Calibration of optical particle counters according to ISO standard 21501-4. Our customers benefit from short lead times thanks to our local presence.



The ISO 21501-4 standard forms the basis for the calibration of optical particle counters in the pharmaceutical industry. Instruments that conform to the standard are used to classify the air purity in cleanrooms and associated controlled environments according to ISO 14644-1 as well as to measure the number and size distribution of particles in different environments.

The ISO 21501-4 standard prescribes an annual particle counter calibration in which parameters such as zero count, particle size, counting efficiency, flow rate or resolution are checked and adjusted if necessary.

The size calibration by means of pulse height analysis (PHA) is carried out to determine the particle size. The customer’s particle measuring device is fed with monodisperse particles and the size channels are adjusted so that a symmetrical PHA distribution is achieved.

In the case of counting efficiency, the ratio of the measured particles of the device under test to a reference is assessed. ISO 21501 states that the counting efficiency of a particle counter should be 50 ± 20% for particles of the first channel size and 100 ± 10% for particles 1.5 to 2 above the smallest device channel.

Particle counter calibration according to ISO 21501-4


Calibration Lighthouse particle counter and PMS particle counter

The calibration of particle counters as well as their maintenance and adjustment is carried out in our calibration laboratory in Basel, Switzerland by trained Bakrona calibration technicians.

As a representative of Lighthouse Worldwide Solutions, we have specialized in the calibration of Lighthouse particle counters. However, since all of our calibrations are carried out according to ISO 21501-4 and our calibration references by METAS are certified, we can also calibrate particle counters from other manufacturers. As a long-standing representative of PMS (Particle Measurement Systems), we have more than 15 years of experience in the calibration of particle counters. We continue to offer calibration, service and support for the PMS particle counters.

Proximity to the customer is an important factor in a successful partnership. Thanks to our presence in Basel, we can offer our customers in Switzerland short lead times for calibration and adjustment.

Particle counter Lighthouse Worldwide Solutions (LWS)

  • Particle counter ApexZ, Solair , Apex P and Handheld
  • Particle sensor Apex R with or without integrated vacuum pump
  • LS Batch Sampler, NanoCount and Remote LPC (liquids)
  • ActiveCount100 and ActiveCount R (microbiological air sampler)

Particle counter from Particle Meauring Systems (PMS)

Particle counters from other manufacturers

  • On request
  • Calibration and calibration certificate according to the international standard ISO 21501-4
  • Calibration laboratory in Switzerland enables greater availability of the particle counters thanks to short lead times and the elimination of customs formalities
  • Reduced risk of transport damage (pick-up service on request)
  • More than 15 years of experience in calibrating particle counters
  • Local contact person and communication in German, French and English