Abstract:
There are provided methods and devices for sensing hydrogen gas. For example, there is provided a method that includes drawing a sample into a channel. The method includes passing the sample over a collection plate to remove an extraneous gas in the sample, thus yielding a purified sample. The method further includes passing the purified sample on a sensing plate and measuring a concentration of hydrogen in the purified sample using the sensing plate. The measuring can include heating the sensing plate and correlating a change in resistance of the sensing plate with a specified concentration of hydrogen. Furthermore, the method can include regenerating the collection plate following the measuring.

Description:
TECHNICAL FIELD 
       [0001]    The present disclosure generally relates to hydrogen detection. More particularly, the present disclosure relates to a hydrogen detector and a hydrogen detection method. 
       BACKGROUND 
       [0002]    Conventional hydrogen (H 2 ) gas sensors suffer from poor sensitivity due to the lack of selectivity in their sensing mechanism. Specifically, hydrogen sensors are prone to contamination from carbon monoxide, carbon dioxide, and acetylene, as well as other hydro-carbons, all of which can contribute to an erroneous estimation of the concentration of hydrogen gas in a sample. 
         [0003]    In a measurement setting, this cross-contamination can be characterized by a shift from an H 2 baseline. Furthermore, in addition to the presence of these contaminants, variations within the sensing layer structure of the sensor as well as the different spatial thermal gradients that arise in the sample prior to measurement also contribute to the shift from the H 2 baseline, thereby yielding an incorrect estimation of the hydrogen content. These issues, whether taken alone or together, all contribute in raising the detection limit of current hydrogen sensors. 
       SUMMARY 
       [0004]    The embodiments featured herein help solve or mitigate the above-noted issues as well as other issues known in the art. Specifically, the embodiments provide means for removing contaminants in a sample prior to measurement. Further, the embodiments, provide means for constraining the sample volume during the measurement in order to limit spatial thermal gradients. Furthermore, the embodiments provide means for preventing further generation of trace gases, by conversion from longer hydro-carbons (i.e. methane and ethane), when oil mists are present in the sample, thereby allowing a lower detection limit for hydrogen, relative to conventional sensors. 
         [0005]    In one embodiment, there is provided a method that includes drawing a sample into a channel. The method includes passing the sample over a collection plate to remove an extraneous gas in the sample, thus yielding a purified sample. The method further includes passing the purified sample on a sensing plate and measuring a concentration of hydrogen in the purified sample using the sensing plate. The measuring can include heating the sensing plate and correlating a change in resistance of the sensing plate with a specified concentration of hydrogen. Furthermore, the method can include regenerating the collection plate following the measuring. 
         [0006]    In another embodiment, there is provided a device that includes a channel, a collection plate, and a sensing plate insulated from the collection plate. The device is configured to measure a concentration of hydrogen adsorbed onto the sensing plate. Further, the device is configured to correlate a change in resistance of the sensing plate with a specified concentration of hydrogen. 
         [0007]    In yet another embodiment, there is provided a hydrogen sensor including a sensing plate configured to capture hydrogen in a sample. The hydrogen sensor further includes a regenerative collection plate configured to capture extraneous gaseous elements from the sample, prior to capturing hydrogen at the sensing plate. 
         [0008]    Additional features, modes of operations, advantages, and other aspects of various embodiments are described below with reference to the accompanying drawings. It is noted that the present disclosure is not limited to the specific embodiments described herein. These embodiments are presented for illustrative purposes only. Additional embodiments, or modifications of the embodiments disclosed, will be readily apparent to persons skilled in the relevant art(s) based on the teachings provided. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    Illustrative embodiments may take form in various components and arrangements of components. Illustrative embodiments are shown in the accompanying drawings, throughout which like reference numerals may indicate corresponding or similar parts in the various drawings. The drawings are only for purposes of illustrating the embodiments and are not to be construed as limiting the disclosure. Given the following enabling description of the drawings, the novel aspects of the present disclosure should become evident to a person of ordinary skill in the relevant art(s). 
           [0010]      FIG. 1  is an illustration of a device, according to an embodiment. 
           [0011]      FIG. 2A  is a cross-sectional view of a device, according to an embodiment. 
           [0012]      FIG. 2B  is a cross-sectional view of a sensing element of the device of  FIG. 2A , according to an embodiment. 
           [0013]      FIG. 3  depicts a flow chart of a method, according to an embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0014]    While the illustrative embodiments are described herein for particular applications, it should be understood that the present disclosure is not limited thereto. Those skilled in the art and with access to the teachings provided herein will recognize additional applications, modifications, and embodiments within the scope thereof and additional fields in which the present disclosure would be of significant utility. 
         [0015]      FIG. 1  is an illustration of a device  100  according to an embodiment. Device  100  can be a hydrogen detector or sensor configured for hydrogen detection. Device  100  can include chamber  105 . Chamber  105  includes an inlet  101  and an outlet  103 . It is noted that outlet  103  can serve as an inlet and that inlet  101  can serve as an outlet, depending on the configuration. Furthermore, device  100  includes a portion dedicated for purification and analysis of a sample that is introduced, i.e. drawn, into chamber  105 . In  FIG. 1 , this portion is shown as a protuberance on the side of chamber  105  of the channel, and it includes collection plates  109  and  113  and sensing plate  111 . Purification and analysis are achieved in the inner surfaces of the portion shown in  FIG. 1 . 
         [0016]    In one embodiment, collection plates  109  and  113  can be made of a material that is inherently configured to absorb specific contaminants typically encountered in hydrogen detection applications. For example, when the sample is air, these contaminants can be carbon monoxide, carbon dioxide, and/or acetylene. As such, collection plates  109  and  113  can be made of silver oxide (Ag 2 O), which can absorb these contaminants, particularly carbon dioxide. Once the contaminants are removed from the sample, the sample is purified, and it then flows on to sensing plate  111 , which can then sense the hydrogen content with no cross-contamination by the extraneous gases originally found in the sample. 
         [0017]    One of ordinary skill in the art will readily appreciate that in some embodiments, the collection plates may not remove the entirety of the contaminants in the sample. Nevertheless, in these embodiments, a much reduced concentration of contaminants in the sample during sensing will contribute in lowering the detection limit of hydrogen gas. 
         [0018]    Collection plates  113  and  111  are regenerative. That is, once they are saturated with contaminants, they can be made free of the contaminants simply by heating the plates to release the contaminants in gas form from the plates. This can be done using a heater (not shown), which can be controlled using a conventional controller. Typically, in the case of silver oxide, the collection plates can be heated to exceed about 220 degrees Celsius in order to achieve regeneration. 
         [0019]    Sensing plate  111  is the element that is used to detect the presence of hydrogen gas in the purified sample. Sensing plate  111  can be made of (or it can include) a tin oxide layer which changes in resistance in response to hydrogen uptake. Upon release of hydrogen from the tin oxide layer, it can return to its original resistance. In a typical measurement scheme using device  100 , sensing plate  111  is heated between about 400 degrees Celsius and about 500 degrees Celsius to make the measurements. This may be done with a heater (not shown) controlled using a conventional temperature controller. 
         [0020]    Once sensing plate  111  is heated to the above-mentioned temperature range, changes in resistance registered at sensing plate  111  can be correlated with hydrogen concentration using a predetermined concentration vs. resistance calibration curve or calibration table. Further, the resistance of sensing plate  111  can be monitored using a pair of electrodes each placed at a different location of sensing plate  111 . In some embodiments, a four-point probe measurement of resistance can be employed using four electrodes; this configuration minimizes the effect of the resistance of the electrodes on the measurement, thereby providing more accurate results than in the two-electrode configuration. Further, it is noted that the present disclosure is not limited to tin oxide as being the sensing material; any hydrogen-sensitive material known in the art is contemplated. 
         [0021]    Further, in a measurement scheme using device  100 , a sample is drawn into chamber  105 . The path undertaken by the sample can be thought of as a channel, which has a T-section (see lines  202  and  204  in  FIG. 2A  illustrating the path of the sample into chamber  105 ). The channel is insulated in order to limit the internal air volume that is subject to the high temperatures necessary for measurement. If no insulation is provided, the high temperatures required to make the measurement (400 degrees Celsius to 500 degrees Celsius) can cause thermal gradients at sensing plate  111 , which would also corrupt the measurement results. In device  100 , an insulation material is also used between sensing plate  111  and collection plates  109  and  113 . After making the measurement at sensing plate  111 , collection plates  109  and  113  can be regenerated as mentioned above. Sensing plate  111  is also allowed to cool to limit the possibility of contaminants freed from collection plates  113  and  109  during regeneration to adsorb onto its surface. 
         [0022]    The cross-section at sensing plate  111  also looks like a ‘T’. This cross-section forms a sensing channel. (See the dashed lines in  FIG. 2A , which is a cross-sectional view of the sensing channel at sensing plate  111 ). This configuration encourages a larger air flow, due to thermal convection currents. If it was only a thin gap, at sensing plate  111 , the surface friction of the thin channel would limit the maximum airflow, but by using a T-Section, this encourages faster flow, while still having a constrained thermal region around the sensor element. 
         [0023]    As shown in  FIG. 2 , the analysis and purification are both confined to a specified region of the channel, i.e. in the protrusion located on the side of chamber  105 . In other words, portions of the sample that are flowing in chamber  105  will not be heated to high temperatures since the analysis and the purification steps are constrained to a much smaller volume located in the protrusion on the side of chamber  105 . This configuration prevents the conversion of excessive amounts of lower length hydro-carbons (such as methane and ethane) that can contaminate sensing plate  111  and lead to erroneous measurement results. 
         [0024]    Constraining the volume and providing additional insulation is further achieved by a gap  201  between the sensing plate  111  and the body of chamber  105 . In some embodiments, gap  201  may be an air gap, whereas in other embodiments it may include an insulation material. 
         [0025]      FIG. 3  depicts a flow chart of an exemplary method  300 , according to an embodiment. Method  300  can be executed by a system comprising one or more devices such as device  100 . Method  300  begins at block  301 . While block  301  is described herein as a “beginning step,” one of ordinary skill in the art will readily recognize that block  301  can generally be a transition point in a flow diagram. In other words, block  301  can be a point at which another method ends or it may mark the end of a series of steps similar to those described below in the context of method  300 . 
         [0026]    Method  300  includes a step  303  in which a sample is introduced in a channel of a hydrogen sensor configured according to the teachings provided in the present disclosure. The sample can be introduced into the channel using conventional means, such as by pumping, thermal convection or merely by diffusion. 
         [0027]    Once the sample is introduced in the channel, the sample is purified at a collection plate (step  305 ). Purification can include removing one more contaminants from the sample. For example, purification can include removing one of carbon dioxide, carbon monoxide, and acetylene. Purification can also include removing at least two of the aforementioned gases in the sample. Furthermore, purification can include, generally speaking, removing hydro-carbons, such as methane and ethane. As mentioned above when discussing exemplary embodiments of the hydrogen sensor, purification can be accomplished at a collection plate. The collection plate can include silver oxide or any other compound that can absorb specific contaminants dictated by the application at hand. 
         [0028]    Method  300  can include a step  307  wherein the purified sample is heated between about 400 degrees Celsius and 500 degrees Celsius. Method  300  can also include a step  309  wherein the heated purified sample is made to adsorb over a sensing plate to perform a measurement of the hydrogen content in the purified sample. The measurement can include comparing a change in resistance or a simply comparing a resistance value of the sensing plate with a calibrated resistance value in order to correlate the instant measurement with a known hydrogen gas concentration. One of skill in the art will readily appreciate that step  309  can include any operation that is typical in the measurement and instrumentation arts, namely data filtering, averaging, etc. 
         [0029]    Furthermore, method  300  can include a regeneration step  311  wherein once the hydrogen content in the purified sample has been measured and/or estimated, the collection plate can be regenerated to remove the contaminants that adsorbed thereto. This can be done by heating the collection plate to a higher temperature (i.e. for silver oxide &gt;200 degrees Celsius). Doing so frees the collection plate from the contaminants and makes it ready for a subsequent measurement cycle that includes all the steps described above. Furthermore, while regeneration is being achieved on the collection plate, the sensing plate is allowed to cool in order to prevent any uptake of the contaminants at the sensing plate. Method  300  can end at step  313 . Generally speaking, however, step  313  can be a transition point, and method  300  can start over at step  301  from step  313 . Lastly, it is noted that method  300  can be implemented partially or in whole, without departing from the scope of the teachings disclosed herein. 
         [0030]    Those skilled in the relevant art(s) will appreciate that various adaptations and modifications of the embodiments described above can be configured without departing from the scope and spirit of the disclosure. Therefore, it is to be understood that, within the scope of the appended claims, the disclosure may be practiced other than as specifically described herein.