Portable spectroscopic device for analyzing gas samples

Abstract

The invention relates to a portable spectroscopic device for analyzing a gas sample and / or for measuring species concentration, number density or column density. The device comprises: a measuring chamber (2) with a gas sample to be analyzed; a light source (1) with at least one laser diode for emitting a laser beam at least in certain areas along a light path passing through the measuring chamber (2); a modulation device (8) for modulating the wavelength of the light beam emitted by the light source (1); and an optical detector device with a first optical detector (3a) and at least one second optical detector (3b, 3c). The first optical detector (3a) and the at least one second optical detector (3b, 3c) are arranged relative to the laser diode so that at least a portion of the light emitted by the laser diode is detected by the first optical detector (3a) after the light emitted by the laser diode has passed through the measuring chamber (2) m times, and at least a portion of the light emitted by the laser diode is detected by the at least one second optical detector (3b, 3c) after the light emitted by the laser diode has passed through the measuring chamber (2) n times, wherein n>m applies. At least one laser diode of the light source (1) is a low-power semiconductor laser diode, in particular a vertical cavity surface emitting laser diode. The portable spectroscopy device further comprises an evaluation unit (10) for evaluating a signal characteristic output by the first optical detector (3a) and / or a signal characteristic output by the at least one second optical detector (3b, 3c).

Description

[0001] The present invention relates to gas concentration measurement, and more particularly to portable detectors for measuring gas concentration.

[0002] In particular, the present invention relates to a portable spectroscopic device for analyzing a gas sample and / or for measuring species concentration, number density or column density, and to a portable spectroscopic method for measuring species concentration, number density or column density.

[0003] Currently, walking inspection surveys for finding natural gas leaks are performed by an investigator moving at a standard gait while dragging a leak detector along the ground. Only when the instrument sounds an alarm will the investigator pause to further investigate an area. Often, a low ppm plume is the only initial indication of a leak. Therefore, a useful instrument for this particular application must respond within about one to two seconds, be sensitive to 1 ppm changes in ambient methane concentrations, and not falsely sound an alarm. Once a leak is found, the ideal instrument can measure gas levels up to pure static levels in order to further quantify the size of the leak and the urgency of corrective action required.

[0004] Light weight, the ability to operate for a full eight-hour workday, and intrinsic safety are also ideal instrument features for this particular application.

[0005] An instrument that meets all of the above criteria is needed. Typically, a combination of instruments is used to complete leak investigations. Specifically, no instrument can respond quickly, continuously draw samples, and measure from ambient methane levels (approximately 1.7ppm) to pure gas. For example, flame ionization detectors, which are commonly used in pedestrian area surveys to find leaking gas, can typically detect a maximum concentration of 5000ppm. These detectors are not inherently safe because they use a fuel mixture consisting of approximately 40% hydrogen and have an internal flame. For higher gas concentrations, combustible gas indicators are typically used. These thermal conductivity sensors have a measurement range from the lower explosion limit (5% gas) to pure gas levels. They cannot measure continuously and require hand aspiration using a squeeze bulb.

[0006] Furthermore, all conventional gas leak detectors react to any hydrocarbon and are not selective for methane. Non-selective detection is problematic in areas where other hydrocarbons may be present.

[0007] A primary objective of the present invention is to measure light absorption over a large dynamic range.

[0008] Another object of the present invention is to make available an inexpensive natural gas leak detector capable of quantitatively measuring methane concentrations between normal atmospheric background values ​​and 100%.

[0009] Another object of the present invention is to replace existing natural gas leak detection systems that require multiple measuring devices with a single device.

[0010] Another object of the present invention is to replace flame ionization detectors, which have explosion hazards, with safer and intrinsically safe sensors and analyzers.

[0011] Another object of the invention is to enable inexpensive gas sensors and analyzers capable of concentration measurements over a large dynamic range.

[0012] Other objects, advantages, novel features and further applicable scopes of the present invention will be partially described in the following detailed description in conjunction with the accompanying drawings, and some of the contents will be obvious to those skilled in the art after reviewing the following or can be learned by practicing the present invention. The objects and advantages of the present invention can be realized and obtained by the means and combinations particularly pointed out in the appended claims.

[0013] The present invention relates to a method and apparatus for quantitatively measuring species concentration, number density or column density over a large area using spectroscopy and sample regions of varying optical path lengths. The species to be measured may be methane.

[0014] Two or more spectral methods are used to cover the entire measurement dynamic range. The first spectral method is selected for high sensitivity quantitative absorbance measurements of low species concentrations (e.g., if the species is methane, up to about 1000 ppm). The second method allows the concentration range of the species to be within the range of about 300 ppm to about 3000 ppm (if the species is methane). The third method can be used to cover the concentration range of intermediate species, for example, between 20000 ppm and 200000 ppm (for methane). The fourth spectral method is selected to be used for absorbance measurements of high species concentrations (e.g., if the species is methane, the species concentration is within the range of about 150000 ppm to about 1000000 ppm).

[0015] The selection of the spectral method and the corresponding control of the spectral light source and the processing of the detector output are performed by a microcontroller programmed specifically for these tasks. The algorithm implemented by the microcontroller includes a selection point that determines when to switch between the methods. The hysteresis of the switching point prevents oscillation between the methods when the sample absorbance crosses the transition point. The present invention preferably has multiple light paths, and all spectral methods can measure the same absorption feature or different absorption features.

[0016] According to some embodiments of the present invention, the device has multiple operating modes for measuring the same absorption feature or different absorption features of the same species, wherein the device switches between the modes according to the measured absorbance.

[0017] The first operating mode may be selected from the group consisting of wavelength modulation spectroscopy, frequency modulation spectroscopy, two-tone frequency modulation spectroscopy, cavity ringdown spectroscopy, and rapid-scan direct absorption spectroscopy. The second operating mode may determine the absorbance based on measurements of the width of an absorption feature. The third operating mode may include direct absorption spectroscopy. The fourth operating mode may determine the absorbance based on measurements of the width of an absorption feature performed by a first optical detector and at least one second optical detector. The fifth operating mode may determine the absorbance based on measurements of the width of at least one absorption feature at different wavelengths tuned to different absorption lines of a species to be detected in the gas sample.

[0018] Useful spectral light sources include, but are not limited to: lasers such as wavelength tunable lasers, for example, diode lasers (including external cavity diode lasers), dye lasers, and optically pumped solid-state lasers (including diode pumped solid state lasers); light sources obtained using nonlinear optical methods such as difference frequency generation, sum frequency generation, harmonic generation, and optical parametric oscillation; broadband light sources such as lamps, light emitting diodes, and thermal emitters combined with wavelength selective optical devices (such as gratings, prisms, and interferometers).

[0019] However, according to the invention, at least one laser diode of the light source is a low-power semiconductor laser diode, in particular a vertical cavity surface emitting laser diode. In this respect, the device is designed to minimize the occurrence of accidents and limit the severity of accidental explosions, so that the device can be used in explosive atmospheres. A vertical cavity surface emitting laser diode is a semiconductor laser diode whose laser beam is emitted perpendicular to the top surface, in contrast to conventional edge emitting semiconductor lasers (also in-plane lasers), which emit from a surface formed by cutting a single chip from a wafer.

[0020] According to one aspect of the invention, the device includes an internal power source that is certified for use in potentially explosive atmospheres. For example, the internal power source may have at least one preferably rechargeable battery and a battery housing for use in hazardous areas. The battery housing may be a rugged stainless steel rechargeable battery housing.

[0021] Preferably, the device of the present invention includes a power supply circuit having intrinsically safe technology for safely operating the electrical equipment of the device in hazardous areas by limiting the energy, electrical energy and thermal energy available for ignition. The signal and control circuits of the device of the present invention are designed so that the signal and control circuits can operate at low current and low voltage.

[0022] Embodiments of the present invention meet all requirements for natural gas leak exploration. It measures all methane levels from ambient concentrations (approximately 1.7ppm) to pure gas and can be used in areas requiring ATEX certification. The device combines an advanced low-power semiconductor sensor that includes a vertical cavity surface emitting laser diode to measure combustible gases, particularly methane. The device is approved for ATEX Directives EN60079-0:2004 & EN60079-11:2007 and includes a corresponding battery design that complies with ATEX compliance. The battery design preferably includes a 3.65V high energy lithium-ion battery having a nominal voltage of 3.75V at a rate of 1A at 20°C, and the battery has a typical capacitance of 4.0Ah (at 1A, at 20°C, the cutoff value is 2.5V).

[0023] According to some embodiments of the present invention, the battery design includes at least one rechargeable lithium-ion battery having a graphite-based anode, a lithium cobalt oxide-based cathode, an organic solvent as an electrolyte, and built-in redundant safety protection devices (shutdown separator, circuit breaker, safety vent).

[0024] The battery design may include multiple lithium-ion cells mechanically and electrically integrated into a battery system. The battery system includes electronics for performance, thermal, and safety management to incorporate multiple levels of redundant safety features to prevent abuse conditions such as overcharge, overdischarge, and short circuit.

[0025] According to some embodiments disclosed herein, each lithium-ion battery of the battery design includes a can (especially an aluminum can) and a cover (especially an aluminum cover), wherein the positive terminal and the negative terminal of the lithium-ion battery protrude from the cover. In addition, a protective cover is provided to cover the cover of the lithium-ion battery, especially the positive terminal and the negative terminal of the lithium-ion battery. In this way, the top of the lithium-ion battery, especially the positive terminal and the negative terminal of the lithium-ion battery, are encapsulated, thereby improving ATEX compliance.

[0026] The first detector and at least one second detector are spectrometer detectors configured to convert the intensity of the light beam into a voltage or current in a well-defined manner and with a response time suitable for all spectroscopic methods used by the spectrometer. Suitable detectors include, but are not limited to, photodiodes and photomultiplier tubes.

[0027] An embodiment of the present invention meets all requirements for natural gas leak exploration. It measures all methane levels from ambient concentrations (approximately 1.7 ppm) to pure gas. Preferably, an embodiment of the present invention is selective for methane and does not detect other hydrocarbons. In other words, other gases do not affect the measurement of methane when this embodiment is used. The one second time response of this embodiment allows it to be used in fast walking area exploration. Embodiments of the present invention also do not use consumables and are configured to be intrinsically safe.

[0028] According to some embodiments of the present invention, a portable spectroscopic device for analyzing a gas sample and / or for measuring a species concentration, number density or column density is provided. The device comprises: a measuring chamber having a gas sample to be analyzed; a light source having at least one laser diode for emitting a laser beam at least in certain regions along a light path passing through the measuring chamber; a modulation device for modulating the wavelength of the light beam emitted by the light source; an optical detector device having a first optical detector and at least one second optical detector, the first optical detector and at least one second optical detector being arranged relative to the laser diode so that after the light emitted by the laser diode has passed through the measuring chamber m times, at least a portion of the light emitted by the laser diode is detected by the first optical detector, and after the light emitted by the laser diode has passed through the measuring chamber n times, at least a portion of the light emitted by the laser diode is detected by the at least one second optical detector, where n>m applies; and an evaluation unit for evaluating a signal characteristic output by the first optical detector and / or a signal characteristic output by the at least one second detector.

[0029] The evaluation unit may comprise signal processing electronics for acquiring data from the first optical detector and the at least one second optical detector and for establishing a comparison signal source and linelocking of at least one absorption feature, and a microcontroller for receiving the data from the signal processing electronics.

[0030] According to some aspects of the invention, the device further comprises a display for displaying the data from the microcontroller, wherein the display can switch between displaying data in PPM, percent LEL, and percent gas (form). In addition, an alarm controlled by the microcontroller can be provided. In some embodiments of the invention, a user button for inputting options and modes is also provided.

[0031] Furthermore, the device may comprise a reference cell containing at least one species to be detected in the gas sample to be analyzed, wherein the reference cell is designed such that at least a portion of the light emitted by the laser diode passes through the reference cell after the light has passed through the measuring chamber and before the light is detected by the first optical detector.

[0032] According to some embodiments of the invention, optionally, the first optical detector and / or the at least one second optical detector are operable for harmonic detection of the light emitted by the laser diode or for direct detection of the light emitted by the laser diode. The evaluation unit may comprise at least one phase detector for a phase locked loop circuit assigned to the at least one second optical detector and / or the first optical detector.

[0033] According to some embodiments of the present invention, at least one laser diode is suitable for selectively emitting light of a first spectrum or at least one second spectrum, wherein the first spectrum matches a first absorption line of a species to be detected in a gas sample to be analyzed, and wherein the second spectrum matches a second absorption line of the species, wherein the first absorption line is stronger than the second absorption line.

[0034] According to some embodiments of the present invention, the evaluation unit may operate in the following modes:

[0035] - operating in a first operating mode, in which the at least one second optical detector is operated for harmonic detection of the light emitted by the laser diode and a signal course recorded by the at least one second optical detector is evaluated;

[0036] - operation in a second operating mode, in which the at least one second optical detector is operated for direct detection of the light emitted by the laser diode and a signal curve recorded by the at least one second optical detector is evaluated;

[0037] - operating in a third operating mode, in which the first optical detector is operated for direct detection of light emitted by the laser diode and a signal curve recorded by the first optical detector is evaluated; and

[0038] -operating in a fourth operating mode, in which at least one laser diode is driven so that the light is emitted in a spectrum tuned to an absorption line of a substance to be detected in a gas sample to be analyzed, wherein the absorption line is weaker than the absorption line to which the spectrum of the light emitted by the at least one laser diode in the first operating mode to the third operating mode is coordinated, and wherein, in the fourth operating mode, at least one second optical detector is optionally operated to perform harmonic detection or direct detection of the light emitted by the at least one laser diode, and evaluate the signal curve recorded by the at least one second optical detector.

[0039] In yet another embodiment of the present invention, the measuring chamber comprises a multiple pass optical cell. In this embodiment, the pump continuously pumps the gas through the multiple pass optical cell. Preferably, the multiple pass optical cell comprises two mirrors configured in a Herriott cell design.

[0040] In another embodiment of the present invention, the light source of the portable spectroscopy device includes a diode laser, which is preferably a semiconductor laser diode called a "vertical cavity surface emitting laser" (VCSEL), the laser beam of which is emitted vertically from the top surface, as opposed to conventional edge-emitting semiconductor lasers (also in-plane lasers), which emit from a surface formed by cutting a single chip from a wafer.

[0041] Optionally, a display is included for displaying data from the microcontroller. Preferably, the display switches between displaying data in PPM, percent LEL, and percent gas (form). An alarm is included in this embodiment. The alarm is controlled by the microcontroller. Optionally, a user button is included for inputting options and modes.

[0042] In another embodiment of the invention, the device comprises a retractable sample probe and is powered by a battery, in particular a lithium-ion battery as described above.

[0043] A portable spectroscopic method for measuring the concentration, number density or column density of a species comprises the steps of holding a portable spectroscopic device in an area to be measured (preferably holding the device with one hand), emitting light from a light source of the portable spectroscopic device through a measurement chamber of the portable spectroscopic device, receiving light by a first optical detector and at least one second optical detector of the device, and evaluating signal characteristics output by the first optical detector and at least one second optical detector of the device. The device has a plurality of operating modes for measuring the same absorption characteristics or different absorption characteristics of the species, and wherein the device switches between the plurality of modes according to the measured absorbance.

[0044] Preferably, the method further comprises the step of determining one or more gas concentrations by signal processing electronics connected to the detector and reporting the gas concentration data to the microcontroller.Preferably, the gas being measured is methane.

[0045] Preferably, the method includes using signal processing electronics to establish a comparative signal source and line lock of the absorption signature.

[0046] Optionally, the method comprises a multi-pass optical chamber. Preferably, a diode laser is used as the light source. The method also continuously pumps the gas to be detected through the multi-pass optical chamber. In this embodiment, preferably, the multi-pass optical chamber comprises two mirrors configured in a Herriott cell design.

[0047] Preferably, the method also displays gas concentration data, controls alarms via the microcontroller, performs calibrations, enters options and modes via user buttons, and shortens the sample probe in the area to be measured.

[0048] Other objects, advantages, novel features and further applicable scope of the present invention will be partially described in the following detailed description in conjunction with the accompanying drawings, and some of the contents will be obvious to those skilled in the art after reviewing the following or can be learned by practicing the present invention.

[0049] The accompanying drawings, which are included in and constitute a part of the specification, illustrate one or more embodiments of the present invention and, together with the description, are used to explain the principles of the present invention. The accompanying drawings are only for the purpose of illustrating one or more preferred embodiments of the present invention and should not be interpreted as limiting the present invention.

[0050] In the figure:

[0051] Figure 1 is a schematic diagram of an embodiment of the present invention preferably for methane detection; and

[0052] Figure 2 is a cross-sectional view of a measurement chamber according to an embodiment of the present invention.

[0053] The present invention relates to a portable spectroscopic device for analyzing a gas sample and / or for measuring the concentration of a species. In particular, the present invention relates to a portable gas leak detector. In a preferred embodiment, the portable gas leak detector is a diode laser sensor that determines the gas concentration, preferably the methane concentration.

[0054] exist Figure 1 A schematic diagram of an embodiment of the present invention is shown in Preferably, the embodiment comprises a portable spectroscopic device for measuring gas concentrations. Preferably, the device is a handheld device.

[0055] Preferably, the spectroscopic device comprises a laser source 1 having at least one laser diode and a fixed length optical path which receives light from the at least one laser diode. The fixed length optical path contains the gas to be detected and preferably comprises a multi-pass optical chamber or measurement chamber 2. Preferably, the gas to be detected is continuously pumped through the multi-pass optical chamber or measurement chamber 2 using a pump.

[0056] The first optical detector 3a preferably receives light at one end of a fixed length optical path after the light passes through the gas to be detected once. The second optical detectors 3b, 3c receive light at one end of a fixed length optical path after the light passes through the gas to be detected multiple times.

[0057] The first optical detector 3a and the second optical detector 3b, 3c are connected to a signal processing electronics 4. The signal processing electronics 4 determines one or more gas concentrations. The microcontroller 5 preferably receives the concentration data from the signal processing electronics 4 and displays the concentration data using a display 6. Preferably, the display 6 can display the gas concentration data in PPM, percent LEL and / or percent gas (form).

[0058] Preferably, the embodiment further comprises a reference signal for line locking and comparing the signal source. To establish the reference signal, the embodiment preferably comprises a reference chamber 7, in which at least one species to be detected in the gas sample to be analyzed is contained. The reference chamber 7 is designed so that at least a portion of the light emitted by the laser source 1 passes through the reference chamber 7 after the light has passed through the measurement chamber 2 and before the light is detected by the first optical detector 3a.

[0059] According to the design, the first optical detector 3a is also used to receive light from the reference chamber 7. Since the first optical detector 3a is connected to the signal processing electronics 4, the signal processing electronics 4 determines the concentration of the reference signal based on the detection amount of the optical detector. Preferably, the reference chamber 7 approximately contains a methane mixture with an absorbance of 0.001 to 0.1.

[0060] Alternatively, the first optical detector 3a and the second optical detector 3b, 3c may be operated for harmonic detection of the light emitted by the laser diode or for direct detection of the light emitted by the laser diode.

[0061] Preferably, at least one laser diode is suitable for selectively emitting light of a first spectrum or light of at least one second spectrum, wherein the first spectrum matches a first absorption line of a species to be detected in a gas sample to be analyzed (here methane), and wherein the second spectrum matches a second absorption line of the species (here methane), wherein the first absorption line is stronger than the second absorption line.

[0062] In order to analyze and evaluate the data provided by the first optical detector 3a and the second optical detector 3b, 3c, the device comprises an evaluation unit 10. Preferably, the evaluation unit 10 comprises the already mentioned signal processing electronics 4 for acquiring data from the first optical detector 3a and the second optical detector 3b, 3c and for establishing a comparative signal source and a line lock of at least one absorption feature. Furthermore, preferably, the evaluation unit 10 comprises the already mentioned microcontroller 5, which receives the data from the signal processing electronics 4. In order to display the data from the microcontroller, a display 6 is provided. Preferably, the display 6 can be switched between displaying the data in PPM, percentage LEL and percentage gas (form).

[0063] The evaluation unit 10 can be operated in the following operating modes:

[0064] - operable in a first operating mode, in which the second optical detectors 3b, 3c are operated for harmonic detection of the light emitted by the laser diode and the signal curves recorded by the second optical detectors 3b, 3c are evaluated;

[0065] - operable in a second operating mode, in which the second optical detector 3b, 3c is operated for direct detection of the light emitted by the laser diode and the signal curve recorded by the second optical detector 3b, 3c is evaluated;

[0066] - operable in a third operating mode, in which the first optical detector 3a is operated to directly detect the light emitted by the laser diode and to evaluate the signal curve recorded by the first optical detector 3a; and

[0067] - can be operated in a fourth operating mode, in which at least one laser diode is driven so that the light is emitted in a spectrum tuned to an absorption line of a substance to be detected in a gas sample to be analyzed (here methane), wherein the absorption line is weaker than the absorption line to which the spectrum of the light emitted by the at least one laser diode in the first operating mode to the third operating mode is coordinated, and wherein, in the fourth operating mode, at least one second optical detector can be selectively operated to perform harmonic detection or direct detection of the light emitted by the at least one laser diode, and evaluate the signal curve recorded by the second optical detectors 3b, 3c.

[0068] According to the present invention, a diode laser sensor measures the optical absorption of methane concentration. Preferably, the optical absorption is at a wavelength between 1630 nm and 1700 nm corresponding to the absorption line of methane. At the specified wavelength, the absorbance of methane is very narrow where there are usually no interfering absorption species. Preferably, a high sensitivity optical absorption technique called wavelength modulation spectroscopy and a closed multi-pass optical chamber are used to obtain sub-ppm sensitivity.

[0069] At higher concentrations, where the light absorbance becomes coarse, conventional absorption spectroscopy is preferably used. In this example, methane is continuously pumped through a multi-pass optical chamber using a small pump.

[0070] In yet another embodiment of the present invention, preferably, the light source 1 is a diode laser. Preferably, the laser characteristics include an output power of about 0.1 to 5 mW, a diode injection current of about 5 to 150 mA, and a diode voltage drop of about 0.5 to 3 V.

[0071] Preferably, at least one laser diode is mounted directly on a micro-thermoelectric cooler that allows thermal control while minimizing power consumption.

[0072] Preferably, the multi-pass optical chamber or measurement chamber 2 comprises two reflectors A, B configured as a Herriott cell design. This design makes the system insensitive to mechanical vibrations. More preferably, the base path of the multi-pass optical chamber or measurement chamber 2 is about 5 to 20 cm, and the total fixed length of the optical path provided by the multi-pass optical chamber or measurement chamber 2 is about 50 to 500 cm. In this embodiment, the volume of the measurement chamber 2 is about 50 ml. The pumping speed through the measurement chamber 2 is about 5 to 50 ml / sec.

[0073] In an embodiment of the present invention, a portion of the laser beam is split by a partially transmissive reflector (mirror B) before entering the first optical detector 3a.

[0074] Below a concentration of about 1000 ppm, at least one of a second optical detector 3b, 3c and wavelength modulation spectroscopy is preferably employed. High sensitivity is achieved by making spectral measurements at a frequency high enough to significantly reduce the excess noise of the laser. This technique is performed by rapidly modulating the laser wavelength and performing phase sensitive photodetection at a harmonic of the modulation frequency.

[0075] Since the wavelength of the diode laser is adjusted with the injected current, the small period oscillations of the diode laser current result in wavelength modulation. Gas absorption converts the wavelength modulation into amplitude modulation of the transmitted light beam. A relatively slow sweep of the laser wavelength (current) across the spectral region produces a spectrum. The spectrum produced by nth harmonic detection is displayed as the nth derivative of the unmodulated absorbance. In sensors, second harmonic detection is preferably used. Since the intensity of the diode laser is generally linear with the wavelength, another benefit of second harmonic detection is that the baseline measurement value is zero. The amplitude of the spectral peak is proportional to the absorbance, and therefore, according to Beer's law, the amplitude of the spectral peak is proportional to the concentration. The peak amplitude is also linear with respect to the beam intensity. Therefore, the signal is normalized by the light intensity.

[0076] At gas concentrations between about 150,000 ppm and about 1,000,000 ppm, the sample becomes optically thick. In this region, a modified form of the absorption spectrum is performed.

[0077] According to an embodiment disclosed herein, a modified form of the absorption spectrum is performed with the aid of at least one second optical detector, wherein the laser is not modulated; however, wherein at least one laser diode is driven so that the at least one laser diode emits light tuned to the spectrum of an absorption line of a species to be detected in a gas sample to be analyzed (here methane), wherein the absorption line is weaker than the absorption line to which the spectrum of light emitted by the at least one laser diode is coordinated in other operating modes.

[0078] In one embodiment of the invention, the device is further provided with a GPS system for assigning a location to the methane spectrum evaluated by the device.

[0079] The user buttons allow the user to answer yes / no questions about instrument options and modes.Preferably, the embodiment includes an alarm controlled by the microcontroller, preferably the alarm includes an audible alarm, a vibrating buzzer, an LED and an audio earphone alarm.

[0080] Embodiments of the present invention include a housing enclosing the instrument. Preferably, the housing is made of plastic. Preferably, an inlet tube is used as a sample probe. More preferably, a telescopic inlet tube is used as a sample probe. Most preferably, a telescopic inlet tube with a 5 micron filter attached near the input end is used as a sample probe. Preferably, the sample probe is connected to a multi-pass optical chamber or measurement chamber 2. In a normal leak survey, the end of the probe is dragged along the ground.

[0081] Optionally, a rigid probe can be attached to the sample probe to detect underground gas. The rigid probe allows the user to easily detect underground gas. When used in this manner, the present invention requires only one hand to operate. When the inlet pressure drops significantly below ambient pressure, a filter blockage warning is provided.

[0082] Preferably, the present invention operates using a wireless energy source such as batteries. More preferably, the present invention operates on four AA size rechargeable nickel metal hydride (or preferably, lithium ion) batteries.

[0083] In one embodiment of the invention, a calibration (preferably a two-point calibration) is performed by the user to establish the span and offset factors. In this embodiment, one calibration point is performed on clean air. The other calibration point is performed on a mixture of about 1000 ppm of methane in air or nitrogen. The calibration mixture is introduced into the instrument using a demand flow regulator. The demand flow regulator supplies gas to the system at a pump rate, thereby maintaining a constant sample pressure. Calibration is performed in both wavelength modulation and normal absorbance modes. Calibration can be performed as little as once a month.

[0084] Figure 2 The previous reference Figure 1 An exemplary embodiment of a measuring chamber 2 of the device according to the invention is discussed in the schematic diagram in FIG.

[0085] The portable unit for gas leak detection mainly consists of: a laser sensor, a pump for sampling the gaseous mixture for analysis, a lithium-ion battery, a graphic LCD for displaying the measured values ​​and interactions, a key + rotary knob, an embedded GPS and Bluetooth and an electronic board to manage all of the above.

[0086] Laser sensors can be divided into optics and measurement electronics.

[0087] The principle behind the selective measurement of methane is TDLAS, used together with direct absorption and the "second derivative - 2F" technique. The laser used is a VCSEL at an appropriate wavelength of approximately 1.654 nm.

[0088] The optical chamber exists in a tube (cell tube) that contains the gaseous mixture to be measured and also provides a mechanical support function. The optical chamber is continuously injected with gas sampled by a pump. There are two recessed custom mirrors (Mirror A, Mirror B) at both ends of the tube that form a multi-pass chamber that provides an optical length of approximately 3.3 meters.

[0089] At one end is placed a laser emitter (laser) with a specific lens to give the laser beam an optimal focus. At the opposite end are placed two photodiodes, one photodiode is the "reference" photodiode and the other photodiode is the "measurement" photodiode.

[0090] The reference photodiode (first optical detector 3a) is placed after the first pass of the laser beam, so its optical path length is the mechanical length of the optical chamber (about 13 cm). The reflector at this end (reflector B) is made to have a small transmittance of about 1%, so there may be some light hitting the photodiode. There is also a closed part of a dedicated metal tube before the photodiode and after the reflector, which forms a chamber in which there is a mixed gas with a relevant amount of CH4 to have a reference absorption line, thereby locking the system on the absorption peak. The measuring photodiode (second optical detector) is placed at the end of the multi-pass optical path.

[0091] This configuration ensures that measurements can be made using two photodiodes simultaneously, one at a long path length and the other at a short path length.

[0092] The electronics managing the laser sensor combines the functions required for the regulation of the laser (thermal stability, laser drive) and for measurements in direct absorption and second-order derivative. It generates the DC bias, ramp and primary RF frequency generation and acquires the photodiode signal in DC (direct absorption) mode and through a lock-in amplifier for second-order derivative measurement.

[0093] Due to the optical path length and the required detection limit as well as the complete measuring range, it is not possible to produce a measurement from a single channel that could cover the entire measuring range (0.1ppm to 1000000ppm), so a strategy to manage these signals was implemented, allowing four measurement phases to be identified:

[0094] Low Range:

[0095] Up to approximately 1000ppm, using the full optical path and operating at the second derivative

[0096] Low to mid range:

[0097] From about 300ppm to about 30,000ppm, using the full optical path and working in direct absorption mode

[0098] Mid-High Range:

[0099] From about 20,000 ppm to about 200,000 ppm, a single pass is used and operation is carried out in direct absorption mode; in this mode, there is a constant absorption due to the presence of the reference chamber 7, so the calibration needs to take this aspect into account

[0100] High Range:

[0101] From about 150,000 ppm to about 1,000,000 ppm, the full optical path is used and operates in direct absorption mode, but the laser emission is switched to the nearby weaker methane absorption line

[0102] The entire switching process is done automatically and seamlessly to the user.

[0103] Although the invention has been described in detail with reference to these preferred embodiments, other embodiments can achieve the same results. Variations and modifications of the invention will be apparent to those skilled in the art, and it is intended to cover all such modifications and equivalents.

Claims

1. A portable spectroscopic device for analyzing a gas sample and / or for measuring species concentration, number density or column density, the device comprising: - a measuring chamber (2) containing the gas sample to be analyzed; a light source (1) having at least one laser diode for emitting a laser beam at least in certain regions along a light path through the measuring chamber (2), wherein the at least one laser diode of the light source (1) is a low-power semiconductor laser diode, the light source being arranged in a first end region of the measuring chamber; - modulation means for modulating the wavelength of the light beam emitted by said light source (1); - an optical detector arrangement, the optical detector arrangement having a first optical detector (3a) and at least one second optical detector (3b, 3c), the first optical detector (3a) and the at least one second optical detector (3b, 3c) being arranged relative to the laser diode in such a way that at least a portion of the light emitted by the laser diode is detected by the first optical detector (3a) after the light emitted by the laser diode has passed through the measuring chamber (2) m times, the at least a portion of the light being detectable by the first optical detector (3a) after the light has passed through the measuring chamber (2) exactly once along the optical path, and at least a portion of the light emitted by the laser diode is detected by the at least one second optical detector (3b, 3c) after the light emitted by the laser diode has passed through the measuring chamber (2) n times, wherein n>m applies; and an evaluation unit (10) for evaluating a signal characteristic output by the first optical detector (3a) and / or a signal characteristic output by the at least one second optical detector (3b, 3c), Wherein, the substance to be detected in the gas sample to be analyzed is methane gas, A reference chamber (7) is also provided, in which at least one species to be detected in the gas sample to be analyzed is contained, wherein the reference chamber (7) is designed so that at least a portion of the light emitted by the laser diode passes through the reference chamber (7) after the light has passed through the measuring chamber (2) and before the light is detected by the first optical detector (3a), A reflector is provided at least at a second end region of the measuring chamber (2) opposite to the first end region, the reflector being used to reflect a portion of the light emitted by the laser diode after the light has passed through the measuring chamber (2) exactly once.

2. The device according to claim 1, in, The device includes an internal power source certified for use in a potentially explosive atmosphere, the internal power source having at least one rechargeable battery and a battery housing for use in hazardous areas, the at least one rechargeable battery including a 3.65V high energy lithium ion battery and / or a protective cover for covering the positive and negative terminals of the lithium ion battery; and / or, The device includes a power supply circuit having intrinsic safety technology for enabling the electrical equipment of the device to operate safely in a hazardous area by limiting the energy, electrical energy and thermal energy that can be used for ignition.

3. The device according to claim 1 or 2, wherein: The evaluation unit (10) comprises: - signal processing electronics (4) for acquiring data from the first optical detector (3a) and the at least one second optical detector (3b, 3c) and for establishing a comparative signal source and line lock of at least one absorption feature; and - a microcontroller (5) which receives the data from the signal processing electronics (4), And wherein, the device also includes: - a display (6) for displaying the data from the microcontroller (5), wherein the display (6) is switchable between displaying data in PPM, percentage LEL and percentage gas; - an alarm, the alarm being controlled by the microcontroller (5); and / or - User buttons for entering options and modes.

4. The device according to claim 1, in, The first optical detector (3a) and / or the at least one second optical detector (3b, 3c) are optionally operable for harmonic detection of the light emitted by the laser diode or for direct detection of the light emitted by the laser diode; and Therein, the evaluation unit (10) comprises at least one phase detector, which is used for a phase-locked loop circuit assigned to the at least one second optical detector (3b, 3c) and / or the first optical detector (3a).

5. The device according to claim 1 or 2, in, The at least one laser diode is suitable for selectively emitting light of a first spectrum or light of at least one second spectrum, wherein the first spectrum matches a first absorption line of a species to be detected in the gas sample to be analyzed, and wherein the second spectrum matches a second absorption line of the species, wherein the first absorption line is stronger than the second absorption line.

6. The device according to claim 4, wherein: The evaluation unit (10) can operate in the following modes: - operation in a first operating mode, in which the at least one second optical detector (3b, 3c) is operated for the harmonic detection of the light emitted by the laser diode and a signal curve recorded by the at least one second optical detector (3b, 3c) is evaluated; - operation in a second operating mode, in which the at least one second optical detector (3b, 3c) is operated for the direct detection of the light emitted by the laser diode and for evaluating a signal curve recorded by the at least one second optical detector (3b, 3c); - operation in a third operating mode, in which the first optical detector (3a) is operated for the direct detection of the light emitted by the laser diode and the signal curve recorded by the first optical detector (3a) is evaluated; as well as -operation in a fourth operating mode, in which the at least one laser diode is driven so that the light is emitted in a spectrum tuned to an absorption line of a species to be detected in the gas sample to be analyzed, wherein the absorption line is weaker than the absorption line of the spectrum of the light emitted by the at least one laser diode in the first operating mode to the third operating mode, and wherein, in the fourth operating mode, the at least one second optical detector (3b, 3c) can be optionally operated to perform harmonic detection or direct detection of the light emitted by the at least one laser diode and evaluate the signal curve recorded by the at least one second optical detector (3b, 3c).

7. The device according to claim 1 or 2, in, The first optical detector (3a) is arranged in the second end region of the measuring chamber (2), wherein the at least one second optical detector (3b, 3c) is arranged so that a receiving axis of the at least one second optical detector (3b, 3c) extends parallel to a receiving axis of the first optical detector (3a).

8. The device according to claim 1, in, The first optical detector (3a) is arranged behind the reflector with respect to the emission direction of the laser diode and is adapted to detect at least a portion of the light that is not reflected by the reflector.

9. The device according to claim 1, in, A reflector is arranged in the first end region of the measuring chamber (2), and the reflector arranged in the first end region of the measuring chamber (2) interacts with the reflector arranged in the second end region of the measuring chamber (2) so that at least a portion of the light emitted by the laser diode passes through the measuring chamber (2) multiple times until at least a portion of the light emitted by the laser diode is detected by the at least one second detector.

10. The device according to claim 1 or 2, in, The apparatus is handheld and configured as a portable spectroscopic device for measuring gas concentrations, and wherein the apparatus can be held in one hand.

11. The device according to claim 1 or 2, Also comprising a pump, which continuously pumps the gas to be analyzed through the measurement chamber (2); and / or Also comprising a telescopic sample probe; and / or Also included are rigid probes for measuring underground gas concentrations.

12. The apparatus of claim 1, the at least one laser diode being a vertical cavity surface emitting laser diode.

13. A portable spectroscopic method for measuring species concentration, number density or column density, the method comprising the steps of: - keeping a portable spectroscopy device in the area to be measured, said portable spectroscopy device being a device according to claim 1; - emitting light from the light source (1) of the portable spectroscopy device through a measurement chamber (2) of the portable spectroscopy device; - receiving light by said first optical detector (3a) and said at least one second optical detector (3b, 3c) of said device; as well as - evaluating signal characteristics output by said first optical detector (3a) and said at least one second optical detector (3b, 3c) of said device; Wherein the device has a plurality of operating modes for measuring the same absorption characteristic or different absorption characteristics of the species, and wherein the device switches between the plurality of modes based on the measured absorbance.

14. The method according to claim 13, wherein: - a first operating mode is selected from the group consisting of wavelength modulation spectroscopy, frequency modulation spectroscopy, two-tone frequency modulation spectroscopy, cavity ring-down spectroscopy and fast scanning direct absorption spectroscopy; - a second operating mode determines the absorbance from the measured value of the width of said absorption feature; - The third operating mode includes direct absorption spectroscopy; - a fourth operating mode determines the absorbance from measurements of the width of the absorption feature performed by the first optical detector (3a) and the at least one second optical detector (3b, 3c); as well as - A fifth operating mode determines the absorbance from measurements of the width of said at least one absorption feature at different wavelengths tuned to different absorption lines of the species to be detected in said gas sample.

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