Air Quality | Indoor Particle Counters

The New BT-645 Particulate Monitor Now Available!

Our particle counters include all the necessary components to start sampling immediately. No extra or hidden costs. We do offer some optional accessories to enhance the operation of our units. View our product comparison chart.

GT-321 Indoor Air Quality Particulate Counter
Single Channel Particle Counter
GT-521S Indoor Air Quality Particulate Counter
Two Channel Particle Counter
GT-526 Indoor Air Quality Particulate Counter
Six Channel Particle Counter
Aerocet 531 Indoor Air Quality Particulate Counter
Aerocet 531S
Mass Particle Counter / Dust Monitor
804 Indoor Air Quality Particulate Counter
Model 804
Four Channel Handheld Particle Counter
831 Indoor Air Quality Particulate Counter
Aerocet 831
Aerosol Mass Monitor
BT-610 Bench-Top Particle Counter
Six Channel Bench Top Particle Counter
BT-620 Bench-Top Particle Counter
Six Channel Bench Top Particle Counter
BT-645 Bench-Top Particle Counter
Six Channel Bench Top Particle Counter

For additional information or a quotation on our line of Indoor Air Monitors, please contact

ISO 21501-4 Optional Calibration

ISO 21501-4 Optional Calibration (P/N SVC0109) Now Available on Select Met One Instruments Inc. Particle Counters

ISO21501 is a standard describing instruments and calibration requirements for determining particle size distribution using light scatter methods. With the increasing trend for real-time air particle monitoring in clean rooms and controlled environments, Met One Instruments, Inc. is prepared to meet the demands of our customers who require this critical calibration. Read more »

Released in May 2007, ISO 21501-4 is a particle counter calibration standard that replaced older standards such as ASTM and JIS. These previous standards outlined calibration of particle counters but lacked repeatability between units. The Pharmaceutical industry immediately adopted and embraced the new ISO 21501 standard. Other industries are slowly following their lead. While this standard is primarily a clean room standard it will likely influence other industries relying on particle counting size and count accuracy.

From the ISO 21501 Standard: "The purpose of ISO 2150-4 is to provide a calibration procedure and verification method for particle counters, so as to minimize the inaccuracy in the measurement result by a counter, as well as the difference in the results measured by different instruments"

The ultimate goal is a correlation of count and size between different particle counters, i.e., two different airborne particle counters calibrated to ISO 21501-4 should accurately count the same number and size of particles. The ability to calibrate any two counters producing the same results when sampling is difficult. The addition of this calibration as an option to our customers dispenses any question in the accuracy of the instruments and improves the repeatability across our line.

Currently Met One Instruments, Inc. can offer ISO 21501-4 compliance, P/N SVC0109 on:

804 4 Channel Handheld Particle Counter
BT-637 Bench-Top Particle Counter
BT-610 Bench-Top Particle Counter
BT-620 Bench-Top Particle Counter
GT-521 Particle Counter
GT-521S 2 Channel Handheld Particle Counter
GT-526 Particle Counter
GT-526S 6 Channel Handheld Particle Counter

For pricing on this option for a new purchase of above models, contact or contact our Customer Service Department for information on 21501-4 Calibration P/N SVC0109 for counters already in your commission.