H.E.L. Limited Subsieve AutoSizer (SAS)

The H.E.L. Limited Subsieve AutoSizer (SAS) is a new addition to the established field of air-permeability particle sizing. It has been developed as a direct and improved successor to the widely used Fisher Model 95 Sub-Sieve Sizer (FSSS). The SAS adds automated functions, and electronically recorded and presented data, to an established particle sizing technique. The SAS uses the principle of pressure drop across a packed bed of powder. By varying the sample height, and hence the “porosity” of the bed, average surface area and particle size can be determined as a function of pressure drop in accordance with the Carmen equation. The SAS measures particle size in the range of 0.2 µm to 75 µm and has a compression accuracy of less than 0.05 mm.

Why Air-permeability Particle Sizing?

Air-permeability techniques generate average Specific Surface Area (SSA) data for a sample of powder. The SSA of particles has a significant impact on the physical properties of powders and has been the focus of much attention from such diverse communities as the pharmaceutical, paint, toner and geologic professions. The SAS has particular applicability to the Pharmaceutical Quality Control field where the quick and reproducible SAS-derived Surface Areas can be used to control batch-to-batch variation in important properties such as bioavail-ability and drug delivery.


  • Superior Software Complete Control HEL Software sets a world-wide standard for instrument operation, data acquisition and handling, reporting and systems integration.
  • Quick and Easy Set-up Simple step by step set-up, easy to follow; ensuring that no parameters are over looked.
  • Easy Mode A “Start” button runs the complete measurement to pre-selected requirements.
  • Real Time Data Display Data can be viewed as it is acquired simplifying method development by ensuring that the user is never divorced from the measurement.
  • Report Generation Company logos, typestyles and formats can be incorporated into printouts.
  • Security Features Optional Password Protection ties samples to user ID’s and protects plans from unauthorised changes.

What is air-permeability particle sizing ?

The air-permeability technique is well established for measurement of the average Specific Surfac Area (SSA) of a sample powder. The SSA measured by this technique has been found to be a useful parameter in industries as diverse as pharmaceutical, metal coat-ings, paints and even geological samples.

The SAS uses the principle of Pressure drop across a packed bed of powder.

By varying the Sample Height and hence the “porosity” of the bed, average Surface Area and hence Particle Size can be determined as a function of Pressure drop in accordance with the Carmen equation.

Direct comparison of SAS & FSSS results

Side-by-side trials have been carried out using both old and new samples, with cooperation from many different and experi-enced users of the FSSS. Typical results are shown in the graphs, where mean particle size data from the two instruments is compared for powders of different sizes. One plot is based on organic samples (mostly pharmaceuticals) and the other on is for inorganic (mainly tungsten) metal. In the latter, samples were contributed by many different companies around the world. There is exceptional correlation between the two sets of data.

Another more extensive and independent study using organic samples by Astrazenca in England, has come to the same conclusion, after using it at various sites and by different individuals.

Repetitive testing of the same sample, to give a measure of reproducibility (precision) has also been reported by the same authors, again using the two devices side-by-side to give the specific surface area. A similar study by Michael Salmen of Osram in Germany, came to the same conclusion while working on tungsten samples.