Operation principle

A cheap and extremely simple fill level inspection is based on a transmitter and receiver of LASER light, with bottles passing between. The system Projector-Receiver is typically set at the height of a low filled bottle, low filled but still into those limits allowing it to be produced and sold.  The receiver system switches when no liquid absorbs the thinly collimated beam of light.


Its operation is simple but the inspection performances are quite poor:

  • typical ~3 mm of underfilling guaranteed 99.9 %;
  • false rejects associated to the inspection are <0.1 %; 
  • performances depend on container's colour;
  • can’t be adopted on foaming beverages;
  • can be exclusively adopted on water based beverages; 
  • container shape in the area of inspection has to be regular.

To have a quantitative idea: a column 3 mm tall of liquid, in a bottle whose capacity is  ≤500 ml, corresponds to >7.5 ml, which is a quite common legal minimum content allowing product sale-ability.   Meaning that a LASER-inspected filling level does not assure saleability to >99.9 % of the containers, when the false rejects are yet as high as <0.1 %, 1 non-defective bottle in the falsely rejected.   The real percentage for a container 500 ml or smaller is lower.   As noted above, the inspection performances are related to the colour of the container: it can be coloured but however transparent, to avoid LASER light diffraction and refraction spurious effects in the container itself, emulating liquid height differences.  Also, the container shape in the neck area of inspection has to be regular, so to limit notoriously light diffraction and refraction negative effects.  

The figure above shows how many of the bottles’ design neck sidewall designs cannot be practically used, apart to be ready to accept huge false rejects OR lower defects’ detection rate digits, say lee Quality delivered to the Market.    It is a fact that bottles’ neck area is particularly prone to an irregular distribution of the glass or, plastic resin (e.g. ellipsoidal distribution), also when the neck area design is regular.  The sum of all of the above named limits buildups that unsatisfactorily high 0.1 % false rejects ratio.   It is a fill level technology cheap to acquire and particularly reliable to the Bottling Line Production  Operators: the total know-how requested to manage it with the inspection results cited above, is limited to the capability to adjust mechanically up or down the fill level inspection bridge during change-overs.   Unnecessary skills in Optoelectronics on the opposite vital when managing, e.g. an Optic fill level inspection based on a CMOS or CCD camera.


  • extremely extended lifetime;
  • extremely cheap price;
  • extremely reliable to Production Operators;
  • no necessity for a specific training of the Plant Maintenance Staff;
  • mechanical robustness.


  • poor inspection performances;
  • the container has to be non-labelled;
  • the container has to be non-foilled;
  • the container has to be transparent;
  • the shape of the container neck area has to be regular.

diffraction reflection refr med

The wave packets corresponding to water molecules are small and their energy density extremely high, when compared with the wave packets of a common green colour LASER.  The interaction forcedly and negatively complicated by multiple diffractions, refractions and reflections whose superposition minimise the imaging or inspection Signal-to-Noise ratio

laser med

LASER technologies are applications of the photoelectric effect discovered by Albert Einstein, published in 1905 on side of the much more famous Theory of the (Special) Relativity.  LASER applications were originally only scientific and widened later to the industrial, like the LASER Fill level Inspection hinted above.   In the figure aside an experiment by the USAF employing a power LASER. Models much more powerful than the (2 - 10)mW models adopted in the Electronic Inspectors and barcode Scanners.  A visible difference lies in the fact the Industrial models we use in the Beverage Bottling Controls never require Operators to dress the safety protective googles.  Yet the military applications are negatively conditioned by the characteristic of all electromagnetic radiations, LASER wavelegths included, to be rapidly diffracted in the medium. Because of this reason, as an example, the newly installed LASER guns on board US Navy and Russian Navy warships, are guaranteed adapt to a task to engage just extremely close targets (Image under Public Domain, CC-BY-SA 3.0)

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