum. The filtered signal is rectified and, if above a threshold amplitude, actuates a jar-reject mechanism after a delay equal to the travel time of a jar from the checking point to the reject point. The delay is provided by a shift register. The filtered and rectified output of a second transducer H2 responsive only to ambient noise is subtracted from the rectified signal from the transducer H1 so that ambient noise picked up by H1 does not cause spurious rejection of jars. The presence of a jar at the checking point is also sensed to ensure jar rejection if the cap lid is distorted and so cannot resonate. Cooling of electromagnet TD1 is aided by heat dissipators 12.