Abstract:
A leak detector having a multi-stage concentrator, consisting of an array of heater elements which desorb analytes in a phased manner, in synch with the sample stream, to maximize sensitivity. The heater elements of the concentrator are coated with adsorber material on both sides of the heater elements, i.e., top and bottom sides, and have small anchor points to minimize power dissipation. The concentrated gas mixture output of the concentrator is electronically injected into a separator, which for separates the constituents of the detected analyte-fluid and recognizing the nature or source of the analyte.

Description:
This application claims the benefit of U.S. Provisional Application No. 60/414,211, entitled “PHASED SENSOR”, filed Sep. 27, 2002, wherein such document is incorporated herein by reference. 
    
    
     BACKGROUND 
     The invention pertains to detection, identification and analyses of gases. Related art fuel gas leak detectors may be low-cost (and in part reasonably sensitive) but cannot identify the nature of the fuel leak (natural gas, swamp gas, propane or gasoline vapors), while others such as portable GCs (gas chromatographs) are both moderately sensitive and able to identify the fuel, but are very costly, slow (greater than about ten seconds response time) and consume much power. 
     Aspects of structures and processes related to gas detectors may be disclosed in U.S. Pat. No. 6,393,894, issued May 28, 2002, and entitled “Gas Sensor with Phased Heaters for Increased Sensitivity,” which is incorporated herein by reference, and in U.S. Pat. No. 4,944,035, issued Jul. 24, 1990, and entitled “Measurement of Thermal Conductivity and Specific Heat,” which is incorporated herein by reference. 
     SUMMARY 
     A gas leak detector and analyzer may be realized via affordable, in-situ, ultra-sensitive, low-power, low-maintenance and compact micro detectors and analyzers, which can wirelessly or by another medium (e.g., wire or optical fiber) send their detection and/or analysis results to a central or other manned station. A micro gas leak detector incorporating a phased heater array, concentrator and separator as an enhanced detector contribute to the availability of a low-cost multi-gas analyzer and system to provide gas leak detection. 
     The present gas leak detector is low-power, fast, compact, low cost, intelligent, wireless or not, low maintenance, robust and highly sensitive. It is a phased heater based leak detector that responds in about one second, uses less than one watt of power, can identify the nature of the fuel via its constituents, and is palm-top-sized and thus very portable 
     The heater elements of a phased heater array may be coated 
     with an adsorber material on both surfaces, i.e., top and bottom sides, for less power dissipation and more efficient heating of the incoming detected gas. The heater elements may have small widths for reduced power dissipation. There is a heater membrane that has a small number anchor points for little heat conduction from the heater elements. 
     The surfaces of inside channels of the heater array, except those surfaces intentionally by design coated with an adsorber material, may be coated with a non-adsorbing, thermal insulating layer. The thickness of the adsorber coating or film is reduced thereby decreasing the time needed for adsorption and desorption. A thrifty pump may be implemented for pulling in a sample of the fluid being checked for detection of a possible gas leak from somewhere. Low-power electronics having a sleep mode when not in use may be utilized. Thus, the present leak detector uses very little power. 
     The gas leak detector may be integrated on a chip with conventional semiconductor processes or micro electromechanical machined system (MEMS) techniques. This kind of fabrication results in low-power consumption, compactness and in situ placement of the detector. The flow rate of the air or gas sample through the detector may be very small. Further, a carrier gas for the samples is not needed and thus this lack reduces the dilution of the samples being tested, besides eliminating the associated maintenance and bulk of pressurized gas-tank handling. This approach permits the detector to provide quick analyses and prompt results, maybe at least an order of magnitude faster than some related art devices. It avoids the delay and costs of labor-intensive laboratory analyses. The detector is intelligent in that it may have an integrated microcontroller for analysis and determination of gases detected, and may maintain accuracy, successfully operate and communicate information in and from unattended remote locations. The detector may communicate detector information, analyses and results via utility lines, or optical or wireless media, with the capability of full duplex communication to a host system over a significant distance with “plug-and-play” adaptation and simplicity. The system is net-workable. It may be inter-connectable with other gas sample conditioning devices (particle filters, valves, flow and pressure sensors), local maintenance control points, and can provide gas leak monitoring via the internet. The detector is robust. It can maintain accuracy in a high electromagnetic interference (EMI) environment such as in the vicinity of electrical power distribution sub-stations where very strong electrical and magnetic fields are present. The detector has high sensitivity. It offers sub-ppm (parts-per-million) level detection which is 100 to 10,000 times better than related art technology, such as conventional gas chromatographs which may offer a sensitivity between the 1 to 10 ppm range. The detector is, among other things, a lower-power, faster, and more compact, more sensitive and affordable version of a gas chromatograph. It may also be lower power-consuming and faster than previous versions of the present kind of phased-heater detectors which require heavy batteries needing many changes or recharges, which may be avoided in the present detector. The latter detector may have structural integrity, and have very low or no risk of leakage in the application of detecting and analyzing pressurized fluid samples, over a very large differential pressure range. 
     In the leak detector, a small pump, such as a Honeywell MesoPump™ preferably draws a sample into the sensor system, while only a portion of it flows through the phased heater sensor at a rate controlled by the valve (which could be a Honeywell MesoValve™ or Hoerbiger PiezoValve™). This enables fast sample acquisition despite long sampling lines, yet provides a regulated, approximately 1 to 3 cm 3 /min flow for the leak detector. The pump of the leak detector may be arranged to draw sample gas through a filter in such a way as to provide both fast sample acquisition for and regulated flow through the phased heater sensor. 
     As the sample pump draws sample gas through the leak detector, the gas is expanded and thus increases its volume and linear velocity. The control circuit is designed to compensate for this change in velocity to keep the heater “wave” in sync with the varying gas velocity in the detector. To compensate for the change in sample gas volume as it is forced through the heater channels, its electronics may need to adjust either the flow control and/or the heater “wave” speed to keep the internal gas flow velocity in sync with the heater “wave”. 
     During leak survey operation, present detector&#39;s ability (like any other slower GCs) may sense multiple trace constituents of air such as about 330 to 700 ppm of CO 2 , about 1 to 2 ppm of CH 4  and about 0.5 to 2.5 percent of H 2 O. This enables on-line calibration of the output elution times as well as checking of the presence of additional peaks such as ethane, indicating natural gas, propane or other gas pipeline leak. The ratio of sample gas constituent peak heights thus reveals clues about the source of the trace gases, which could include car exhaust or gasoline vapors. 
     The leak detector may have sensitivity, speed, portability and low power that make it especially well suited for safety-mandated periodic leak surveys of natural gas or propane gas leaks along transmission or distribution pipeline systems, and gas leaks in chemical process plants. 
     The detector may in its leak sensing application use some or all sample gas constituents (and their peak ratios) as calibration markers (elution time identifies the nature of the gas constituents) and/or as leak source identifiers. If the presence alone of a certain peak such as methane (which is present in mountain air at about one to two ppm) may not be enough information to indicate that the source of that constituent is from swamp gas, natural/pipeline gas or another fluid. 
     The proposed leak sensor may be used as a portable device or installed at a fixed location. In contrast to comparable related art sensors, it is more compact than portable flame ionization detectors without requiring the bulkiness of hydrogen tanks, faster and more sensitive than hot-filament or metal oxide combustible gas sensors, and much faster, more compact and more power-thrifty than conventional and/or portable GCs. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 is a block diagram of a possible leak detector monitor system. 
     FIG. 2 shows details of a micro gas detector apparatus; 
     FIG. 3 is a layout to show the principle of operation of an illustrative sensor apparatus; 
     FIG. 4 is a cross-sectional side view of the illustrative sensor apparatus in FIG. 3; 
     FIG. 5 is a cross-sectional end view of the illustrative sensor apparatus of FIG. 3 
     FIG. 6 is a graph showing illustrative heater temperatures, along with corresponding concentration pulses produced at each heater element of the sensor apparatus; 
     FIG. 7 is a graph showing a number of heater elements to illustrate their way of step-wise build-up on analyte concentration; 
     FIG. 8 is a graph showing a concentration pulse that reaches about a 100 percent concentration level; 
     FIG. 9 is a layout of another illustrative sensor assembly; 
     FIG. 10 is a schematic view of how to apply the sensor to sample a fluid stream (e.g., stack gas) for its gas composition analysis; 
     FIG. 11 is a timing chart showing the operation of the sensor assembly of FIG. 10; 
     FIG. 12 is a basic layout of an integrated circuit that includes a sensor, a concentrator, a separator, and a sensor; and 
     FIG. 13 shows a table revealing various power consumption levels of parts of the gas leak detector. 
    
    
     DESCRIPTION 
     FIG. 1 reveals an illustrative diagram of a low power leak detector system  11 . An input fluid  25  from an ambient space or volume  41  may enter a conduit or tube  19  which is connected to an input  34  of a low power leak detector  15 . Fluid  25  is processed by detector  15 . Processed fluid  37  exits output  36  of detector  15  and is exhausted to a volume, wherever designated, via a conduit or tube  39 . “Fluid” may be used as a generic term that includes gases and liquids as species. The results or findings may be sent to a microcontroller or processor  29  for analysis. Microcontroller or processor  29  may send various signals to detector  36  for control, adjustment, calibration or other purposes. The analysis calculations, results or other information may be sent to modem  35  for conversion into signals to be sent to a station  31  via lines, fiber or other like media. Also, such output to modem  35  may be instead or simultaneously sent to transmitter  33  for wireless transmission to a station  31 , together with information on the actual location of the detector obtained, e.g., via GPS, especially if it is being used as a portable device. Also, stations  31  may send various signals to modem  35  and receiver  33 , which may be passed on to microcontroller or processor  29  for control, adjustment, calibration or other purposes. 
     FIG. 2 reveals micro gas leak detection apparatus  15 . Sample stream  25  containing gas from a possible leak may enter input port  34  from pipe or pick-up tube  19 . There may be a particle filter  43  for removing dirt and other particles from the stream of fluid  25  that is to enter apparatus  15 . This removal is for the protection of the apparatus and the filtering should not reduce the apparatus&#39; ability to accurately analyze the composition of fluid  25 . Dirty fluid (with suspended solid or liquid non-volatile particles) could possibly impair proper sensor function. A portion  45  of fluid  25  flows through a thermal-conductivity detector or sensor  127  and a portion  47  of fluid  25  flows through tube  49  to a one-way valve  51 . By placing a “T” tube immediately adjacent to the inlet of fluid  45 , sampling with minimal time delay is achieved, because of the relatively higher flow of fluid  47 , which helps to shorten the filter purge time. Pump  53  causes fluid  47  to flow from the output of particle filter  43  through tube  49  and valve  51 . Modulating valve  51  controls the flow through the sensor via tube  57  by adjusting the suction pressure of pump  55  in tube  129 . The above flow configuration may thus achieve two benefits simultaneously. These benefits may include minimal sampling delay time and flow control. Pump  55  causes fluid  45  to flow from the output of filter  43  through detector  127 , concentrator  124 , flow sensor  125 , separator  126 , thermal-conductivity detector or sensor  128  and tube  129 . Pump  55  pumps the fluid through tube  57  to tube  59  where it joins fluid  47  as a combined fluid  61 . Pump  55  may be used in the system, depending on suction capacity of pump  53  (10-300 cm3/min) and sufficiently low-flow-capacity of pump  55  (0.1-3 cm3/min). Fluid  61  is pumped to output port  36  by pump  53 . Fluid  61  may flow out as stream  37  through exit tube or pipe  39 . Data from detectors  127  and  128  may be sent to control  130 , which in turn relays data to microcontroller and/or processor  29  for processing. Resultant information may be sent to station  31 . 
     FIG. 3 is a schematic diagram of part of the sensor apparatus  10  or  15 , representing concentrator  124  or separator  126  in FIG.  2 . The sensor apparatus may include a substrate  12  and a controller  14 . Controller  14  may or may not be incorporated into substrate  12 . Substrate  12  may have a number of thin film heater elements  20 ,  22 ,  24 , and  26  positioned thereon. While only four heater elements are shown, any number of heater elements may be provided, for instance, between two and one thousand, but typically in the 20-100 range. Heater elements  20 ,  22 ,  24 , and  26  may be fabricated of any suitable electrical conductor, stable metal, or alloy film, such as a nickel-iron alloy sometimes referred to as permalloy having a composition of eighty percent nickel and twenty percent iron, platinum, platinum silicide, and polysilicon. Heater elements  20 ,  22 ,  24 , and  26  may be provided on a thin, low-thermal mass, low-in-plane thermal conduction, support member  30 , as shown in FIGS. 4 and 5. Support member or membrane may be made from Si 3 N 4  or other appropriate or like material. The heater elements may be made from Pt or other appropriate or like material. 
     FIGS. 4 and 5 reveal a double-channel phased heater mechanism  41  having channels  31  and  32 . Substrate  12  and portion or wafer  65  have defined channels  31  and  32  for receiving a streaming sample fluid  45 . The channels may be fabricated by selectively etching silicon channel wafer or substrate  12  beneath support member  30  and channel wafer or portion  65  above the support member. The channels include an entry port  34  and an exhaust port  36  for streaming sample fluid  45 . 
     The sensor apparatus may also include a number of interactive elements inside channels  31  and  32  so that they are exposed to the streaming sample fluid  45 . Each of the interactive elements may be positioned adjacent, i.e., for closest possible contact, to a corresponding heater element. For example, as in FIG. 4, interactive elements  40 ,  42 ,  44 , and  46  may be provided on the lower surface of support member  30  in channel  32 , and adjacent to heater elements  20 ,  22 ,  24 , and  26 , respectively. Additionally, interactive elements  140 ,  142 ,  144 , and  146  may be provided on the upper surface of support member  30  in channel  31 , and adjacent to heater elements  20 ,  22 ,  24 , and  26 , respectively. There may be other channels with additional interactive film elements which are not shown in the present illustrative example. The interactive elements may be formed from any number of films commonly used in liquid or gas chromatography, such as silica gel, polymethylsiloxane, polydimethylsiloxane, polyethyleneglycol, porous silica, Nanoglass™, active carbon, other similar polymeric substances. Furthermore, the above interactive substances may be modified by suitable dopants to achieve varying degrees of polarity and/or hydrophobicity, to achieve optimal adsorption and/or separation of targeted analytes. 
     FIG. 5 shows a cross-section end view of phased heater mechanism  41 . Support member  30  is attached to top structure  65 . Anchors  67  hold support member  30  in place relative to channel  31 . Fewer anchor  67  points minimize heat conduction losses from support  30  to other portions of structure  41 . In contrast to a normal anchoring scheme, the present example has a reduction of anchor points that may result in the saving about 1.5 times of the remaining heater element input power. 
     Interactive film elements may be formed by passing a stream of material carrying the desired sorbent material through channel  32 . This provides an interactive layer throughout the channel. If separate interactive elements are desired, the coating may be selectively “developed” by providing a temperature change to the coating, via heater elements  20 ,  22 ,  24  and  26 . After the coating is developed, a stream of solvents may be provided through channel  32  to remove the coating everywhere except where the coating has been developed or polymerized with suitable solvents such as acetone, leaving only the sorbent material that is adjacent the heater elements. A coating  63  of a non-adsorbing, thermal insulating material may be applied to the inside walls of channels  31  and  32 , except where there is adsorber coated surfaces, by design, such as the interactive elements. This coating may reduce the needed heater element power by about 1.5 times. The material should have thermal conduction that is substantially less than the material used in the channel walls. The latter may be silicon. Alternative materials for coating  63  may include SiC 2  or other thermal oxides. Coating  63  may reduce power used for the heater elements in support  30 . A minimizing or reduction of the size (width, length and thickness) of the heater element membranes as well as the adsorber film, while retaining a reasonable ratio of mobile/stationary phase volume, may result in about a four times power reduction. The minimized or reduced adsorber film thickness may reduce the time needed for adsorption-desorption and save about 1.5 times in energy needed per fluid analysis. The use of a particularly thrifty but adequately function pump  53  and/or  55  and  120 , which may run only about or less than one second before he start of a concentrator and/or measurement cycle of detector system  11 , and the use of low-power electronics for control  130  and/or microcontroller/processor (which uses a sleep mode when not in use) may result in about a two times reduction in such power. 
     The table in FIG. 13 shows the overall power needed to run leak detector system  11  to similar system to be about 100 milliwatts or less with the mentioned herein design features of the system running one analysis cycle every three seconds. As shown in the table, energy conservation measures on the system  11  can reduce the energy needed per analysis (initiated once every 3 seconds) from about 1.7 Joules and peak power of about 1280 mW, down to about 0.4 Joules, with peak power of 220 mW. 
     Controller  14  or  130  may be electrically connected to each of the heater elements  20 ,  22 ,  24 ,  26 , and detector  50  as shown in FIG.  3 . Controller  14  or  130  may energize heater elements  20 ,  22 ,  24 , and  26  in a time phased sequence (see bottom of FIG. 6) such that each of the corresponding interactive elements  40 ,  42 ,  44 , and  46  become heated and desorb selected constituents into a streaming sample fluid  45  at about the time when an upstream concentration pulse, produced by one or more upstream interactive elements, reaches the interactive element. Any number of interactive elements may be used to achieve the desired concentration of constituent gases in the concentration pulse. The resulting concentration pulse may be provided to detector  50 ,  128 ,  164  for detection and analysis. Detector  50 ,  127 ,  128  or  164  may be a thermal conductivity detector, discharge ionization detector, or any other type of detector such as that typically used in gas or fluid chromatography. 
     FIG. 6 is a graph showing illustrative heater temperatures, along with corresponding concentration pulses produced at each heater element. As indicated above, controller  14  or  130  may energize heater elements  20 ,  22 ,  24 , and  26  in a time phased sequence. Illustrative time phased heater temperatures for heater elements  20 ,  22 ,  24 , and  26  are shown by temperature profiles or lines  60 ,  62 ,  64 , and  66 , respectively. 
     In the example shown, controller  14 ,  130  (FIG. 3) may first energize first heater element  20  to increase its temperature as shown at line  60  of FIG.  6 . Since first heater element  20  is thermally coupled to first interactive element  40 , the first interactive element desorbs selected constituents into the streaming sample fluid  45  to produce a first concentration pulse  70  at the detector  128  or  50  or  164 , if no other heater elements were to be pulsed. The streaming sample fluid carries the first concentration pulse  70  downstream toward second heater element  22 , as shown by arrow  72 . 
     Controller  14  (or  130 ) may next energize second heater element  22  to increase its temperature as shown at line  62 , starting at or before the energy pulse on element  20  has been stopped. Since second heater element  22  is thermally coupled to second interactive element  42 , the second interactive element also desorbs selected constituents into streaming sample fluid  45  to produce a second concentration pulse. Controller  14 ,  130  may energize second heater element  22  such that the second concentration pulse substantially overlaps first concentration pulse  70  to produce a higher concentration pulse  74 , as shown in FIG.  6 . The streaming sample fluid carries larger concentration pulse  74  downstream toward third heater element  24 , as shown by arrow  76 . 
     Controller  14 ,  130  may then energize third heater element  24  to increase its temperature as shown at line  64  in FIG.  6 . Since third heater element  24  is thermally coupled to third interactive element  44 , third interactive element  44  may desorb selected constituents into the streaming sample fluid to produce a third concentration pulse. Controller  14 ,  130  may energize third heater element  24  such that the third concentration pulse substantially overlaps larger concentration pulse  74  provided by first and second heater elements  20  and  22  to produce an even larger concentration pulse  78 . The streaming sample fluid carries this larger concentration pulse  78  downstream toward an “Nth” heater element  26 , as shown by arrow  80 . 
     Controller  14 ,  130  may then energize “Nth” heater element  26  to increase its temperature as shown at line  66 . Since “Nth” heater element  26  is thermally coupled to an “N-th” interactive element  46 , “N-th” interactive element  46  may desorb selected constituents into streaming sample fluid  45  to produce an “N-th” concentration pulse. Controller  14 ,  130  may energize “N-th” heater element  26  such that the “N-th” concentration pulse substantially overlaps larger concentration pulse  78  provided by the previous N−1 interactive elements. The streaming sample fluid carries “N-th” concentration pulse  82  to either a separator  126  or a detector  50 ,  128  or  164 , as described below. 
     As indicated above, heater elements  20 ,  22 ,  24 , and  26  may have a common length. As such, controller  14 ,  130  can achieve equal temperatures of the heater elements by providing an equal voltage, current, or power pulse to each heater element. The voltage, current, or power pulse may have any desired shape including a triangular shape, a square shape, a bell shape, or any other shape. An approximately square shaped voltage, current, or power pulse is used to achieve temperature profiles  60 ,  62 ,  64 , and  66  shown in FIG.  6 . 
     FIG. 7 is a graph showing a number of heater elements to illustrate, first, how the concentration increases stepwise as the desorption of subsequent elements is appropriately synchronized with the streaming sample fluid velocity and, second, how the lengths of individual elements are matched to the expected increased rate of mass diffusivity flux as the concentration levels and gradients increase. It should.be pointed out here that prior to the elements shown in FIG. 7, the analyte concentration may have been already magnified by a factor, F, by virtue of pulsing an initial element with a length F-times longer than the one shown as element  100  (H 1  or, alternatively, by simultaneously pulsing elements  1 ,  2 , . . . , F and collecting all the desorbed analyte with the still cool element  100  (H 1 ), before pulsing it. It is recognized that each of the concentration pulses may tend to decrease in amplitude and increase in length when traveling down channel  32  due to diffusion. To accommodate this increased length, it is contemplated that the length of each successive heater element may be increased along the streaming sample fluid. For example, a second heater element  102  may have a length W 2  that is larger than a length W 1  of a first heater element  100 . Likewise, a third heater element  104  may have a length W 3  that is larger than length W 2  of second heater element  102 . Thus, it is contemplated that the length of each heater element  100 ,  102 , and  104  may be increased, relative to the adjacent upstream heater element, by an amount that corresponds to the expected increased length of the concentration pulse of the upstream heater elements due to diffusion. 
     To simplify the control of the heater elements, the length of each successive heater element may be kept constant to produce the same overall heater resistance between heater elements, thereby allowing equal voltage, current, or power pulses to be used to produce similar temperature profiles. Alternatively, the heater elements may have different lengths, and the controller may provide different voltage, current, or power pulse amplitudes to the heater element to produce a similar temperature profile. 
     FIG. 8 is a graph showing a concentration pulse  110  that achieves a  100  percent concentration level. It is recognized that even though concentration pulse  110  has achieved a predetermined concentration threshold, such as  100  percent, the concentration of the corresponding constituent can still be determined. To do so, detector  50 ,  128 ,  164  may detect the concentration pulse  110 , and controller  14 ,  130  may integrate the output signal of the detector over time to determine the concentration of the corresponding constituent in the original sample of stream  45 . 
     Heater elements  20 ,  22 ,  24  and  26  may be GC-film-coated on both the top and bottom sides so that the width and power dissipation of the heater element surface by about two times. The fabrication of these heater elements involves two coating steps, with the second step requiring wafer-to-wafer bonding and coating after protecting the first coat inside the second wafer and dissolving the first wafer. 
     FIG. 9 is a schematic view of another illustrative sensor assembly  15  similar to that of FIG.  3 . The sensor assembly may include a simpler solenoid pump  120 , a streaming sample fluid input  122 , a concentrator  124 , a separator  126 , a detector  128 , and a controller  14  or  130 . At the request of the controller  14 ,  130 , solenoid pump  120  may draw a sample  45  from a flue gas stream  132  through a one-way valve  134 . Controller  14 ,  130  may then direct solenoid pump  120  to provide streaming sample fluid  45 , at a desired pressure, to concentrator  124 . 
     Concentrator  124  may include two or more interactive elements that are in communication with streaming sample fluid  45 . Concentrator  124  also may include two or more heater elements that are in thermal communication with the interactive elements. When energized, each heater element heats a corresponding interactive element, causing the interactive element to desorb selected constituents into the streaming sample fluid. As described above, controller  14 ,  130  may energize the heater elements in a time phased sequence to provide an increased concentration pulse. 
     Streaming sample fluid  45  may carry the concentration pulse to separator  126 . Separator  126  may separate selected constituents of the concentration pulse and provide the separated constituents to detector  50 ,  128 ,  164 . This detector may provide a signal to controller  14 ,  130  indicating the concentration level of each constituent. Controller  14 ,  130  may determine the actual concentration level of each constituent in the original gas sample by dividing the sensed concentration level by the concentration amplification provided by the sorbent material of each interactive element and the multiplier effect provided by the phased heater arrangement. 
     FIG. 10 is a schematic view of another illustrative sensor assembly  15 . FIG. 11 is a timing chart showing the operation of sensor assembly  15  of FIG.  10 . Sensor assembly  15  may include a pump  152 , a gas preheater  154 , and a microbridge type integrated circuit chip  156 . The microbridge type integrated circuit includes a channel  158 ,  32 , a number of heater elements  160   a ,  160   b ,  160   c , and  160   d , a separation heater  162 , and a detector  164 ,  128 ,  50 . Each of heater elements  160   a ,  160   b ,  160   c , and  160   d , separation heater  162 , and detector  164  are provided on a support member  30  that extends over the channel  158 ,  32  (e.g., FIG.  5 ). Interactive elements (not explicitly shown) are placed in channel  158 ,  32  and in thermal communication with each of heater elements  160   a ,  160   b ,  160   c , and  160   d.    
     Microbridge type integrated circuit chip  156  also may include a heater control block  166  and a number of energizing transistors  168   a ,  168   b ,  168   c ,  168   d , and  170 . Heater control block  166  can individually energize each of heater elements  160   a ,  160   b ,  160   c , and  160   d , by activating a corresponding energizing transistor  168   a ,  168   b ,  168   c ,  168   d , respectively. Likewise, heater control block  166  can energize separation heater  162  by turning on transistor  170 . Heating or cooling block  169  (of FIG. 10) complements preheater  154  in maintaining an average or overall temperature that is optimal for operation of sensor assembly  15 . 
     A sensor assembly control block  180  directs the overall operation of sensor assembly  15 . Sensor assembly control block  180  first asserts a flow control signal  190  to pump  152 . Flow control signal  190  is shown in FIG.  11 . In response, pump  152  draws a sample from flue  182  and provides the sample, at a desired pressure, to preheater  154  and eventually to channel  158 ,  32 . Preheater  154  preheats and the heater maintains the sample gas at optimal operating element temperature and thus helps to prevent loss of sample due to condensation and to increase the amount of constituents that can be accumulated in each of the interactive elements. 
     The streaming sample fluid passes down channel  158 ,  32  for a predetermined time period  192  until the interactive elements reach a state of substantially saturation of adsorption of one or more constituents from the streaming sample fluid and reach equilibrium. Thereafter, sensor assembly control block  180  notifies heater control block  166  to begin heating the heater elements in a time phased sequence. Heater control block  166  first provides a first heater enable signal  194  and a separation heater enable signal  196 , as shown in FIG.  11 . First heater enable signal  194  turns on transistor  168   a , and separation heater enable signal  196  turns on transistor  170 . Transistor  168   a  provides current to first heater element  160   a , causing first heater element  160   a  to increase in temperature. This heats the corresponding interactive element, which desorbs one or more constituents into the streaming sample fluid in the form of a first concentration pulse. The first concentration pulse is carried downstream toward second heater element  160   b  by the streaming sample fluid. This process is repeated for the 3rd, 4th and N-th elements. 
     Heater control block  166  then provides a second heater enable signal  198 , which turns on transistor  168   b . Transistor  168   b  provides current to second heater element  160   b , causing second heater element  160   b  to increase in temperature. This heats the corresponding interactive element, which desorbs one or more constituents into the streaming sample fluid in the form of a second concentration pulse. Heater control block  166  may time second heater enable signal  198  such that the second concentration pulse substantially overlaps the first concentration pulse. Both the first and second concentration pulses are carried downstream toward third heater element  160   c.    
     The timing of second heater enable signal  198  relative to first heater enable signal  194  may be established by prior calibration. However, the heater control block  166  may sense the resistance of second heater element  160   b . It is recognized that the resistance of second heater element  160   b  will begin to change when the first concentration pulse arrives at second heater element  160   b  because the first concentration pulse is typically hotter than the streaming sample fluid. Once a predetermined resistance change is sensed in second heater element  160   b , heater control block  166  may energize second heater element  160   b  via transistor  168   b . The remaining heater enable signals may be likewise controlled. 
     Heater control block  166  may then provide a third heater enable signal  200 , which turns on transistor  168   c . Transistor  168   c  provides current to third heater element  160   c , causing third heater element  160   c  to increase in temperature. This heats the corresponding interactive element, which desorbs one or more constituents into the streaming sample fluid in the front of a third concentration pulse. Heater control block  166  may time third heater enable signal  200  such that the third concentration pulse substantially overlaps the first and second concentration pulses. The first, second, and third substantially overlapping concentration pulses are carried downstream toward “Nth” heater element  160   d.    
     Heater control block  166  may then provide an “Nth” heater enable signal  202 , which turns on transistors  168   c . Transistor  168   c  provides current to “Nth” heater element  160   d , causing “Nth” heater element  160   d  to increase in temperature. This heats the corresponding interactive element, which desorbs one or more constituents into the streaming sample fluid in the form of an “Nth” concentration pulse. The heater control block  166  may time “Nth” heater enable signal  202  such that the “Nth” concentration pulse substantially overlaps the previously generated concentration pulses. The resulting concentration pulse is carried downstream to separator heater  162 . Separator heater  162 , in conjunction with the channel  158 , may separate selected constituents in the concentration pulse into individual constituent components. The separator&#39;s temperature ramp should not start before the end of the Nth pulse to the Nth concentrator element. Thus, pulse  196  begins after pulse  202  ends, as shown in FIG.  11 . The individual constituent components may include one or more compounds, depending on a number of factors including the sample gas provided. 
     Transistor  170  then energizes separation heater  162  at the beginning of pulse  196  in FIG. 11 resulting in the heater  162  temperature having an increasing amplitude from room temperature up to about 200 degrees C. (or other temperature of design) versus time up to about one-half of the length of pulse  196  and then to remain at that temperature for the remaining time of pulse  196 . Heater  162  separates the various constituents into individual components, as described above. The separated constituents are carried downstream to detector  164  by the streaming sample fluid. Detector  164  may be a thermal conductivity detector, discharge ionization detector, or any other type of detector such as those commonly used in gas chromatography. Detector  164  may sense the concentration levels of each individual constituent component, and provides a corresponding signal to amplifier  210 . Amplifier  210  may amplify the detector output signal and provide the detector output signal to a data processing unit for analysis. Heater control block  166  may provide a detector enable signal  212  to enable the detector only when the individual constituent components are present. 
     FIG. 12 is a basic layout of an integrated circuit that includes a concentrator, a separator, and a detector of micro gas apparatus  15 . The integrated circuit may include a channel  250  that traverses back and forth across the chip as shown in FIG. 12. A first part of channel  250  has a detector  263  and number of heater elements  252  extending thereover on a support member, like support member  30  as described above. Interactive elements (not explicitly shown) are positioned in-channel  250  adjacent each of the heater elements. While only one column of heater elements  252  is shown, it is contemplated that each of the channel legs  254   a-h  may have a column of heater elements  252 . There may be between two and one thousand heater elements spaced along channel  250 . 
     A second downstream portion of channel  250  has a separation heater  260  extending thereover. The separation heater helps separate the various constituents in the concentration pulses provided by the heater elements  252 . Finally, a detector  264  is provided over the channel  250  downstream of the separation heater  260 . The detector may sense the concentration of each of the separated constituent components provided by the separator. 
     Because the concentrator, separator, and detector are provided on an integrated circuit, other conventional electronic circuits can be easily integrated therewith. A phased heater control block  270  and amplifier  272  may be fabricated on the same substrate. Chemical sensors, especially chemical microsensors as described, potentially afford many attractive features such as low cost, high sensitivity, ruggedness, and very small size. 
     Although the invention has been described with respect to at least one illustrative embodiment, many variations and modifications will become apparent to those skilled in the art upon reading the present specification. It is therefore the intention that the appended claims be interpreted as broadly as possible in view of the prior art to include all such variations and modifications.