Laser gas analyzer

Abstract

The present disclosure provides a laser gas analyzer including a laser diode that irradiates a measurement target gas with laser light, a photodiode that receives the laser light that has passed through the measurement target gas, an arithmetic unit that calculates a concentration of a component contained in the measurement target gas from an amount of light of the laser light received by the photodiode, and an LED that irradiates light so that the light is received by the photodiode without passing through the measurement target gas.

Description

[0001] Cross-reference to related applications

[0002] This application claims priority to Japanese Patent Application No. 2022-062873, filed on April 5, 2022. The entire contents of that application are incorporated herein by reference. Technical Field

[0003] This invention relates to a laser gas analyzer. Background Technology

[0004] A laser gas analyzer irradiates a target gas with a laser within a specific wavelength range, measures the amount of laser light that has passed through the target gas, and calculates the attenuation of the laser within that specific wavelength range to calculate the concentration of the components contained in the target gas (e.g., JP 2008-134076 A).

[0005] There is a laser gas analyzer where, if the light receiving unit does not respond to the laser output when irradiated with a laser, it is considered a malfunction of the light receiving unit. However, in the laser gas analyzer described in JP 2008-134076A, if the gas being measured contains a certain amount or more of obstructions (such as dust) that impede the laser's optical path, the light receiving element may not output or its output may become extremely low, which could also be considered a malfunction of the light receiving element. Therefore, in the configuration of the laser gas analyzer in JP 2008-134076A, it is not possible to accurately determine the malfunction of the light receiving element. Summary of the Invention

[0006] One or more embodiments provide a laser gas analyzer that can accurately determine the fault of a light receiving unit.

[0007] One or more embodiments of a laser gas analyzer include a first irradiation unit (laser diode), a light receiving unit (photodiode), a computing unit (processor), and a second irradiation unit (LED). The first irradiation unit irradiates the target gas with a laser. The light receiving unit receives the laser light that has passed through the target gas. The computing unit calculates the concentration of components contained in the target gas based on the amount of laser light received by the light receiving unit. The second irradiation unit irradiates light (LED light) such that the light does not pass through the target gas but is received by the light receiving unit.

[0008] One or more embodiments are able to accurately determine the fault of the optical receiving unit. Attached Figure Description

[0009] Figure 1 It is based on the block diagram of the laser gas analyzer in Example 1;

[0010] Figure 2 This is a diagram illustrating the light emission timing of the laser diode and LED in Example 1;

[0011] Figure 3A This is a diagram showing the waveform of the optical received signal detected by the optical receiving unit of Example 1;

[0012] Figure 3B This is a diagram showing the waveform of the optical received signal detected by the optical receiving unit of Example 1;

[0013] Figure 3C This is a diagram showing the waveform of the optical received signal detected by the optical receiving unit of Example 1;

[0014] Figure 3D This is a diagram showing the waveform of the optical received signal detected by the optical receiving unit of Example 1;

[0015] Figure 4 This is a diagram illustrating the light emission timing of the laser diode and LED in Example 2;

[0016] Figure 5 This is a block diagram of the laser gas analyzer in Example 3;

[0017] Figure 6 This is a block diagram of a comparative example laser gas analyzer;

[0018] Figure 7 This is a diagram showing the emission timing of a laser diode in a comparative example. Detailed Implementation

[0019] The laser gas analyzer according to an embodiment will now be described with reference to the accompanying drawings.

[0020] <Example 1>

[0021] Figure 1 This is a block diagram of the laser gas analyzer in Example 1. (Refer to...) Figure 1The laser gas analyzer of Example 1 will be described below. Laser gas analyzer 1 is a tunable diode laser absorption spectroscopy (TDLAS) laser gas analyzer. Laser gas analyzer 1 irradiates a target gas with a laser in a specific wavelength range, measures the amount of laser light that has passed through the target gas, and calculates the concentration of components contained in the target gas based on attenuation at the specific wavelength. Laser gas analyzer 1 includes: a light emitting unit 10 that irradiates a laser in a specific wavelength range; a target gas receiving unit 20 to which the target gas is supplied; a light receiving unit 30 that receives the laser light that has passed through the target gas; and an arithmetic unit 40 that calculates the concentration of components contained in the target gas. Note that laser gas analyzer 1 does not necessarily include target gas receiving unit 20. For example, if the light emitting unit 10 and the light receiving unit 30 are installed on a facility supplying the target gas to a user using laser gas analyzer 1 for use, laser gas analyzer 1 does not necessarily include target gas receiving unit 20. Alternatively, the arithmetic unit 40 may be a computer system built into the laser gas analyzer 1, or it may be a computer system (e.g., a cloud server) capable of communicating with the laser gas analyzer 1.

[0022] (Optical emission unit 10)

[0023] The light emitting unit 10 includes an output controller 11, a digital-to-analog converter (DAC) 12, a voltage-to-current conversion circuit 13, and a laser diode 14. The output controller 11 generates and outputs a pattern of laser drive current based on a synchronization signal from an input controller 34 of the light receiving unit 30, which will be described later. The DAC 12 converts the pattern (digital signal) of the laser drive current output by the output controller 11 into an analog signal and outputs it. The voltage-to-current conversion circuit 13 outputs the laser drive current based on the analog signal output by the DAC 12. The laser diode 14 irradiates a laser within a specific wavelength range based on the laser drive current output from the voltage-to-current conversion circuit 13. The laser diode 14 is a first irradiation unit for irradiating the gas to be measured with laser light. The laser light irradiated by the laser diode 14 passes through the gas to be measured supplied to the unit under test 20 and is received by a photodiode 31 in the light receiving unit 30.

[0024] (Unit under test 20)

[0025] The target gas is supplied to the measured unit 20. The target gas is, for example, fuel exhaust gas and process gas. The laser gas analyzer 1 can calculate the concentration of components (e.g., O2, CO, CH4, CO2, NH3) contained in the target gas.

[0026] (Optical receiving unit 30)

[0027] The light receiving unit 30 includes a photodiode 31, a filter / amplifier circuit 32, an analog-to-digital converter (ADC) 33, an input controller 34, a memory 35, and an LED 36. The photodiode 31 receives laser light that has been irradiated by the laser diode 14 and has passed through the gas to be measured supplied to the unit under test 20, and outputs an analog signal corresponding to the amount of light received by the laser. The photodiode 31 is the light receiving unit that receives laser light that has passed through the gas to be measured. The photodiode 31 is positioned opposite the laser diode 14 in the light emitting unit 10, with the unit under test 20 inserted between them. The filter / amplifier circuit 32 filters and amplifies the predetermined frequency components contained in the received analog signal. The ADC 33 converts the analog signal received from the filter / amplifier circuit 32 into a digital signal and outputs it. The input controller 34 performs basic arithmetic processing (e.g., integration) on the digital signal received from the ADC 33 and stores it in the memory 35. The digital signal stored in the memory 35 indicates the waveform of the amount of laser light received that has passed through the gas to be measured. In the following text, the digital signal stored in memory 35 will be appropriately referred to as the optical received signal waveform.

[0028] LED 36 is positioned relative to the unit under test 20 on the side of photodiode 31. LED 36 is a second illumination unit that illuminates light so that the light does not pass through the gas being measured but is received by photodiode 31. The light illuminated by LED 36 is received by photodiode 31 without passing through the gas being measured. Therefore, even if there are obstacles (such as dust) in the gas being measured, the light illuminated by LED 36 is received by photodiode 31 without being affected by the obstacles. Input controller 34 controls the timing of LED 36 emitting light.

[0029] The arithmetic unit 40 reads the light-receiving signal waveform stored in the memory 35 and calculates the concentration of the components contained in the target gas. The arithmetic unit 40 is a calculation unit that calculates the concentration of the components contained in the target gas based on the amount of laser light received by the photodiode 31. The arithmetic unit 40 is a computer and includes a processor (e.g., a central processing unit (CPU), a field-programmable gate array (FPGA), or a digital signal processor (DSP)), a memory (e.g., random access memory (RAM)), an auxiliary storage unit (e.g., a hard disk drive (HDD) and a solid-state drive (SSD)), an output unit for information to external devices (e.g., current output, contact output, or Ethernet communication), a display unit, etc. For example, the processor reads a program for calculating the concentration from the auxiliary storage unit, loads the program into the memory, and executes the program. The display unit displays the calculated concentration, for example, and the information output unit outputs the calculated concentration to an external device, for example, the information output unit. Additionally, the processor reads a program for determining whether the light-receiving unit 30 is faulty from the auxiliary storage unit, loads the program into the memory, and executes the program.

[0030] Figure 2 This is a diagram illustrating the timing of light emission from the laser diode and LED in Example 1. (As shown...) Figure 2 As shown, interval (period) (a) is the interval where no laser is emitted, and interval (period) (d) is the interval where laser is emitted. The laser diode 14 intermittently irradiates with laser at predetermined intervals (interval (a)). Interval (a) is, for example, approximately 0.1 ms. Interval (d) varies depending on the gas being measured, for example, ranging from approximately 1 ms to 3 ms. The first half (b) of interval (a) is a settlement waiting interval (settlement waiting period) for calculating the output of photodiode 31, and the second half (c) is a dark current measurement interval (dark current measurement period) for measuring dark current. In other words, the first half (b) is not used for arithmetic operations by the arithmetic unit 40. The second half (c) is used for calculating the reference value for arithmetic operations by the arithmetic unit 40. The settlement waiting interval can be a predetermined time, or it can be the time until a predetermined time has elapsed when it is determined that the output of photodiode 31 is below a threshold or lower. The dark current measurement interval is a predetermined time.

[0031] LED 36 emits light during the calculation waiting period of the light receiving signal in the first half of the interval (b). The arithmetic unit 40 continuously observes the presence of the spike signal caused by the light emission of LED 36 in the light receiving signal waveform in the first half of the interval (b) to confirm the integrity of the light receiving unit 30.

[0032] Figures 3A to 3D This is a diagram showing the optical received signal waveform of Example 1.

[0033] The waveform of the optical received signal is divided into the following four modes.

[0034] Mode A: A mode that includes both the signal corresponding to the laser beam emitted by laser diode 14 and the spike signal corresponding to the light emitted by LED 36 (see [link]). Figure 3A ).

[0035] Mode B: A mode that does not include the signal corresponding to the laser emitted by laser diode 14, but includes the spike signal corresponding to the light emitted by LED 36 (see [link to mode]). Figure 3B ).

[0036] Mode C: A mode that includes the signal corresponding to the laser emitted by laser diode 14 but excludes the spike signal corresponding to the light emitted by LED 36 (see [link to mode]). Figure 3C ).

[0037] Mode D: A mode that includes neither the signal corresponding to the laser emitted by laser diode 14 nor the spike signal corresponding to the light emitted by LED 36 (see [link]). Figure 3D ).

[0038] Arithmetic unit 40 is an arithmetic unit that determines whether photodiode 31 is faulty based on its output. Photodiode 31 receives both laser light from laser diode 14 and light from LED 36. After arithmetic unit 40 has confirmed that... Figure 3A Given the optical signal waveform shown in Mode A, the arithmetic unit 40 determines that both the optical transmitting unit 10 and the optical receiving unit 30 are functioning normally. Furthermore, after the arithmetic unit 40 has confirmed that... Figure 3B In the case of the light-receiving signal waveform shown in Mode B, the arithmetic unit 40 determines that both the light-emitting unit 10 and the light-receiving unit 30 are normal. In this situation, it is assumed that although a signal corresponding to the laser beam irradiated by the laser diode 14 cannot be confirmed, there are a certain amount or more obstacles blocking the laser beam path in the gas being measured. Furthermore, since the arithmetic unit 40 has already confirmed that... Figure 3C In the case of the light-receiving signal waveform shown in Mode C, the arithmetic unit 40 determines that the light-emitting unit 10 is normal while the LED 36 in the light-receiving unit 30 is abnormal. The arithmetic unit 40 has already confirmed that... Figure 3D In the case of the optical received signal waveform shown in Mode D, the arithmetic unit 40 determines that the optical emitting unit 10 is normal, while at least one of the photodiode 31, filter / amplifier circuit 32, or ADC 33 in the optical receiving unit 30 is abnormal. The display unit in the arithmetic unit 40 can display each determination result. In addition, each determination result can be transmitted to an external device via the information output unit.

[0039] (The effect of Example 1)

[0040] The light emitted by LED 36 is received by photodiode 31 without passing through the gas being measured. Therefore, photodiode 31 can receive the light emitted by LED 36 without being affected by the gas being measured. As a result, even if there are a certain amount of obstacles in the gas being measured, the integrity of the light receiving unit 30 can be confirmed. Consequently, the reliability of fault detection is improved, thereby improving the fault detection rate. Furthermore, the fault detection rate is an important indicator of functional safety, thus it is also advantageous in terms of functional safety standards.

[0041] Input controller 34 causes LED 36 to be in the settlement waiting period ( Figure 2 The light is emitted at a predetermined time in the first half of the interval (b) of the laser gas analyzer. Therefore, by utilizing the interval during which arithmetic operations are not performed during the normal operation of the laser gas analyzer 1, a fault in the light receiving unit 30 can be determined. In other words, in Example 1, a fault in the light receiving unit 30 can be determined without stopping the normal operation of the laser gas analyzer 1.

[0042] <Example 2>

[0043] Figure 4 This diagram illustrates the emission timing of the laser diode and LED in Example 2. The emission time of LED 36 is reversed between Example 1 and Example 2. In Example 1, LED 36 illuminates light at a predetermined time during the light reception signal settlement waiting interval (b). In Example 2, LED 36 is turned off at a predetermined time during the light reception signal settlement waiting interval (b) (light illumination stops during the stop cycle). In Example 2, LED 36 continuously illuminates light in intervals other than the predetermined time (stop cycle). In the first half of the interval (b), the arithmetic unit 40 continuously observes whether there is a negative spike signal generated by turning off LED 36 in the light reception signal waveform to confirm the integrity of the light receiving unit 30.

[0044] (The effect of Example 2)

[0045] By continuously emitting light from LED 36 outside of a predetermined time interval, the amount of offset light caused by the emission of LED 36 is added to the amount of light received by photodiode 31. By adjusting the amount of light emitted by LED 36, photodiode 31 can receive laser light and output within a range with high accuracy relative to the input of photodiode 31. Therefore, photodiode 31 is able to output a value with high accuracy relative to the received laser light. Since other effects are similar to those in Example 1, their description will be omitted.

[0046] <Example 3>

[0047] Figure 5 This is a block diagram of the laser gas analyzer in Example 3. (Refer to...) Figure 5 The laser gas analyzer 5 of Example 3 will be described below. Similar to the laser gas analyzer 1 of Example 1, the laser gas analyzer 5 of Example 3 includes a light emitting unit 10, a measured unit 20, a light receiving unit 30, and an arithmetic unit 40. The measured unit 20 of the laser gas analyzer 5 is a probe that retrieves the gas to be measured. In addition, the laser gas analyzer 5 includes a reflective unit 50 for reflecting laser light. The laser light irradiated by the laser diode 14 passes through the gas supplied to the measured unit 20 and is reflected by the reflective unit 50. The reflected laser light is received by the photodiode 31. The light emitting unit 10 and the light receiving unit 30 of Example 3 are arranged on the same side relative to the measured unit 20.

[0048] (The effect of Example 3)

[0049] The laser gas analyzer 5, which includes a probe-type test unit 20, enables the achievement of similar effects to Example 1.

[0050] Although this disclosure has been described with respect to only a limited number of embodiments, those skilled in the art will understand, upon benefiting from this disclosure, that various other embodiments can be devised without departing from the scope of the invention. Therefore, the scope of the invention should be defined only by the appended claims.

[0051] For example, the number of LEDs 36 in Examples 1 to 3 is 1, but it can also be more than 2.

[0052] Alternatively, the LED 36 in Examples 1 to 3 can be another light-emitting element (e.g., a laser diode), and the amount and wavelength of light emitted by this light-emitting element can be changed. By changing the amount and wavelength of light emitted by the light-emitting element and evaluating the change in light amount detected by the photodiode 31, the robustness and performance of the photodiode 31 can be evaluated. The aforementioned wavelength change can be achieved by combining the on and off states of multiple light-emitting elements.

[0053] Furthermore, in the case where the laser gas analyzer of Examples 1 to 3 has an automatic gain function, it is preferable that the automatic gain function does not apply to the pulse signal of LED 36.

[0054] Furthermore, in cases where LED 36 is to be continuously illuminated as in Example 2, AC coupling is preferred.

[0055] Furthermore, in Examples 1 to 3, a settlement waiting period is used to determine the fault of the light receiving unit 30. However, for example, it is only necessary to prepare the fault diagnosis mode of the laser gas analyzer and to make the photodiode 31 and LED 36 illuminate in the fault diagnosis mode.

[0056] <Comparison Example>

[0057] Figure 6 This is a block diagram illustrating a laser gas analyzer as a comparative example. (Refer to...) Figure 6 The circuit configuration and operation of the laser gas analyzer 100, which is a comparative example, will be described.

[0058] In the light emitting unit 110, the output controller 111 receives a synchronization signal from the input controller 134 in the light receiving unit 130 and generates a pattern for the laser drive current. This pattern, as the drive current, is supplied to the laser diode 114 via the digital-to-analog converter (DAC) 112 and the voltage / current conversion circuit 113. Therefore, the laser diode 114 irradiates the laser. The laser light passing through the target gas is detected by the photodiode 131 in the light receiving unit 130. The output of the photodiode 131 is input to the input controller 134 via the filter / amplifier circuit 132 and the analog-to-digital converter (ADC) 133. The input controller 134 sequentially stores the output of the photodiode 131 in the memory 135. The arithmetic unit 140 reads the output of the photodiode 131 stored in the memory 135 and calculates the concentration value.

[0059] Figure 7 This is a graph showing the waveform of the optically received signal detected by the laser gas analyzer of the comparative example. (Refer to...) Figure 7 Describe the timing of laser emission. In Figure 7 In the diagram, interval (a) is the interval where no laser is emitted, and interval (d) is the interval where laser is emitted. The laser emission and non-emission are repeated alternately.

[0060] Next, a fault diagnosis method for the photodiode 131, filter / amplifier circuit 132, and ADC 133 in the optical receiving unit 130 of the comparative example laser gas analyzer 100 will be described. If any one of the photodiode 131, filter / amplifier circuit 132, or ADC 133 fails, the output value of the ADC 133 is likely to be fixed at a constant value. Therefore, in the comparative example laser gas analyzer 100, if the output variation of the ADC 133 is within a certain range, it is determined that the optical receiving unit 130 (any one of the photodiode 131, filter / amplifier circuit 132, or ADC 133) has failed.

[0061] However, the output variation of ADC 133 may remain within a constant range not only when any of the photodiode 131, filter / amplifier circuit 132, or ADC 133 malfunctions, but also when there is a sufficient amount of obstruction (e.g., dust) in the gas being measured that hinders the laser beam path. Therefore, in the fault diagnosis method of the comparative example, the presence of a sufficient amount of obstruction (e.g., dust) in the gas being measured is determined as a fault of the light receiving unit 130, thus failing to accurately determine the fault of the light receiving unit 130.

[0062] Symbol Explanation

[0063] 1 Laser Gas Analyzer

[0064] 10 optical emission units

[0065] 11 Output Controller

[0066] 12DAC

[0067] 13 Voltage / Current Conversion Circuit

[0068] 14 Laser Diodes

[0069] 20 Units Under Test

[0070] 30 optical receiving units

[0071] 31 photodiode

[0072] 32 Filter / Amplifier Circuit

[0073] 33ADC

[0074] 34 Input Controller

[0075] 35. Memory

[0076] 36LED

[0077] 40 Arithmetic Units

[0078] 50 reflective units

Claims

1. A laser gas analyzer, comprising: A laser diode that uses a laser to illuminate the gas being measured. An optical receiving unit, comprising: A photodiode that receives the laser light that has passed through the gas being measured; and A light-emitting diode that illuminates an LED light source, such that the LED light does not pass through the gas being measured but is received by the photodiode; and A processor calculates the concentration of components in the measured gas based on the amount of laser light received by the photodiode, and determines whether the photodiode is faulty based on its detection status of the laser and the LED light. The laser diode intermittently irradiates the laser. The light-emitting diode illuminates the LED light at predetermined times during periods when the laser diode is not illuminating the laser, and The processor determines whether the photodiode is faulty based on whether a combination of the laser and the LED light is detected in the output of the photodiode.

2. The laser gas analyzer according to claim 1, wherein, The period includes: Settlement waiting period, during which the settlement of the photodiode output is paused; and The dark current measurement period used to measure dark current, and The light-emitting diode illuminates the LED light during the settlement waiting period.

3. The laser gas analyzer according to claim 1, wherein, The processor determines whether the photodiode is faulty based on the output of the photodiode, which receives both the laser light and the LED light.

4. The laser gas analyzer according to claim 1, wherein, The laser diode intermittently irradiates the laser, and The light-emitting diode continuously illuminates the LED light except during the stop cycle when the laser diode does not illuminate the laser.

5. The laser gas analyzer according to claim 1, wherein, The light-emitting diode changes at least one of the light intensity or wavelength of the LED light.

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