Whitehouse Scientific has been producing calibration standards for particle size analyzers for over 35 years. Polydisperse and Monodisperse glass microspheres are available for most instruments while a unique range has been prepared for calibrating sieves.
Polydisperse Standards have a nominal 10:1 range of sizes and 7 grades are available from 0.1 – 2000 microns. Specially developed 100 stage spinning rifflers are used to produce identical samples in single-shot bottles from 10mg to 10g. Operator bias caused by sub-sampling is therefore eliminated. An international team of 20 leading particle size laboratories have analyzed the standards using primary techniques such as microscopy. sedimentation, electroformed precision sieving and the Coulter counting method where unambiguous and direct traceability to NIST is possible.
Monodisperse Standards provide one of the largest size ranges with standards ranging from below 10 microns to over 1mm! The microspheres are shape as well as size sorted to produce an exceptionally high quality spherical product. The NIST traceable standards can be used for checking specific size resolutions. Supplied as dry powder, there is no possibility of degradation with time as in the case of many liquid based latex standards.
Sieve Calibration Standards produced exclusively by Whitehouse Scientific, are a range of single-shot, narrow size distribution standards for calibrating individual test sieves from 20 - 5000 microns. Over 80% of the sieve apertures are analyzed in about 1 minute and the results are independent of the method of shaking. Narrow size distributions mean that resolutions to 1 micron are possible and the results are almost identical to the time-consuming microscope calibration methods.. The standards are again traceable to NIST. In addition to speed and accuracy, a major advantage is that sieves do not need to be sent away for recalibration.
Image Analysis Standards: Particle size analysis by laser diffraction has become a significant analytical tool for sizing up to 5mm and has made major inroads in to sieve analysis methods over recent years. The principle of the technique is to measure the particles either statically or dynamically and the images analysed. With 4 different ranges, 50-250um, 170-710um, 500-200um and 1400-500um, the weight per single-shot sample has been calculated to provide robust statistical results with minimal deviation from bottle to bottle.
Filter Cut Point Testing: Whitehouse Scientific is relied upon around the world as a provider of high quality particle sizing standards and calibration microspheres, and utilises this expertise in their exclusive method for determining the cut point of filter media. Using specially prepared, precision glass microspheres to challenge the filter, it is possible to measure filter efficiencies within micron resolutions. The Whitehouse Scientific method uses narrow particle size distribution standards and covers pore sizes from just a few microns to more than 600 microns. Results are highly reproducible and traceable to international standards, NIST for example. Dr Graham Rideal CEO says “As the name suggests, challenge testing involves challenging the surface of a filter with actual particles. Particle sizes are then measured upstream and downstream of the filter. The maximum size passing through reflects the largest pore size. Challenge testing is one of the most robust methods of filter testing because we use spherical particles analysed by microscopy, where any out of shape particles can be eliminated.”
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