English:
[0001] Toxic gas, such as hydrogen sulfide gas, can be deadly even at low concentrations. Generally, when one is exposed to such a toxic gas, it is imperative to seek medical attention relatively quickly. Accordingly, in many industrial situations, it is very important to be able to detect toxic gas in very low concentrations as soon as possible when a leak occurs, even in the most challenging and remote conditions. Moreover, it is important that a toxic gas sensor be ready to perform its function even when the occurrence of a toxic gas leak is extremely rare.
[0002] Health and safety standards in many countries have been slowly decreasing the acceptable exposure levels as sensor response times and overall stability of sensing elements have improved. For example, in the United States, the Occupational Safety and Health Administration (OSHA) provides an acceptable concentration limit for exposure to hydrogen sulfide at 20 parts per million (ppm) for an 8-hour period, with the maximum peak exposure at 50 ppm for 10 minutes.
[0003] An important goal of any fixed-location toxic gas detector is to safeguard workers and the public by warning of the presence of hazardous levels of such toxic gas in the proximity of the sensor. Electrochemical and Metal Oxide Semiconductor (MOS) cells have, for many years, been field-proven toxic gas sensing technologies. MOS-based sensors have a long life compared to electrochemical sensors and continue to operate in wide ranging temperatures, particularly high temperatures, as well as in extremely dry conditions.
[0005] This type of sensor typically utilizes the polycrystalline structure of the sensing material (semiconductor metal oxide) and the existence of the negatively charged surface oxygen species, which controls the height of the Schottky barrier and the electrical resistance of the material. When the sensor is exposed to certain reducing gases, the surface oxygen will be consumed, reducing the Schottky barrier, and the resistance, which is the sensing signal.
[0006] In order to ensure that a metal oxide semiconductor toxic gas sensor is able to provide a viable signal, it is important for diagnostics to be able to test, or otherwise determine if the sensor has become damaged, or otherwise deteriorated.
[0007] A metal oxide semiconductor-based toxic gas detector is provided. The metal oxide semiconductor-based detector includes a metal oxide semiconductor-based gas sensor that has an electrical characteristic that varies with concentration of a toxic gas. Measurement circuitry is coupled to the metal oxide semiconductor-based gas sensor and is configured to measure the electrical characteristic and provide a digital indication of the measured electrical characteristic. A controller is coupled to the measurement circuitry and is configured to provide a toxic gas output based on the digital indication. The controller is also configured to provide a diagnostic output relative to the metal oxide semiconductor-based sensor based on fluctuations of the measured electrical characteristic over time.
[0008] FIG. 1 is a diagrammatic view of a metal oxide semiconductor toxic gas detector with which embodiments of the present invention are particularly useful.
[0009] FIG. 2 is a block diagram of a metal oxide semiconductor toxic gas detector in accordance with an embodiment the present invention.
[0010] FIG. 3 is a diagrammatic scatter plot of analog-to-digital signal measurements over time for a metal oxide semiconductor toxic gas sensor.
[0012] As set forth above, diagnostics of toxic gas sensors is an important aspect of ensuring that the toxic gas sensor is operating effectively and will be able to provide a trustworthy signal in the event that toxic gas becomes present. Utilization of toxic gas sensors based on semiconductor metal oxide sensing technology in safety applications requires various diagnostics to detect failure modes in the sensor. For such safety applications, it is necessary to detect all failure modes that the sensor may be subjected to, such as a short of the sensor element and an open sensor element.
[0013] Embodiments of the present invention generally detect a more subtle failure mode in solid state metal oxide semiconductor toxic gas sensors. Specifically, the failure mode is known as a stale sensor. When this failure mode occurs, the sensor reading will not effectively indicate a toxic gas concentration. However, the sensor will continue to indicate an actual resistance. Thus, sensor diagnostics based on detecting a short or an open circuit will not detect a stale failure. Instead, embodiments of the present invention generally leverage an aspect of a metal oxide semiconductor toxic gas sensor signal in order to detect a stale failure. Specifically, when a metal oxide semiconductor toxic gas sensor is operating correctly, the sensor resistance will have a natural variation or fluctuation. Generally, sensor electronics have subjected the sensor input signal to a low pass filter in order to remove these variations. Thus, the resistance of the sensor is processed or otherwise characterized in order to remove the fluctuations prior to providing a toxic gas sensor output. However, in accordance of embodiments of the present invention, as set forth below, these variations are specifically measured and used to provide a diagnostic indication relative to the metal oxide semiconductor toxic gas sensor.
[0014] FIG. 1 is a diagrammatic view of a metal oxide semiconductor toxic gas detector with which embodiments of the present invention are particularly useful. Detector 10 includes electronics enclosure 12 coupled to sensor body 14. Sensor body 14 includes a metal oxide semiconductor-based toxic gas sensor, such as a hydrogen sulfide gas sensor, which may be a "traditional" metal oxide semiconductor sensor or an NEMOS based semiconductor gas sensor. Lower portion 16 of sensor body 14 is configured to expose the toxic gas sensor to ambient air in order to determine a concentration of a toxic gas, such as hydrogen sulfide gas, in the ambient air. The sensor within sensor body 14 is coupled to suitable electronics (shown in FIG.2) within enclosure 12 via conduit 18. Electronics within enclosure 12 can amplify, linearize, and otherwise characterize the sensor response in order to provide an indication of toxic gas concentration. This indication can be provided over a process communication loop or segment, via process wiring through conduit 20, and/or provided locally. A local indication of toxic gas can include a local operator interface (LOI) displaying a toxic gas concentration, an audible or visual alarm, or any combination thereof.
[0015] FIG. 2 is a block diagram of a metal oxide semiconductor toxic gas detector in accordance with an embodiment the present invention. Detector 10 includes electronics enclosure 12 coupled to sensor body 14. Disposed within electronics enclosure 12 are controller 22, communication module 24, power module 26, and measurement circuitry 28. Metal oxide semiconductor-based toxic gas sensor 30 is disposed within sensor body 14 and is coupled to measurement circuitry 28.
[0016] Controller 22 may be any suitable processing circuitry that is able to apply digital processing techniques or filtering to the sensor measurement in order to determine or otherwise characterize variability or fluctuations in the sensor signal. Additionally, controller 22 is also configured to generate a toxic gas concentration output based on the sensor measurement(s). In one embodiment, controller 22 is a microprocessor. Controller 22 is coupled to communication circuitry 24 to allow controller 22 to communicate with other devices in the process control and monitoring system. Communication circuitry can include circuitry that allows controller 22 to communicate in accordance with a process industry standard communication protocol, such as the Highway Addressable Remote Transducer (HART®) protocol, the FOUNDATIONTM Fieldbus protocol, or others. Additionally, in some embodiments, device 10 may communicate wirelessly in addition to or instead of using wired process communication. For example, in one embodiment, communication circuitry 24 may allow communication in accordance with IEC62591. Finally, communication circuitry may provide communication of local outputs, such as a local display or alarm.
[0017] Power module 26 is coupled to all components within enclosure 12, as indicated by the arrow labeled "To All." Power module 26 is configured to receive power from a suitable source and provide voltage adjustment or suitable power conditioning to the circuitry within enclosure 12. In some embodiments, power module 26 may be coupled to a wired process communication loop such that device 10 can receive all of its operating energy from the wired process communication loop. In other embodiments, power module 26 may be coupled to a suitable source AC or DC power.
[0018] Measurement circuitry 28 is coupled to controller 22 and is able to obtain measurements from semiconductor-based toxic gas sensor 30 and provide digital indications thereof to controller 22. Measurement circuitry 28 may include one or more analog-to-digital converters, suitable multiplexor circuitry, as well as amplification and/or linearization circuitry. Further, measurement circuitry 28 may include suitable filter circuitry, such as a low-pass filter, that is selectively interposable between the sensor and an analog-to-digital converter. In such embodiment, interposing such a low- pass filter between the sensor and an analog-to-digital converter would allow a direct measurement of a signal representative of a toxic gas sensor concentration. Then, bypassing the low pass filter would allow an analog-to-digital converter to measure fluctuations relative to the sensor signal, which fluctuations are indicative of proper sensor functioning. However, it should be noted, that embodiments of the present invention can be practiced where no analog filtering is used, and where both fluctuations and the toxic gas sensor concentration are obtained mathematically from a plurality of analog-to-digital sensor measurements.
[0019] FIG. 3 is a diagrammatic scatter plot of analog-to-digital signal measurements over time for a metal oxide semiconductor toxic gas sensor. As shown in FIG. 3, the sensor exhibits detectable fluctuations or variability. In the example shown in FIG. 3, the toxic gas concentration is shown varying from a time of approximately five minutes to a time of approximately 70 minutes. The vertical axis is an analog-to-digital converter count for each individual measurement. The toxic gas concentration varies with a gradual increase from a time of 5 minutes to time of 40 minutes when the sensor has an output of approximately 57,850 counts. At time a time of about 40, the toxic gas concentration begins to diminish gradually until at approximately time T=65 minutes, when the analog-to-digital count is approximately 57,775. As shown in the example, the variability is typically on the order of approximately 25 counts. In accordance with various embodiments of the present invention, while the toxic gas concentration may be processed in any suitable manner to remove effects of variation or otherwise average values over a short window of time in order to provide a relatively stable toxic gas concentration output, a diagnostic output is generated based substantially on the fluctuations. The fluctuations may be detected or otherwise observed in any suitable manner. For example, an array or other suitable memory structure may be filled with a sequence of analog-to-digital converter measurements over a fixed period of time, or simply a certain number of measurements. The memory structure may be updated such that when a new measurement is obtained, the oldest measurement is discarded. Controller 22, or any other suitable processor, may operate digitally upon the stored array or sequence of measurements in order to obtain information about fluctuation characteristics, such as variability. For example, the variance of the set of measurements may simply be calculated in accordance with known statistical techniques. However, any other suitable mathematic operations that can provide useful information regarding the degree of fluctuation can be used in accordance of the embodiments of the present invention.
[0020] FIG. 4 is a flow diagram of a method of generating a diagnostic indication relative to a semiconductor metal oxide toxic gas sensor in accordance with an embodiment of the present invention. Method 100 begins at block 102 where a plurality of sensor measurements are obtained. These sensor measurements are obtained over a suitable period of time, for example, a span of several seconds or even minutes. Next, at block 104, fluctuations in the sensor signal measurements are detected. As set forth above, in one embodiment, a number of sensor measurements may be stored in memory and processed in accordance with any suitable mathematic techniques in order to detect variability. For example, statistical processing techniques 106 can be used to detect such fluctuations. Additionally, or alternatively, the differences between individual measurements can be processed or otherwise subjected to a threshold process 108. Finally, the stored measurements may be subjected to a digital filter 110 in order to amplify or otherwise highlight variability in the sensor signal measurements. Next, at block 112, the detected fluctuations or variability is compared to a preselected limit. This limit may be defined or otherwise set during manufacture of the device or it may be set during commissioning of the device. For example, one particular toxic gas sensor may exhibit more variability than another type of toxic gas sensor. Thus, when the detector is commissioned with a specific toxic gas sensor, a variability threshold suitable for that sensor can be set. If the detected variability of the semiconductor based toxic gas sensor is below the selected limit, control passes to block 114 where controller 22 will generate a diagnostic indication. This diagnostic indication may be the generation of a fault or error message that is conveyed over a process communication loop or segment, a local indication indicated visually or audibly at the detector, or any combination thereof. Alternatively, if the detected variability is not below the selected limit, control passes to block 116 and method 100 ends. Accordingly, the detector will simply provide a toxic gas concentration output without providing any indication of fault.
[0021] Method 100 can be executed periodically, such as once a minute, or in response to any suitable input signal. For example, a technician may press a button or otherwise send a command to device 10 causing device 10 to execute method 100. Additionally, the frequency with which method 100 is executed can also be a function of the toxic gas sensor concentration value. For example, if device 10 is indicating a toxic gas sensor concentration above a selected threshold, method 100 can execute with a first frequency, while if the toxic gas sensor concentration is below the selected threshold, method 100 can execute with a different frequency.
[0022] It is believed that embodiments of the present invention will provide important diagnostics for metal oxide semiconductor-based toxic gas sensors by detecting when a sensor signal is stale. This will allow remedial action to be taken before the sensor deteriorates further and either opens or shorts. Further still, embodiments of the present invention are able to detect when an otherwise functioning metal oxide -based semiconductor toxic gas sensor (e.g. neither open nor shorted) is nonetheless failing to accurately indicate toxic gas concentration.

中文:
[0001]例如硫化氢气体的有毒气体甚至在较低浓度下可能是致命的。通常地,当人暴露给该有毒气体时,需要相对快速地寻找医疗护理。因此,在许多工业环境中,即使在最复杂和远程的环境下,当泄露出现时,能够尽快在非常低的浓度下检测到有毒气体是非常重要的。此外,即使当有毒气体泄露的发生非常罕见时,有毒气体传感器始终准备好执行其功能是非常重要的。
[0002]在许多国家,随着传感器响应时间和感测元件的整体稳定性得到改进,健康和安全标准已经一直在慢慢降低可接受的暴露等级。例如,在美国,职业安全与卫生管理局(OSHA)提供了可接受浓度极限——暴露的硫化氢在8小时期间为百万分之二十(20ppm),以及最大峰值暴露为10分钟50ppm。
[0003]任何固定位置的有毒气体探测器的重要目标是通过警示出现的在传感器附近的该有毒气体的危险等级来保护工作人员和公众。多年来,电化和金属氧化物半导体(MOS)电池已经被实地证实为有毒气体感测技术。基于MOS的传感器具有与电化传感器相比较长的寿命,并且在宽范围的温度内,特别是在高温下,以及在非常干燥的条件下连续工作。
[0005]该类型的传感器通常利用感测材料(半导体金属氧化物)的多晶结构和存在的带负电荷的表面氧物种,该表面氧物种控制肖特基势垒的高度和材料的电阻。当传感器暴露给某些还原气体时,该表面氧将被消耗,减少了肖特基势垒和电阻,这构成感测信号。
[0006]为了确保金属氧化物半导体有毒气体传感器能够提供可行的信号,对于诊断而言重要的是能够检测,或者确定传感器是否已经被损坏,或者恶化。
[0007]本发明提供了一种基于金属氧化物半导体的有毒气体探测器。基于金属氧化物半导体的探测器包括基于金属氧化物半导体的气体传感器,该基于金属氧化物半导体的气体传感器具有随着有毒气体的浓度变化的电特性。测量电路连接到基于金属氧化物半导体的气体传感器,并且被配置为测量所述电特性并且提供所测量的电特性的数字指示。控制器连接到所述测量电路,并且被配置为基于所述数字指示提供有毒气体输出。控制器还被配置为基于在一段时间上所测量的电特性的波动提供关于基于金属氧化物半导体的传感器的诊断输出。
[0008]图1是本发明的实施例所特别用于的金属氧化物半导体有毒气体探测器的图解视图。
[0009]图2是根据本发明的实施例的金属氧化物半导体有毒气体探测器的框图。
[0010]图3是金属氧化物半导体有毒气体传感器在一段时间上模拟数字转换的信号测量值的图解的散布图。
[0012]如上所述,有毒气体传感器的诊断是确保有毒气体传感器正在有效工作、并且在有毒气体出现的情况下能够提供可信赖的信号的重要方面。在安全应用中,基于半导体金属氧化物感测技术的有毒气体传感器的利用需要多种诊断以检测传感器的失效模式。对于该安全应用,需要检测传感器可能经受的所有失效模式,例如传感器元件的短路和开路的传感器元件。
[0013]本发明的实施例大致检测固态金属氧化物半导体有毒气体传感器的更微妙的失效模式。具体地,该失效模式被认为是老化的传感器。当该失效模式出现时,传感器读数将不再有效地指示有毒气体的浓度。然而,传感器将继续指示实际电阻。因而,基于检测短路或开路的传感器诊断将不会检测到老化的失效。替代地,本发明的实施例总体上补充一方面金属氧化物半导体有毒气体传感器的信号以检测老化的失效。具体地,当金属氧化物半导体有毒气体传感器被正确地操作时,传感器电阻将具有自然的变化或波动。通常地,传感器电子器件已经将传感器输入信号发送至低通滤波器,以移除这些变化。因而,传感器的电阻被处理或者不然被特征化,以在提供有毒气体传感器输出之前移除该波动。然而,根据本发明的实施例,如下所述,这些变化被具体地测量并且用于提供关于金属氧化物半导体有毒气体传感器的诊断指示。
[0014]图1是本发明的实施例所特别用于的金属氧化物半导体有毒气体探测器的图解视图。探测器10包括连接到传感器主体14的电子器件外壳12。传感器主体14包括基于金属氧化物半导体的有毒气体传感器,例如硫化氢气体传感器,该传感器可以是“传统的”金属氧化物半导体传感器或基于NE-MOS的半导体气体传感器。传感器主体14的下部16被构造成用于将有毒气体传感器暴露给环境空气以确定环境空气中例如硫化氢气体的有毒气体的浓度。传感器主体14中的传感器经由导管18连接到外壳12中的合适的电子器件(图2中示出)。外壳12中的电子器件能够使传感器响应被放大、线性化和特征化,以提供有毒气体浓度的指示。该指示可以经由穿过导管20的过程布线通过过程通信回路或过程通信部被提供,和/或被本地地提供。有毒气体的本地指示可以包括本地操作员界面(LOI),该本地操作员界面显示有毒气体浓度、听觉或视觉警报或它们的任何组合。
[0015]图2是根据本发明的实施例的金属氧化物半导体有毒气体探测器的框图。探测器10包括连接到传感器主体14的电子器件外壳12。控制器22、通信模块24、电源模块26和测量电路28设置在电子器件外壳12中。基于金属氧化物半导体的有毒气体传感器30设置在传感器主体14中并且连接到测量电路28。
[0016]控制器22可以是任何合适的处理电路,该处理电路能够将数字处理技术或滤波技术应用到传感器测量值中,以确定或特征化传感器信号的变化或波动。另外,控制器22还被构造成用于基于传感器测量值(或多个传感器测量值)产生有毒气体浓度输出。在一个实施例中,控制器22是微处理器。控制器22连接到通信电路24以允许控制器22与过程控制和监控系统中的其它装置通信。通信电路可以包括允许控制器22根据过程工业标准通信协议进行通信的电路,该通信协议例如为可寻址远程传感器高速通道协议、FOUNDATIONTM现场总线协议或者其它协议。另外,在一些实施例中,除了或取代使用有线过程通信,装置10可以无线通信。例如,在一个实施例中,通信电路24可以允许根据IEC62591进行通信。最后,通信电路可以提供本地输出的通信,例如本地显示或警报。
[0017]电源模块26连接到外壳12中的所有构件,如标记为“连接到全部”的箭头所示。电源模块26被构造成用于从合适的源接收电力,并且给外壳12中的电路提供电压调节或合适的功率调节。在一些实施例中,电源模块26可以连接到有线过程通信回路,使得装置10可以从有线过程通信回路接收它的所有的工作能量。在其它的实施例中,电源模块26可以连接到合适来源的交流或直流电源。
[0018]测量电路28连接到控制器22并且能够从基于半导体的有毒气体传感器30获得测量值,并且向控制器22提供它的数字指示。测量电路28可以包括一个或多个模数转换器,合适的多路转接器电路,以及放大和/或线性化电路。进一步,测量电路28可以包括例如低通滤波器的合适的滤波电路,该滤波电路选择性地置于传感器和模数转换器之间。在该实施例中,将该低通滤波器置于传感器和模数转换器之间将允许对代表有毒气体传感器浓度的信号进行直接测量。而绕过低通滤波器将允许模数转换器测量关于传感器信号的波动,该波动表示适当的传感器功能。然而,应该说明,本发明的实施例可以在没有使用模拟滤波的情况下实践,并且在波动和有毒气体传感器浓度由多个模数传感器的测量值算数地获得的情况下实践。
[0019]图3是金属氧化物半导体有毒气体传感器在一段时间上模拟数字转换的信号测量值的图解的散布图。如图3所示,传感器显示了可检测到的波动或变化。在图3示出的示例中,有毒气体浓度被示出从约五分钟的时间到约70分钟的时间内的改变。竖直轴线是用于每个个体测量(individual measurement)的模数转换器计数。有毒气体浓度在从5分钟的时间到40分钟的时间内逐渐增加地变化,在40分钟的时间时传感器具有约57850个计数的输出。在约40分钟的时间时,有毒气体浓度开始逐渐减少,直到在大约时间T=65分钟时,此时模数转换计数约为57775。如示例所示,变化通常在大约25个计数的量级。根据本发明的各种实施例,尽管有毒气体浓度可以以任何合适的方式被处理以移除变化的影响,或者不然在一小段窗口时间上对数值进行平均,以提供相对稳定的有毒气体浓度输出,但是诊断输出基本基于波动而生成。该波动可以以任何合适的方式被检测到或被观察到。例如,阵列的或其它合适的存储器结构可以保存在固定的一段时间内的一系列的模数转换器测量值,或者简单地一定量的测量值。存储器结构可以被更新使得当新的测量值被获得时,最旧的测量值被丢弃。控制器22,或任何其它合适的处理器,可以对存储阵列或序列的测量值进行数字地操作,以获得关于例如变化的波动特性的信息。例如,该组测量值的变化可以根据现有的统计技术简单地进行计算。然而,根据本发明的实施例,可以使用能够提供关于波动程度的有用信息的任何其它合适的数学运算。
[0020]图4是生成关于根据本发明的实施例的半导体金属氧化物有毒气体传感器的诊断指示的方法的流程图。方法100在方块102处开始,在方块102处多个传感器测量值被获得。这些传感器测量值在一段合适的时间内被获得,例如为数秒或甚至数分钟的范围内。然后,在方块104处,传感器信号测量值的波动被检测。如上所述,在一个实施例中,多个传感器测量值可以被存储在存储器中并且根据任何合适的数学技术被处理以检测变化。例如,统计处理技术106可被用于检测该波动。另外,或可选地,个体测量值之间的差异可以被处理或者不然经历阈值处理108。最后,被存储的测量值可以经历数字滤波器110以放大或突出传感器信号测量值的变化。然后,在方块112处,被检测到的波动或变化与预选定限值进行比较。该限值可以在装置的制造过程中被限定或被设置,或该限值可以在该装置的服役期间被设置。例如,一种特定的有毒气体传感器可以比另一种类型的有毒气体传感器展示更多变化。因而,当探测器与特定的有毒气体传感器一起服役时,适合于该传感器的变化阈值可以被设置。如果基于半导体的有毒气体传感器的被检测到的变化在被选定的限值以下,控制进入方块114,在方块114处控制器22将生成诊断指示。该诊断指示可以是生成的故障或错误信息,该故障或错误信息是通过过程通信回路或过程通信部传送的、在探测器处视觉上或听觉上指示的本地的指示或它们的任何组合。替代地,如果被检测到的变化不在被选定的限值以下,则控制进入方块116并且方法100结束。因此,探测器将在不提供任何的故障指示的情况下简单地提供有毒气体浓度输出。
[0021]方法100可以被定期地执行,例如一分钟一次,或响应于任何合适的输入信号执行。例如,技术员可以按压按钮或者将命令发送到装置10,促使装置10执行方法100。另外,执行方法100的频率还可以是有毒气体传感器浓度值的函数。例如,如果装置10指示大于被选定的阈值的有毒气体传感器浓度,则方法100可以在第一频率下执行,而如果有毒气体传感器浓度小于被选定的阈值,则方法100可以在不同的频率下执行。
[0022]可以相信,本发明的实施例将通过检测何时传感器信号失效为基于金属氧化物半导体的有毒气体传感器提供重要的诊断。这将允许在传感器进一步恶化和开路或短路之前采取补救措施。更进一步地,本发明的实施例能够检测何时另外功能的基于金属氧化物的半导体有毒气体传感器(例如,既未开路也未短路)未能精确地指示有毒气体浓度。