Particulate detection, counting, and identification
Particulate sensing systems or processes identify particulates suspended in an air sample by irradiating the air sample with UV light and measuring light from individual particles in the air sample. Two photodiodes having different wavelength sensitivity may be used to measure the fluorescent light emitted from a single particle, and a type of the particle may be identified using outputs from photodiodes. Repeating the process for multiple particles may produces distributions that further distinguish or identify particulate types.
1. A particulate matter sensor comprising:
a beam source positioned to direct a beam through gas sample in a sensing volume, the beam being a monochromatic beam;
a first light sensor positioned to repeatedly measure light from interactions of the beam with particulates in the sensing volume, the first light sensor having a first measurement sensitivity;
a second light sensor positioned to repeatedly measure the light from the interactions of the beam with the particulates in the sensing volume, the second light sensor having a second measurement sensitivity having a dependence on wavelength of the light measured and that differs from a dependence of the first measurement sensitivity on the wavelength of the light measured; and
an analysis system coupled to receive a first stream of measurements from the first light sensor and a second stream of measurements of the second light sensor, the analysis system being configured to use the first stream and the second stream to identify types of particulates that interact with the beam.
2. The particulate matter sensor of claim 1 , wherein the beam is a beam of ultraviolet light.
3. The particulate matter sensor of claim 1 , wherein:
the first light sensor includes a first photodiode; and
the second light sensor includes a second photodiode, the second photodiode having a relative spectral responsivity that differs from a relative spectral responsivity of the first photodiode.
4. The particulate matter sensor of claim 1 , wherein the analysis system is further configured to determine a fluorescence characteristic of a particle using a first measurement that is in the first stream and corresponds to an interaction of the particle with the beam and using a second measurement that is in the second stream and correspond to the interaction of the particle with the beam.
5. The particulate matter sensor of claim 4 , wherein the analysis system determines the fluorescence characteristic of the particle from a ratio of the first measurement and the second measurement.
6. The particulate matter sensor of claim 5 , wherein the fluorescence characteristic is one factor in a multifactor analysis that the analysis system performs to identify the types of particulates.
7. The particulate matter sensor of claim 1 , further comprising a sensor interface coupled to the first light sensor, the sensor interface generating the first stream by sampling output from the first light sensor at a sampling frequency greater than 100 kHz.
8. The particulate matter sensor of claim 7 , wherein the sampling frequency is less than 500 kHz.
9. The particulate matter sensor of claim 1 , wherein the analysis system is further configured to determine one or more distributions of characteristics for a collection of individual particles that interact with the beam, and to use the one or more distributions as one or more factors in a multifactor analysis that the analysis system performs to identify the types of particulates.
10. The particulate matter sensor of claim 9 , wherein the one or more distributions comprises one or more of a distribution of sizes of the particles in the collection, a distribution of fluorescence characteristics of the particles in the collection, a distribution of reflectivity of the particles in the collection, and a distribution of shapes of the particles in the collection.
11. The particulate matter sensor of claim 1 , wherein the analysis system is further configured to detect a series of pulses in the first stream, wherein each of the pulses corresponds to an interaction of the beam with a particle that corresponds to the pulse.
12. The particulate matter sensor of claim 11 , wherein for each of the pulses, the analysis system determines a pulse width and using the pulse width determines a size of the particle that corresponds to the pulse.
13. The particulate matter sensor of claim 11 , wherein for each of the pulses, the analysis system determines a pulse height and using the pulse height determines a reflectivity of the particle that corresponds to the pulse.
14. The particulate matter sensor of claim 11 , wherein for each of the pulses, the analysis system determines a pulse shape and using the pulse shape identifies a shape of the particle that corresponds to the pulse.