Fill level inspection

Links to the pages:


Fill level inspection and closure presence inspection were the first inspections conceived for Full Bottles, equipping the most modern Beverage Bottling Lines of forty years ago, when they were commonly named controls.  We start here a chapter in several sections devoted to the technologies existing to inspect the fill level of all possible kinds of container.   Glass, metal or PET bottles, cans or kegs, by mean of all actually existing techniques:

  • X-rays, with single bridge, for under filling;
  • X-rays, with single bridge, for under and over fill level;
  • X-rays, with two inspection bridges (under and over fill);
  • Gamma-rays, with single bridge, for under filling;
  • Gamma-rays, with two inspection bridges (under and over fill);
  • High Frequency, for still beverages;
  • High Frequency, for foaming beverages;
  • High Frequency, with thermal compensation;
  • LASER under filling level;
  • Infrared filling level;
  • Optic, with CMOS or CCD camera.


The observed performances of the fill level inspection, whichever the Technology, in terms of  defects' detection ratio and false rejects’ ratio, applied to a statistically significative population of containers, are heavily conditioned by the constancy of several factors.   The common factors, those negatively affecting the inspection, whatever its Technology, are:

  • beverage temperature, affecting the height of the column of liquid in the neck of the bottle or in the head space of the can or keg;
  • containers' speed, preventing a tilted upper surface of the liquid in the container, for an Electronic Inspector impossible to reconduct to a definite level for the beverage;
  • physical properties of the container (e.g., irregularities on the container density in the area of inspection, like ellipsoidic rather than circular bottle necks);
  • chemical properties of the container (irregularities in the container molecular structure, in the area of inspection);
  • foaming, affecting the beverage in the neck and head space area of the container.

As a consequence, the Electronic Inspector’s performances named:

  • false rejects’ relative ratio %;
  • defects’ detection ratio (or, hit ratio) %;

in general, whatever the technology we choose to check containers' fill level, cannot be measured at all during: 

  • Filler or Labeller Machines ramp-up or ramp-down phases;
  • Time intervals so wide to have implied a change on the thermal conditions of the Filler Machine, itself in equilibrium with the ambient apart an unavoidable hysteresis implied by its huge metal mass, changes on thermal conditions transferred to the liquid in the container and to the air medium in which the container and the HF fill livel bridge both lies.

Statistically significative samples

They can only be measured in the conditions of constant nominal speed of the Filler or Labeller.  More, they can only be measured over samples of production whose size is coherent with the criticity of the inspection and with the amount of bottles inspected each one hour.   To make an example: how to check the Fill Level Inspection of an Inspector in the out feed of a Labeller Machine producing more than  1 100 000 bottles in a day, 5 days in a week ?     If for a fill level inspection operating at e.g., only 10 000 bph (< 240 000 bottles in a day) a test for the false rejects including the complete control of all of the rejects along 2 hours is enough (< 20000 processed bottles) in the prior much more critical high-speed case it results necessary to control the rejects of > 8 (non consecutive) hours of production.  This way, it results possible to ameliorate the estimation of the Inspector performances.

Links to other pages:


                                                                                                            Copyright Graphene Limited 2013-2019