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A particle counter works by drawing air through a laser beam and measuring the light each particle scatters. A photodetector converts each flash into a pulse, and the pulse height is sorted into size channels, typically 0.3, 0.5, 1.0, 3.0, 5.0 and 10 micrometres on the handheld instruments sold for indoor air and cleanroom checks. The count is then divided by the volume of air sampled to give a concentration. Two things make the reading trustworthy or not: the flow rate must be known and stable, and the sample must be long enough to count a meaningful number of particles. A handheld counter with a 2.83 litre per minute pump, as several of the instruments here state, samples about 47 cubic centimetres per second, so a one minute sample is under three litres of air. That is enough to see a gross difference between a clean room and a workshop, and not enough to certify a cleanroom to a formal standard.
The optics: one particle, one flash, one size bin
Inside the instrument, a small pump pulls air through a narrow viewing volume. A laser or laser diode illuminates that volume, and a photodetector sits at an angle to the beam. When the air is clean, the detector sees a steady low light level. When a particle passes through the beam, it scatters light, and the detector sees a brief pulse.
The height of that pulse depends mostly on the particle’s size and its refractive index. A larger particle scatters more light, so a taller pulse. The electronics compare each pulse against thresholds and drop it into a size channel. That is the whole trick: the counter does not photograph the particle or weigh it. It infers size from scattered light intensity, which is why the result is called an optical equivalent diameter.
This matters because a transparent particle and a dark particle of the same physical size scatter differently. Soot and silica dust do not give identical pulse heights. The manufacturer calibrates the channel thresholds against a reference aerosol, usually polystyrene latex spheres of known size, and the instrument is accurate for particles that scatter like that reference. For general dust and smoke the error is acceptable for comparison work. For research on a specific aerosol, it is not.
The smallest channel is the hardest. A 0.3 micrometre particle scatters very little light, so the laser, the optics and the detector noise floor all have to be good. That is why the 0.3 micrometre channel is the one quoted first on almost every handheld, including the JD 3003 six channel handheld and the two generic six channel meters below. A counter that claims a 0.3 micrometre channel is claiming a certain optical quality, not a certain accuracy.
Flow rate and sample time: the arithmetic that decides whether the count means anything
A particle counter reports concentration, usually particles per cubic metre or per cubic foot. To get there it must know how much air it sampled. The pump flow rate is the divisor. If the flow is 2.83 litres per minute, as the listing states for the active pump air particle meter and for the cleanroom and HVAC six channel meter, then in one minute the instrument has sampled 2.83 litres, which is 0.00283 cubic metres. A count of 283 particles in that minute becomes 100,000 particles per cubic metre.
Now the important part. At low concentrations, the count in a short sample is small, and small counts are statistically noisy. If the true concentration gives you an expected 3 counts per minute, you will sometimes see 1 and sometimes see 6. The percentage error is large. The fix is to sample longer. Many counters offer a sample time setting, and the correct setting depends on how clean the air is. A cleanroom at rest might need several minutes per location. A workshop with visible dust gives a stable reading in seconds.
The listing for the Air Particle Meter for and the Generic 6-Channel 03-10 states 2.83 litres per minute, which is 0.1 cubic feet per minute. That is a common handheld flow rate because it is small enough for a battery pump and large enough to accumulate counts. It is not the 28.3 litres per minute (1 CFM) of a benchtop cleanroom counter, so a one minute handheld sample is one tenth of the volume of a one minute benchtop sample. Ten times less air means ten times fewer counts and roughly three times the statistical noise for the same true concentration. That is the trade a handheld makes.
| Quantity | What the listing states | What it means in practice |
|---|---|---|
| Flow rate | 2.83 L/min (0.1 CFM) on the Air Particle Meter for and the Generic 6-Channel 03-10; not stated for the JCKJEDAT Particle Counter and the Eujgoov 03-10m | About 47 cubic centimetres per second. One minute samples under three litres. |
| Size channels | 0.3, 0.5, 1.0, 2.5, 5.0, 10 micrometres on the JCKJEDAT Particle Counter; 0.3, 0.5, 1.0, 3.0, 5.0, 10 on the Eujgoov 03-10m, the Air Particle Meter for and the Generic 6-Channel 03-10 | Channel edges differ between models, so counts are not directly comparable across brands unless the edges match. |
| Coincidence loss | Not stated in the listing bullets | At high concentrations two particles can pass the beam together and be counted as one. The concentration at which this becomes significant is a published figure on laboratory counters and is usually absent on handhelds. |
| Zero count or false count rate | Not stated in the listing bullets | The count a clean instrument reports on filtered air. Without it you cannot know the noise floor. |
If you want to compare how different optical sensors behave before buying, the guide to comparing laser particle sensors goes through the sensor-level differences. The point here is that the flow rate and the sample time are not footnotes. They are half the measurement.
Size channels are not interchangeable between brands
The six channel layout looks standard, but the edges differ. The JCKJEDAT Particle Counter lists 0.3, 0.5, 1.0, 2.5, 5.0 and 10 micrometres. The Eujgoov 03-10m, the Air Particle Meter for and the Generic 6-Channel 03-10 list 0.3, 0.5, 1.0, 3.0, 5.0 and 10 micrometres. The difference is the fourth channel: 2.5 versus 3.0 micrometres. That single edge change means a count in the fourth channel from the JCKJEDAT Particle Counter is not the same quantity as a count in the fourth channel from the Air Particle Meter for. If you are comparing two rooms measured with different instruments, match the channel edges first or the comparison is meaningless.
There is a second subtlety. A count in the 0.5 micrometre channel usually means particles of 0.5 micrometres and larger, not particles exactly 0.5 micrometres. The channel is cumulative from its lower edge upward, or it is a differential bin between two edges, depending on how the firmware presents it. The listing bullets do not say which convention each instrument uses. Not stated in the listing bullets. On most handhelds the display shows differential counts per channel, and the user is expected to sum them if a cumulative figure is wanted. Check the manual before you compare a channel reading to a standard, because cleanroom standards are written in cumulative terms.
The PM2.5 and PM10 figures on the Eujgoov 03-10m are a different kind of number. Those are mass-based estimates derived from the optical counts using an assumed particle density and refractive index. They are useful for air quality context and are not the same as a gravimetric reference measurement. The listing states that Eujgoov 03-10m detects PM2.5 and PM10 concentrations alongside the six size channels; it does not state the conversion assumptions. Not stated in the listing bullets.
What the handheld can and cannot tell you about a cleanroom or a filter
A particle counter is at its best when you use it to compare. Sample the same room before and after cleaning, or upstream and downstream of a filter, or inside and outside a spray booth. The absolute number may carry an optical uncertainty of tens of percent, but the ratio between two readings taken with the same instrument in the same session is much more reliable. That is why commissioning technicians use particle counts to find the leak in a HEPA installation: the count jumps at the leak and falls when the leak is sealed.
What the handheld cannot do is certify. Cleanroom classification standards define the sample volume, the number of locations, the probe height and the statistical treatment. A handheld with a 2.83 litre per minute pump and a short sample does not meet the volume requirement for the cleaner classes, and the listing does not publish a calibration certificate or a counting efficiency curve. Not stated in the listing bullets. So the honest answer is: a handheld particle counter is a diagnostic and comparison tool, not a certification instrument. If you need a certified classification, you need a calibrated benchtop counter with a documented calibration traceable to a standard, and you need to follow the standard’s sampling plan.
For general indoor air work, the same logic applies at a lower stakes level. The roundup of particle counters covers the models sold for that job. Use the handheld to answer “is this room dustier than that one” and “did the filter change help”. Do not use it to answer “is this room safe” without a reference method behind the number.
Maintenance, zero checks and the drift that changes the baseline
The optics get dirty. Every particle that passes through the viewing volume leaves a fraction of its mass on the lens or the window, and over months the scattered light baseline rises. A dirty instrument reads high, and it reads high by an amount that grows slowly, so you do not notice. The maintenance nobody mentions is the zero check: run the instrument on air passed through a high efficiency filter and confirm the count is near zero. If the listing does not state a zero count specification, you can still perform the check and watch for change over time. A rising zero count is the signal to clean the optics or send the unit for service.
The pump is the other wear item. A diaphragm pump in a handheld runs at a low flow rate and lasts a long time, but the flow can drift as the pump ages or as the tubing clogs. If the flow falls, the instrument still divides by the nominal flow rate, so the reported concentration rises even though the air is unchanged. Some instruments have an internal flow sensor and will flag a flow fault; the listing bullets here do not state whether the JCKJEDAT Particle Counter, the Eujgoov 03-10m, the Air Particle Meter for or the Generic 6-Channel 03-10 do. Not stated in the listing bullets. If yours does not, check the flow against a small flow meter periodically, or at least listen to the pump and note any change in sound.
Battery behaviour matters more than it seems. A pump counter draws more current than a passive dust sensor, and a low battery can cause the pump to slow before the instrument shuts down. That gives a falsely high concentration on the last few samples of a session. Charge before a survey rather than during it.
Where the particle counter stops being the right instrument
A particle counter counts particles. It does not tell you what they are. It cannot distinguish pollen from welding fume from concrete dust, and it cannot tell you whether the particles are infectious or toxic. If the question is “what is this dust”, you need a sampling filter and laboratory analysis, or a different instrument. If the question is “is there a gas leak”, a particle counter is the wrong tool entirely; the guide to how gas leak detectors work covers that category.
It also does not measure carbon dioxide, carbon monoxide, volatile organic compounds or humidity. Those need their own sensors, and the guide to how CO2 monitors work explains why CO2 is a useful occupancy indicator in a way that particle count is not. A room can have a low particle count and a high CO2 level at the same time, because the particles settled and the exhaled CO2 did not.
Finally, the particle counter is not an alarm. Some models, including the six channel meter with adjustable alarms, let you set thresholds per channel, and that is useful for spotting a trend during a survey. It is not a safety device. It will not wake you up, it will not shut down a process, and it will not satisfy a workplace exposure limit. Those limits are mass-based and substance-specific, and an optical count in particles per cubic metre is not the same quantity. If you need to demonstrate compliance with an exposure limit, you need gravimetric sampling and analysis, not a handheld counter.
Used within those limits, a particle counter is one of the most informative instruments you can carry into a building. It shows you the invisible, it responds in seconds, and it lets you compare one place with another. The skill is in knowing which number on the screen is the one you can defend.
The number to trust is the one you can explain
A particle counter converts scattered light into size bins and divides by a known air volume. The physics is simple; the interpretation is not. Before you quote a reading, know the flow rate, the sample time, the channel edges and the zero check. If any of those is unknown, the number is a hint, not a measurement. For a broader view of the instruments available, the particle counter buying guide puts the models side by side, and the guide to choosing an anemometer for HVAC work covers the airflow side of the same investigations.
Frequently Asked Questions
Does a particle counter measure PM2.5 directly?
No. It counts particles in size bins and, on some models such as the Eujgoov 03-10m, converts those counts to an estimated PM2.5 mass concentration using assumptions about density and refractive index. The listing for the Eujgoov 03-10m states that it detects PM2.5 and PM10 concentrations but does not publish the conversion assumptions. A reference PM2.5 measurement is gravimetric: collect the particles on a filter and weigh them.
Why does my counter show a count in a room that looks clean?
Because the air is not particle free. A typical indoor room has thousands to hundreds of thousands of particles per cubic metre in the 0.3 micrometre and larger range, most of them invisible. The counter is doing its job. If the count seems implausibly high, check the zero count on filtered air and check that the flow rate has not dropped.
Can I use a handheld particle counter to certify a cleanroom?
Not to a formal standard. Cleanroom classification standards specify the sample volume, the number of locations and the calibration requirements. A handheld with a 2.83 litre per minute pump and a short sample does not meet the volume requirement for the cleaner classes, and the listings here do not publish a calibration certificate or counting efficiency. Use it for comparison and troubleshooting, and use a calibrated benchtop counter for certification.
What is coincidence loss and why does it matter?
At high particle concentrations, two particles can pass through the laser beam at the same moment and be recorded as one larger particle. The concentration at which this becomes significant is a published figure on laboratory counters and is not stated in the listing bullets for the JCKJEDAT Particle Counter, the Eujgoov 03-10m, the Air Particle Meter for or the Generic 6-Channel 03-10. In practice, if you are sampling heavy dust, dilute the sample or use a counter with a smaller viewing volume.
Do the six size channels on different brands mean the same thing?
No. The JCKJEDAT Particle Counter lists a 2.5 micrometre channel where the Eujgoov 03-10m, the Air Particle Meter for and the Generic 6-Channel 03-10 list a 3.0 micrometre channel. The other edges match, but that one difference means the fourth channel counts a different size range. Compare channel edges before comparing counts. Also check whether the display shows differential or cumulative counts; the listings do not state which convention each instrument uses.
How often should a particle counter be calibrated?
The manufacturer's interval is the one to follow, and it is not stated in the listing bullets for any of the products here. A common interval for handheld optical counters is annual, with a zero check before each survey. If the instrument is used for anything that resembles compliance work, follow the calibration requirement in the relevant standard rather than the manufacturer's minimum.