Non-contact Sensor has lots of bottle.
A US company has developed a sensor that detects the
presence or absence of liquid at a specified fill level inside
a plastic bottle or container, without it having to be opened.
Developed for the in-vitro diagnostics market, it is ideally suited for
systems filling and handling bottles of aggressive chemicals, those
containing liquids deemed to be potential biohazards, and situations
where it is essential to avoid the possibility of contamination.
The 'ExOsense' is a PVDFbased ultrasonic piezoelectric transducer
with a 'Rexolite' lens that sticks to the outside of a bottle when an
adhesive cover is removed. The amount of acoustic signal that is
reflected from the inside surface of the bottle depends on the
impedance mismatch between the bottle material and whatever is
inside it. If the bottle contains liquid, the acoustic impedances are
similar, 1.8 and around 1.5, and most of the ultrasound signal passes
into the liquid without being reflected. Whereas if there is no liquid,
the acoustic impedances of the bottle and air are sufficiently different,
1.8 and 0, that most of the ultrasound energy is reflected back to the
transducer.
The transducers are sufficiently low cost
that they can be considered disposable
in some applications. They are separate
from the electronic switch units, and are
attached by a cable fitted with a miniature
USB connector, which plugs into the
transducer head.
The lens focuses the ultrasonic signal to
a point on the inside of the bottle. The
system requires no calibration: it is
'plug and go'. It works with bottles
made of polyethylene, polypropylene,
polysulfone and polycarbonate but not
those made of PTFE or any foamed
core plastics. Heads are available for
flat-sided and round bottles and
containers with a minimum bottle diameter of 50.8mm. WaIl thickness
can be from 0.5mm to 3.8mm.
Response time is less than 100ms and the transducer works over
the temperature range 0°C to 70°C. Sealing is to 1P65.
Power requirements are 4.75 to 5.25V DC or 6 to 32V DC. Power
consumption is 50mA max and output configuration is open collector,
40mA max.
Fluids whose levels can be detected include: reagents; wastes;
diluents; detergent washes; coolants; saline; or pure water. The
device is used in equipment for clinical chemistry, haematology,
immuno-chemistry, histology, medical laser systems, haemodialysis
and cytology.
The device is available worldwide from Gems Sensors.
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April 2006
