Pressure monitoring

Apparatus for monitoring the pressure within a sealed container, the apparatus comprising:

• (a) a combined closure means and pressure sensor including:
• a closure member for sealingly closing an opening of the container, said closure member having first and second oppositely disposed sides which, in use, are respectively disposed inside and outside the container;
• a sealed, expansible, capsule secured to the first side of the closure member, said capsule being arranged to expand if the pressure within the container falls;
• a movable member coupled to the capsule and disposed so that expansion of the capsule moves the movable member with respect to the first side of the closure member;
• wherein said capsule contains an acoustically transmissive liquid disposed between the movable member and the first side of the closure member;
• and
• (b) means disposed outside the container for directing ultrasonic pulses into the second side of the closure member and towards the first side thereof and thence into the container, said directing means including means for sensing said ultrasonic pulses transmitted into the container and for detecting changes in the position of the movable member with respect to the first side of the closure member, said sensing means includes means for receiving echo pulses which have been reflected back through the closure member, whereby in response to each ultrasonic pulse directed into the closure member, a first echo pulse is received by said sensing means from the first side of the closure member and a second echo pulse is received by said sensing means from the face of the movable member facing the first side of the closure member, the temporal spacing between each first echo pulse and its corresponding second echo pulse being representative of the spacing between the movable member and the first side of the closure member and thus representative of the pressure within the container.