Abstract:
An equipment or environment health monitor having a micro gas apparatus incorporating a phased heater array, concentrator, separator and detector for achieving the sensitivity needed for detection of extremely small amounts of fluids. The apparatus is capable of detecting trace gases, and may be utilized to detect “fault” gas of operating equipment so as to determine, for example, the prospects of imminent failure of the equipment. Also, the micro gas apparatus is capable of detecting miniscule amounts of pollutants in ambient environment of a conditioned or tested space. The output of the apparatus may go to a microcontroller and/or processor for prompt analysis. The output from the microcontroller or processor may go to either a transmitter/receiver for wireless communication or a modem for utility line, cable or optical communication with a station for data and results observation and review.

Description:
BACKGROUND  
         [0001]    The invention pertains to detection, identification and analyses of gases. Particularly, it pertains to the detection of gases that indicate potential problems with equipment or the ambient environment. More particularly, the invention relates to health monitoring of the same.  
           [0002]    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.  
           [0003]    The power industry relies on the operation of large, one to ten mega watt (MW) and 15,000 gallon or so oil-immersed electric power distribution transformers, of which there are about 100,000 installed in the United States and about 400,000 in the rest of the world. These transformers cost between one-half and five million dollars and thus amount to an installed base of around 200 billion dollars. Their design lifetime is forty to fifty years; their average life is presently about thirty-five years. The transformers are failing at the rate of about one percent per year. Unexpected failures of the transformers have cost utilities upwards of about eighteen million dollars.  
           [0004]    However, it is far too expensive for utilities to replace all this aging equipment at once. So there is great interest in monitoring the “health” of the equipment so that any equipment susceptible to failure can be detected, watched and/or repaired or replaced. The potential multi-million damage, electric service interruption and financial cost resulting from unanticipated failure of utility-power transformers make it necessary to monitor the state of their “health”. Such monitoring is being suggested and presently being implemented via labor-intensive periodic off-line or high-capital-cost online analysis of the tell-tale changes in the composition and concentration of gases appearing in the transformer oil and in its head-space.  
           [0005]    The “fault gases” in the insulating oil or in the head space of the transformer may provide an early indication of transformer failure. Fault gases are produced by high voltage breakdown in oil-filled transformers. Analysis of the dissolved gases in oil or in the head-space of a transformer has shown that they include acetylene (C 2 H 2 ), methane (CH 4 ), ethane (C 2 H 6 ), carbon monoxide (CO), carbon dioxide (CO 2 ), hydrogen (H 2 ), oxygen (O 2 ) and ethylene (C 2 H 4 ). The gas composition is indicative of the type of impending transformer failure and is the reason that low-cost, single gas monitoring does not provide a very high percentage of fault coverage. Detection and analysis of very small amounts of such gases in an inexpensive, efficient and inexpensive manner is desired.  
         SUMMARY  
         [0006]    Multi-gas detection and analysis may be automated 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 analysis results to a central or other manned station. A micro gas detector incorporating a phased heater array, concentrator and separator as an enhanced detector contributes to the availability of a low-cost multi-gas analyzer and system to provide equipment health monitoring (EHM) that can increase the probability of detecting equipment failures in time to mitigate the effects of costly downtime and disruption. The micro gas detector was developed as a low-cost approach to sense ozone to meet impending 50 part-per-billion (ppb) maximum emission objectives for electrostatic air cleaners. It is capable of detecting a mixture of trace gases.  
           [0007]    This gas detector along with a connective configuration to the equipment and associated microcontroller or processor constitutes a “health monitor” (HM) of the equipment. Monitoring of tell-tale trace gases in utility power transformers is just one of many possible health monitor applications. The critical reliability attribute/expectation is not limited to utility power distribution transformers. Those that provide power to key communication networks as in airports or sustain operation in hospitals or power-sensitive industries (e.g., semiconductor facilities) are also in need for such monitoring. Another application of the health monitor may be the detection and analyses aircraft-cabin air pollutants such as aldehydes, butyric acid, toluene, hexane, and the like, besides the conventional CO 2 , H 2 O and CO. Other monitoring may include conditioned space such as that indoor space of buildings and submarines for levels of gases such as CO 2 , H 2 O, aldehydes, hydrocarbons and alcohols, and monitoring outdoor space and/or process streams of processing industries such as in chemical, refining, product purity, food, paper, metal, glass and pharmaceutical industries. Also, health monitoring has a significant place in environmental assurance and protection. It may provide defensive security in and outside of facilities by early detection of chemicals before their concentrations increase and become harmful.  
           [0008]    The present health monitor is low-power, fast, compact, low cost, intelligent, wireless or not, low maintenance, robust and highly sensitive. A vast portion of the health monitor 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 monitor. The flow rate of the air or gas sample through the monitor 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 monitor 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 monitor 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 monitor 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 is inter-connectable with other gas sample conditioning devices (particle filters, valves, flow and pressure sensors), local maintenance control points, and can provide monitoring via the internet. The monitor 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 health monitor 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. The monitor is, among other things, a lower-power, faster, and more compact, more sensitive and affordable version of a gas chromatograph. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0009]    [0009]FIG. 1 is an illustration of a health monitor for equipment;  
         [0010]    [0010]FIG. 2 is an illustration of the health monitor for environmental spaces;  
         [0011]    [0011]FIG. 3 shows details of a micro gas apparatus;  
         [0012]    [0012]FIG. 4 is a layout of an illustrative sensor apparatus;  
         [0013]    [0013]FIG. 5 is a cross-sectional view taken along line  2 - 2  of FIG. 4;  
         [0014]    [0014]FIG. 6 is a graph showing illustrative heater temperatures, along with corresponding concentration pulses produced at each heater element of the sensor apparatus;  
         [0015]    [0015]FIG. 7 is a graph showing a number of heater elements having lengths to match the expected increased lengths of the concentration pulses due to diffusion;  
         [0016]    [0016]FIG. 8 is a graph showing a concentration pulse that reaches a 100 percent concentration level;  
         [0017]    [0017]FIG. 9 is a layout of another illustrative sensor assembly;  
         [0018]    [0018]FIG. 10 is a schematic view of a version the sensor assembly;  
         [0019]    [0019]FIG. 11 is a timing chart showing the operation of the sensor assembly of FIG. 10; and  
         [0020]    [0020]FIG. 12 is a basic layout of an integrated circuit that includes a concentrator, a separator, and a sensor. 
     
    
     DESCRIPTION  
       [0021]    [0021]FIG. 1 reveals a health monitor  11  that may be set up for monitoring the “health” of utility power transformer  13 . A micro gas detector apparatus  15  may have two tubes or pipes  17  and  19  connected to a head space  21  of transformer  13 . Apparatus  15  may pump a fluid  23  through tube  17  into head space  21 . Fluid  23  may displace a fluid  25  in head space  21 . Fluid  25  may be “pushed” by displacing fluid  23  through tube  19  to entry port  34  of micro gas apparatus  15 . “Fluid” is a generic term that includes liquids and gases as species. For instance, air, gas, water and oil are fluids. In the transformer health monitor, fluid  23  is typically air and fluid  25  may be gas including “fault” gases emanating from insulating oil  27  in transformer  13 . Sample stream or gas  25  may be pumped through micro gas detector  15  as shown in FIG. 2. Some excess gas  37  may be discharged via apparatus  15  through tube or pipe  39  from exhaust port  36  as shown in FIGS. 1 and 3. There are certain fault gases that may indicate potential transformer  13  failure. An example is the breakdown of insulation. Such gases may include acetylene, methane, ethane, carbon monoxide, carbon dioxide, hydrogen, oxygen and ethylene. Detection and analysis by monitor  11  may detect, identify and quantify the fluid, i.e., determine the amount of or parts-per-million of the fluid detected. Monitor  11  may be used to detect fluids, monitor the environment around and determine the health of internal and external combustion equipment or mechanisms. An external combustion mechanism may be a space heater, furnace, boiler, or the like. Also, monitor  11  is capable of detecting miniscule amounts of pollutants in ambient environment of a conditioned or tested space. Monitor  11  may indicate the health and the level of toxins-to-people in ambient air. Detectors  127  and  128  results may be sent to microcontroller/processor  29  for analysis, and immediate conclusions and results. This information may be sent on to observer stations  31  for review and further analysis, evaluation, and decisions about the health of transformer  13 . Data and control information may be sent from stations  31  to microcontroller/processor  29 . Data and information may be sent and received via the wireless medium by a transmitter/receiver  33  at monitor  11  and at stations  31 . Or the data and information may be sent and received via wire or optical lines of communication by a modem  35  at monitor  11  and station  31 . The data and information may be sent to a SCADA (supervisory control and data acquisition) system. These systems are used in industry to monitor and control plant status and provide logging facilities.  
         [0022]    The monitor  11  may be used to detect hazards to people in the environment of or around equipment.  
         [0023]    In FIG. 1, transformer  13  may replaced with another kind of equipment such as an electric motor, a generator, an internal combustion engine, air conditioner or other types of equipment. Microcontroller/processor  29  may be programmed to provide a prognosis of the equipment whose health is being monitored in view of the expected fault gases that would be emanated by a certain piece of equipment having potential “health problems.” 
         [0024]    [0024]FIG. 2 reveals health monitor  11  with a hook-up that may be used in a space  41  such as an aircraft-cabin, machinery room, factory, or some place in another environment. The end of input tube or pipe  19  may be in space  41  and exhaust of exit tube  37  may be placed at a distance somewhat removed from space  41 . There is no return or air supply tube  17  as in health monitor  11  for equipment in FIG. 1. Monitor  11  for space  41  may itself be within space  41  except that tube  39  may exit space  41 .  
         [0025]    [0025]FIG. 3 reveals certain details of micro gas apparatus  15 . Further details and variants of it are described below in conjunction with subsequent figures. Sample stream  25  may enter input port  34  from pipe or 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  127  and a portion  47  of fluid  25  flows through tube  49  to a one-way valve  51 . 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  45  by adjusting the suction pressure of pump  55  in tube  129 . 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  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 . Fluid  61  is pumped to output port  36  by pump  53 . Fluid  61  may split into two streams  23  and  37  which flow through tubes or pipes  17  and  39 , respectively. 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  11 .  
         [0026]    [0026]FIG. 4 is a schematic diagram of part of the sensor apparatus  10  or  15 . 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 e 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, with 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 FIG. 5.  
         [0027]    Substrate  12  also has a well-defined channel  32  for receiving the sample fluid stream  45 . Channel  32  may be fabricated by selectively etching silicon substrate  12  beneath support member  30 . The channel includes an entry port  34  and an exhaust port  36 .  
         [0028]    The sensor apparatus may also include a number of interactive elements inside channel  32  so that they are exposed to the sample fluid stream  45 . Each of the interactive elements may be positioned adjacent, i.e., for closest possible contact, to a corresponding heater element. For example, and referring, to FIG. 5, interactive elements  40 ,  42 ,  44 , and  46  may be provided on the lower surface of support member  30 , and adjacent to heater elements  20 ,  22 ,  24 , and  26 , respectively. The interactive elements may be formed from any number of films commonly used in liquid or gas chromatography, such as silica gel or active carbon.  
         [0029]    Interactive 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 the heater elements. 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, leaving only the sorbent material that is adjacent the heater elements.  
         [0030]    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. 4. Controller  14  or  103  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 sample fluid stream  45  at precisely 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.  
         [0031]    [0031]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.  
         [0032]    In the example shown, the controller  14 ,  130  (FIG. 4) may first energize first heater element  20  to increase its temperature as shown at line  60 . Since first heater element  20  is thermally coupled to first interactive element  40 , the first interactive element desorbs selected constituents into the sample fluid stream  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 sample fluid stream carries the first concentration pulse  70  downstream toward second heater element  22 , as shown by arrow  72 .  
         [0033]    Controller  14  (or  130 ) may next energize second heater element  22  to increase its temperature as shown at line  62 . Since second heater element  22  is thermally coupled to second interactive element  42 , the second interactive element also desorbs selected constituents into sample fluid stream  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 sample fluid stream carries larger concentration pulse  74  downstream toward third heater element  24 , as shown by arrow  76 .  
         [0034]    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 sample fluid stream 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 sample fluid stream carries this larger concentration pulse  78  downstream toward an “Nth” heater element  26 , as shown by arrow  80 .  
         [0035]    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 sample fluid stream  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 sample fluid stream carries “N-th” concentration pulse  82  to either a separator  126  or a detector  50 ,  128  or  164 , as described below.  
         [0036]    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.  
         [0037]    [0037]FIG. 7 is a graph showing a number of heater elements having lengths to match the expected increased length of the concentration pulses due to diffusion. It is recognized that each of the concentration pulses may tend to reduce 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 sample fluid stream. 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.  
         [0038]    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.  
         [0039]    [0039]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 .  
         [0040]    [0040]FIG. 9 is a schematic view of another illustrative sensor assembly  15  similar to that of FIG. 3. The sensor assembly may include a solenoid pump  120 , a sample fluid stream  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 sample fluid stream  45 , at a desired pressure, to concentrator  124 .  
         [0041]    Concentrator  124  may include two or more interactive elements that are in communication with sample fluid stream  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 sample fluid stream. As described above, controller  14 ,  130  may energize the heater elements in a time phased sequence to provide an increased concentration pulse.  
         [0042]    Sample fluid stream  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.  
         [0043]    [0043]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.    
         [0044]    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 .  
         [0045]    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.  
         [0046]    The sample fluid stream 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 sample fluid stream 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 sample fluid stream in the form of a first concentration pulse. The first concentration pulse is carried downstream toward second heater element  160   b  by the sample fluid stream. This process is repeated for the 3rd, 4th and N-th elements.  
         [0047]    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 sample fluid stream 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.    
         [0048]    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 sample fluid stream. 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.  
         [0049]    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 sample fluid stream 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.    
         [0050]    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 sample fluid stream 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 N-th 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.  
         [0051]    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 sample fluid stream. 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.  
         [0052]    [0052]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. 13. A first part of channel  250  has a 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 one two hundred and one thousand heater elements spaced along channel  250 .  
         [0053]    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.  
         [0054]    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.  
         [0055]    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.