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To use a particle counter, place the inlet in the air you want to characterise, let the pump pull a known volume through the laser scattering chamber, and record counts per size channel over a defined sample time. The two numbers that decide whether the result is defensible are flow rate and coincidence loss. A counter with a stable 2.83 L/min (0.1 CFM) pump, such as the six-channel air particle meter, gives you a standard sample volume to compare against; a counter that stores millions of records, such as the USB-export cleanroom model, lets you build a time series rather than a single snapshot. Neither will tell you the mass of the particles unless the firmware converts count to mass, and neither replaces a calibrated reference when the result has to be signed off.
What the instrument is actually counting, and why the size channels matter
A particle counter does not weigh dust. It pulls a known volume of air through a beam of laser light and counts the flashes. Each flash is sorted into a size bin by how much light it scatters. That is why the specifications are written as channels: 0.3 micrometres, 0.5, 1.0, 3.0, 5.0, 10. The channel number is the lower edge of the bin, not the exact diameter of every particle in it. A count in the 0.5 channel means particles of 0.5 micrometres and larger, up to the next channel edge.
This matters because the same air can look clean on one channel and dirty on another. Fine particles below 1 micrometre stay airborne for hours and penetrate deep into the lung. Coarse particles above 5 micrometres settle quickly and are more likely to come from resuspension, skin, or outdoor soil tracked in. A six-channel counter such as the Eujgoov dust particle counter lets you see the shape of the distribution, not just a single PM2.5 number. If the 0.3 and 0.5 channels are high but the 5 and 10 channels are low, you are probably looking at combustion or secondary aerosol. If the 5 and 10 channels spike when somebody walks past, you are looking at resuspension.
The listing for the Eujgoov 03-10m states six sizes from 0.3 to 10 micrometres and also PM2.5 and PM10 mass concentrations. The listing does not publish the counting efficiency at 0.3 micrometres, which is the figure that decides whether the smallest channel is trustworthy. Not stated in the listing bullets. Treat the smallest channel as indicative unless the manufacturer publishes a calibration curve against a reference instrument.
Flow rate, sample volume, and the arithmetic that turns counts into concentration
A particle count on its own is meaningless. What you report is a concentration: particles per cubic metre, or per cubic foot. To get there you need to know how much air passed through the chamber. That is why flow rate is the specification that quietly decides accuracy. A pump running at 2.83 litres per minute, which is 0.1 cubic feet per minute, is the standard sampling rate for many handheld counters. In one minute it pulls 2.83 litres. To express a count as particles per cubic metre, divide the count by the volume in cubic metres. 2.83 litres is 0.00283 cubic metres, so a count of 283 particles in one minute is 100,000 particles per cubic metre. The arithmetic is simple; the mistake is not doing it, or not knowing the actual flow.
Both the six-channel particle counter with active pump sampling and the cleanroom and HVAC particle counter state a flow rate of 2.83 L/min (0.1 CFM). That is a published figure you can use. The Eujgoov listing does not state a flow rate. Not stated in the listing bullets. If you need to report concentration per cubic metre, you cannot do it from that listing alone unless the instrument displays concentration directly, which the listing implies through its concentration measurement mode but does not quantify.
Sample time matters as much as flow. A ten second sample at 2.83 L/min pulls 0.47 litres. In clean air that may contain zero particles, which tells you very little. In dirty air it may contain so many that the counter cannot separate them, which is the next problem.
Coincidence loss: the error that appears exactly when the air is dirty
A laser particle counter counts flashes. If two particles pass through the beam at almost the same instant, the detector sees one larger flash and records one particle in a larger size bin. This is coincidence loss, and it means the counter undercounts high concentrations and overstates the size of what it does count. Every optical counter has a coincidence limit, usually expressed as a maximum concentration in particles per cubic foot or per litre. The listings here do not publish that limit. Not stated in the listing bullets.
The practical consequence is that you should not use a handheld counter to characterise a heavy dust cloud, a construction tear-out, or the exhaust of a vacuum cleaner. The number will be lower than the truth. If you must sample dirty air, shorten the sample time, dilute the sample, or use a counter with a published coincidence limit and stay below it. For cleanrooms and filtered spaces, coincidence loss is rarely the limiting error; for occupational hygiene in a workshop, it often is.
This is also why a counter that reports mass concentration, such as the Temtop handheld airborne particle counter, is not a substitute for a gravimetric sample when the exposure has to be legally defensible. The mass figure is derived from count and an assumed density, not weighed. The listing states PM2.5, PM10 and TSP alongside the 0.3, 0.5 and 1.0 micrometre channels. It does not state the assumed density or the conversion algorithm. Not stated in the listing bullets.
Zero counts, calibration, and the paperwork that makes a number defensible
Before you trust a count, you need to know the counter reads zero when it should. A zero count check, sometimes called a zero test, is done by pulling air through a high efficiency filter and confirming the instrument reports no particles above the noise floor. The listings do not state whether a zero filter is supplied or what the noise floor is. Not stated in the listing bullets. If you are using the counter for cleanroom classification or for a report that somebody else will audit, ask the supplier for the calibration certificate and the zero test procedure before you buy.
Calibration for a particle counter is usually against a reference instrument using polystyrene latex spheres of known size. The certificate states the counting efficiency at each channel. Without that certificate, you have a relative instrument: good for comparing before and after, or room against room, but not for claiming compliance with a standard. The same logic applies to the environmental sensors built into some units. The Temtop listing states built-in temperature and humidity sensors. That is useful context, and you can cross-check the humidity against a psychrometer reading if you need to know whether the air is dry enough for static to be a problem. But the particle channels are the reason you bought the instrument, and they are the channels that need the certificate.
Data storage matters here. A counter that stores thousands of sets, such as the Eujgoov 03-10m, or more than two million records, such as the Generic 6-Channel 03-10, lets you keep the raw counts alongside the time and place. That is what turns a reading into evidence. A single number written on a clipboard is not evidence.
Where a handheld particle counter stops being the right answer
A handheld counter is a survey instrument. It is good at finding a source, comparing spaces, and checking whether a filter or a cleaning procedure made a difference. It is not good at proving compliance with a cleanroom standard, because the standard specifies sample volume, sample locations, and a calibrated instrument with a published counting efficiency. It is not good at measuring personal exposure, because the inlet is where you hold it, not where the person breathes. And it is not good at measuring mass concentration to a legal standard, because it infers mass from count.
If the question is whether the ventilation in a bedroom is adequate, a particle counter can show you a decay curve when you open a window, but a CO2 monitor gives you a more direct answer about occupancy and fresh air. The two instruments answer different questions, and the CO2 data guide explains the ventilation side. If the question is whether a wall is damp, a particle counter is the wrong tool entirely; a moisture meter on drywall measures the thing you actually care about.
The honest limit is this: a particle counter tells you how many particles are in the air it sampled, in the size bins it has, at the flow rate it states. Everything beyond that, including whether the particles are harmful, whether the count is compliant, and whether the air is safe, requires a standard, a calibration, and a context that the instrument alone does not provide.
The number is the start of the question, not the answer
A particle counter is a tool for making invisible contamination visible. Use it to compare, to locate, and to check whether an intervention worked. Do not use it to certify, to diagnose, or to replace a calibrated reference when the result has to stand up to scrutiny. The most useful habit is to record the flow rate, the sample time, and the zero check alongside every count, because those three details are what let you or anybody else interpret the number later.
Frequently Asked Questions
Do I need a particle counter to check my home air quality?
Usually not. A particle counter is useful if you are investigating a specific problem, such as a new HVAC filter, a renovation, or a persistent dust complaint. For general confidence about ventilation, a CO2 monitor is more directly useful because it tells you whether fresh air is reaching the room. A particle counter tells you what is suspended, not why.
What does the 0.3 micrometre channel actually mean?
It means the counter is binning particles of 0.3 micrometres and larger into that channel. It does not mean it counts every 0.3 micrometre particle with perfect efficiency. The counting efficiency at that size is a separate specification, and none of the listings here publish it. Treat the smallest channel as a relative indicator unless you have a calibration certificate.
Why does my count go down when the air gets dustier?
That is coincidence loss. At high concentrations, two particles can pass through the laser beam close enough together that the detector records them as one larger particle. The counter undercounts and overstates size. Shorten the sample time, dilute the sample, or use a counter with a published coincidence limit and stay below it.
Can I use a particle counter to verify a cleanroom?
Not with a handheld alone. Cleanroom classification standards specify the sample volume, the number and location of sample points, and a calibrated instrument with a published counting efficiency. A handheld counter can tell you whether a space is trending dirty, but it cannot certify compliance. You need the calibration certificate and the standard's sampling plan.
What is the difference between particle count and PM2.5?
Particle count is a number of particles per volume in a size bin. PM2.5 is a mass concentration, usually micrograms per cubic metre, of particles below 2.5 micrometres. A counter that reports both is converting count to mass using an assumed density and shape. The listing does not state the assumption, so treat the mass figure as indicative unless the manufacturer publishes the conversion method.
How often should a particle counter be calibrated?
The manufacturer's interval is the one that matters, and none of the listings here state it. Not stated in the listing bullets. For any use where the result has to be defensible, follow the manufacturer's calibration schedule and keep the certificates. For relative before-and-after comparisons, a zero check before each session is the minimum good practice.