Patent Application
20080168826
This invention relates generally to a method and system for gas leak detection.
Chemical factories, refineries, warehouses, and semiconductor fabrication laboratories sometimes process and/or transport dangerous gases. These gases can be flammable, such as natural gas or methane. Toxic gases are also sometimes produced as a result of a chemical reaction. Such gases are normally transported through a series of pipes or containers in the factories. Problems arise when the gas starts to leak out of the pipes or other containers, as this can result in a fire, explosion, or some other type of damage to the factories, workers, and/or equipment within such facilities.
According to some systems, leaks are commonly detected manually, and if there is a gas leak, the source can be difficult to pinpoint. To manually detect the source, a safety inspector or other authorized individual often walks around the facility in which the leak has occurred while holding a portable sensor device to attempt to detect the actual location of leakage.
Additional automated gas leak detection systems have been proposed. In one of the proposed systems, a series of gas sensors are utilized to detect a concentration of gas. In the event that the sensed concentration is greater than a pre-set threshold, an alarm is sounded. The gas sensors are currently spaced relatively close together. In the event of a gas leak, the gas sensors near the leak will each sound an alarm when the amount of gas leaking is greater than a pre-set threshold level. Manually reading sensor levels can be expensive and time consuming. Moreover, the current sensors are limited by the way in which they are deployed. If the sensor readings are taken manually, a gas leak cannot be resolved timely.
A problem with current solutions, however, is that potentially hundreds of gas sensors may be required for a large area being monitored. Current sensors that are spaced close together cannot, however, precisely resolve the location of a gas leak. More specifically, the current systems are only accurate to a margin of error equal to the distance between each sensor. This margin of error can be problematic when dealing with an area having multiple pipes or containers, as several pipes might need to be shut down and an inspector might have to manually locate the source of the leak. This can be very time-consuming and may require that the entire area be evacuated while the inspector searches for the exact source of the leak so that the leak can be repaired.
Wireless Sensor Networks (“WSNs”) are networks consisting of a large number of small, autonomous sensor devices equipped with processing and wireless communications capabilities. By taking advantage of miniaturization technologies, wireless sensor nodes are becoming an integral part of our environment and the ways in which we interact with it. Of the myriad applications enabled by WSNs, the ones dealing with monitoring, tracking, and control are the most common. These capabilities have the potential to greatly impact safety-related applications. In a typical safety application, the WSN performs one or more of the following: (a) monitoring and detecting of the environment for harmful events, (b) tracking the development of such events, and (c) initiating an action to respond to the harmful events.
There are commercially available sensors in the art for detecting different gases. One such sensor, integrated with a micro-controller and a communication module, could form a node of a WSN. Simply putting together a number of such nodes in a network, however, would only provide for the detection of the presence of a gas leak and its proximity to certain nodes. Therefore, a large number of nodes would again still be required to localize the leak source and determine the rate of gas emission.
The accompanying figures, where like reference numerals refer to identical or functionally similar elements throughout the separate views and which together with the detailed description below are incorporated in and form part of the specification, serve to further illustrate various embodiments and to explain various principles and advantages all in accordance with the present invention.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help improve understanding of various embodiments of the present invention. Also, common and well-understood elements that are useful or necessary in a commercially feasible embodiment are often not depicted in order to facilitate a less obstructed view of these various embodiments of the present invention.
According to various embodiments described below, a gas leak detection system and method is provided that requires fewer gas sensors than the number of sensors deployed in current solutions and generates greater precision and timeliness in locating the source of a gas leak. Three or more gas sensors may monitor gas concentration levels in a given area. The physical distance between the gas sensors is a function of the sensitivity of the gas sensors. If highly sensitive gas sensors are used, the gas sensors may be placed further apart than would be possible if less sensitive gas sensors were used.
The gas sensors measure the concentration of gas surrounding each respective gas sensor. The gas sensors may wirelessly transmit such measurements to each other or to a server. In other embodiments wired gas sensors may be utilized. A person of skill in the art would readily appreciate, however, that cost savings may be achieved by utilizing wireless gas sensors because expensive infrastructure to wire the gas sensors together would therefore not be required.
Each of the gas sensors contain their own processing device and/or transmit signals corresponding to detected gas levels to an external processing device. In the event that, for example, a gas sensor contains a processing device, the gas is sensed or detected by the sensor and a corresponding electrical signal is generated based on the amount of gas detected in the air around the gas sensor. This electrical signal may indicate a concentration of the gas in terms of parts-per-million. The gas sensor contains or is in communication with a memory device. The electrical signals corresponding to the detected gas levels may be stored as a string of data in the memory device or in some other memory buffer. Such information is subsequently analyzed by a processor.
The processor measures a rate of change of the concentration of the gas for a given time interval. Based on the measured rate of change, the processor can determine how far away the gas leak is located. Measuring the distance in this manner is based on the diffusion properties of the sensed gas. That is, the further away from the gas leak, the lower the concentration of the gas will be at a given time and the slower the rate of increase of the concentration over a given time period. Gases tend to spread out in the air around a gas leak in approximately a spherical manner if there is no significant airflow. The areas closest to the gas leak will typically have the greatest concentration of the gas and experience the greatest rate of change of the concentration of the gas. As the distance from the gas leak increases, the concentration decreases by a factor proportional to about 1/R3, where R is the radius from the gas leak.
Because the properties of diffusion are physical laws, the distance from the gas leak is determined based on the rate of change of the concentration of the gas in the air over a given time interval. The closer the gas sensor is to the gas leak, the greater the rate of change, and the further away from the gas leak, the lower the rate of change. The rate of change may be compared against values of a look-up table to determine a distance from the gas leak corresponding to the rate of change. Alternatively, the distance may be mathematically determined via a gas concentration equation that may be executed by the processor.
The distance indicates the distance from the sensor to the gas leak. One distance measurement does not, however, indicate the exact location of the gas leak because the gas leak could be located anywhere in a 360° sphere around the sensor. If distances can be calculated for at least three different gas sensors, a substantially exact location of the gas leak may be determined via a triangulation method. Specifically, in the event that three radiuses/distances from the gas leak are known for each of three gas sensors, of two locations where these radiuses intersect, it is typically very easy to arrange the sensors so that only one of the two locations is logical, or a fourth sensor can be added to remove the ambiguity.
The intersection location is, of course, where the gas leak is located. Once the gas leak location is pinpointed, such location information may be sent to a server or some other device accessible by an inspector or warning system. Alternatively, raw sensor data may be sent directly to a server. The server may calculate the distances between the various sensors based on the raw data and may implement the triangulation method to pinpoint the location of the gas leak.
Such embodiments provide a number of advantages over current systems. For example, a precise location of the gas leak is determined while using fewer gas sensors than current systems. Moreover, the location of the gas leak is determined with greater accuracy than current systems, which have a relatively high margin of error. This can result in cost savings and a simpler system to maintain. Moreover, determining the rate of change of the gas concentration is further advantageous because the system can anticipate that the gas concentration will soon be above a dangerous threshold level and sound a warning before the threshold concentration level is reached. Many current systems, on the other hand, only sound an alarm after the dangerous concentration threshold level has already been reached.
The first sensor 110, the second sensor 115, and the third sensor 120 may be substantially evenly spaced in some embodiments, although this is not required. The first sensor 110, the second sensor 115, and the third sensor 120 may communicate wirelessly with each other and with a server 125. In alternative embodiments, the sensors and the server may instead be hard-wired to each other.
The first sensor 110, the second sensor 115, and the third sensor 120 detect gas levels and report their sensor readings to the server. The gas sensor measures a gas concentration in parts-per-million or similar unit of measure. In some embodiments, the sensors report the detected gas levels periodically. In other embodiments, the gas levels are reported only when they exceed a threshold detected gas concentration. In the event that the detected gas levels exceed a dangerous threshold level, the server 125 communicates with an alarm 130 which may audibly or visually initiate an alarm to indicate that the area 105, or a portion of the area 105, should be evacuated or that attention is otherwise warranted.
In the event that a gas leak is detected with the area 105, distances from each of the first sensor 110, the second sensor 115, and the third sensor 120 to the gas leak are respectively determined and a processor pinpoints the location of the gas leak based on a triangulation method, as discussed below with respect to
A processor may calculate the slope of each of these data lines and compare the slope with a pre-stored slope value in a lookup table. The lookup table maps various slopes with distances from a gas leak. Accordingly, based on the slope, the distance from the gas leak may be determined.
Alternatively, the following equation based on physical laws of diffusion and may be utilized to measure the distance from the gas leak:
C=[Ø/4πDr]*erfc*r/[2*(Dt)̂0.5]
where C is a gas concentration amount, Ø is a constant rate at which the gas is being released, erfc is a complimentary error function, D is a diffusion coefficient, and r is the distance from the gas source/leak at a time t.
Using a first order approximation to the derivative of the above-listed equation, the distance r can be written as a function of the slope of the rate of increase in gas concentration. The distance r is then obtained by using an estimate of the slope from the measured data at various gas sensors. Alternatively, both the calculation above and a lookup table may be utilized to calculate the distance to increase the accuracy of the estimates.
The above-listed equation may be utilized to measure the distance the from the gas leak when the air movement or flow is below a certain threshold such that it is substantially constant. The lookup table may be utilized to measure the distance regardless of the air movement. For the most precise measurement of the distance, the equation and the lookup table may both be utilized to measure the distance when the air movement is low. For example, the distances determined by the equation and via reference to the lookup table may be averaged to determine a potentially more accurate measurement of the distance.
In the event that there is a single gas leak location 415, the distance measurements from three or more gas sensors may be utilized to pinpoint the location of the gas leak location 415 via a triangulation method. More specifically, because the first gas sensor 400, the second gas sensor 410, and the third gas sensor 410 all have fixed locations, there is only one location where the first distance 420, the second distance 425, and the third distance 430 intersect. The point of intersection is the location of the gas leak location 415. There may be a small margin of error in each of the distance calculations. Accordingly, when determining the gas leak location 415, a small area where the gas leak is located may be determined as opposed to a specific pinpointed location.
It should be appreciated that more than three gas sensors may be utilized in determining the location of the gas leak location 415. In the event that four sensors are utilized, for example, distances would be determined between each of the gas sensors and the detected gas leak (or, if desired, by only using information as corresponds to a given selection of such sensors, such as the three sensors that sense the greatest concentrations of the gas). The triangulation method may subsequently be implemented on sets of three sensors and the calculated location may be averaged based on the distances calculated via the different sets of data.
The power source 525 provides power to the processor 510, the gas detector 505, the communication device 515, and the memory 520. The communication device 515 may be utilized to send data or any other relevant information to any of the other gas sensors or the server. The communication device 515 may also be utilized to receive data or other information from the other gas sensors or the server.
The teachings described therein provide efficient and cost-effective techniques for accurately and precisely determining the location of a gas leak. The location of the gas leak can be determined with a relatively small number of nodes in a WSN and may provide early detection and warning.
For example, the methods described herein achieve superior localization resolution while requiring only a small number of sensors arranged in a sparsely populated grid. As such, these techniques significantly reduce the deployment costs of such a gas detection safety system. This differs from current gas detection systems which provide only gas concentration readings but which are not capable of detecting rates of emission.
Techniques described herein are capable of predicting emission rates without employing different types of sensors. Gas sensor nodes of current systems provide only instantaneous readings of gas concentration and are incapable of predicting future gas concentrations. According to the teachings herein, on the other hand, future gas concentrations may be determined based on a regression technique by measuring the rate of increase of gas concentration (i.e., the slope of the rate of change of gas concentration). Based on the rate of increase, the future gas concentration may be estimated, assuming that conditions do not change in the future assuming the conditions relating to the gas leak do not change.
The techniques described herein account for gas dissipation in a given medium and, as such, a WSN which includes such techniques is capable of estimating future gas concentration providing invaluable early detection of a gas leak. For example, in the event that a relatively large rate of change of gas concentration is detected, an alarm can be initiated even though the gas concentration has not yet reached a hazardous threshold because the rate of change is used to estimate the gas concentration at some point in the near future.
Those skilled in the art will recognize and appreciate that these teachings can be applied in various ways and are readily leveraged in a variety of application settings. It will also be understood and appreciated that these teachings can be relatively economically facilitated and are highly scalable in practice.
Those skilled in the art will recognize that a wide variety of modifications, alterations, and combinations can be made with respect to the above described embodiments without departing from the spirit and scope of the invention, and that such modifications, alterations, and combinations are to be viewed as being within the ambit of the inventive concept. For example, in some cases, a given sensor may be located in an area that is proximal to some condition, such as an operating fan, that will tend to increase or reduce the opportunity of that sensor to detect a gas. In such a case, if desired, one could provide a weighting factor (or factors) to reflect and accommodate such an operating environment when making the above-described calculations.
