 |
Description  |
|
|
BACKGROUND OF THE INVENTION
The present invention relates to a miniature gas chromatograph apparatus
and, more particularly, to one which uses a substrate wafer with grooves
etched by techniques from integrated circuit technology.
The technology of gas chromatography is well-known in the art. In recent
years, however, there has been great development in the field of gas
chromatography in which the etching technology that is used to make
integrated circuit devices is used to etch the gas channels in a
semi-conductor substrate wafer. With this technology, the size of gas
channels in a substrate wafer can be reduced, thereby making miniaturized
gas chromatography systems possible.
In a report entitled "A Feasibility Study Of A Pocket-Size Gas
Chromatographic Air Analyzer" dated July 1977, prepared under the National
Institute For Occupational Safety And Health Contract NIOSH2100-76-0140, a
pocket-size gas chromatograph apparatus is disclosed. The present
invention is an improvement over that device.
SUMMARY OF THE INVENTION
Therefore, in accordance with the present invention, there is provided a
substrate wafer which has a carrier gas groove means, a valve seat means
connected to the carrier gas groove means for controlling the flow of gas
therethrough, and a sample gas groove means which also passes through the
valve seat means. A plate cooperates with the wafer and the groove means
to define gas channels. A valve actuating means is attached to the valve
seat means for controlling the flow of gas from the sample gas channel
means into the carrier gas channel means. A pump means is attached to the
wafer, connected to the sample gas channel means with the pump cooperating
with the valve actuating means for injecting sample gas from the sample
gas channel means into the carrier gas channel means. A modular capillary
tube means is attached to the wafer, one end of which is connected to the
carrier gas channel means. A detector means is connected to the other end
of the capillary tube means for measuring properties of gas flowing from
the capillary tube means.
The present invention is also an improvement to a gas chromatography
system, which has a carrier gas channel means, a valve means, with the
carrier gas channel means passing through the valve means, a sample gas
channel means, and with the sample gas channel means also passing through
the valve means. The valve means is for controlling the flow of gas from
the sample gas channel means into the carrier gas channel means. A
capillary tube means is connected to the carrier gas channel means. A
detector means is connected to the capillary tube means for measuring the
properties of the gas flowing from the capillary tube means. The
improvement of the present invention comprises a pump means which is
connected to the sample gas channel means. The pump means cooperates with
the valve means to inject gas from the sample gas channel means through
the valve means into the carrier gas channel means. The volume of the
sample gas channel means between the valve means and the pump means is
such that no gas from the pump means is injected into the carrier gas
channel means.
Finally, the present invention is directed to a miniature valve apparatus,
a miniature gas injection pump apparatus, and a miniature coupling device
for fitting an external tube to a gas channel in a substrate wafer.
DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic diagram of a gas chromatography system with the
assembly of the present invention.
FIG. 2 is a footprint of the gas chromatography assembly of the present
invention.
FIG. 3 is a cross-sectional view of the assembly of FIG. 2 taken along the
line 3--3.
FIG. 4 is a partial cross-sectional view of a normally closed valve
actuator used in the assembly of the present invention.
FIG. 5 is a partial cross-sectional view of a normally open valve actuator
used in the assembly of the present invention.
FIG. 6 is a partial cross-sectional view of the injection pump used in the
assembly of the present invention.
FIG. 7 is a partial cross-sectional side view of the modular capillary tube
mounted on the assembly of the present invention.
DETAILED DESCRIPTION OF THE DRAWINGS
Referring to FIG. 1, there is shown a schematic view of a miniature gas
chromatography system, generally designated as 10. The system 10 comprises
a helium supply tank 12, which provides a carrier gas for the system 10.
The carrier gas leaves the supply tank 12 and enters a line 14. The line
14 has disposed therein a restrictor 16, which is used to reduce the flow
volume of the carrier gas. The carrier gas passes through the restrictor
16 to a first valve 18. From the first valve 18, the carrier gas is
entered into a surge tank 20. The carrier gas, from the first valve 18,
also enters into to a relief valve 22. The relief valve 22 is used to
relieve any pressure over that which is necessary for charging the surge
tank 20. Carrier gas from the surge tank 20 is entered into the carrier
gas input 28 of the assembly 26 of the present invention.
The assembly 26 of the present invention is comprised of a substrate wafer
102, which has grooves etched therein. A typical material for the wafer
102 is single crystalline silicon. A plate 104, typically Pyrex glass, is
attached to one side 103 of the wafer 102 and cooperates with the wafer
102 and the grooves therein to form gas channels. On the other side 105 of
the plate 104 is a support 106. Typically, the support 106 is made of
aluminum. The surge tank 20 is in the aluminum support 106. A conduit 30
passes through the plate 104, connecting the surge tank 20 to the carrier
gas input 28. From the helium input 28, a first channel 29 is etched in
the wafer 102 on the one side 103. The other end of the first channel 29
is connected to a first pressure sensor 34, which is used to determine the
proper operating pressure for the carrier gas within the assembly 26. The
first pressure sensor 34 is external to the assembly 26 and is mounted on
the assembly 26. The first pressure sensor 34 is mounted on the other side
107 of the wafer 102 and is connected to the first channel 29 by a
feedthrough. A second channel 35 within the wafer 102 connects the helium
input 28 to a second valve seat 38. Within the second channel 35 is a
second restrictor 36, the function of which will be described hereinafter.
From the second valve seat 38, one end of a third channel 40 is connected.
The other end of the third channel 40 is connected to an external column
42. From the external column 42 a fourth channel 44 connects it to a
detector 46. A fifth channel 48 in the assembly 26 connects the detector
46 to a vent.
A source 50 provides the sample gas to be analyzed in the gas system 10.
The sample gas enters the assembly 26 through a sixth channel 52 and into
a third valve seat 54. A seventh channel 55 connects the third valve seat
54 to the second valve seat 38. From the second valve seat 38, the sample
gas passes through an eighth channel 56 to a pump connection point 58. At
the pump connection point 58, a high pressure pump 64 is connected
thereto. The high pressure pump 64 has an inlet 66 and an outlet 68. The
inlet 66 of the high pressure pump 64 is connected at the pump connection
point 58. The outlet 68 of the high pressure pump 64 is connected to a
diaphragm vacuum pump 70. The diaphragm vacuum pump 70 draws the sample
gas from the high pressure pump 64 and sends it out to vent. A ninth
channel 60 connects the pump connection point 58 to a second pressure
sensor 62.
The second and third valve seats 38 and 54, respectively, are of the types
shown and described in the report prepared under the National Institute
for Occupational Safety and Health, as set forth in the Background of the
Invention. A second and third valve actuating means 38a and 54a (shown in
FIGS. 4 and 5, respectively) are mounted on the second and third valve
seats 38 and 54, respectively. The first valve 18 can also comprise a
valve actuator operating on a valve seat, similar to the second valve
actuator 38a on the second valve seat 38. The valve actuating means 38a
and 54a will be described in greater detail hereinafter, and are attached
to the substrate wafer 102 on the other side 107 thereof. Also attached to
the other side 107 of the substrate 102 is the first pressure sensor 34,
the second pressure sensor 62, the pump 64, the external column 42 and the
detector 46. Feedthroughs in the substrate wafer 102 communicate each of
the aforementioned external devices with the channels which are etched on
the one side 103 of the wafer 102. The detector 46 can be of the type
described in the patent application Ser. No. 141,269, filed on Apr. 18,
1980, now abandoned. The first and second pressure sensors 34 and 62,
respectively, can be of commercially available type of sensor, such as
Kulite Semiconductor Inc. Model PTQH. The external column 42 can also be
of a commercially available type of column, such as the fused silica
capillary column manufactured by Hewlett-Packard Corporation. The pump 64
used in the assembly 26 will be described in detail hereinafter.
In normal operations, the carrier gas will flow from the tank 12 through
the first valve 18 and into the surge tank 20. Once the surge tank 20 has
been charged or pressurized, the first valve 18 is closed. Thereafter, the
carrier gas will flow from the surge tank 20, through the conduit 30 into
the second channel 35, through the restrictor 36 therein. The carrier gas
then flows through the second valve seat 38, through the third channel 40
to the external column 42. The carrier gas will then re-enter the assembly
26 from the external column 42 and pass through the fourth channel 44 to a
detector 46 and through a fifth channel 48 to vent. During normal
operation, the sample gas will travel from the source 50, through a
normally open third valve seat 54, through the second valve seat 38 into
the inlet 66 of the pump 64. From the pump 64, the sample gas is drawn
through the outlet 68 of the pump 64 by the diaphragm vacuum pump 70 and
to vent 72. The diaphragm vacuum pump 70 draws the sample gas from the
sample gas channel line (i.e. sixth, seventh and eighth channels 52, 55,
and 56 respectively) out to vent. The vacuum action of the pump 70 draws
in new sample gas from the source 50 into the sample gas channel line.
When it is desired to inject sample gas into the carrier gas line for
testing by the external column 42, the third valve seat 54 is closed by
the third valve actuating means 54a, thereby shutting the flow of sample
gas from the source 50. The pump 64 is activated. When the pressure in the
seventh, eighth and ninth channels, 55, 56, and 60, respectively, as
measured by the second pressure sensor 62 is greater than the pressure in
the first and second channels 29 and 35, respectively, as measured by the
first pressure sensor 34 by a pre-determined amount, the second valve
actuating means 38a which is seated on the second valve seat 38 is then
operated to permit the sample gas from the eighth channel 56 to enter into
the carrier gas line. The second valve seat 38 is opened for a
pre-determined amount of time (typically on the order of a few
milliseconds). During the injection of the sample gas from the eighth
channel 56, the sample gas enters through the second valve seat 38 and
into the second and the third channels 35 and 40, respectively, of the
carrier gas line. The second restrictor 36 in the second channel 35
prevents the sample gas from flowing upstream into the surge tank 32 to
contaminate it. Therefore, although some sample gas will enter into the
second channel 35, substantially all of the sample gas from the eighth
channel 56 will be injected into the third channel 40, into the external
column 42 and will be measured by the detector 46.
To eliminate the problem of pump contamination, i.e., gas from within the
pump 64 entering into the carrier gas line and the external column 42, the
volume of the eighth channel 56 is chosen such that it acts as a buffer
between the sample gas from the pump 64 and the second valve seat 38. In
particular, the volume of the eighth channel 56 is such that, upon
activation of the pump 64, no sample gas which has been in the pump 64
reaches the second valve seat 38. The volume of the eighth channel 56 must
be greater than the compression ratio of the pump 64 times the volume of
the gas which is in the second valve seat 38, seventh channel 55 and that
portion of the third valve seat 54 which is in communication with the
seventh channel 55 and is not closed by the third actuator 54a. In this
manner, contamination of gas from the pump 64 into the carrier gas line is
avoided.
As soon as the second actuator 38 returns to its normally closed position,
the pump 64 stops its injection process and withdraws to its normal open
position permitting gas flow from the inlet 66 to the outlet 68. Third
valve seat 54 is then opened permitting sample gas to flow from the source
50 to the pump 64, and out to vent by the diaphragm pump 70.
With the external column 42 exterior to the wafer 104, the manufacturing of
gas chromatography systems 10 for different applications is greatly eased.
The external column 42 contains chemical means for the separation of the
sample gas mixture into its constituent components. For analysis of
different sample gases in different applications, the external column 42
may have to be different. However, the assembly 26 for the different
applications can all be the same. Thus, for analyzing different gases, the
different external columns 42 can be attached to the same assembly 26 for
various applications. In this manner, only the external column 42 is
different for different uses. Commonality of parts with decrease in
inventory stock result in savings in manufacturing cost.
Referring to FIG. 4, there is shown a partial cross-sectional view of the
second valve actuator 38a, used in the assembly 26 of the present
invention. The valve actuator 38a consists of a housing 200, with the
housing 200 connected to the silicon wafer 102, plate 104 and support 106
by bolt 202. As shown in FIG. 2, there are three bolts 202 attaching the
actuator 38a to the valve seat 38. Disposed above the housing 200 is an
electrically operated solenoid 204, which is used to activate the valve
200 when desired. The solenoid 204 threadably engages the housing 200, and
is locked into place by a nut 206.
The housing 200 has disposed therein a valve assembly 210. The valve
assembly 210 is bound securely in the housing 200 between the silicon
wafer 102 and the solenoid 204. The assembly 210 has disposed therein a
sleeve 228 with an end 229. The sleeve 228 has an orifice 226 in the end
229 thereof. A pin 224 is within the orifice 226. A circular ring 225 is
at the outer surface of the end 229. The ring 225 engages the diaphragm
230 and when the solenoid 204 is threadably tightened, the ring 225 is
pressed against the diaphragm 230 and the wafer 102 forming a tight seal.
The sleeve 228 also has disposed therein a first plunger 208. The first
plunger 208 slides through a first annular ring 212. The first annular
ring 212 is clamped between the solenoid 204 and the sleeve 228. The first
plunger 208 is mounted in the solenoid 204, such that upon activation of
the solenoid 204, the first plunger 208 is moved in the direction shown by
the arrow A. At the end of the first plunger 208 which is within the
sleeve 228 is a body 214. A first spring 216 is between the body 214 and
the first annular ring 212. The first spring 216 urges the body 214 away
from the solenoid 204.
Within the body 214 is a second plunger 218. The body 214 has a lip 220
therein which captures the second plunger 218. A second spring 222 is also
within the body 214. The second spring 222 urges one end of the second
plunger away from the first plunger 208. At the other end of the second
plunger 218, the plunger 218 is in free contact with the pin 224. The pin
224 is aligned to impinge the diaphragm 230. The diaphragm 230 controls
the flow of gas through the valve seat 38. The pin 224 is aligned to move
in a direction substantially perpendicular to the plane of the diaphragm
230.
In the operation of the valve actuator 38a, when solenoid 204 is not
activated, the first spring 216 urges the body 214 away from the solenoid
204 until the shoulder on the plunger 208 stops against the ring 212.
Similarly, the second spring 222 urges the second plunger 218 away from
the first plunger 208. The action of the second spring 222 against the
second plunger 218 causes the second plunger 218 to impinge the pin 224,
pushing it against the diaphragm 230, closing off the gas flowing to the
valve seat 38.
When the solenoid 204 is activated, the first plunger 208 is pulled in a
direction shown substantially by the arrow A. The first plunger 208 pulls
the body 214 with it in the direction as shown by the arrow A. As the body
214 moves in the direction of "A", the lip 220 of the body 214 pulls the
second plunger 218 also in the direction shown by the arrow A. The effect
of solenoid 204 pulling on the first plunger 208 is then to compress the
first spring 216. The pin 224, however, is only in free contact with the
second plunger 218. The pin 224 moves in the direction shown by the arrow
A only due to the springlike resilient restoring force of the diaphragm
230 and by the force of the gas pushing against the diaphragm 230.
When the solenoid is deactivated, the spring action of the first spring 216
pushes the body 214 away from the solenoid 204. As the bottom end of the
plunger 218 impinges upon pin 224, the plunger 218 stops its movement in
the direction opposite to that shown by arrow A and disengages from the
lip 220 of the body 214. Spring 222 is compressed by the further movement
of plunger 218 in the direction opposite shown by arrow A. The force of
the second spring 222, pushing against the second plunger 218, also pushes
the pin 224 against the diaphragm 230 to close off the valve seat 38.
As can be seen from the foregoing description, in the absence of the force
of activation by the solenoid 204, the valve seat 38 is normally closed to
the flow of gas. Moreover, the pin 224 which impacts the diaphragm 230 to
open or close the valve 38 is moved by the valve assembly 210 only in the
direction opposite to that shown by the arrow A. When the solenoid 204 is
activated, moving the valve assembly 210 away from the pin 224, the pin
224 is moved in the direction opposite to that shown by the arrow A only
by the diaphragm 230 and the force of gas flowing through the valve seat
38.
The function of the valve assembly 210 is to act as a force-transmitting
means, such that during the closing of the valve seat 38, a gentle and
gradual force is applied on the pin 224. In fact, the force which is
applied against the pin 224 to close off the valve seat 38 is applied by
the force of the second spring 222. The second spring 222 can be made to
apply a very gentle and gradual force, such as on the order of 50 grams of
force. Gradual and gentle forces are needed because sudden forces applied
against the pin 224 can cause breakage of the pin 224 and/or greatly
deteriorate the life of the diaphragm 230 when the diaphragm is repeatedly
and suddenly struck by the pin 224 and impinged against the wafer 102.
Finally, because the orifice 226 in which the free pin 224 is situated is
part of the housing 200, and the housing 200 is aligned substantially
perpendicular to the diaphragm 230, and the wafer 102, the pin 224 would
also be aligned substantially perpendicular to the diaphragm 230 and the
wafer 102. This provides greater accuracy in the operation of the valve
38a.
Referring to FIG. 5, there is shown a partial cross-sectional view of the
third valve actuator 54a used in the assembly 26 of the present invention.
The valve actuator 54a consists of a housing 250, with the housing 250
connected to the silicon wafer 102, the plate 104 and the support 106 by
bolts 252. Again, as shown in FIG. 2, there are three bolts 252 attaching
the valve actuator 54a to the assembly 26. Disposed above the housing 250
is an electrically operated solenoid 254 which is used to activate the
valve 54a when desired. The solenoid 254 threadably engages housing 250
and is locked into place by a nut 256.
The housing 250 has disposed therein a valve assembly 260. The valve
assembly 260 is bound securely in the housing 250 between the silicon
wafer 102 and the solenoid 254. The assembly 260 has disposed therein a
sleeve 262. This sleeve 262 is similar to the sleeve 228 described for the
second valve actuator 38a, as shown in FIG. 4. The sleeve 262 has an
orifice 264 at one end 265 thereof. A free pin 266 is disposed within the
orifice 264. The housing 250 is attached to the wafer 102, plate 104, and
support 106, such that the orifice 264 and, therefore, the pin 266 is in
substantially perpendicular alignment with the diaphragm 280 of the valve
seat 54. The sleeve 262 also has a circular ring 263 which engages the
diaphragm 280. When the bolts 252 are tightened, the circular ring 263 is
pressed against the diaphragm 280 and against the wafer 102 forming a
tight seal for the valve seat 54.
Within the valve assembly 260 is a first plunger 268. The first plunger 268
extends through the valve assembly 260 into the solenoid 254. Upon
activation of the solenoid 254, the first plunger 268 is moved in the
direction shown by the arrow "B". A first ring 270 is attached around the
first plunger 268 near the solenoid 254. A second ring 274 is attached
around the plunger 268 by E-ring 269 near the end of the plunger 268, away
from the solenoid 254. A first spring 272 is disposed between the first
ring 270 and the second ring 274 and is always in compression. The second
ring 274 is in contact with one end of a cylindrical body 276. The other
end of the cyclindrical body 276 is in free contact with the pin 266. A
second spring 278 is disposed around the other end of the cyclindrical
body 276 and urges the body 276 away from the one end 265 of the sleeve
262. The action of the second spring 278 is to urge the body 276 against
the second ring 274. The body 276 is urged against the second ring 274
until the second ring 274 comes to a rest against the stop 282.
In the operation of the actuator 54a, when the solenoid 254 is activated,
the plunger 268 is moved in the direction shown by the arrow B. The
movement of the plunger 268 pushes the first ring 270 thereby compressing
the spring 272. The spring 272 then pushes against the second ring 274.
The force of the first spring 272 is then transmitted to the cylindrical
body 276. This force, i.e., the force of the first spring 272, then works
against the force of compression of the second spring 278. Therefore, the
amount of force acting on cylindrical body 276 is the difference in force
between the first spring 272 and the second spring 278. This force acting
on the body 276 is then transmitted to the pin 266. The pin 266 impinges
against the diaphragm 280 closing off the flow of gas through the valve
seat 54.
When the solenoid 254 is de-energized, the force of the second spring 278
would urge the cylindrical body 276 upward, i.e., in the direction
opposite to that shown by the arrow B. The body 276 would then urge
against the second ring 274 pushing the plunger 268 back into the state
shown in FIG. 5. The pin 266 is in free contact with the one end of the
body 276. The pin is retracted and is moved in a direction opposite to
that shown by the arrow B by the springlike force of the diaphragm 280,
returning to its normal position. Therefore, the pin 266 is affected by
the force of activation of the valve actuator 54a in only the direction
shown by the arrow "B". The restoration of the pin 266 to its normal state
is not directly caused by the de-energization of the solenoid 254.
Similar to the description for the actuator 38a shown in FIG. 4, the
function of the valve assembly 260 is to act as a force transmitting means
such that during the activation of the solenoid 254, a more gentle and
gradual force is applied on the pin 266, and consequently against the
diaphragm 280. The amount of force applied against the pin 266 is the
difference in the spring compression between the first spring 272 and the
second spring 278. This difference can be adjusted such that the amount of
force applied against the pin 266 can be extremely gradual and gentle.
Finally, because the orifice 264 in which the pin 266 is situated is part
of the housing 250, the housing 250 can be aligned substantially
perpendicular to the diaphragm 280 and the wafer 102 providing accuracy in
the operation of the valve 54a.
FIG. 6 shows a partial, cross-sectional view of a high-pressure injection
pump 64 used in the assembly 26 of the present invention. The pump 64 has
a housing 402. The housing 402 is attached to the wafer 102, the plate
104, and the aluminum support 106 by a bolt 404. As shown in FIG. 2, there
are three bolts 404 attaching the pump 64 to the assembly 26. The housing
402 has an orifice 403 for connection to a diaphragm vacuum pump 70.
Threadably connected to the housing 402 is a solenoid 406. The solenoid
406 has an operable member 424 which is used to actuate the pump 64.
Inside the housing 402 is a glass tube 411.
A piston 408 is disposed within the glass tube 411. The piston 408 is
prevented from any upward movement past the glass tube 411 by spring stops
410. Piston 408 has an annular groove 409 which is aligned with orifice
403 of housing 402 to allow sample gas flow to the diaphragm vacuum pump
70 during normal operations, when sample gas is not being injected into
the external column 42. The piston 408 also has seals 416 to prevent flow
of gas between the piston 408 and the glass tube 411. The piston 408 has a
base 418, which has an aperture 420 therein.
The piston 408 also has a bore, which has affixed therein a valve guide
430. The valve guide 430 is threaded on to the piston 408 and extends
upward between the base 418 of the piston 408 up to the solenoid operable
member 424. The upper portion of the valve guide 430 has an annular groove
which has therein disposed a spring retainer 432. The spring retainer 432
impinges upon the nylon shoulder washer 412 which, with spring stop 410,
provide spring retainer means for the spring 414.
Within the valve guide 430 is a valve plunger 434. The valve plunger 434
extends from the operable portion 424 of the solenoid 406 down to the base
418. Near the base of the valve plunger 434 is an annular groove 442 which
has disposed thereon sealing O-ring 436. The O-ring 436 prevents the flow
of gas past the O-ring 436 such that gas will not enter between the valve
guide 430 and valve plunger 434. The end of the valve plunger 434 has an
end 440. Disposed about the end 440 is a second O-ring 438. The end 440
and the second O-ring 438 can be sealably engaged with the orifice 420. At
the other end of the plunger 434 is a bore which has | | |
