LASER GAS ANALYZER

A laser gas analyzer includes: 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; a processor that calculates a concentration of a component contained in the measurement target gas based on an amount of light of the laser light received by the photodiode; and a light emitting diode (LED) that irradiates LED light such that the LED light is received by the photodiode without passing through the measurement target gas.

CROSS REFERENCE TO RELATED APPLICATION

The present application claims priority to Japanese patent application No. 2022-062873 filed on Apr. 5, 2022. The contents of this application are incorporated herein by reference in their entirety.

BACKGROUND

Technical Field

The present invention relates to a laser gas analyzer.

Description of the Related Art

A laser gas analyzer irradiates a measurement target gas with a laser light in a specific wavelength range, measures an amount of light of laser light that has passed through the measurement target gas, and calculates an attenuation of the laser light in the specific wavelength range to calculate a concentration of a component contained in the measurement target gas (for example, JP 2008-134076 A).

There is a laser gas analyzer that makes determination as failure of a light receiving unit when the light receiving unit of laser light does not perform output in response to the laser light while the light receiving unit is irradiated with laser light. However, in the laser gas analyzer described in JP 2008-134076 A, a light receiving element does not output or the output becomes extremely small in a case where an obstacle, such as powder dust, that blocks an optical path for laser light is present by a certain amount or more in a measurement target gas, and it causes a possibility of determination as failure of the light receiving element. Thus, the configuration of the laser gas analyzer in JP 2008-134076 A failed to accurately determine failure of the light receiving element.

SUMMARY

One or more embodiments provide a laser gas analyzer that allows accurately determining failure of a light receiving unit.

A laser gas analyzer of one or more embodiments includes a first irradiation unit (a laser diode), a light receiving unit (a photodiode), a calculation unit (a processor), and a second irradiation unit (an LED). The first irradiation unit irradiates a measurement target gas with laser light. The light receiving unit receives the laser light that has passed through the measurement target gas. The calculation unit calculates a concentration of a component contained in the measurement target gas based on an amount of light of the laser light received by the light receiving unit. The second irradiation unit irradiates light (LED light) such that the light is received by the light receiving unit without passing through the measurement target gas.

One or more embodiments can accurately determine failure of the light receiving unit.

DESCRIPTION OF THE EMBODIMENTS

The following will describe a laser gas analyzer according to embodiments with reference to the drawings.

FIG.1is a block diagram of a laser gas analyzer of Example 1. With reference toFIG.1, the laser gas analyzer of Example 1 will be described. A laser gas analyzer1is a Tunable Diode Laser Absorption Spectroscopy (TDLAS) laser gas analyzer. The laser gas analyzer1irradiates a measurement target gas with a laser light in a specific wavelength range, measures an amount of light of laser light that has passed through the measurement target gas, and calculates a concentration of a component contained in the measurement target gas based on an attenuation at a specific wavelength. The laser gas analyzer1includes a light emitting unit10that irradiates a laser light in a specific wavelength range, a measured unit20to which a measurement target gas is supplied, a light receiving unit30that receives a laser light that has passed through the measurement target gas, and an arithmetic unit40that calculates a concentration of a component contained in the measurement target gas. Note that the laser gas analyzer1need not include the measured unit20. For example, in a case where the light emitting unit10and the light receiving unit30are mounted for use on a facility to which the measurement target gas of a user who uses the laser gas analyzer1is supplied, the laser gas analyzer1need not include the measured unit20. Additionally, the arithmetic unit40may be a computer system built into the laser gas analyzer1or may be a computer system (for example, a cloud server) that can communicate with the laser gas analyzer1.

The light emitting unit10includes an output controller11, a Digital Analog Converter (DAC)12, a voltage/current conversion circuit13, and a laser diode14. The output controller11generates a pattern of laser drive current in accordance with a synchronous signal from an input controller34in the light receiving unit30described later and outputs it. The DAC12converts the pattern (digital signal) of the laser drive current output by the output controller11into an analog signal and outputs it. The voltage/current conversion circuit13outputs the laser drive current in accordance with the analog signal output by the DAC12. The laser diode14irradiates a laser light in a specific wavelength range in accordance with the laser drive current output from the voltage/current conversion circuit13. The laser diode14is a first irradiation unit that irradiates the measurement target gas with laser light. The laser light irradiated by the laser diode14passes through the measurement target gas supplied to the measured unit20and is received by a photodiode31in the light receiving unit30.

The measurement target gas is supplied to the measured unit20. The measurement target gas is, for example, a fuel exhaust gas and a process gas. The laser gas analyzer1can calculate concentrations of components, such as O2, CO, CH4, CO2, and NH3, contained in the measurement target gas.

The light receiving unit30includes the photodiode31, a filter/amplifier circuit32, an Analog Digital Converter (ADC)33, the input controller34, a memory35, and an LED36. The photodiode31receives the laser light that has been irradiated by the laser diode14and has passed through the measurement target gas supplied to the measured unit20, and outputs an analog signal corresponding to the amount of light of the received laser light. The photodiode31is a light receiving unit that receives the laser light that has passed through the measurement target gas. The photodiode31is disposed so as to be opposed to the laser diode14in the light emitting unit10between which the measured unit20is interposed. The filter/amplifier circuit32filters a predetermined frequency component contained in the received analog signal and amplifies it. The ADC33converts the analog signal received from the filter/amplifier circuit32into a digital signal and outputs it. The input controller34performs primary arithmetic processing, such as integration processing, on the digital signal received from the ADC33and stores it in the memory35. The digital signal stored in the memory35indicates a waveform of the amount of received light of the laser light that has passed through the measurement target gas. Hereinafter, the digital signal stored in the memory35is referred to as a light receiving signal waveform as appropriate.

The LED36is disposed on the photodiode31side with respect to the measured unit20. The LED36is a second irradiation unit that irradiates light such that the light is received by the photodiode31without the light passing through the measurement target gas. The light irradiated by the LED36is received by the photodiode31without the light passing through the measurement target gas. Accordingly, even when an obstacle, such as powder dust, is present in the measurement target gas, the light irradiated by the LED36is received by the photodiode31without being affected by the obstacles. The input controller34controls a light emission timing of the LED36.

The arithmetic unit40reads the light receiving signal waveform stored in the memory35and calculates the concentration of the component contained in the measurement target gas. The arithmetic unit40is a calculation unit that calculates the concentration of the component contained in the measurement target gas based on the amount of light of the laser light received by the photodiode31. The arithmetic unit40is a computer, and includes a processor (for example, a Central Processing Unit (CPU), a field-programmable gate array (FPGA), or a Digital signal processor (DSP)), a memory (for example, a Random Access Memory (RAM)), an auxiliary storage unit (for example, a Hard Disk Drive (HDD) and a Solid State Drive (SSD)), an information output unit (for example, current output, contact output, or Ethernet communication) to an external device, a display unit, and the like. The processor, for example, reads a program for calculating the concentration from an auxiliary storage unit, loads it into a memory, and executes it. The display unit displays, for example, the calculated concentration, and the information output unit outputs, for example, the calculated concentration to the external device. Additionally, the processor reads, for example, a program for determination of presence of failure of the light receiving unit30from the auxiliary storage unit, loads it into the memory, and executes it.

FIG.2is a drawing illustrating the light emission timings of a laser diode and the LED of Example 1. As illustrated inFIG.2, a section (a period) (a) is a section in which laser light is not emitted, and a section (a period) (d) is a section in which laser light is emitted. The laser diode14intermittently irradiates the laser light at an interval of the predetermined section (section (a)). The section (a) is, for example, about 0.1 ms. The section (d) differs depending on the measurement target gas, and is, for example, in a range of about from 1 ms to 3 ms. The first half (b) in the section (a) is a settlement waiting section (a settlement waiting period) in which the settlement of the output of the photodiode31is waited for (i.e., paused), and the second half (c) is a dark current measurement section (a dark current measurement period) for measuring a dark current. That is, the first half (b) is the section not used for arithmetic operation by the arithmetic unit40. The second half (c) is the section used to calculate a reference value of the arithmetic operation by the arithmetic unit40. The settlement waiting section may be a predetermined time or may be a time until it is determined that a predetermined time has elapsed while the output of the photodiode31is under a threshold or less. The dark current measurement section is a predetermined time.

The LED36emits light in the settlement waiting section of the light receiving signal in the first half (b). The arithmetic unit40constantly observes presence of a spike signal by emission of light by the LED36in the light receiving signal waveform in the first half (b) to confirm soundness of the light receiving unit30.

FIG.3AtoFIG.3Dare drawings illustrating the light receiving signal waveform of Example 1.

The light receiving signal waveform is divided into the following four patterns.

Pattern A: a pattern that includes both of a signal corresponding to the laser light irradiated by the laser diode14and a spike signal corresponding to the light irradiated by the LED36(seeFIG.3A)

Pattern B: a pattern that does not include the signal corresponding to the laser light irradiated by the laser diode14and includes the spike signal corresponding to the light irradiated by the LED36(seeFIG.3B)

Pattern C: a pattern that includes the signal corresponding to the laser light irradiated by the laser diode14but does not include the spike signal corresponding to the light irradiated by the LED36(seeFIG.3C)

Pattern D: a pattern that includes neither the signal corresponding to the laser light irradiated by the laser diode14nor the spike signal corresponding to the light irradiated by the LED36(seeFIG.3D)

The arithmetic unit40is an arithmetic unit that determines presence of failure of the photodiode31based on the output of the photodiode31that receives both of the laser light irradiated by the laser diode14and the light irradiated by the LED36. When the arithmetic unit40has confirmed the light receiving signal waveform of Pattern A illustrated inFIG.3A, the arithmetic unit40determines that both of the light emitting unit10and the light receiving unit30are normal. Additionally, when the arithmetic unit40has confirmed the light receiving signal waveform of Pattern B illustrated inFIG.3B, the arithmetic unit40determines that both of the light emitting unit10and the light receiving unit30are normal. In this case, it is considered that while the signal corresponding to the laser light irradiated by the laser diode14cannot be confirmed, a certain amount or more of obstacles that block an optical path for laser light are present in the measurement target gas. Additionally, when the arithmetic unit40has confirmed the light receiving signal waveform of Pattern C illustrated inFIG.3C, the arithmetic unit40determines that the light emitting unit10is normal while the LED36in the light receiving unit30is abnormal. When the arithmetic unit40has confirmed the light receiving signal waveform of Pattern D illustrated inFIG.3D, the arithmetic unit40determines that the light emitting unit10is normal while at least one of the photodiode31, the filter/amplifier circuit32, or the ADC33in the light receiving unit30is abnormal. The display unit in the arithmetic unit40can display each of the determination results. Additionally, each of the determination results can be transmitted to the external device via the information output unit.

(Effects of Example 1)

The light irradiated by the LED36is received by the photodiode31without passing through the measurement target gas. Thus, the photodiode31can receive the light irradiated by the LED36without being affected by the measurement target gas. As a result, even when a certain amount or more of obstacles are present in the measurement target gas, soundness of the light receiving unit30can be confirmed. As a result, reliability of failure detection is increased, leading to improvement in failure detection rate. Further, the failure detection rate is an important index in terms of functional safety, and therefore it is beneficial also in terms of functional safety standard.

The input controller34causes the LED36to emit light at the predetermined timing in the settlement waiting section (the first half (b) inFIG.2). Accordingly, using the section not used for the arithmetic operation during the usual operation in the laser gas analyzer1, failure of the light receiving unit30can be determined. That is, in Example 1, without stopping the usual operation of the laser gas analyzer1, failure of the light receiving unit30can be determined.

FIG.4is a drawing illustrating light emission timings of the laser diode and the LED of Example 2. The light emission timings of the LED36are inverted between Example 1 and Example 2. In Example 1, the LED36irradiates light at the predetermined timing in the settlement waiting section (b) of the light receiving signal. In Example 2, the LED36turns off at the predetermined timing (stops irradiating the light during a stop period) in the settlement waiting section (b) of the light receiving signal. In Example 2, the LED36constantly irradiates light in the section other than the predetermined timing (the stop period). In the first half (b), the arithmetic unit40constantly observes whether a negative spike signal by turning off the LED36is present in the light receiving signal waveform to confirm soundness of the light receiving unit30.

(Effects of Example 2)

By constantly causing the LED36to emit light in the section other than the predetermined timing, an amount of offset light due to emission of light by the LED36is added to the amount of received light of the photodiode31. By adjusting the amount of light of the light irradiated by the LED36, the photodiode31can receive the laser light and perform output in the range where accuracy of the output with respect to the input of the photodiode31is high. Consequently, the photodiode31can output the value at high accuracy with respect to the received laser light. Since the other effects are similar to those of Example 1, the description thereof will be omitted.

FIG.5is a block diagram of a laser gas analyzer of Example 3. With reference toFIG.5, a laser gas analyzer5of Example 3 will be described. Similarly to the laser gas analyzer1of Example 1, the laser gas analyzer5of Example 3 includes the light emitting unit10, the measured unit20, the light receiving unit30, and the arithmetic unit40. The measured unit20of the laser gas analyzer5is a probe that retrieves the measurement target gas. Additionally, the laser gas analyzer5includes a reflecting unit50that reflects laser light. The laser light irradiated by the laser diode14passes through a gas supplied to the measured unit20and is reflected by the reflecting unit50. The reflected laser light is received by the photodiode31. The light emitting unit10and the light receiving unit30of Example 3 are disposed on the same side with respect to the measured unit20.

(Effects of Example 3)

The laser gas analyzer5including the probe type measured unit20allows obtaining the effects similar to those of Example 1.

For example, the number of the LEDs36of Examples 1 to 3 is one, but may be two or more.

Additionally, the LEDs36of Examples 1 to 3 may be another luminous body, such as a laser diode, and may be able to change an amount of light and a wavelength of the light irradiated by the luminous body. By changing the amount of light and the wavelength of the light irradiated by the luminous body and evaluating the change in the amount of light detected by the photodiode31, soundness and performance of the photodiode31can be evaluated. The above-described change in the wavelength may be achieved by a combination of turning on and turning off lights of a plurality of luminous bodies.

Additionally, when the laser gas analyzers of Examples 1 to 3 have an Auto Gain function, it is preferred that the Auto Gain function does not work on a pulse signal by the LED36.

Moreover, when the LED36is constantly lit as in Example 2, use of AC coupling is preferred.

Additionally, in Examples 1 to 3, failure of the light receiving unit30is determined using the settlement waiting section. However, for example, it is only necessary to prepare a failure diagnosis mode for the laser gas analyzer and emit lights of the photodiode31and the LED36in the failure diagnosis mode.

Comparative Example

FIG.6is a block diagram illustrating a laser gas analyzer of Comparative Example. With reference toFIG.6, a circuit configuration and an operation of a laser gas analyzer100of Comparative Example will be described.

In a light emitting unit110, an output controller111receives a synchronous signal from an input controller134in a light receiving unit130and generates a pattern of laser drive current. The pattern is supplied as drive current to a laser diode114via a Digital Analog Converter (DAC)112and a voltage/current conversion circuit113. Thus, the laser diode114irradiates laser light. The laser light after passing through the measurement target gas is detected by a photodiode131in the light receiving unit130. The output of the photodiode131is input to the input controller134via a filter/amplifier circuit132and an Analog Digital Converter (ADC)133. The input controller134sequentially stores the output of the photodiode131in a memory135. An arithmetic unit140reads the output of the photodiode131stored in the memory135and calculates a concentration value.

FIG.7is a drawing illustrating a light receiving signal waveform detected by the laser gas analyzer of Comparative Example. The light emission timing of the laser light will be described with reference toFIG.7. InFIG.7, a section (a) is a section in which laser light is not emitted, and a section (d) is a section in which laser light is emitted. Emission and no emission of the laser light are alternately repeated.

Next, a method for failure diagnosis of the photodiode131, the filter/amplifier circuit132, and the ADC133in the light receiving unit130in the laser gas analyzer100of Comparative Example will be described. When any of the photodiode131, the filter/amplifier circuit132, and the ADC133has failure, there is a high possibility of the output value of the ADC133fixed to a certain constant value. Therefore, in the laser gas analyzer100of Comparative Example, when the variation of the output of the ADC133is in a constant range, it is determined that the light receiving unit130(any of the photodiode131, the filter/amplifier circuit132, and the ADC133) has failure.

However, not only the case where any of the photodiode131, the filter/amplifier circuit132, and the ADC133has failure, but also the case where a certain amount or more of an obstacle, such as powder dust, blocking the optical path for laser light is present in the measurement target gas, the variation of the output of the ADC133possibly is in a constant range. Accordingly, in the method for failure diagnosis of Comparative Example, the case where a certain amount or more of an obstacle, such as powder dust, blocking the optical path for laser light is present in the measurement target gas, it is determined as failure of the light receiving unit130, and therefore the failure of the light receiving unit130was not able to be accurately determined.

DESCRIPTION OF SYMBOLS