Particulate Matter Sensor Calibration Using OPS and QCM Feedback
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Solution Overview
Problem
Existing optical particle spectrometers (OPS) provide inaccurate mass concentration measurements due to assumptions about particle density and reflectivity, and miniature devices that measure mass concentration suffer from loading issues, leading to inaccurate and continuous use limitations.
Innovation Solution
Combining an OPS with a particle mass concentration device like a film bulk acoustic resonator (FBAR) or quartz crystal microbalance (QCM) to apply correction factors, enabling accurate mass concentration measurements by intermittently diverting a portion of the airstream for calibration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If optical particle spectrometer (OPS) is used to measure particle concentration, then device compactness and cost are improved, but measurement precision of mass concentration deteriorates due to assumptions about particle density and reflectivity
Solution Approach 1:
The patent implements a feedback mechanism where the QCM device continuously monitors particle mass concentration and provides real-time calibration data to the OPS. The system calculates calibration factors based on QCM measurements and applies these factors to correct OPS readings, creating a closed-loop feedback system that maintains measurement accuracy without requiring manual recalibration
Solution Approach 2:
The QCM device serves as an intermediary that bridges the gap between the OPS particle count measurements and true mass concentration. By introducing this intermediate calibration device, the system translates optical particle counts into accurate mass concentration values without requiring the OPS itself to directly measure mass
2Ease of manufacture
If miniature mass concentration devices (FBAR/QCM) are used to measure mass concentration, then device miniaturization and cost-effectiveness are improved, but reliability deteriorates due to particle loading issues
Solution Approach 1:
The system employs periodic action by intermittently diverting a portion of the airstream to the QCM device for calibration purposes while the OPS continuously monitors particle concentrations. This periodic calibration approach allows the QCM to be exposed to particles only during designated calibration intervals, reducing cumulative particle loading while maintaining measurement accuracy through regular calibration updates
Solution Approach 2:
The patent segments the airstream into two paths: a main path that continuously flows through the OPS for real-time monitoring, and a diverted calibration path that periodically directs a portion of the airstream to the QCM device. This segmentation allows the QCM to perform calibration functions without being constantly exposed to particle loading conditions
3Measurement precision
If QCM device is used for calibration, then measurement precision of OPS is improved, but device complexity increases due to combination of multiple sensors
Solution Approach 1:
The QCM device is designed to serve multiple functions: it acts as both a standalone mass concentration measurement device and a calibration reference for the OPS. By making the QCM multi-functional, the system reduces the need for separate calibration equipment, thereby managing complexity while maintaining measurement precision
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
Provides accurate and precise mass concentration measurements by correcting OPS readings with real-time calibration, overcoming loading issues and enhancing measurement accuracy while maintaining miniaturization and cost-effectiveness.
Implementation Method 1
optical particle spectrometer (OPS)
Implementation Method 2
measure mass concentration based on a resonant frequency change as particles are deposited
Data Source
Figure 1A
Figure 1B
Figure 2
AI summary
Various embodiments include methods and systems to measure and calibrate an optical particle spectrometer for reporting mass concentration. In one embodiment, an optical particle spectrometer is used to measure a concentration of particulate matter in a sampled particle-laden airstream. A particle diverter, in fluid communication with the spectrometer, diverts at least a portion of the particle-laden airstream at predetermined intervals. In one example, a mass filter receives the portion of the particle-laden airstream and filters a fraction of the particles within the airstream that are above a predetermined particle size. A mass sensor measures a mass of the fraction of the particles received from the mass filter or from the particle diverter and uses a calibration communication loop to provide the measured mass to the spectrometer to apply a correction factor to report mass concentration from the optical particle spectrometer. Other methods and systems are disclosed.