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A particle counter works by drawing a fixed volume of air through a beam of light, usually a laser diode, and measuring the light scattered by each particle that crosses the beam. The brightness of each flash scales roughly with particle size, so the instrument sorts each event into a size channel such as 0.3 micrometres or 5 micrometres, counts events per channel, and divides by the sampled air volume to give a count per unit volume. A unit that also reports PM2.5 or PM10 is converting those counts into an estimated mass using assumptions about particle density and shape, which is why a count and a mass reading are not the same measurement. The six-channel instruments here, such as the Eujgoov dust particle counter and the six-channel cleanroom and HVAC counter, follow that pattern; the Temtop unit adds mass channels and environmental sensors, which is a different job done in the same box.
What happens to a particle between the inlet and the detector
The mechanism is easier to hold in your head if you follow one particle. Air enters the inlet, usually through a small nozzle designed to keep the flow smooth. A pump pulls that air through at a controlled rate. In the middle of the path a laser beam crosses the airflow at right angles. Most of the time nothing is there and the beam passes straight to a beam stop. When a particle crosses the beam, some light is scattered sideways and a photodiode picks up that flash.
The photodiode converts the flash to a voltage pulse. The height of the pulse depends on the particle’s cross-section and its refractive index, so a larger particle generally produces a taller pulse. A comparator circuit sorts each pulse into a size bin: below the first threshold, between the first and second, and so on. The counter then adds one to that bin. After a set sampling period the instrument divides each bin count by the volume of air drawn, giving a result in particles per cubic foot or per litre.
Two consequences follow directly. First, the instrument never sees a particle it did not illuminate, so the beam and the flow path have to stay aligned. Second, the count is a sample, not a census. A counter drawing 2.83 litres per minute for one minute has looked at 2.83 litres of air. In a room of thirty cubic metres that is a tiny fraction, which is why sampling time and sampling location matter as much as the sensor.
Why the first channel is 0.3 micrometres on nearly every handheld
The 0.3 micrometre channel appears on almost every instrument in this class, including all four products here. That is not an accident of marketing. Light scattering becomes strong enough to detect reliably at around a third of a micrometre with a modest laser and photodiode, so 0.3 micrometres is the practical floor for a handheld laser counter. Below that you are into condensation particle counters, which grow particles in alcohol vapour before counting them, and those are a different instrument at a different level of complexity.
The channel boundaries also follow a standard series. The familiar set is 0.3, 0.5, 1.0, 3.0, 5.0 and 10 micrometres, which is the six-channel layout on the six-channel air particle meter and on the Generic 6-Channel 03-10. The boundaries are not arbitrary. They bracket the sizes that behave differently in the air: fine particles that stay suspended for hours, and coarse particles that settle or get caught in the upper airway. When you compare two counters, compare the channel edges first. A counter with a 0.5 micrometre first channel is not a worse instrument, but it cannot see the smallest fraction, and that fraction is often where combustion and new filters show up.
One honest limit: a counter reports a count in a size bin, not a true size distribution. A particle of 0.45 micrometres and a particle of 0.49 micrometres both land in the same bin. The bin is a category, not a measurement of that individual particle.
Counts, mass and the conversion that is not a measurement
Many instruments report both a particle count and a mass concentration such as PM2.5 or PM10. The count is what the sensor physically measures. The mass figure is derived. To get from a count to a mass you need an assumed density and an assumed shape for every particle in each bin, and those assumptions are baked into a conversion curve. Real dust is a mixture: skin flakes, textile fibres, soot, salt, pollen. Each has a different density and a different scattering behaviour. The conversion is therefore an estimate, and two counters with different curves can report different PM2.5 from the same air.
This is the single most common source of confusion when two instruments disagree, and it is worth reading why particle sensors disagree before concluding that one of them is broken. A six-channel counter that reports only counts is being more honest about what it knows. A unit that reports PM2.5, PM10 and TSP alongside counts, such as the Temtop handheld airborne particle counter, is giving you a convenient number and a derived one; the count channels underneath are the raw evidence.
The arithmetic is simple once you accept the assumption. If a bin holds N particles per cubic metre and you assign each an average mass m, the mass contribution is N times m. Sum the bins and you have an estimated mass concentration. Nothing in that sum was weighed. The instrument inferred it.
Flow rate, coincidence loss and why 2.83 litres per minute is the common figure
Flow rate sets how much air the instrument examines, and therefore how quickly a count becomes statistically meaningful. The recurring figure in this class is 2.83 litres per minute, which is 0.1 cubic feet per minute. It appears on the Air Particle Meter for and the Generic 6-Channel 03-10, and it is the flow rate that makes a one-minute sample equal to 0.1 cubic feet, so a count taken over one minute can be read directly as particles per cubic foot without further arithmetic. That convenience is why the figure is so common.
Flow rate also interacts with a limit called coincidence loss. If two particles cross the beam at almost the same instant, the detector sees one larger pulse and the counter records one event. At low concentrations this is negligible. In heavy contamination it causes undercounting, and the instrument may not warn you. A faster flow reduces the chance of coincidence but demands a faster detector. This is one reason a cleanroom-grade counter costs more than a consumer unit even when both quote six channels.
If a listing does not publish a flow rate, do not assume one. For the products here, the Eujgoov 03-10m does not state a flow rate in the listing bullets, and neither does the Temtop PM25. Where the figure is absent, the honest position is that the sampling volume per unit time is unknown, and any comparison of sensitivity between those units and a 2.83 litre per minute instrument is not like for like.
Six channels compared: what the listings actually publish
The table below collects only the figures the listings state. Blank cells are marked, not guessed. It is deliberately short, because the useful comparison in this class is about what each instrument measures and how it stores the result, not about a long list of features.
| Instrument | Size channels | Mass channels | Flow rate | Data storage | Other sensors |
|---|---|---|---|---|---|
| Eujgoov | 0.3, 0.5, 1.0, 3.0, 5.0, 10 micrometres | PM2.5, PM10 | Not stated in the listing bullets | Thousands of sets, USB | Not stated in the listing bullets |
| Air Particle Meter for six-channel air particle meter | 0.3, 0.5, 1.0, 3.0, 5.0, 10 micrometres | Not stated in the listing bullets | 2.83 L/min (0.1 CFM) | Records saved for review | Not stated in the listing bullets |
| Generic 6-Channel 03-10 six-channel cleanroom and HVAC meter | 0.3, 0.5, 1.0, 3.0, 5.0, 10 micrometres | Not stated in the listing bullets | 2.83 L/min (0.1 CFM) | Over 2 million groups, Type-C USB | Not stated in the listing bullets |
| Temtop handheld | 0.3, 0.5, 1.0 micrometres | PM2.5, PM10, TSP | Not stated in the listing bullets | Not stated in the listing bullets | Temperature, humidity |
Read the table by column, not by row. The Eujgoov 03-10m, the Air Particle Meter for and the Generic 6-Channel 03-10 share the same six channel edges; the difference is in flow, storage and alarm features. The Temtop PM25 stops at 1.0 micrometres, so it cannot separate coarse from fine dust above that size, but it adds mass channels and environmental sensors. That is a different instrument for a different question, and the choice between them is the subject of how to compare laser particle sensors.
Where the numbers stop being trustworthy
A particle counter is a sampling instrument, and sampling instruments fail in predictable ways. The most common is isokinetic error: if the inlet faces into a moving airstream, large particles are not drawn in at the same efficiency as small ones, so the count skews fine. In a duct or near a fan, hold the probe so the inlet is parallel to the flow, not facing it. The second is contamination of the optical chamber. A dirty window scatters light continuously and raises the baseline, which shows up as a persistent count in the smallest channel even in filtered air. Clean the chamber according to the manufacturer’s instructions, and if a listing does not publish a cleaning procedure, treat that as a gap.
Zero counts are not proof of clean air. A counter with a 0.3 micrometre first channel cannot see a 0.1 micrometre particle, and a counter sampling for ten seconds has examined very little air. The correct reading of a zero is that no particle above the detection threshold crossed the beam during the sample. That is a narrower statement than clean.
Finally, a counter is not a monitor and not an alarm unless the listing says so. The Air Particle Meter for states configurable alarm thresholds for all six channels. The Eujgoov 03-10m and the Generic 6-Channel 03-10 describe storage and export but the bullets do not describe alarms. If you need a device that warns you, check that the alarm function is published; do not infer it from the presence of a display.
What to hold on to
A particle counter is a light-scattering event counter with a known sample volume. Everything else, the size channels, the flow rate, the mass conversion, the storage, is a layer on top of that fact. Once you know the first channel and the flow rate, you know most of what the instrument can and cannot tell you. Where a listing is silent on those figures, the right response is to ask, not to assume. For a wider view of the instruments available, see the particle counter roundup, and for the sensor inside a domestic monitor, the Temtop particle counter review covers how a consumer unit behaves in practice.
Frequently Asked Questions
Does a particle counter measure PM2.5 directly?
No. It counts particles in size bins. PM2.5 is a mass concentration derived from those counts using assumed density and shape. The count is measured; the mass is estimated. A unit that publishes both, such as the Eujgoov 03-10m or the Temtop PM25, is giving you the measured count and the derived mass side by side.
Why do two counters give different readings in the same room?
Different first channels, different flow rates, different sampling times and different mass conversion curves all contribute. If one unit starts at 0.3 micrometres and the other at 0.5, they are counting different populations. If both are six-channel units with the same flow, check that the inlets are at the same height and orientation before blaming the sensors.
What does 2.83 litres per minute mean in practice?
It is 0.1 cubic feet per minute. Over a one-minute sample the instrument examines 0.1 cubic feet of air, so a raw count over that minute reads directly as particles per cubic foot. It is a convenience, not a guarantee of accuracy; the accuracy still depends on the optical chamber and the coincidence limit.
Can a particle counter tell me whether my air is safe?
No. It tells you how many particles above a size threshold crossed the beam. It does not identify the particles, does not detect gases, and does not measure carbon monoxide or volatile organic compounds. Safety decisions need the right instrument for the hazard, and a particle count is one input, not a verdict.
How often should the optical chamber be cleaned?
The listing for these products does not publish a cleaning interval. In general, a counter used daily in a dirty environment needs more frequent cleaning than one used occasionally in a cleanroom, and the symptom of a dirty chamber is a persistent count in the smallest channel when sampling filtered air. Follow the manufacturer's procedure; if none is published, ask the supplier.
Is a six-channel counter better than a three-channel one?
It depends on the question. Six channels let you separate fine from coarse and watch how a filter or a cleaning routine changes the distribution. Three channels, as on the Temtop PM25, are enough for a general fine-dust picture and come with mass and environmental readings. More channels are not automatically better; matching the channels to the decision is what matters.