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Particle Counter Calibration Procedure and Concerns

Experts who discuss airborne particle counter calibration procedure issues
Members of panel experience in particle counter issues concerning calibration for clean rooms and IAQ
Particle Counters and Calibration

At Particlecounters.Org we talked with our industry experts about maintenance and calibration of particle counters.  First of all, what is particle counter calibration?  It's a procedure that maximizes your instrument's performance repeatability, reproducibility and accuracy.  The process uses applied industrial metrology methods.  This is an application of the science of measurements.  U.S. standards of measurement accuracy and precision are maintained by the National Institute of Standards and Technology (NIST).  According to metrology methods, proper air particle counter calibration procedure should include detailed records of adjustments made during calibration to ensure traceability of its accuracy and uncertainty.  This tells you the limits of accuracy and enables you to trace them back to a calibration event.  During particle counter calibration procedure, optical alignment methods are used to match the performance to a reference particle counter often called a "known good".  The final step of calibration is testing to verify equipment performance.  This is called verification and revalidation.

In addition to NIST traceable practices, other standards of particle counter calibration include Japanese Industrial Standard (JIS) B 9921, Light Scattering Automatic Particle Counter, and ASTM F 328-98, Standard Practice for Calibration of an Airborne Particle Counter Using Monodisperse Particles.

How often do you really need to calibrate your particle counter? Once a year is usually all you need to keep your particle counter calibrated. This may require that you send your particle counter to the manufacturer that you purchased your system from, or the manufacturer may have a service technician in your area who is qualified to work on your particle counter.  Well established particle counter manufacturers such as Lighthouse and Met One, have several service locations around the world.

By the way, one calibration per year assumes normal particle counter use.  If you are a traveling certifier or you frequently ship rental or loaner particle counters, they should be checked more frequently, since they have a higher likelihood of literally being "knocked out of whack" during travel.  Vibration, temperature changes and impact can disturb the finely tuned laser optics.  Also, if your particle counter is made for a clean room, and you use it in a dirty environment, optics can be clogged beyond what a purge filter can fix.  If this happens, you will need to have the optics manually cleaned or replaced.

NOTE: If you are working with hazardous contaminates such as biological material, wastes, toxic, radioactive or animal by-products you will NOT be able to have these units calibrated. You will need to buy a new one. Manufacturers will not let you send your particle counter for calibration if there is this a risk of spreading any form of contamination.

If you have not yet purchased your particle monitoring system, you may want to take in consideration a brand that has a fast turn around time for calibration so you don't experience significant down time with facility monitoring for particulate contamination.  Some manufacturers, such as Lighthouse, provide a spare loaner instrument if a suitable replacement is available, as well as removal and installation.

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