ACTIVE BI-DIRECTIONAL OPEN PATH GAS DETECTION SYSTEM

An open path gas detection system includes a transmitter and a receiver. The transmitter is configured to generate illumination across an open path. The receiver is positioned to detect the illumination from the transmitter after the illumination has passed through the open path and detect a gas of interest based on the illumination. However, the laser can also be used for gas detection systems in other circumstances. The transmitter and receiver are configured to communicate wirelessly. A method of operating an open path gas detection system is also provided.

BACKGROUND

Open Path Gas Detectors (OPGD) are line-of-sight gas monitors commonly installed to monitor for gas presence over long distances. Open Path Gas Detectors provide a high speed of response, they operate in extreme conditions, and require fewer instruments to monitor large areas. These detectors generally, detect the unique spectral fingerprint of an individual chemical substances. Such gas detectors typically consist of a pair of devices; a source unit and a detector unit. The source unit generates a high energy beam electromagnetic energy. The target gas absorbs some of the electromagnetic energy and transmits the rest. The detector unit then detects the transmitted energy at specific spectral ranges, based on the target gas.

Some open path gas detection systems employ wired communication between source unit (transmitter) and the detector unit (receiver). Such wired approaches require complicated infrastructure, complex installation, cables wear and tear and require frequent maintenance. Furthermore, with that kind of system interface, the wired communication is used to obtain information regarding the units (transmitter and receiver) themselves and not information regarding the medium/atmosphere between the units—which is particularly important data when talking about open path gas detection systems. Having feedback from transmitter and receiver and the path between them is necessary in order to obtain clear understanding of system surroundings, which is not possible when using wired communication.

SUMMARY

An open path gas detection system includes a transmitter and a receiver. The transmitter is configured to generate illumination across an open path. The receiver is positioned to detect the illumination from the transmitter after the illumination has passed through the open path and detect a gas of interest based on the illumination. The transmitter and receiver are configured to communicate wirelessly. A method of operating an open path gas detection system is also provided.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

FIG.1is diagrammatic view of a unidirectional open path gas detection system. System100includes transmitter102and receiver104, which are arranged such that an optical pulse108delivered from transmitter102will travel along path106to receiver104. Receiver104receives the optical pulse and is configured to analyze the spectral characteristics of the received signal to determine whether the optical pulse passed through a gas of interest. As shown inFIG.1, the communication from transmitter102to receiver104is entirely unidirectional. Thus, passive receiver104has no ability to communicate to transmitter102. This limitation of system100can give rise to crosstalk in situations where multiple such systems100are used in proximity with one another. Open path gas detection systems that do not employ any kind of synchronization between the transmitter and receiver are known to suffer from issues such as crosstalk and have difficulties detecting gas during harsh environmental conditions. Crosstalk is a significant issue in open path gas detection systems. In terms of optical systems, “crosstalk” refers to the phenomenon by which a signal that is transmitted by the transmitter for its relevant receiver creates an undesired effect in receiver of a separate set nearby. Harsh weather conditions can also cause system difficulties since the receiver may be getting a much lower signal from the transmitter compared to normal operation. This can lead to faulty operation of the system as it affects the optical performance and the detection capabilities and will eventually cause the receiver to miss actual gas reading in the monitored path.

FIG.2is a diagrammatic view of two open path gas detection systems illustrating the problem of crosstalk.FIG.2illustrates a first open path gas detection system having source102-1and detector104-1operating in proximity to a second open path gas detection system having source102-2and detector104-2. Each of the open path gas detection systems shown inFIG.2operates as described above with respect to system100. However, the proximity of the two systems allows optical pulses or energy110from one source, such as source102-1, to be detected by a different detector (104-2) than the intended detector (104-1). This detection of erroneous optical pulses or energy is known as cross-talk and can cause errors in the affected systems.

In order to have authentic information about system environment the interface between transmitter and receiver should be optical and wireless. Essentially, it is desirable to provide an open path gas detection system with the ability to learn its environment continuously or at least periodically. Employing wireless communication presents the challenge of having optical radiation intensity above allowed limits, which may be a significant obstacle in applications which require optical intrinsically safety approval. In many applications where a long distance needs to be covered, the energy required to communicate optically over the long distance likely exceeds the limits of the standard, while the system still needs to comply to explosion proof regulations. In addition, high class lasers could expose a user in danger due to eye safety standard. At least some embodiments described herein provide an open path gas detection system that includes a source (transmitter) and detector (receiver) that can employ UV and/or IR electromagnetic energy for gas detection as well as employ laser IR energy for bi-directional communication between the source and the detector.

FIG.3is a diagrammatic view of an active, bi-directional open path gas detection system200in accordance with an embodiment of the present invention. System200includes a transmitter202and a receiver204. Like transmitter102, transmitter202is configured to send an optical pulse108along path106to receiver104, which is configured to detect spectral attributes of the received pulse108in order to detect a gas of interest along path106. However, in accordance with an embodiment of the present invention, receiver204includes an optical source (shown inFIG.7) that allows receiver204to send an optical pulse, or other suitable signal or waveform, along path120to transmitter202. In one embodiment, the optical source is a laser transmitter. Additionally, transmitter202also includes a detector and suitable detection logic to detect the optical pulse/signal from receiver204. Adding an optical source on the receiver side allows the use of wireless communication between the two units, making the system active and bi-directional. In this way additional features and control options for the transmitter and receiver are enabled. Such new features include, without limitation, monitoring medium characteristics (harsh weather/fog/snow etc.) as part of an Environment Learning System, distance calculation (using time-of-flight (ToF) technology), pulse repetition frequency (PRF) increasing when transmitter signal is low as part of environmental compensation module, preventing crosstalk from nearby transmitters et cetera.

Providing an active optical source on the receiver side as well as detection electronics on the source side transforms an otherwise unidirectional system into an active bi-directional one, having the ability to communicate wirelessly, getting digital communication and spectral information from it. Additionally, bi-directional communication enables the two units to have increased awareness about the environment as well as the units themselves. This awareness can help provide the units with the ability to dynamically adjust working mode of the transmitter, such as when interference like heavy rain, fog, or a blizzard occur. Thus, adjusting the working mode of the units facilitates compensation for environmental conditions so that the receiver will be able to get viable signal from the transmitter, despite the harsh weather conditions, and the system will continue to operate normally, and detect gas.

Many of the environments in which open path gas detectors operate are highly volatile or explosive and could be ignited by a spark or elevated surface temperature in the gas detection system. Thus, for such gas detection systems, it is highly desirable to comply with explosion-proof ratings. Such ratings require that any explosion or flame generated within a complying electrical device will not ignite the environment of the device. These ratings drive such design constraints as housing wall thickness and material and the provision of a flame quenching pathway from an interior of the device to the external environment. One example of an explosion-proof rating is an ATEX certification to Ex-d standards EN60079-0 and EN60079-1 for potentially explosive atmospheres. Generally, explosion-proof housings are relatively bulky in order to be mechanically robust enough to contain an internal explosion without rupturing. Generally, such explosion-proof containers are very robust metal enclosures that are designed to withstand explosive pressures. However, for optical devices, the enclosure must accommodate a window of some sort in order to allow the illumination to pass through to the environment.

Another way to protect hazardous environments is to require that devices operating therein comply with intrinsic safety requirements. When the electronics are intrinsically safe, they inherently cannot generate the required temperature or spark to generate an explosion, even under fault conditions. An example of an intrinsic safety specification is the standard promulgated by Factory Mutual Research in October 1998 entitled APPROVAL STANDARD INTRINSICALLY SAFE APPARATUS AND ASSOCIATED APPARATUS FOR USE IN CLASS I, II, AND III, DIVISION 1 HAZARDOUS (CLASSIFIED) LOCATIONS, CLASS NUMBER 3610. Intrinsic safety requirements generally specify such low energy levels that compliance is simply not possible with circuitry that involves high voltages, high currents, and/or high wattage, such as AC circuits. In at least some embodiments described herein, the circuitry is designed and configured to comply with an intrinsic safety requirement, such as that set forth above.

FIGS.4and5are side elevation and perspective views of a laser module for an active bi-directional open path gas detection system in accordance with an embodiment of the present invention. Providing a laser module that is compact helps reduce the cost of the system, which is of particular importance for explosion-proof systems. Further it is desirable to provide a laser module that has sufficient energy for low-energy long-distance communication and/or detection, but that can still comply with class 1 laser standards. Laser module250meets these criteria. Laser module250has a laser output end252that is shaped circularly and preferably has a diameter of about 8.5 mm. Laser output end252extends approximately 6 mm. The overall length “L” of laser module250is about 20 mm. Laser module250also includes a pair of twisted pair conductors254that extend to a 2-pin connector256that connects to suitable energization circuitry within the unit. As shown inFIG.5, laser module250also generally includes an output lens258. In one embodiment, laser module250is configured to generate an infrared (IR) laser beam.

FIG.6is a diagrammatic view of an experimental setup illustrating efficacy of an active bi-directional open path gas detection system in accordance with an embodiment of the present invention. System280includes a transmitter202provided with a laser module250, described above with respect toFIGS.4and5. Laser module250of transmitter202generates an IR laser beam260toward receiver204. Receiver204includes a detector262that is configured to detect the IR laser beam. In order to simulate the attenuation caused by environmental conditions, such as rain or a blizzard, a ND filter264was placed in the path of beam260. The experimental setup indicated successful operation at a detection distance of 200 meters even with a 90% obscuration from filter264. This indicates a satisfactory signal-to-noise ratio and balanced design utilizing a compact laser module250that complies with class 1 laser standards.

FIG.7is a system block diagram of a bi-directional open path gas detection system in accordance with an embodiment of the present invention. System300includes a transmitter302and receiver304. Each of transmitter302and receiver304preferably includes an explosion-proof housings305,306, respectively. Transmitter302includes a controller308coupled to laser drive module310. Laser drive module310can include power handling components as well as frequency control and pulse generation logic such that upon receiving a signal from controller308, laser drive module312is configured to cause laser module250to generate a suitable pulse or signal316toward receiver304through housing window317. Transmitter302can employ any suitable laser module, but preferably employs laser module250, described above. Controller308can be any suitable arrangement of circuitry or logic that is able to cause laser module250to generate a pulse or signal316as well as to employ communication module314to communicate with receiver304using wireless communication318. In one embodiment, controller308is a microprocessor.

Receiver304includes an optical detector320positioned near detector window322in housing306. Optical detector320is configured to generate an electrical signal representative of optical pulse or signal316passing through window322. Optical detector320is coupled to detection logic module324, which is configured to receive the electrical signal from optical detector320and amplify the signal as well as analyze spectral components of the received signal to provide an indication of the spectral composition of the signal to controller326. In some embodiments, optical detector320and detection logic324may be combined in a single physical device. Controller326can be any suitable arrangement of circuitry or logic that is able to receive the spectral composition information from detection logic324and generate useful gas detection information based on the spectral composition information. In one embodiment, controller326is a microprocessor.

As shown inFIG.7, controller326is coupled to laser drive module334, which is coupled to laser332. Laser332is configured to generate laser illumination through window340as indicated at reference numeral336. Note, window340may be a separate window from window320, or it may be the same component. The laser336travels to transmitter302where it passes through window338and is detected by optical detector330. Note, window338may be a separate window from window317, or it may be the same component. Optical detector330is coupled to detection logic328, which provides information indicative of the detected signal to controller308. In this way, receiver304is able to communicate wirelessly with transmitter302using laser communication. Thus, receiver304is able to transmit wireless information to and receive wireless information from transmitter302. This bi-directional communication ability between transmitter302and receiver304enables a variety of new features and modes for open path gas detection sensor300. For example, environmental conditions may attenuate some of laser pulse316such that the signal-to-noise ratio falls below a selected threshold as detected by receiver304. When this occurs, receiver304communicates wirelessly to transmitter302to instruct transmitter302to increase the intensity of the laser beam.

One particular synergy of system300is that since each device is capable of transmitting and receiving an optical signal, bi-directional communication can be performed using the optical signal itself. Further, as can be appreciated, since each device can both generate and receive optical pulses or signals, the detection ability of system300is redundant in the event that one of a laser or detector should fail for a single unit.

In some embodiments, laser drive module312may be combined into the same physical component as the laser, such as compact laser source module250(shown inFIGS.4and5). Additionally, detection logic, such as detection logic328and an optical detector, such as optical detector330, may also be combined in a single physical device.

FIG.8is a flow diagram of a method of operating an active, bi-directional open path gas detection system in accordance with an embodiment of the present invention. Method500begins at block502where system startup occurs. System startup can include one or more self-tests for each of the transmitter or receiver. For example, a self-test may include verifying sufficient operating voltage, testing optical components (such as a laser or detector), et cetera. System startup502can also include a pairing operation to pair a receiver to its respective transmitter. The pairing can occur in any suitable manner. As part of the pairing process, or shortly thereafter, the receiver and the transmitter synchronize their respective timers. Next, at block506, a trigger is generated for a signal transmission start. In one example, this trigger can be generated by the receiver instructing the transmitter to begin transmission of an optical pulse at a pre-defined timeframe. Note, embodiments of the present invention can also be practiced where the transmitter instructs the receiver of a pre-defined timeframe in which it will transmit the optical pulse. Regardless, as a result of block506, the receiver will open its integration window for the pre-defined timeframe to receive the optical pulse or signal from the transmitter, as indicated at block508.

At block510, the receiver performs data processing on the received signal. The data processing can include analyzing the spectral characteristics of the received signal to detect one or more gasses of interest, as indicated at block512. This analysis generates the primary output of the gas detection system. The spectral characteristics can also be stored and analyzed over time to identify environmental medium condition and/or status. Further, artificial intelligence and machine learning can be employed and trained on the spectral characteristics to predict future values or conditions. However, the receiver also analyzes the received signal in other regards to determine additional parameters of interest. For example, the signal strength or quality can be determined, as indicated at block514. Variations in the signal strength or quality may provide an indication of signal degradation due to rain/fog/snow/mist. Further, the measuring the signal level during known periods of zero signal can provide an indication of background noise or cross-talk, as indicated at block516. Additionally, since the receiver and transmitter have synchronized timers and the receiver knows the exact time at which the transmitter launches the optical pulse, the time it takes for the pulse to cross the open path can be measured by the receiver. This time-of-flight measurement518provides a direct indication of distance, which may be an important variable to monitor for a particular application. The receiver may also analyze the received signal to determine unit status for the transmitter and/or the receiver itself, as indicated at block520.

As a result of the analysis performed at block510, the receiver may determine that some aspect of the transmitted optical pulse needs to be adjusted. In such case, optional block522can be executed where the receiver transmits an adjustment request to the transmitter. For example, at block510, the receiver may determine that signal strength has fallen below a low-signal threshold and that the intensity of the laser beam should be increased by a particular amount. This intensity increase command, as well as an intensity increase amount parameter can be communicated from the receiver to the transmitter at optional block522. The transmitter will then responsively increase the laser beam intensity by the requested amount.

At block524, the system output is provided. In embodiments, where the receiver/transceiver includes wireless communication circuitry, such as using WirelessHART communication protocol, the receiver/transceiver may report the output directly to a process communication network. Additionally, or alternatively, the system may provide the output directly on a display of the receiver/transceiver. Further, in situations where the gas detection level is above a certain threshold, the output may also include a visual or audible alarm. Finally, since the receiver and transmitter can communicate with one another, the output may also be communicated from the receiver to the transmitter to be displayed locally on a display/alarm of the transmitter as well. With the output generated, method500repeats by returning to block506.

As set forth above, some of the embodiments described herein provide a small, low-energy, long-distance optical communication system for an open path gas detection system that complies with at least one explosion-proof specification, and/or complies with Class 1 Laser requirements. In some embodiments, wireless communication module is designed to prevent crosstalk between different pairs (pair/set means receiver and transmitter) using wireless communication between the receiver and the transmitter. By that, each receiver will identify and pair with the relevant transmitter to avoid crosstalk.

Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention. For example, while embodiments described herein generally provide a gas detection system with a number of additional parameters of interest, additional capabilities are also enabled, such as using the system to map the surrounding area using LIDAR technology.