Acoustic level sensor never touches liquid
February 22nd 2007 A non-intrusive liquid level gauge from Gems Sensors & Controls, measures the level of fluid materials in plastic containers from outside the vessel, eliminating any chance of contamination.
Designed for in-vitri diagnostics, the ExOsense uses piezo resonant technology to measure level with very accurate, very repeatable results.
The unit has two parts, a sensor which is stuck to the outside of the wall of the vessel at the required height, and an electronic module with mini usb connector. The sensor incorporates proprietary transducer technology employing piezoelectric material. When piezoelectric transducer material is excited, it creates an acoustic signal as a function of the natural resonance of the material. ExOsense sensors generate this acoustic signal, direct it through the bottle wall and sense the reflected pulse.
The amount of energy that is reflected depends on this relative acoustic impedance of the vessel wall and its contents. Air has an acoustic impedance of 0, compared to 1.8 for the wall of a typical plastic bottle, so if the vessel is empty at the level of the sensor there will be a strong reflected signal. Water, for example, has an acoustic impedance of 1.5, similar to the bottle wall, so there will be little reflection. This enables the ExOsense to measure fluid levels to an accuracy of ±1.6mm, with a repeatebility of ±1mm.
The sensor has a very small footprint, and can be used with almost any size and shape of vessel, from small bottles to large tanks, and most plastic materials. Since it never comes into contact with the contents of the vessel, it eliminates any risk of contamination and the need for compatability testing. Application of the sensor is very simple: no special mounting is required as the units have a built-in-peel-and-stick adhesive pad. A connector plug is available to seal the unit when not connected to the control module, enabling bottles to be washed with the sensor in place.
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