Particle Sensor Pre-Filter for Size Distribution Compensation
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Solution Overview
Problem
Existing particle sensors face challenges in accurately interpreting sensor current due to dependency on particle size distribution, especially when not all charged airborne particles are precipitated, leading to unclear measurements of apparent ultrafine particle number concentration.
Innovation Solution
Incorporating a pre-filter, such as an activated carbon filter, to reduce the dependency of the sensor signal on particle size distribution by compensating for the effects of particle size through calibration constants, allowing for a more independent measurement of apparent particle number concentration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a parallel-plate electrostatic precipitator is used for particle removal, then the device size can be reduced and manufacturability is improved, but the precipitation efficiency decreases and sensor current interpretation becomes ambiguous
Solution Approach 1:
The patent applies preliminary action by introducing a pre-filter before the particle charging section to remove larger particles (diameter > 100 nm) from the sampled airflow. This pre-filtering step prepares the particle size distribution in advance, ensuring that only particles within a specific size range reach the charging and precipitation sections. Consequently, the sensor current becomes more reliably interpretable in terms of apparent particle number concentration, as the pre-filter compensates for the incomplete precipitation efficiency of the compact parallel-plate precipitator.
2Reliability
If a high particle precipitation voltage (>100 V) is applied to ensure complete particle removal, then precipitation efficiency improves, but electronic complexity and device attractiveness decrease
Solution Approach 1:
The patent extracts the function of removing large particles from the main sensor body by introducing a separate pre-filter component. This pre-filter handles the removal of particles with diameter > 100 nm before the airflow enters the compact parallel-plate precipitator. As a result, the precipitator can operate at lower voltages (≤100 V) while still achieving sufficient precipitation efficiency for the remaining smaller particles, thereby reducing electronic complexity while maintaining reliability.
3Reliability
If a small flow rate (<0.3 liters per minute) is used to ensure complete particle precipitation, then precipitation efficiency improves, but sensitivity decreases
Solution Approach 1:
The pre-filter performs preliminary removal of large particles that would otherwise require long precipitation lengths or low flow rates for complete precipitation. By removing these particles in advance, the system can maintain higher flow rates (>0.3 liters per minute) while still achieving effective precipitation of the remaining smaller particles, thus preserving sensitivity without sacrificing precipitation efficiency.
4Reliability
If a long precipitation length is used within the particle precipitator to ensure complete particle removal, then precipitation efficiency improves, but device size increases
Solution Approach 1:
The patent extracts the function of removing large particles from the main precipitator by introducing a pre-filter. This allows the parallel-plate precipitator to have a short precipitation length while still achieving high overall precipitation efficiency, as the pre-filter has already removed particles that would require long precipitation paths. Consequently, the device maintains compact dimensions without sacrificing precipitation efficiency.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The pre-filter design minimizes the deviation of the calibration constant with respect to particle size, enabling accurate measurement of apparent particle number concentration across a range of particle diameters, even with incomplete precipitation, and reduces electrode contamination from silicon-containing gases.
Implementation Method 1
A pre-filter is placed before the charging section of a particle sensor
Implementation Method 2
a particle charging section having an ionization electrode for electrically charging airborne particles
Implementation Method 3
a parallel-plate electrostatic particle precipitator
Implementation Method 4
a current meter for measuring the electrical current (I sensor) that results from the deposition of particle-bound charge per unit time
Data Source
Figure 1~2
Figure 3(a)~3(b)
Figure 4
AI summary
A particle sensor comprises an electrostatic particle charging section and a parallel-plate particle precipitation section, and a sensor for detecting the precipitated particles to produce a sensor signal. A pre-filter is placed upstream from the particle charging section. The pre-filter characteristics are such that the sensor signal in response to entrained particles which are not filtered out by the pre-filter relates to the apparent particle number concentration N app of the particles entering the particle sensor by a calibration constant S which is less dependent on the count mean particle diameter d p,av of the particles entering the particle sensor than the dependence on d p,av that exists in the absence of the pre-filter. Thus, the dependency of the sensor signal derived from the particle deposition in the parallel- plate precipitation section on the particle size distribution (caused by incomplete particle deposition in the precipitation section) is at least partly compensated for by a pre-filter which has a suitable dependency of its filtering function on the particle size.