An ISO 16890 result depends on the complete measurement chain—not only the particle counters.
Контроль воздушного потока, образование аэрозоля, sampling, кондиционирование, system leakage and data processing can all affect the final result. A highly automated test bench can still produce unreliable data if these basic conditions are not verified.
The following problems deserve particular attention.
1. Testing at the Wrong Airflow
Efficiency and pressure drop can change with airflow. The test airflow must match the declared test condition and remain stable throughout the measurement.
The laboratory should verify:
- Airflow measurement range
- Статус калибровки
- Temperature and pressure compensation
- Flow stability
- Filter dimensions and face area
- Pressure capability at higher resistance
Testing outside the applicable range of the system or measurement device can invalidate the result.
2. Leakage Around the Filter or Test Duct
Air bypassing the filter can be measured as downstream penetration. Leakage may occur through:
- The filter fixture
- Adapter joints
- Sampling connections
- Duct sections
- Gaskets and clamps
A leakage check should be completed before efficiency testing. The fixture must seal the filter without deforming it.
3. Unstable or Non-Uniform Aerosol
The upstream aerosol must be sufficiently stable and mixed before reaching the sampling location.
Poor aerosol distribution can make the upstream sample unrepresentative of the concentration reaching the filter.
The laboratory should verify concentration stability and spatial uniformity under the required airflow conditions rather than assuming that a generator setting is sufficient.
4. Poor Sampling Arrangement
Upstream and downstream samples must represent the aerosol in the duct.
Errors can be introduced by:
- Incorrect probe location or orientation
- Excessively long sampling tubes
- Particle losses in bends or tubing
- Different transport conditions upstream and downstream
- Contamination remaining from a previous test
Sampling lines should be kept controlled, clean and suitable for the required particle-size range.
5. Particle-Counter Concentration Errors
An upstream concentration that is too high can cause coincidence error or exceed the instrument range. A downstream concentration that is too low can produce poor counting statistics.
Dilution may be required upstream, but the dilution ratio must be known and stable.
The laboratory should also check:
- Instrument zero count
- Background particle concentration
- Скорость потока
- Size-channel response
- Статус калибровки
- Synchronization of upstream and downstream measurements
Changing instruments or dilution configurations without updating the calculation can create a large efficiency error.
6. Ignoring Background Concentration
For high-efficiency filters, downstream penetration may be close to the background particle level.
If background concentration is not measured and controlled, particles from the duct, test room or sampling system may be incorrectly attributed to filter penetration.
The test system should be cleaned and stabilized before measurement.
7. Incorrect Conditioning
ISO 16890 conditioning is a controlled procedure used to determine minimum fractional test efficiency after reducing the influence of electrostatic charge.
It should not be shortened, modified or described as a simulation of a specific period of field ageing.
After conditioning, the filter must be handled and tested according to the applicable procedure. Uncontrolled storage or contamination can affect the result.
8. Mixing ePM Classification with Dust Loading
Initial and conditioned fractional-efficiency results are used for ePM classification.
Dust loading evaluates different parameters, including gravimetric efficiency, dust capacity and resistance versus captured dust mass. It does not determine the ePM class.
Reports should separate these results clearly.
9. Using Software Without Verifying the Calculation
Automation reduces manual work, but it does not replace validation.
The laboratory should verify:
- Particle-size channel mapping
- Upstream and downstream corrections
- Dilution factors
- Efficiency and penetration calculations
- ePM calculation logic
- Rounding and classification rules
- Test-condition records
- Report templates
Software changes should be controlled and checked using known datasets.
A Practical Pre-Test Check
Before starting an ISO 16890 тест, confirm:
- The system is within calibration
- The duct and fixture pass the leakage check
- Airflow is stable
- Aerosol concentration is stable and uniform
- Sampling lines are clean
- Particle counters are within range
- Dilution settings are correct
- Background concentration is acceptable
- The correct test procedure and filter condition are selected
SCPUR systems combine automated control with airflow, аэрозоль, sampling and calculation functions. Reliable results still depend on a validated measurement chain and a laboratory procedure that operators follow consistently.
