Whether in silos, tanks or process containers – the exact detection of fill levels is crucial for stable, safe and economical production processes. However, many common measuring methods quickly reach their limits in practice. This technical article compares established technologies such as radar, ultrasound or capacitive sensors with the gravimetric method – and shows why weighing technology is superior where it really matters.
In many sectors, such as the Food, Chemical and Pharmaceutical industries, precision is one of the key requirements in daily production operations. Reliable level measurement plays a decisive role here – whether it is to avoid being overfilled, to ensure material availability for dosing processes or for continuous process control. The selection of suitable measurement technology depends on a variety of influencing factors: from product properties and structural conditions to regulatory requirements in sensitive areas. A central requirement is to reliably and accurately determine the actual content of a container under all conditions – regardless of shape, medium or environment.
Traditional measuring methods and their limitations
In practice, various measuring principles are used – from radar and microwave sensors to ultrasonic and capacitive methods through to hydrostatic or optical systems. However, many of these technologies only record an indirect measured value – such as the distance to the surface or the pressure at the bottom of the container – from which the fill level is calculated. This inevitably leads to uncertainties, for example in the case of foam or bridge formation, uneven pouring cones, caking or variable density.
Industrial experience, for example at the chemical company Solvay Fluor in Frankfurt, also shows the practical limits of conventional systems. There, non-contact measuring methods led to unsatisfactory results, as changes in temperature and density severely impaired accuracy. The solution was only found by retrofitting the PanCake load cells® series by Minebea Intec, a leading global manufacturer of weighing and inspection technologies, which enabled precise and reliable level measurement by weight – with a maximum deviation of just 1.1 %, compared to around 2.5 % with the previous methods.
Gravimetric measurement: objective, non-contact, precise
Unlike all other methods, gravimetric level measurement does not measure a derived process signal – it measures the mass. Load cells such as the PanCake® or Inteco® record the weight of the entire container including its contents – regardless of material properties, density changes or form factors. The result is a consistently precise, linear measurement across the entire filling range – even with demanding media such as viscous liquids, bulk materials or aggressive chemicals.
Another advantage: the sensor technology is located completely outside the container. This eliminates the need for perforation of the container which means the elimination of the effects of incrustations, corrosion and error-prone calibrations. This is particularly important for hygiene-critical applications in food or pharmaceutical production. Load cells in hygienic design are CIP/SIP-capable, cleanroom-compatible and have been developed in accordance with EHEDG and FDA requirements.
Process reliability and cost-effectiveness – a system that pays off
The PanCake® load cells have been specially developed for retrofitting and integration into existing systems. They can be installed quickly and without any structural changes to the container – a clear advantage over alternatives such as radar or ultrasonic technology. Internal analyses and market comparisons show: Savings of up to 50 % can be achieved even on the acquisition costs.
The PanCake® also impresses with low overall costs during operation. Maintenance is practically unnecessary as there are no wearing parts. At the same time, the measuring accuracy remains stable for years. This reduces service costs and extends the service life – factors that significantly improve the total cost of ownership.
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Joseph Clarke
Editor, International Snacks
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