APPARATUS FOR SENSING AIR-BORNE PARTICULATE MATTER

• US 3,715,911 A
• Filed: 05/11/1970
• Issued: 02/13/1973
• Est. Priority Date: 05/11/1970
• Status: Expired due to Term

• Current Assignee: Raymond L. Chuan
• Original Assignee: Raymond L. Chuan
• Inventors: Chuan, Raymond L.
• Primary Examiner(s): Gill, James J.
• Assistant Examiner(s): Snee, III, C. E.
• Application Number:
  US05/036,222
• Time in Patent Office: 1,009 Days
• Field of Search: 73/23,28,17R,432R,432PS,24-27,29 340/236,237R,237S,421 324/71CP,71R 260/413
• US Class Current: 73/24.03
• CPC Class Codes: G01N 5/00 Analysing materials by weighing, e.g. weighing small particles separated from a gas or liquid G01N9/00 takes precedence ; weighing per se G01G

Abstract

The sensing apparatus of the present invention combines the impaction action of a decelerated small air jet with a quartz crystal microbalance to detect, by mass sensing, the presence of micron size air-borne particulate matter. A quartz crystal, coated with a tacky material and oscillating in a shear mode as part of a resonant circuit, responds to very small changes of mass on its surface by changes in the resonant frequency. This frequency is mixed with that of a reference oscillator and the differential frequency, which is proportional to collected mass, may be counted or converted to an analog signal suitable for direct recording or display, or for the performing of control functions.

Claims

1. Apparatus for sensing and measuring the mass of particulate matter in an atmosphere, comprising:

a housing having an inlet, means for drawing an atmospheric sample into said housing through said inlet, nozzle means mounted within said housing for accelerating an atmospheric sample entering said inlet, a sensing crystal mounted within said housing and having a surface positioned adjacent said nozzle means on which the accelerated atmospheric sample is impinged, a tacky coating of sulfated ricinoleic acid on said sensing crystal surface to retain by adhesion predetermined particulate matter in the atmospheric sample impinged thereon, means for oscillating said sensing crystal in a shear mode such that the resonant frequency thereof is substantially inversely proportional to the mass thereof, a sealed reference crystal mounted within said housing in spaced relation to said sensing crystal, means for oscillating said reference crystal at a predetermined frequency, and means for detecting and comparing the frequencies of oscillation of said sensing crystal and said reference crystal and for providing an output frequency which is a measure of the frequency difference between said sensing and reference crystals and thereby a measure of the mass of particulate matter retained on said sensing crystal surface.

2. The apparatus of claim 1 wherein said sensing crystal and said reference crystal are matched quartz crystals.

3. The apparatus of claim 1 wherein said oscillating means and said detecting and comparing means comprise a sensing oscillator circuit, a reference oscillator circuit and a mixer circuit.

4. Apparatus for sensing and measuring the mass of particulate matter in an atmosphere, comprising:

a housing having an inlet, means for drawing an atmospheric sample into said housing through said inlet, nozzle means mounted within said housing for accelerating an atmospheric sample entering said inlet, a sensing crystal mounted within said housing and having a surface positioned adjacent said nozzle means on which the accelerated atmospheric sample is impinged, said sensing crystal being Approximately 1 cm. in diameter and approximately 0.015 cms. in thickness, a tacky coating on said sensing crystal surface to retain by adhesion predetermined particulate matter in the atmospheric sample impinged thereon, said tacky coating being approximately 10 4 gm. in mass, approximately 3 mm. in a diameter and approximately 1 micron in thickness, means for oscillating said sensing crystal in a shear mode such that the resonant frequency thereof is substantially inversely proportional to the mass thereof, a sealed reference crystal mounted within said housing in spaced relation to said sensing crystal, means for oscillating said reference crystal at a predetermined frequency, and means for detecting and comparing the frequencies of oscillation of sensing crystal and said reference crystal and for providing an output frequency which is a measure of the frequency difference between said sensing and reference crystals and thereby a measure of the mass of particulate matter retained on said sensing crystal surface.

5. The apparatus of claim 4 wherein the atmospheric sample flow rate through said inlet nozzle is approximately 50 to 500 cm3 sec 1.

6. Apparatus for collecting particulate matter in an atmosphere, comprising:

an outer housing having inlet and outlet openings, an inner housing movably mounted within said outer housing and having inlet and outlet openings adapted to be aligned with said inlet and outlet openings of said outer housing when said inner housing is in a first position and to be disposed out of alignment therewith when said inner housing is in a second position, means in said outlet opening of said outer housing for drawing an atmospheric sample into said inlet openings of said inner and outer housings when said inner housing is in said first position, nozzle means in said inlet opening of said inner housing for accelerating an atmospheric sample entering said last mentioned inlet opening, a sensing crystal mounted within said inner housing having a surface positioned adjacent said nozzle means on which the accelerated atmospheric sample is impinged, a tacky coating on said sensing crystal surface adapted to retain by adhesion predetermined particulate matter in the atmospheric sample impinged thereon, means for oscillating said sensing crystal, a sealed reference crystal mounted within said inner housing in spaced relation to said sensing crystal, means for oscillating said reference crystal at a predetermined frequency, means for detecting and comparing the frequencies of oscillation of said sensing crystal and said reference crystal, and for providing an output frequency which is a measure of the frequency difference between said sensing and reference crystals, and means for moving said inner housing between said first and second positions.

7. The apparatus of claim 6 wherein said tacky coating is chemically inert.

8. The apparatus of claim 6 wherein said tacky coating has a low vapor pressure.

9. The apparatus of claim 6 wherein a collector means is mounted within the inlet opening of said outer housing to collect particulate matter above a predetermined size and prevent it from entering said inner housing.

10. The apparatus of claim 9 wherein an inlet block is mounted on said outer housing in communication with said inlet opening thereof, and nozzle means is mounted within said inlet block for accelerating an atmospheric sample entering said block prior to passage through said collector means.

11. The apparatus of claim 10 wherein a thermal baffle assembly is mounted on said inlet block for adjusting the temperature of the atmospheric sample to a predetermined temperature;

and for smoothing out small fluctuations in temperature.