Abstract:
A fluid sampling device including a manifold having inputs, common purge and sampling pathways, valves disposed to couple and decouple a first set of the inputs to the common purge pathway and a second set of the inputs to the common sampling pathway, and a differential sensor coupled to the pathways. A controller connected to the valves produces control signals that enable the valves to couple and decouple the inputs to the common sensor and purge pathways. In addition, a method for operating a fluid sampling system that is connected to a set of sample zones that includes the steps of sampling fluid from first and second sample zones in respective first and second sample locations, isolating third and fourth sample zones from the first and second sample locations, and measuring a differential parameter across the sample locations.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to systems that measure parameters of a fluid. 
     The sampling of fluid within a system allows the fluid to be tested for concentration of various substances. Typically, the fluid within an environmental system such as the air in an office building or a hospital is monitored to determine the level of pollutants such as carbon monoxide and carbon dioxide in the system. The information obtained during the monitoring can be used to control a heating ventilation and air conditioning (HVAC) system, e.g., to control indoor air quality (IAQ). In one approach to monitoring IAQ, remote sampling systems are connected to various locations in the system by a network of tubes that shunt fluid to a central location where in-line measurements are made on air components. In other monitoring systems, sensors are distributed throughout a building and electronically communicate with a central controller. 
     In addition to monitoring the level of pollutants, it is desirable to monitor and control the flow of pollutants such as carbon monoxide (CO), carbon dioxide (CO 2 ), odors, and dust by monitoring and controlling the fluid flow within the system. Thus, the pressure within the system, especially the pressure differential between two locations within the system, often is measured to determine fluid flow within the system. For example, pressure differentials across the external walls of a building are important to maintain a positive indoor pressure, especially at the lower levels of a building where negative pressures are more likely to form due to the buoyant force of heated air. The positive indoor pressure prevents air from entering the building as a draft and forces outdoor air to be introduced through the HVAC system where it is conditioned properly and filtered. Because pressure differentials within a building dictate the flow of air, they are important in the control of contaminants in sterile environments as in hospitals. In addition, pressure differentials across the wall of an air duct can be used to determine volumetric airflow within a component of an environmental system. 
     A typical method for measuring pressure includes connecting pressure sensors to various locations within the system and comparing the pressure measurements to determine the magnitude and direction of fluid flow. A set of sensors may be used at each location with each sensor being most accurate in a different range. 
     SUMMARY OF THE INVENTION 
     One aspect of the invention is a fluid sampling device that includes a manifold having a plurality of inputs, a common purge pathway, a common sampling pathway, a plurality of valves to couple and decouple some inputs to the common purge pathway and other inputs to the common sampling pathway. The system also includes a differential pressure sensor coupled to the common sampling pathways. 
     Preferred embodiments of this aspect include the following features. 
     A controller connected to the plurality of valves produces control signals that enable the valves to couple and decouple the inputs to the common pathways. The controller produces control signals to configure the valves such that one of the valves couples an input to the common sensor pathway, another one of the valves couples a different input to the common purge pathway, and a set of valves decouples the common pathways from other inputs. The controller produces control signals to cause the differential pressure sensor to measure differential pressure across the common pathways. The differential pressure sensor either is two individual sensors coupled to one each of the common pathways, or is a plurality of sensors that measures pressure in different pressure ranges. The controller causes the pressure sensors to each measure differential pressure across the common sampling pathway and the common purge pathway to provide indications, e.g., an electronic or other signal, of the differential pressure between the input ports. 
     In another aspect of the invention, a manifold has multiple input ports, at least two common output ports, and a set of valve pairs. Each pair of valves corresponds to an input port. One of the valves of the pair couples and decouples the input port to one output port, and the other valve of the pair couples and decouples the input port to the other output port. A differential pressure sensor is coupled between the two output ports. 
     In another aspect of the invention, a manifold has two common pathways and at least one input port. The manifold has a plurality of passages, and the input port is in fluid communication with one common pathway through one of the passages. A valve is disposed along the passage and is capable of blocking the flow of fluid between the input port and the common pathway. A pressure sensor is disposed across the sensor pathway and the purge pathway. 
     Preferred embodiments of this aspect of the invention include the following features. 
     A second valve is disposed along another passage and is capable of blocking the flow of fluid between the input port and the second common pathway. Another input port is in fluid communication with one of the common pathways through a third passage and is in fluid communication with the other common pathway through a fourth passage. Third and fourth valves are disposed along the third and fourth passages respectively. Both valves are capable of blocking the flow of fluid between the second input port and one of the common pathways. A controller is connected to the first, second, third and fourth valves, and can configure the valves such that the first valve couples the first input port to the first common pathway, the fourth valve couples the second input port to the second common pathway, the second valve decouples the first input port from the second common pathway, and the third valve decouples the second input port from the first common pathway. In an alternate arrangement, the controller can configure the valves such that the second valve couples the first input port to the second common pathway, the third valve couples the second input port to the first common pathway, the first valve decouples the first input port from the first common pathway and the fourth valve decouples the second input port from the second common pathway. 
     In another aspect of the invention, a manifold has at least two output pathways and at least two input ports. One input port is in fluid communication with one output pathway through one passage of a plurality of passages, and another input port is in fluid communication with another output pathway through another of the passages. A valve of a plurality of valves is disposed along each passage and has a coupled and a decoupled position. A differential pressure sensor is disposed across the output pathways. A sample tube establishes fluid communication between a sample zone and one of the input ports. A sensor is connected to one of the output pathways, and a system controller operates the system. 
     In another aspect of the invention, a method for measuring differential pressure in a fluid sampling system includes three steps. First, fluid is sampled from a sample zone, through a manifold. The manifold has at least two inputs, at least two outputs, and a plurality of passageways. The inputs are in fluid communication with at least one output through a passageway. A set of valves are disposed along the passageways and have coupled and decoupled positions. Second, the valves are opened such that an output is in fluid communication with a sample zone and another output is in fluid communication with another sample zone. Third, the pressure difference across the two coupled outputs are measured. 
     Preferred embodiments of this aspect of the invention include the following features. 
     The pressure difference across the outputs is measured with a plurality of pressure sensors. The pressure difference is processed based both on the value of the sensor indications and on a plurality of pressure ranges that correspond to the pressure sensors. 
     In another aspect of the invention, a method for operating a fluid sampling system that is connected to a set of sample zones includes two steps. First, fluid from two sample zones is sampled in two sample locations. Second, a differential parameter is measured across the two sample locations. Additionally, two other sample zones can be isolated from the two sample locations. 
     In another aspect of the invention, a manifold has a plurality of input ports, at least two output ports, and a plurality of paired valves. Each pair of valves corresponds to an input port, one valve of each pair couples and decouples the input port to an output port, the other valve of the pair couples and decouples the input port to the second output port. 
     In another aspect of the invention, a manifold has at least two output pathways, at least two input ports, and a plurality of passages. An input port is in fluid communication with an output pathway through one of the passages. Another input port is in fluid communication with a second output pathway through a different passage. A plurality of valves, which couple and a decouple an input port from an output pathway, are disposed along the passage connecting the input port and the output pathway. 
     Preferred embodiments of this aspect of the invention include the following features. 
     The manifold has at least two common branches. The first common branch connects two input ports to an output pathway; another common branch connects the two input ports to another output pathway. 
     Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, suitable methods and materials are described below. The materials, methods, and examples are illustrative only and not intended to be limiting. 
     Among other advantages, a differential parameter can be measured at a central location by a single sensor or set of sensors. A fluid can be sampled from any sample zone at a central location in multiple combinations selected by the controller. The system can sample fluid efficiently from a large number of sample zones. 
     Other features and advantages of the invention will be apparent from the following detailed description, and from the claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross-sectional view of a building containing a fluid sampling system. 
     FIG. 2 is a block diagram representation of the fluid sampling system of FIG.  1 . 
     FIG. 3 is a schematic representation of an embodiment of the fluid sampling system of FIG.  2 . 
     FIG. 4 is a schematic representation of an embodiment of a manifold used in the fluid sampling system of FIG.  2 . 
     FIG. 5 is a schematic representation of an alternate embodiment of a manifold for the fluid sampling system of FIG.  2 . 
     FIG. 6 is a schematic representation of a pressure sensor used in conjunction with the fluid sampling system of FIG.  2 . 
     FIG. 7 is a flow chart of the of the measurement logic associated with the pressure sensor of FIG.  6 . 
     FIG. 8 is an embodiment of the fluid sampling system of FIG.  2 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIG. 1, an open environmental system  10 , includes an office building  12 , and a fluid sampling system  14 . The fluid sampling system  14  samples a fluid, e.g. air, that is within the system  10 , such as in rooms, air ducts, and reference areas, and air that is outside the system  10  such as outdoor air. The fluid sampling system  14  includes sampling tubes  16  that are connected at a central location to the remote sampling system  14 . The tubes are constructed of a plastic material and have an internal diameter that is selected to provide sufficient airflow to the sensors and a resistance tolerable by the vacuum source. For example, the sampling tubes  16  are constructed of, e.g., Plexco®, a black fire retardant plastic material manufactured by Chevron, and have an inner diameter of ⅛″. The sampling tubes  16  couple fluid samples from sample zones, e.g., room x or air duct y, to the sampling area  15  where a fluid sample is processed. 
     Referring to FIG. 2, the fluid sampling system  14  processes the samples by drawing air from the sample zone through the sample tubes  16  and into a manifold  18  within sampling area  15 . The manifold  18  funnels the air into a sensor line  20  and/or a purge line  22 . In one mode of operation, the fluid sampling system  14  measures differential parameters. A differential sensor bank  24  is used to measure a differential value of a parameter between the sensor line  20  and purge line  22 . The bank of differential sensors  24  is shown coupled across sensor line  20  and purge line  22 . A pressure differential measurement is made across the sensor and purge lines  20 ,  22  using the differential sensor bank  24 . The sensor bank  24  includes four individual differential pressure sensors  24   a,    24   b,    24   c,    24   d.    
     In another mode of operation, the fluid sampling system  14  measures singular parameters. The sensor line  20  shunts the air sample to an in-line sensor mechanism  26  where sensor readings are taken and then out of the fluid sampling system  14  via exhaust port  28 . Alternatively, the fluid sample is funneled to a purge line  22  and is exhausted from the fluid sampling system  14  via exhaust port  30 . The purge line  22  exhausts larger volumes of fluid from the system  14  to purge the system  14  of stale (i.e., outdated) samples to ensure that only fresh (i.e., current) samples are shunted through the sensor line  20  to the sensor mechanism  26 . This arrangement would be used to measure values of a parameter at a single sample location rather than a differential parameter between two locations. Parameters that can be measured include concentrations of various substances in the air sample such as, e.g., carbon dioxide and carbon monoxide, and other related measurements such as, e.g., dew point and temperature. In addition, this arrangement of sensor and purge lines  20  and  22  allows a sample line  16  to be flushed simultaneously while a measurement is taken in the sensor line  20  and, thus, increases the sampling rate of the system  14 . 
     The manifold  18  contains a set of input ports  32  and two output ports  34   a,    34   b.  Typically, the manifold could have any number of input ports  32 , e.g., 12 or 24 input ports. The sample tubes  16  are connected to the input ports  32  such that, e.g., one sample zone would be in fluid communication with one input port. The sensor and purge lines  20  and  22  are connected respectively to the output ports  34   a  and  34   b.  A bank  24  of pressure sensors are shown disposed across the sensor and the purge lines  20 ,  22 . This arrangement allows the system  14  to measure differential pressure between two selected sample zones. The pressure sensors  24   a,    24   b,    24   c,  and  24   d  are coupled across the sensor and purge lines  20 ,  22 . Each of the sensors  24   a,    24   b,    24   c,    24   d  is designed to measure pressure accurately in different pressure ranges, e.g., four sensors measure the differential pressure with the first sensor  24   a  accurate in the narrowest range, the second sensor  24   b  accurate in a broader range, the third sensor  24   c  accurate in an even broader range, and the fourth sensor  24   d  accurate in the broadest range. The pressure ranges overlap to allow for more accurate measurements in the narrower ranges. For example, a pressure difference between two rooms is likely to be only 0.051″ H 2 O. A narrower range sensor will give a more accurate reading than a broader range sensor with the same accuracy, e.g., 2%. 
     Alternatively, the individual sensors  24   a,    24   b,    24   c,    24   d  can transmit a positive indication rather than a measurement when the pressure falls within the given range of the individual sensor  24 . 
     The fluid sample system  14  is operated by a system controller  36  that controls the flow of air, the selection of sample zones, the measurements, and the data processing. The system controller  36  is, e.g., a microprocessor that is connected to the manifold  18  and the sensors via control signal lines  38 . The system controller  36  transmits signals to and/or receives signals from the manifold  18  and the sensors  24 ,  26 . The system controller  36  controls the system according to a software algorithm customized to the attributes of the system  14 . 
     FIG. 3 shows an embodiment of a sensor subsystem  13  of the fluid sampling system  14 . Fluid samples are drawn into the manifold  18  through the twenty-four input ports and are shunted to either a purge line  22  or a sensor line  20 . Typically, before a measurement, the fluid within the manifold  18  and the selected sample tube  16  is purged so that fresh air from the sample zone is sensed. To do this, a vacuum pump isolation valve  40  is positioned by the system controller  36  to couple the purge line  22  to an exhaust port  42 , and a purge end vacuum pump  44  is activated. A pressure transmitter isolation valve  46  is positioned by the system controller  36  to decouple the pressure sensors  24   a,    24   b,    24   c,    24   d.  A pressure switch  48  is activated to ensure that the valve  40  and the vacuum pump  44  are operating correctly. The fluid, e.g., air, is forced through a restrictor  50  that causes a back pressure that ensures the activation of the pressure switch  48 . Filtered fluid is supplied to the vacuum pump  44  through a filtration line  52  that connects with the purge line  22  through valve  40 . The filtration line  52  includes a filter  54  and a restrictor  56 . The supply of fluid through filtration line  52  ensures that the vacuum pump  44  is able to draw an adequate amount of fluid at all times regardless of the amount of fluid flow from the manifold  18  and prevents excess wear on the vacuum pump  44 , especially the diaphragm of the pump. 
     Alternatively, the fluid can be drawn through the sensor line  20 . In this mode, the sensor vacuum pump isolation valve  58  is positioned by the system controller  36  to couple the sensors  26   a,    26   b,    26   c  to sensor line  20  and a vacuum pump  62  is engaged. A sensor pressure transmitter isolation valve  60  is positioned by the system controller  36  to decouple the pressure sensors  24   a,    24   b,    24   c,    24   d  and a pressure switch  64  is activated to ensure that the valve  58  and the vacuum pump  62  are operating correctly and to confirm fluid is flowing through the sensors  26   a,    26   b,    26   c.  The presence of additional components on the end of sensor line  20  creates a back pressure to activate pressure switch  64 . A flow monitor valve  66  is adjusted by the system controller  36  to maintain the velocity of the fluid in the sensor line  20  within tolerable ranges. Specifically, the valve  66  is adjusted manually to exhaust excess fluid from the system  14  through an exhaust port  68  to maintain fluid flow to the sensors  26   a,    26   b,    26   c  below maximum allowable levels. Therefore, the excess capacity of the vacuum pump  62  is utilized without damaging the sensors  26 . However, the sensors  26   a,    26   b,    26   c  are supplied with a constant flow of 500 cc/min when the system is active. Filtered fluid is supplied to the vacuum pump  62  through a filtration line  70  that connects with the sensor line  20 . The filtration line  70  includes a filter  72  and a restrictor  74  to ensure the vacuum pump  62  receives adequate fluid flow and, thus, prevents excess wear on the pump. 
     The fluid sample is filtered by the sensor filter  76  and is shunted to the on-line sensor mechanism  26 , shown in FIG.  2 . The on-line sensor mechanism  26  is attached to the sensor line  20  such that it is capable of sensing the sample. The on-line sensor mechanism  26  includes five sensor ports  78 ,  80 ,  82 ,  84 ,  86  and three different sensors  26   a,    26   b,    26   c  attached to the sensor line  20 : CO 2  sensor  26   a,  dewpoint sensor  26   b,  and CO sensor  26   c.  Each of these sensors  26   a,    26   b,    26   c  is attached to one of the sensor ports  82 ,  84 ,  86 . The remaining two ports  78 ,  80  are external sample ports and normally are plugged, i.e., the flow of fluid is blocked. One of the external sample ports  78  normally is decoupled from the sensor line  20  by an external sample valve  88  operated by the system controller  36 . 
     Each of the three sensors  26   a,    26   b,    26   c  can be coupled or decoupled from the sensor line  20  by one of three isolation valves  90 ,  92 ,  94 , e.g., manually operated or automatically controlled by the system controller  36 . Each of the sensors  26   a,    26   b,    26   c  also includes a calibration gas port  96 ,  98 ,  100  which normally is plugged, and a flowmeter  102 ,  104 ,  106 , e.g., a rotational flow meter having an integral needle valve ( 102   a,    104   a,    106   a ). 
     In addition to the sensor data measured by the sensors  26   a,    26   b,    26   c  through the sensor line  20 , differential pressure can be measured across the sensor and purge lines  20  and  22  by the four pressure sensors  24   a,    24   b,    24   c,    24   d.  The pressure sensors  24   a,    24   b,    24   c,    24   d  are in fluid communication with the sensor line  20  via connection line  108  and with the purge line  22  via connection line  110 . The ends of the connection lines  108 ,  110  contain a calibration port  112 ,  114  that normally is plugged. Differential pressure is measured in a static state with the vacuum pumps  44 ,  62  disengaged by the system controller  36 . The sensor and purge isolation valves  58  and  40  are switched to decouple the sensors  26   a,    26   b,    26   c  and the exhaust port  42  from the sensor and pressure lines  20  and  22  and to couple the pressure sensors  24   a,    24   b,    24   c,    24   d  to the sensor and purge lines  20  and  22 . The pressure sensor  26  measurements and the sensor mechanism  24  measurements are not taken at the same time because the sensor mechanism  24  measurements are taken while the system is in a dynamic state. Alternatively, the fluid sampling system  14  could be configured to measure pressure in a dynamic state, e.g., with the vacuum pumps  44  and  62  engaged and fluid moving through the system  14 . 
     Referring to FIGS. 4 and 5, the manifold  18 ′,  18 ″ is constructed of, e.g., a metal or a plastic machined or formed to include an arrangement of passages  116  and valves  118  to connect a number of input ports  32 ′,  32 ″ to both the sensor and purge lines  20 ,  22 . A possible material is the machineable plastic Delrin®, an acetal resin manufactured by DuPont. Other materials and combinations are possible. For example, the manifold can be an arrangement of plastic tubes. The manifold  18 ′,  18 ″ has a set of input ports  32 ′,  32 ″ and two output ports  34 ′,  34 ″. Each input port  32 ′,  32 ″ is located at the end of a passage that branches with one branch leading to the output port  34 ′,  34 ″ connected to the sensor line  20  of FIG.  2  and with the other branch leading to the output port  34 ′,  34 ″ connected to the purge line  22  of FIG. 2. A valve  118 , e.g., a solenoid valve operated by the system controller  36  is disposed across each branch so that each input port  32 ′,  32 ″ may be coupled and decoupled from each of the output ports  34 ′,  34 ″. Thus, any selected input port or set of input ports  32 ′,  32 ″ can be coupled to either or both of the output ports  34 ′,  34 ″. 
     In the configuration shown in FIG. 4, there are pairs of input ports  32 ′ aligned along a first plane of the manifold  18 ′ while the two output ports  34 ′ lie at one end of the manifold  18 ′. In the configuration shown in FIG. 5, a line of unpaired input ports  32 ″ are aligned along a first plane of the manifold  18 ″ while the two output ports  34 ′ lie at one end of the manifold  18 ″. Though either eight or four input ports  32 ′,  32 ″ are depicted in FIGS. 4 and 5 respectively, a manifold  18  having either twelve single or twenty-four paired input ports typically would be used. A manifold  18 ″ with twelve input ports contains twenty-four valves  118 . A manifold  18 ′ with twenty-four input ports contains forty-eight valves  118 . 
     FIG. 6 shows an embodiment of the differential pressure sensor  24  shown in FIG. 2, and includes four different individual pressure sensors  24   a,    24   b,    24   c,    24   d.  Each individual sensor  24   a,    24   b,    24   c,    24   d  is coupled across the sensor line  20  and the purge line  22 ; the sensor and purge lines  20 ,  22  are connected respectively to the two output ports  34   a  and  34   b  of the manifold. Therefore, each of the pressure sensors  24   a,    24   b,    24   c,    24   d  is capable of making a differential pressure measurement across any two input ports  32  (shown in FIG. 2) when coupled to the output ports  34   a  and  34   b  by the valves  118  (shown in FIGS. 4 and 5) of the manifold  18 . 
     Each of the sensors  24   a,    24   b,    24   c,    24   d  has a different pressure range in which the sensor is most accurate. The first sensor  24   a,  which is regarded as a very low pressure sensor, is most accurate in the narrowest range of pressures. The second sensor  24   b,  which is regarded as a low pressure sensor, is most accurate in a relatively broader range of pressures. The third sensor  24   c,  which is regarded as a high pressure sensor, is most accurate in a range of pressures that relatively is broader than the first two ranges. The fourth sensor  24   d,  which is regarded as a very high pressure sensor, is most accurate in a range of pressures that relatively is broader than the other three ranges. The pressure sensors  24   a,    24   b,    24   c,    24   d  are selected such that the pressure ranges of each individual sensor  24   a,    24   b,    24   c,    24   d  forms overlapping ranges in which accurate pressure measurements may be taken. Other combinations of sensors, e.g., two, three, or five, could be used. 
     The flow chart of FIG. 7 illustrates the logic used to measure, select, and record the pressure across the sensor and purge lines  20 ,  22 . First, the system  14  is brought to a static state by the system controller  36  and the differential pressure sensors  24   a,    24   b,    24   c,    24   d  measure the differential pressure of the sensor and purge lines  20 ,  22 . The system controller  36 , compares the pressure measurements of the individual sensors  24   a,    24   b,    24   c,    24   d  to the range in which the individual sensors are accurate. The system controller  36  first compares the measurement produced by sensor  24   a  to the accuracy range of sensor  24   a.  If sensor  24   a  produces a pressure measurement in the very low range (−P LL -P LL ), the pressure P 1  is recorded as the differential pressure. Similarly, the system controller examines data from each sensor in turn. If sensor  24   b  produces a pressure measurement in the low range (−P L -P L ), the pressure P 2  is recorded as the differential pressure. If sensor  24   c  produces a pressure measurement in the high range (−P H -P H ), the pressure P 3  is recorded as the differential pressure. If sensor  24   d  produces a pressure measurement in the very high range (−P HH -P HH ), the pressure P 4  is recorded as the differential pressure. If none of the pressure measurements are within the range of the associated sensors  24   a,    24   b,    24   c,    24   d,  then the system controller  36  records an error message that the differential pressure is out of range. As an example, the ranges sensors  24   a,    24   b,    24   c,  and  24   d  are bi-directional sensors with ranges, respectively, of 0 to +/−0.10″ H 2 O, 0 to +/−0.25″ H 2 O, 0 to +/−1.0″ H 2 O, and 0 to +/−5.0″ H 2 O. The accuracy of the sensors  24   a,    24   b,    24   c,  and  24   d  is +/−2%. 
     FIG. 8 shows an alternate embodiment of the fluid sampling system  14  shown in FIG. 2 that includes a system controller  36 ′ connected to multiple manifolds  18  (here four manifolds being shown). The single system controller  36 ′ controls the entire system rather than one system controller  36  controlling each manifold. Typically the manifolds  18  would have either twelve or twenty-four input ports and two output ports. The system controller  36 ′ sends signals to control all of the elements of subsystem  13  shown in FIG. 3, e.g., the valves  118  of the manifold and the automatic valves  46  and  60  of lines  20  and  22 , the sensors  26 , the differential sensors  24 , the vacuum sources  44  and  62 , the pressure switches  48  and  64 , and any additional elements of an alternate embodiment of the system that are actuated automatically. 
     As shown, the sensor subsystems  13   a-d  are connected to the system controller  36 ′ via respective network interfaces  41   a-d.  The interfaces  41   a-d  send signals from the controller  36 ′ to the manifold  18 , the sensor bank  26 , the differential pressure bank  24  via respective connections  39   a,    39   b,  and  39   c.  The interfaces  41   a-d  are connected to the system controller via connection  38 . 
     Other Embodiments 
     It is to be understood that while the invention has been described in conjunction with the detailed description thereof, the foregoing descriptions are intended to illustrate and not limit the scope of the invention, which is defined by the scope of the appended claims. Other aspects, advantages, and modifications are within the scope of the appended claims. 
     For example, the manifold can have more than two output lines, a different number of input ports, or a different coupling arrangement, e.g., some, but not all input ports coupled to all output ports. A second sensor line can be connected to an additional output port to measure differential temperature or other measurements. The fluid sampling system can include more, fewer, or different sensor arrangements as well as a different arrangement of components to actuate the system. The sampled fluid can be gases other than air such as the exhaust gases of a landfill, or the sampled fluid can be liquids such as water and oil.