Search
Change language
CloseOpacimeters and particle counters are often confused, even though they measure different quantities and serve different purposes. Here’s what sets them apart, in practical terms, for a testing center or repair shop.
Confusion is common because both devices deal with emissions from a diesel engine. However, they do not measure the same thing, and their results are not interchangeable.
This distinction is key: smoke that is not very opaque can contain a large number of fine particles. This is precisely what opacity fails to detect.
Understanding the measurement principle helps you understand the limitations of each device.
| Opacimeter | Particle counter | |
|---|---|---|
| Measured quantity | Exhaust opacity (light attenuation). | Number of particles per unit volume. |
| Principle | A light beam passes through a volume of gas; the attenuation is measured. | The particles contained in a gas sample are counted. |
| Sensitivity to fine particles | Limited: very fine particles only slightly attenuate the beam. | This is the very purpose of the measurement. |
| What the result indicates | The visible density of the emitted smoke. | The quantity of emitted particles, whether visible or not. |
This has a practical implication: a vehicle with a degraded particulate filter system may exhibit moderate opacity while emitting a high number of particles. The two measurements are therefore not directly comparable.
Opacity measurement is a long-established test for diesel engines. Particulate number measurement addresses a more recent concern: evaluating the actual effectiveness of filtration systems, which opacity alone only partially reflects.
Several European countries have updated their testing protocols accordingly, on their own schedules and according to their own procedures. Others continue to rely solely on opacity measurement. A repair shop may also use either measurement for diagnostic purposes, outside of any regulatory framework.
Applicable requirements vary by country and are subject to change. A requirement in effect in one market does not automatically apply elsewhere, and the required certifications differ from one market to another. Before making any investment, confirm which regulations apply to your business and the country in which you operate.
Smoke opacity or particle count: both measurements are covered.
Design office and factory together in Montpellier: you deal directly with the designer and manufacturer of your equipment, from design to maintenance. Equipment in use on every continent, with subsidiaries in Germany and India.
designing and manufacturing measuring equipment
certified production, every unit checked at the end of the line
of revenue invested in research and development
to receive a proposal tailored to your project
Does a particle counter replace the opacimeter?
Not as a matter of principle. The two devices measure different quantities, and the required measurement depends on the protocol applicable in your market. Depending on the situation, one, the other, or both may be necessary.
Are the two results comparable?
No. Opacity and particle count are not expressed in the same unit and cannot be derived from one another. There is no general conversion rule.
Are these devices suitable for heavy-duty trucks?
Diesel engines in heavy-duty vehicles are subject to these regulations, but access to the exhaust system and sampling conditions differ. Compatibility and required accessories must be verified on a model-by-model basis.
What kind of editing is required?
Both families of devices require periodic inspections and routine maintenance, with consumables and wear parts that vary by model. See contract enrollment and repairs.
Tell us about your business, your market, and the vehicles you work with: our specialists will help you find the right measurement solution and device.
Back to top
