An air monitoring device (100) includes an outer casing (101) configured to receive an airflow (102) comprising particulate; a bore (103) located inside the outer casing (101); and a collection probe (104) located inside the outer casing (101), the collection probe (104) being configured such that there is a gap (105) between an exit of the bore (103) and an entrance of the collection probe (104), such that particulate in the airflow (102) having a diameter larger than a threshold flows through an interior of the collection probe (104)

Tissandier, Michael D.

NASA Technical Reports Server

105 
(12) United States Patent 
Tissandier 
(54) AIR MONITORING DFVICF 
(75) Inventor: Michael D. Tissandier, Alto Loma, CA 
(US) 
(73) Assignee: Hamilton Sundstrand Space Systems 
International, Inc., Windsor Locks, CT 
(US) 
(*) Notice: 	 Subject to any disclaimer, the term of this 
patent is extended or adjusted under 35 
U.S.C. 154(b) by 140 days. 
(21) Appl. No.: 12/709,739 
(22) Filed: 	 Feb. 22, 2010 
(65) 	 Prior Publication Data 
US 2011/0203363 Al 	 Aug. 25, 2011 
(51) Int. Cl. 
G01 W 1/00 	 (2006.01) 
(52) U.S. Cl . .................................................... 73/170.01 
(58) Field of Classification Search ........................ None 
See application file for complete search history. 
(1o) Patent No.: 	 US 8,240,201 B2 
(45) Date of Patent: 	 Aug. 14, 2012 
(56) References Cited 
U.S. PATENT DOCUMENTS 
	
4,670,135 A 	 6/1987 Marple et al. 
	
5,425,802 A * 	 6/1995 Burton et al . ..................... 95/32 
	
5,788,741 A * 	 8/1998 Burton et al . ..................... 95/32 
	
6,062,392 A 	 5/2000 Birmingham et al. 
	
6,698,592 B2 	 3/2004 Kenning et al. 
2007/0240520 Al* 10/2007 Kim et al . .................. 73/861.71 
2008/0028869 Al* 	 2/2008 Kim et al . .................. 73/861.71 
OTHER PUBLICATIONS 
Hinds, Aerosol Technology Properties, Behavior, and Measurement 
ofAirborne Particles, 1999, pp. 134-136, second edition, John Wiley 
& Sons, Inc., Los Angeles, California. 
* cited by examiner 
Primary Examiner Andre Allen 
(74) Attorney, Agent, or Firm Cantor Colburn LLP 
(57) ABSTRACT 
An air monitoring device (100) includes an outer casing (101) 
configured to receive an airflow (102) comprising particulate; 
a bore (103) located inside the outer casing (101); and a 
collection probe (104) located inside the outer casing (101), 
the collection probe (104) being configured such that there is 
a gap (105) between an exit of the bore (103) and an entrance 
of the collection probe (104), such that particulate in the 
airflow (102) having a diameter larger than a threshold flows 
through an interior of the collection probe (104). 
7 Claims, 1 Drawing Sheet 
100 
111 112 
102 
I 
107 
I I I 
107 
I 
I ► 
I I 
I I 
109 
104 I 
102 1& ASS 102 106 I 
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U.S. Patent 	 Aug. 14, 2012 	 US 8,240,201 B2 
US 8,240,201 B2 
1 
AIR MONITORING DEVICE 
FEDERAL RESEARCH STATEMENT 
This invention was made with Government support under 
Government Contract NN706TA25C, awarded by the 
National Aeronautics and Space Administration (NASA). 
The Government has certain rights in this invention. 
FIELD OF INVENTION 
The subject matter disclosed herein generally relates to the 
field of air monitoring. 
DESCRIPTION OF RELATED ART 
The separation of particulate matter from gas is necessary 
for various air monitoring applications, including atmo-
spheric analysis of the gas, characterization of particulates in 
the gas, and for protecting mechanical or electronic equip-
ment from the particulates in the gas. In some air monitoring 
applications, the gas is sampled at an interface between the 
gas located outside the monitoring device, which is at atmo-
spheric pressure, and a vacuum located inside the monitoring 
device. The interface may comprise a frit comprising sintered 
metal configured to have a series of micron-sized pores. The 
pores may become blocked if particulate having a diameter 
greater than or equal to the pore size is allowed to impinge on 
the surface of the frit. 
A virtual impactor is a type of air monitoring device that 
addresses frit clogging by separating large particulate and the 
gas being monitored into two separate airflows for sampling. 
However, the two flow paths in a virtual impactor device 
require separate pumps and separate flow control devices, 
which may increase the size, weight, power drain, and com-
plexity of the air monitoring device. 
BRIEF SUMMARY 
According to one aspect of the invention, an air monitoring 
device includes an outer casing configured to receive an air-
flow comprising particulate; a bore located inside the outer 
casing; and a collection probe located inside the outer casing, 
the collection probe being configured such that there is a gap 
between an exit of the bore and an entrance of the collection 
probe, such that particulate in the airflow having a diameter 
larger than a threshold flows through an interior of the col-
lection probe. 
Other aspects, features, and techniques of the invention 
will become more apparent from the following description 
taken in conjunction with the drawings. 
BRIEF DESCRIPTION OF THE SEVERAL 
VIEWS OF THE DRAWINGS 
Referring now to the drawings wherein like elements are 
numbered alike in the several FIGURES: 
FIG. 1 illustrates a cross-section of an embodiment of an 
air monitoring device. 
DETAILED DESCRIPTION 
Embodiments of an air monitoring device are provided, 
with exemplary embodiments being discussed below in 
detail. 
A cross-section of an embodiment of an air monitoring 
device is shown in FIG. 1. Air monitoring device 100 com- 
2 
prises an outer casing 101 containing a bore 103 and a col-
lection probe 104; outer casing 101, bore 103, and collection 
probe 104 may be cylindrical in some embodiments. A gap 
105 is located between the exit of the bore 103 and the 
5 entrance to collection probe 104. Particulate-filled airflow 
102 enters the outer casing 101 and is accelerated through 
bore 103. The bore 103 has a diameter (indicated by dashed 
line 111) that is smaller than a diameter (indicated by dashed 
line 110) of the outer casing 101; therefore, bore 103 acts to 
io accelerate airflow 102. Bore 103 is sufficiently long to ensure 
the particles in airflow 102 reach a relatively high velocity, 
and therefore have a large momentum. As the airflow 102 
exits the bore 103, airflow 102 splits into airflow 106 and 
airflow 107 (airflow 106 and 107 are also referred to as por- 
15 tion 106 and 107 of airflow 102). Particles in airflow 102 
having a diameter larger than a particle size threshold become 
part of airflow 107. Due to the large momentum imparted by 
the acceleration of airflow 102 in bore 103, the particles larger 
than the threshold in airflow 102 are unable to make the turn 
20 throughthe gap 105, and enterthe collectionprobe 103 as part 
of airflow 107. Airflow 107 may also comprise particles hav-
ing a diameter smaller than or equal to the particle threshold. 
Airflow 106 comprises only particles having a diameter 
smaller than or equal to the particle threshold. The particles 
25 smaller than the threshold in airflow 106 have relatively low 
momentum, and may successfully turn through gap 105 and 
flow between the exterior of collection probe 104 and the 
interior of outer casing 101. Airflow 106 interacts with frit 
108 for sampling and analysis. Because airflow 106 only 
30 contains particulate having a diameter smallerthan orequal to 
the threshold size, airflow 106 may be sampled without clog-
ging the frit 108. Frit 108 may be located in any appropriate 
location in the outer diameter of outer casing 101 in between 
the gap 105 and the end of collection probe 104, and may be 
35 relatively close to the gap 105 in some embodiments. Air-
flows 106 and 107 exit the outer casing 101 after passing 
around (in the case of airflow 106) or through (in the case of 
airflow 107) collection probe 104. Bore 103 and collection 
probe 104 may be relatively simple to produce, and require no 
4o active control once appropriate airflow is established through 
air monitoring device 100. 
The particle threshold may be a particle diameter of about 
0.2 microns in some embodiments; the particle threshold may 
be made larger or smaller by adjusting the ratio of the flow 
45 velocities between the outside and inside of the collection 
probe 104. The ratio of flow velocities may be adjusted by 
adjusting the diameter (indicated by dashed line 112) of the 
necking 109, the size of the gap 105, the flow rate of airflow 
102, and/or the diameter 111 of bore 103 (which determines 
5o amount of acceleration imparted to airflow 102 in bore 103). 
However, there are physical limits on the range of flow veloci-
ties that may be attained, which also act to limit the particle 
threshold at relatively small sizes. As the particle threshold 
approaches smaller and smaller sizes, the gap 105 between 
55 the collection probe 104 and the bore 103 must become 
smaller. This decreases the conductance through the gap 105, 
and thus, airflow 106 to the frit 108, to the point that none of 
airflow 102 may flow through gap 105. In this case, frit 108 
may only measure air trapped outside the collection probe 
60 104. This may be mitigated by reducing the diameter 112 of 
the necking 108; however, this has the effect of restricting 
total airflow through the air monitoring device 100. 
The technical effects and benefits of exemplary embodi-
ments include a relatively small, lightweight air monitor that 
65 prevents clogging of the sampling frit. 
The terminology used herein is for the purpose of describ-
ing particular embodiments only and is not intended to be 
US 8,240,201 B2 
3 
limiting of the invention. While the description of the present 
invention has been presented for purposes of illustration and 
description, it is not intended to be exhaustive or limited to the 
invention in the form disclosed. Many modifications, varia-
tions, alterations, substitutions, or equivalent arrangement 
not hereto described will be apparent to those of ordinary skill 
in the art without departing from the scope and spirit of the 
invention. Additionally, while various embodiment of the 
invention have been described, it is to be understood that 
aspects of the invention may include only some of the 
described embodiments. Accordingly, the invention is not to 
be seen as limited by the foregoing description, but is only 
limited by the scope of the appended claims. 
The invention claimed is: 
1. An air monitoring device (100), comprising: 
an outer casing (101) configured to receive an airflow (102) 
comprising particulate; 
a bore (103) located inside the outer casing (101); 
a collection probe (104) located inside the outer casing 
(101), the collection probe (104) being configured such 
that there is a gap (105) between an exit of the bore (103) 
and an entrance of the collection probe (104), such that 
particulate in the airflow (102) having a diameter larger 
than a threshold flows through an interior of the collec-
tion probe (104), wherein a portion (106) of the airflow 
(102) comprising particulate having a diameter smaller 
than or equal to the threshold flows through the gap 
4 
(105) and between an exterior of the collection probe 
(104) and an interior of the outer casing (101); and 
a frit (108) located on the outer casing (101) between the 
gap (105) and an exit of collection probe (104), the frit 
5 (108) configured to sample the portion (106) of the air-
flow (102) comprising particulate having a diameter 
smaller or equal to than the threshold. 
2. The air monitoring device (100) of claim 1, wherein the 
collection probe (104) comprises necking (109) at an exit of 
io the collection probe (104), the necking (109) having a diam-
eter (112), and wherein the threshold is determined based on 
the diameter (112) of the necking (109). 
3. The air monitoring device (100) of claim 1, wherein the 
threshold is determined based on a flow rate of the airflow 
15 (102). 
4. The air monitoring device (100) of claim 1, wherein the 
threshold is about 0.2 microns. 
5. The air monitoring device (100) of claim 1, wherein the 
bore (103) has a diameter (111) that is smaller than a diameter 
20 (110) of the outer casing (101), and wherein the bore (103) is 
configured to increase a velocity of the airflow (102). 
6. The air monitoring device (100) of claim 5, wherein the 
threshold is determined based on the diameter (111) of the 
bore (103). 
25 	 7. The air monitoring device (100) of claim 1, wherein the 
threshold is determined based on a size of the gap (105). 


Air monitoring device

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