Gas analyzers

Abstract

To provide a gas analyzer in which a quantization error in converting an analog signal into a digital signal is reduced when detecting an absorption amplitude signal.SOLUTION: A gas analyzer for measuring the concentration of a measurement object gas present in a measurement object space, comprises: a laser element for emitting a laser beam having been modulated with a modulating frequency; a light receiving element for receiving a laser beam having passed through the measurement object space; a ΔΣ modulator including a subtraction unit supplied with a received light signal obtained from the light receiving element, a bandpass filter unit, an AD converter for converting the analog signal having gone through the subtraction unit and the bandpass filter unit to a digital signal, and a DA conversion unit for converting the digital signal to an analog signal and feeding it back to the subtraction unit; and a gas concentration computation unit for computing the concentration of a measurement object gas on the basis of the digital signal outputted from the ΔΣ modulator. The ΔΣ modulator has a signal pass band at twice the modulating frequency.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a gas analyzer.

[0002] Known laser-type gas analyzers emit laser light modulated at a modulation frequency (see, for example, Patent Document 1). The gas analyzer in Patent Document 1 detects an absorption amplitude signal having a frequency twice the modulation frequency and calculates the gas concentration based on the magnitude of the absorption amplitude signal. Furthermore, although not related to gas analyzers, Non-Patent Document 1 describes a bandpass ΔΣ modulator technique. Patent Document 2 describes a technique for applying a bandpass ΔΣ modulator to a technique for measuring harmonics of semiconductors. Patent Document 1: JP 2017-166842 A Patent Document 2: International Publication No. 2007 / 066431 Non-Patent Document 1: Multi-bandpass ΔΣ Modulator Technology and Its Applications (The Institute of Electronics, Information and Communication Engineers, Journal C, Vol. J90-C, No. 2, pp. 143-158) Summary of the Invention [Problem to be solved by the invention]

[0003] When detecting an absorption amplitude signal in a gas analyzer, it is desirable to reduce quantization errors when converting an analog signal to a digital signal. [Means for solving the problem]

[0004] In order to solve the above problems, a first aspect of the present invention provides a gas analyzer. The gas analyzer may measure the concentration of a target gas present in a measurement space. The gas analyzer may include a laser element. The laser element may emit laser light modulated at a modulation frequency. The gas analyzer may include a light-receiving element. The light-receiving element may receive the laser light that has passed through the measurement space. The gas analyzer may include a delta-sigma modulator. The delta-sigma modulator may have a subtraction unit, a band-pass filter unit, an AD conversion unit, and a DA conversion unit. The subtraction unit may be supplied with a received light signal obtained from the light-receiving element. The AD conversion unit may convert the analog signal that has passed through the subtraction unit and the band-pass filter unit into a digital signal. The DA conversion unit may convert the digital signal into an analog signal and feed it back to the subtraction unit. The gas analyzer may include a gas concentration calculation unit. The gas concentration calculation unit may calculate the concentration of the target gas based on the digital signal output from the delta-sigma modulator. The delta-sigma modulator may have a signal passband at twice the modulation frequency.

[0005] The delta-sigma modulator may have a first signal passband and a second signal passband, the first signal passband may pass a first signal component at a modulation frequency, and the second signal passband may pass a second signal component at twice the modulation frequency.

[0006] The AD conversion section may be followed by a digital filter section having a plurality of passbands corresponding to the first signal passband and the second signal passband.

[0007] The gas concentration calculation section may calculate the concentration of the measurement target gas based on the magnitude of the second signal component.

[0008] The gas analyzer may further include a correction unit that corrects the calculation result of the concentration of the measurement target gas based on the first signal component.

[0009] The gas analyzer may further include a light emission intensity adjuster that adjusts the intensity of light emitted by the laser element based on the first signal component.

[0010] The bandwidth of the second signal passband may be greater than the bandwidth of the first signal passband.

[0011] The center frequency and bandwidth of the second signal passband may be variable depending on the type of gas to be measured.

[0012] The ΔΣ modulator may operate in phase lock with the modulation of the laser light.

[0013] The ΔΣ modulator may operate in phase lock with the frequency of the power supply.

[0014] The above summary of the invention does not list all of the necessary features of the present invention, and subcombinations of these features may also constitute inventions. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a diagram showing a schematic configuration of a gas analyzer according to a first embodiment of the present invention. [Figure 2] 3A and 3B are diagrams schematically showing a light reception signal, a light intensity amplitude signal component, and an absorption amplitude signal component. [Figure 3] FIG. 2 is a diagram illustrating an example of the ΔΣ modulator of FIG. [Figure 4] FIG. 10 is a diagram illustrating an example of frequency characteristics when the band-pass filter unit is a multi-band-pass filter. [Figure 5] 10 is a diagram showing an example of an output signal S1 from an AD conversion unit of a ΔΣ modulator. FIG. [Figure 6] FIG. 10 is a diagram showing an example of an output signal S2 from a digital filter unit. [Figure 7] 10A and 10B are diagrams illustrating another example of frequency characteristics when the band-pass filter unit is a multi-band-pass filter. [Figure 8] 10 is a diagram showing another example of the output signal S1 from the AD conversion unit of the ΔΣ modulator. FIG. [Figure 9] FIG. 2 is a diagram illustrating another example of the ΔΣ modulator of FIG. [Figure 10]FIG. 4 is a diagram showing a schematic configuration of a gas analyzer according to a second embodiment of the present invention. [Figure 11] FIG. 10 is a diagram showing a schematic configuration of a gas analyzer according to a third embodiment of the present invention. [Figure 12] 10 is a diagram illustrating an example of frequency characteristics when the band-pass filter unit is a single band-pass filter. FIG. [Figure 13] FIG. 10 is a diagram showing another example of the output signal S2 from the digital filter unit. [Figure 14] FIG. 10 is a diagram showing a schematic configuration of a gas analyzer according to a fourth embodiment of the present invention. [Figure 15] FIG. 2 is a diagram illustrating an example of synchronization of each signal. DETAILED DESCRIPTION OF THE INVENTION

[0016] The present invention will be described below through embodiments of the invention, but the following embodiments do not limit the scope of the invention according to the claims. Furthermore, not all of the combinations of features described in the embodiments are necessarily essential to the solution of the invention.

[0017] FIG. 1 is a diagram showing the schematic configuration of a gas analyzer according to a first embodiment of the present invention. The gas analyzer 1 uses a laser beam to measure the concentration of a target gas present in a measurement space. The gas analyzer 1 may measure the concentration of the target gas in the atmosphere, flue gas, or combustion gas. The gas analyzer 1 includes a light-emitting unit 10, a light-receiving unit 20, and a delta-sigma modulator 30. The gas analyzer 1 according to this embodiment includes a delta-sigma modulator 30 having a signal passband at twice the modulation frequency of the laser beam, thereby reducing quantization errors when converting an analog signal to a digital signal.

[0018] The light emitting unit 10 has a laser element 12. The laser element 12 emits laser light modulated at a modulation frequency. The laser light is irradiated onto a measurement target space. The laser light emitted by the laser element 12 has a wavelength at which the measurement target gas has an absorption line. For example, if the measurement target gas is oxygen gas, the laser light emitted by the laser element 12 has a wavelength between 760 nm and 763 nm at which the oxygen gas has an absorption line.

[0019] The measurement target gas is not limited to oxygen. The laser element 12 irradiates laser light having a wavelength that includes an absorption line of the measurement target gas, and more preferably, a wavelength that does not overlap with the absorption lines of miscellaneous gases other than the measurement target gas.

[0020] The light-emitting unit 10 has a wavelength sweep / modulation current control circuit 14. The wavelength sweep / modulation current control circuit 14 controls the drive current of the laser element 12 so that the wavelength of the light emitted by the laser element 12 is swept across the absorption line of the gas to be measured and modulated at a modulation frequency. The laser element 12 alternates between an on period during which laser light is emitted and an off period during which laser irradiation is paused. During the on period, the wavelength sweep / modulation current control circuit 14 sweeps the drive current to increase or decrease it while superimposing a sine wave with a modulation frequency of 1f on the drive current. The wavelength sweep / modulation is repeated during the on period. The modulation frequency of the sine wave is set higher than the frequency (the reciprocal of the repetition period) at which the on period and the off period are repeated. The laser element 12 may be a DBR laser, DFB laser, or VCSEL that oscillates in a single wavelength mode and is wavelength tunable by temperature and drive current.

[0021] The light-emitting unit 10 may include a laser element temperature control circuit 16. The output power and wavelength of the light emitted by the laser element 12 vary depending on the temperature. The laser element temperature control circuit 16 controls the temperature of the laser element 12, thereby controlling and stabilizing the output power and wavelength of the light emitted by the laser element 12.

[0022] The light receiving unit 20 has a light receiving element 22. The light receiving element 22 receives the laser light that has passed through the measurement target space. The light receiving element 22 is an element that is sensitive to the wavelength of the laser light. If the wavelength of the laser light is 760 nm to 763 nm, the light receiving element 22 may be a silicon photodiode.

[0023] The light receiving element 22 may also receive light emitted from a space where gas is present. If the light receiving element 22 is a photodiode, a dark current will occur. The sweep repetition period may be set so that fluctuations in the light receiving signal caused by these factors are sufficiently longer than the laser light sweep repetition period (in other words, the repetition period between the on period and the off period).

[0024] The light receiving unit 20 has a preamplifier / filter unit 24. The preamplifier / filter unit 24 includes a preamplifier circuit that amplifies the signal from the light receiving element 22. If the light receiving element 22 is a photodiode, the preamplifier circuit may be a transimpedance amplifier that amplifies the current from the photodiode while converting it into a voltage. The amplification factor of the preamplifier / filter unit 24 may be set to a level that prevents the signal from the preamplifier / filter unit 24 from saturating under conditions where the laser light is least attenuated, i.e., under conditions where there is no dust or the like on the optical path.

[0025] The output from the preamplifier circuit generally contains a DC component. This DC component is caused by dark current or light emitted from the measurement target space. The preamplifier / filter section 24 may include a filter to reduce the DC component.

[0026] The gas analyzer 1 includes a ΔΣ modulator 30. The ΔΣ modulator 30 acquires a received light signal from the light receiving unit 20. The ΔΣ modulator 30 then converts the received light signal from an analog signal to a digital signal and outputs the digital signal. Therefore, the ΔΣ modulator 30 is also called a ΔΣ AD converter. The ΔΣ modulator 30 can reduce quantization errors that occur when converting an analog signal to a digital signal.

[0027] The ΔΣ modulator 30 has a signal passband (second signal passband) at an absorption frequency that is 2f, which is twice the modulation frequency 1f of the laser light. In particular, in this example, the ΔΣ modulator may have a first signal passband and a second signal passband. The first signal passband passes a light intensity amplitude signal component (first signal component) with the modulation frequency 1f. The second signal passband passes an absorption amplitude signal component (second signal component) with a frequency 2f, which is twice the modulation frequency 1f. The internal configuration of the ΔΣ modulator 30 will be described later.

[0028] FIG. 2 schematically illustrates the received light signal, the light intensity amplitude signal component, and the absorption amplitude signal component. The absorption amplitude signal component (2f) has an amplitude that is approximately 1 / 1000 of the light intensity amplitude signal component (1f). Therefore, in FIG. 2, the absorption amplitude signal component (2f) is exaggerated. The received light signal obtained by the light receiving unit 20 includes a light intensity amplitude signal component and an absorption amplitude signal component. The light intensity amplitude signal component is a signal component received by the light receiving unit 20 without being absorbed by the gas to be measured. The light intensity amplitude signal component is a 1f signal (first signal component) having a modulation frequency 1f. The absorption amplitude signal component is a signal component resulting from absorption by the gas to be measured. The absorption amplitude signal component is, for example, a 2f signal (second signal component) having a frequency 2f that is twice the modulation frequency 1f.

[0029] 1, the gas analyzer 1 of this example includes an absorption amplitude calculation unit 40, a gas concentration calculation unit 50, a light intensity amplitude calculation unit 60, a light emission intensity adjustment unit 70, and a timing control unit 80. The absorption amplitude calculation unit 40 calculates the magnitude of the absorption amplitude signal component (2f signal) based on the output of the ΔΣ modulator 30. The magnitude of the absorption amplitude signal component (2f signal) may be the difference between the maximum value and the minimum value of the absorption amplitude signal component.

[0030] The gas concentration calculation unit 50 calculates the concentration of the measurement target gas based on the digital signal output from the ΔΣ modulator 30. Specifically, the gas concentration calculation unit 50 calculates the concentration of the measurement target gas based on the magnitude of the absorption amplitude signal component (second signal component 2f signal) obtained by the absorption amplitude calculation unit 40.

[0031] The light intensity amplitude calculation unit 60 calculates the magnitude of the light intensity amplitude signal component (1f signal) based on the output of the ΔΣ modulator 30. The light emission intensity adjustment unit 70 adjusts the light emission intensity of the laser element 12 based on the digital signal output from the ΔΣ modulator 30. Specifically, the light emission intensity adjustment unit 70 adjusts the light emission intensity of the laser element 12 based on the light intensity amplitude signal component (first signal component 1f signal) obtained by the light intensity amplitude calculation unit 60. The light intensity amplitude signal component (1f signal) includes information about the light emission intensity of the laser element 12 and absorption by miscellaneous gases other than the gas to be measured.

[0032] The transmittance of laser light through the gas to be measured follows the Beer-Lambert law:

[0033] [Number 1] T=exp(-ε c L)

[0034] Here, T is the transmittance of laser light L transmitted through the gas, ε is the molar absorption coefficient, c is the concentration of the gas to be measured, and L is the optical path length. ε depends on the type and wavelength of the gas to be measured, and is uniquely determined once the type and wavelength of the gas to be measured are determined. L is a constant known in advance, and T is an exponential function with c as a variable. Therefore, the concentration of the gas to be measured can be calculated by measuring T.

[0035] However, there are several factors that cause attenuation along the optical path, such as reflection and scattering by various optical systems, scattering and attenuation by dust, and absorption of laser light by miscellaneous gases other than the target gas, making it difficult to measure T directly.

[0036] Therefore, an indirect method may be used. The absorption amplitude signal component (second signal component) V2 is a function with c×L as a variable. This relationship can be expressed, for example, as follows: Q is the light intensity amplitude signal component.

[0037] [Number 2] V2=k·f(c×L, Q)

[0038] This function is stored in advance in the gas concentration calculation unit 50, and the measurement target gas concentration c can be calculated using the optical path length L and the absorption amplitude signal component V2 obtained in an actual measurement. The larger the absorption amplitude signal component V2, the higher the measurement target gas concentration. For example, the magnitude of the absorption amplitude signal component V2 is proportional to the measurement target gas concentration. Note that the light intensity amplitude signal component Q can be treated as a constant when the light intensity amplitude calculation unit 60 and the light emission intensity adjustment unit 70 adjust the laser light emission intensity to a constant value.

[0039] The function of Equation 2 is calculated, for example, as follows: A standard gas of the measurement target gas calibrated to a certain concentration c is circulated through a space having a certain optical path length L (for example, a calibration cell), and the value of the absorption amplitude signal component V2 at a certain light intensity is stored in the gas concentration calculation unit 50. The absorption amplitude signal component V2 obtained as a result for multiple concentrations c and multiple optical path lengths L is then registered in advance as a function table. In an actual measurement using this function table, one optical path length L and one absorption amplitude signal component V2 are input, and the corresponding measurement target gas concentration c is calculated from this function table.

[0040] The timing control unit 80 controls the on period and off period of the laser light, the modulation of the laser light, and the operation timing of the ΔΣ modulator 30. The timing control unit 80 may synchronize the clock signal of the ΔΣ modulator 30 with the modulation of the laser light.

[0041] Fig. 3 is a diagram showing an example of the ΔΣ modulator of Fig. 1. The ΔΣ modulator 30 has a subtraction unit 31, a bandpass filter unit 32, an AD conversion unit 33, and a DA conversion unit 34. The subtraction unit 31 is supplied with a received light signal obtained from the light receiving element 22. In this example, the received light signal is supplied to the subtraction unit 31 from the preamplifier / filter unit 24.

[0042] The band-pass filter unit 32 is a loop filter. The ΔΣ modulator 30 used in this embodiment includes a band-pass filter unit 32 instead of a low-pass filter as a loop filter. In this example, the output of the subtraction unit 31 is supplied to the band-pass filter unit 32. The AD conversion unit 33 converts the analog signal that has passed through the subtraction unit 31 and the band-pass filter unit 32 into a digital signal. The DA conversion unit 34 converts the digital signal obtained by the AD conversion unit 33 into an analog signal and feeds it back to the subtraction unit 31. The subtraction unit 31 calculates the difference between the received light signal and the output of the DA conversion unit 34. The band-pass filter unit 32 is provided between the subtraction unit 31 and the AD conversion unit 33.

[0043] The ΔΣ modulator 30 may include a digital filter unit 35. The digital filter unit 35 is provided subsequent to the AD conversion unit 33. The digital filter unit 35 has a plurality of passbands corresponding to the first signal passband and the second signal passband. However, the digital filter unit 35 may be provided as an external component of the ΔΣ modulator 30, rather than being part of the ΔΣ modulator 30.

[0044] FIG. 4 is a diagram showing an example of frequency characteristics when the band-pass filter unit 32 is a multi-band-pass filter. The band-pass filter unit 32 in this example is a multi-band-pass filter having a plurality of pass bands. As shown in FIG. 4, the transfer function Z of the band-pass filter unit 32 may be such that the gain exhibits maximum values ​​at frequencies 1f and 2f. For example, the transfer function Z of the band-pass filter unit 32 is (-z -N ) / (1+z -N ), and (z -N ) / (1-z -N However, the transfer function Z of the band-pass filter unit 32 is not limited to these.

[0045] In a typical ΔΣ modulator (ΔΣ AD converter), a low-pass filter, which is an integrating circuit, is used as the loop filter arranged immediately after the subtraction unit 31. This is because a typical ΔΣ modulator is a system that places emphasis on removing noise from DC components. Therefore, when a typical ΔΣ modulator (ΔΣ AD converter) is used, the noise shaving effect is reduced in the 2f frequency range, resulting in increased quantization error. On the other hand, in this embodiment, a band-pass filter unit 32 whose gain has a maximum value at least in a range including the 2f frequency is used as the loop filter. Therefore, the noise shaving effect of the ΔΣ modulator 30 is increased even in a range including the 2f frequency range.

[0046] FIG. 5 shows an example of an output signal S1 from the AD conversion unit 33 of the ΔΣ modulator 30. The ΔΣ modulator 30 includes a band-pass filter unit 32 with a passband covering frequencies 1f and 2f, which is provided upstream of the AD conversion unit 33. The output of the AD conversion unit 33 is subjected to DA conversion, and the difference between the output and the input signal is taken upstream of the band-pass filter unit 32. With this configuration, as shown in FIG. 5, the ΔΣ modulator 30 has a first signal passband 37 that passes a first signal component with a modulation frequency of 1f and a second signal passband 38 that passes a second signal component with a frequency of 2f, which is twice the modulation frequency of 1f. Quantization error in the passband of the band-pass filter unit 32 is reduced. Therefore, by using the ΔΣ modulator 30, quantization error can be reduced more effectively than by using a simple band-pass filter.

[0047] According to this example, the delta-sigma modulator 30 has multiple signal passbands, namely, the first signal passband 37 and the second signal passband 38, so there is no need to provide separate filters for the first signal and the second signal. Quantization errors can be reduced not only for the absorption amplitude signal component (second signal component) but also for the light intensity amplitude signal component (first signal component) without providing a separate delta-sigma modulator 30.

[0048] FIG. 6 illustrates an example of an output signal S2 from the digital filter unit 35. The digital filter unit 35 is provided downstream of the AD conversion unit 33 and has multiple passbands 37a and 38a corresponding to the first and second signal passbands 37 and 38. The passbands 37a and 38a may coincide with the first and second signal passbands 37 and 38, or may be wider than the first and second signal passbands 37 and 38. In other words, the digital filter unit 35 may be a multi-bandpass digital filter having multiple signal passbands. By using a digital multi-bandpass digital filter that passes only the necessary frequency bands of 1f and 2f for the output signal S1 from the AD conversion unit 33, it is possible to remove quantization noise superimposed on portions other than the first and second signal passbands 37 and 38, thereby reducing overall noise.

[0049] On the other hand, with the ΔΣ modulator 30, the light intensity amplitude signal component (first signal component) at frequency 1f and the absorption amplitude signal component (second signal component) at frequency 2f are obtained without attenuation. Therefore, the light intensity amplitude signal component (first signal component) and the absorption amplitude signal component (second signal component) at frequency 2f can be measured with high accuracy, making it possible to realize a high-performance laser gas analyzer. In particular, by adjusting the light intensity of the laser element 12 using the light intensity amplitude signal component (first signal component), the influence of unexpected fluctuations in the light intensity of the laser element 12 can be reduced, allowing the gas concentration to be calculated with high accuracy.

[0050] Fig. 7 is a diagram showing another example of frequency characteristics when the bandpass filter unit 32 is a multi-bandpass filter. In Fig. 7, the bandpass filter unit 32 has a signal passband including frequency 2f that is larger than the signal passband including frequency 1f.

[0051] Fig. 8 is a diagram showing another example of the output signal S1 from the AD conversion unit of the ΔΣ modulator. By making the signal pass band including frequency 2f wider than the signal pass band including frequency 1f as shown in Fig. 7 for the band-pass filter unit 32, it is possible to configure a ΔΣ modulator 30 having the characteristics shown in Fig. 8.

[0052] 8, the bandwidth of the second signal pass band 38 is larger than the bandwidth of the first signal pass band 37. This allows accurate calculation of the absorption amplitude signal component (second signal component) without attenuation, even when the frequency distribution of the absorption amplitude signal component (second signal component) broadens due to absorption by the measurement target gas. The center frequency and bandwidth of the second signal pass band 38 may be variable depending on the type of the measurement target gas.

[0053] Figure 9 is a diagram showing another example of the delta-sigma modulator of Figure 1. In Figure 9, a band characteristic changing unit 36 ​​is added to the delta-sigma modulator 30 of Figure 3. Other configurations of the delta-sigma modulator 30 of Figure 9 are similar to those of the delta-sigma modulator 30 of Figure 3, so repeated explanations will be omitted.

[0054] The band characteristics modification unit 36 ​​acquires information about the type of gas to be measured based on input from a user, etc. The band characteristics modification unit 36 ​​pre-stores circuit parameter information for changing the Q value of the bandpass filter unit 32 for each type of gas to be measured. The band characteristics modification unit 36 ​​acquires circuit parameter information according to the type of gas to be measured and changes the band characteristics of the bandpass filter based on the acquired circuit parameter information. Specifically, the band characteristics modification unit 36 ​​changes the center frequency and bandwidth of the second signal passband 38 according to the type of gas to be measured. Note that, along with the change in the center frequency and bandwidth of the second signal passband 38, the center frequency and bandwidth of the passband 38b in the digital filter unit 35 may also be changed.

[0055] 9, the absorption amplitude signal component (second signal component) can be accurately calculated without attenuation depending on the type of gas to be measured, thereby enabling accurate calculation of the gas concentration.

[0056] Fig. 10 is a diagram showing a schematic configuration of a gas analyzer according to a second embodiment of the present invention. The gas analyzer 1 according to the first embodiment shown in Fig. 1 has a light emission intensity adjustment unit 70 that adjusts the amount of light emitted by the laser element 12 based on the light intensity amplitude signal component (first signal component 1f signal) obtained by the light intensity amplitude calculation unit 60. On the other hand, the gas analyzer 1 shown in Fig. 10 has a correction unit 90 instead of the light emission intensity adjustment unit 70. The other configuration is the same as that of the gas analyzer 1 shown in Fig. 1, so repeated explanation will be omitted.

[0057] The correction unit 90 corrects the calculation result of the gas concentration based on the light intensity amplitude signal component (first signal component 1f signal). Specifically, the greater the amount of laser light received by the light receiving element 22, the larger the absorption amplitude signal component (second signal component) V2. Therefore, the correction unit 90 corrects the calculation result of the gas concentration by the gas concentration calculation unit 50 based on the light intensity amplitude signal component (first signal component 1f signal) so as to normalize the magnitude of the laser light.

[0058] As described in the first and second embodiments, in order to process the light intensity amplitude signal component (first signal component 1f signal) and the absorption amplitude signal component (second signal component), the bandpass filter unit 32 and the digital filter unit 35 are preferably multi-bandpass filters. However, the light intensity amplitude signal component (first signal component 1f signal) can also be obtained by calculating the difference between the light reception signals during the laser light on and off periods. In this case, the ΔΣ modulator 30 only needs to calculate the absorption amplitude signal component (second signal component).

[0059] 11 is a diagram showing a schematic configuration of a gas analyzer according to a third embodiment of the present invention. In this example, the light intensity amplitude calculation unit 60, the light intensity adjustment unit 70, and the correction unit 90 shown in FIGS. 1 and 10 are omitted.

[0060] FIG. 12 is a diagram showing an example of frequency characteristics when the bandpass filter unit 32 is a single bandpass filter. FIG. 12 is used as the bandpass filter unit 32 in the ΔΣ modulator 30 of the gas analyzer 1 shown in FIG. 11. As shown in FIG. 12, the bandpass filter unit 32 has a single signal passband that includes frequency 2f. In other words, the bandpass filter unit 32 exhibits a maximum gain at frequency 2f. Except for the fact that the bandpass filter unit 32 is a single bandpass filter, the ΔΣ modulator 30 may be similar to the ΔΣ modulator 30 shown in FIG. 3. Therefore, repeated description will be omitted.

[0061] Fig. 13 is a diagram showing another example of the output signal S2 from the digital filter unit. Fig. 13 shows an example of the output signal S2 of the digital filter unit 35 in the delta-sigma modulator 30 of the gas analyzer 1 shown in Fig. 11. As shown in Fig. 13, even when the delta-sigma modulator 30 does not have the first signal passband 37 but has the second signal passband 38, it is possible to reduce the quantization error in the 2f frequency range compared to when a general delta-sigma modulator that employs a low-pass filter as a loop filter is used.

[0062] Fig. 14 is a diagram showing a schematic configuration of a gas analyzer according to a fourth embodiment of the present invention. Fig. 14 includes a phase synchronization unit 100 for achieving phase synchronization between a power supply 110 and an instrument. The configuration other than the phase synchronization unit 100 may be the same as the configuration of the gas analyzer 1 according to the first to third embodiments. Therefore, repeated explanation will be omitted.

[0063] The phase synchronization unit 100 operates to phase-synchronize at least a portion of the operation timing of the power supply 110, the ΔΣ modulator 30, the modulation of the laser light in the wavelength sweep / modulation current control circuit 14, and the switching of the on period and off period of the laser light in the wavelength sweep / modulation current control circuit 14. The phase synchronization unit 100 itself may be a normal phase synchronization circuit. In particular, the power supply 110 may be a commercial power supply, or may be a power supply for a ship or the like.

[0064] FIG. 15 is a diagram illustrating an example of synchronization of each signal. The range of phase synchronization with the power supply 110 (period T4) may be at least a portion of the clock period (T1) of the ΔΣ modulator 30, the modulation period (T2) of the laser light, and the sweep period (the period for switching between the on and off periods of the laser light) T3 of the laser light. In the example shown in FIG. 15, the operation of the ΔΣ modulator 30, the modulation of the laser light, the switching between the on and off periods of the laser light, and the power supply 110 are all phase-synchronized. That is, T2 may be n1 times (n1 is an integer) the clock period (T1) of the ΔΣ modulator 30, T3 may be n2 times (n2 is an integer) the clock period (T1) of the ΔΣ modulator 30, and T4 may be n3 times (n3 is an integer) the clock period (T1) of the ΔΣ modulator 30.

[0065] The operation of the AD conversion unit 33 (oversampling clock), the operation of the DA conversion unit 34, the system clock of the digital filter unit 35, etc. of the ΔΣ modulator 30 may be phase-synchronized with the power supply 110, the modulation of the laser light in the wavelength sweep / modulation current control circuit 14, and the switching of the on period and off period of the laser light in the wavelength sweep / modulation current control circuit 14. In this example, the ΔΣ modulator 30 operates in phase synchronization with the modulation of the laser light. The ΔΣ modulator 30 operates in phase synchronization with the frequency of the power supply 110.

[0066] In the gas analyzer 1, noise caused by the power supply 110 is likely to occur in the light-receiving signal of the high-impedance light-receiving element 22. In particular, noise is likely to occur due to changes in the phase of the power supply 110. By phase-synchronizing each operation in the gas analyzer 1 with the power supply 110, the rate at which the power supply phase fluctuates to the lag or lead side is equalized. Therefore, by taking a time average, noise caused by the phase fluctuation of the power supply 110 is canceled out, thereby reducing the influence of noise.

[0067] Although the present invention has been described above using the embodiments, the technical scope of the present invention is not limited to the scope described in the above embodiments. It will be apparent to those skilled in the art that various modifications and improvements can be made to the above embodiments. It is clear from the claims that such modifications and improvements can also be included within the technical scope of the present invention. [Explanation of symbols]

[0068] 10...light emitting unit, 12...laser element, 14...wavelength sweep / modulation current control circuit, 16...laser element temperature control circuit, 20...light receiving unit, 22...light receiving element, 24...preamplifier / filter unit, 30...ΔΣ modulator, 31...subtraction unit, 32...bandpass filter unit, 33...AD conversion unit, 34...DA conversion unit, 35...digital filter unit, 36...band characteristic change unit, 37...first signal passband, 38...second signal passband, 40...absorption amplitude calculation unit, 50...gas concentration calculation unit, 60...light intensity amplitude calculation unit, 70...light intensity adjustment unit, 80...timing control unit, 90...correction unit, 100...phase synchronization unit, 110...power supply

Claims

1. A gas analyzer for measuring the concentration of a measurement target gas present in a measurement target space, a laser element that emits laser light modulated at a modulation frequency; a light receiving element that receives the laser light that has passed through the measurement target space; a ΔΣ modulator having a subtraction unit to which a received light signal obtained from the light receiving element is supplied, a band-pass filter unit, an AD conversion unit that converts an analog signal that has passed through the subtraction unit and the band-pass filter unit into a digital signal, and a DA conversion unit that converts the digital signal into an analog signal and feeds it back to the subtraction unit; a gas concentration calculation unit that calculates the concentration of the measurement target gas based on the digital signal output from the ΔΣ modulator, the ΔΣ modulator has a first signal passband that passes a first signal component at the modulation frequency and a second signal passband that passes a second signal component at a frequency twice the modulation frequency; The bandwidth of the second signal passband is greater than the bandwidth of the first signal passband. Gas analyzer.

2. A gas analyzer for measuring the concentration of a target gas present in a target space, comprising: a laser element that emits laser light modulated at a modulation frequency; a light receiving element that receives the laser light that has passed through the measurement target space; a ΔΣ modulator having a subtraction unit to which a received light signal obtained from the light receiving element is supplied, a band-pass filter unit, an AD conversion unit that converts an analog signal that has passed through the subtraction unit and the band-pass filter unit into a digital signal, and a DA conversion unit that converts the digital signal into an analog signal and feeds it back to the subtraction unit; a gas concentration calculation unit that calculates the concentration of the measurement target gas based on the digital signal output from the ΔΣ modulator, the ΔΣ modulator has a first signal passband that passes a first signal component at the modulation frequency and a second signal passband that passes a second signal component at a frequency twice the modulation frequency; a digital filter unit provided downstream of the AD conversion unit and having a plurality of passbands corresponding to the first signal passband and the second signal passband; The digital filter unit does not include a DC component in the plurality of passbands. Gas analyzer.

3. The digital filter unit has, as the plurality of passbands, only a passband corresponding to the first signal passband and a passband corresponding to the second signal passband.

3. The gas analyzer of claim 2.

4. the gas concentration calculation unit calculates the concentration of the measurement target gas based on the magnitude of the second signal component. A gas analyzer according to any one of claims 1 to 3.

5. The measuring device further includes a correction unit that corrects a calculation result of the concentration of the measurement target gas based on the first signal component.

5. The gas analyzer of claim 4.

6. further comprising a light emission amount adjustment unit that adjusts the amount of light emitted by the laser element based on the first signal component.

5. A gas analyzer according to any one of claims 1 to 4.

7. 4. The gas analyzer according to claim 1, wherein a center frequency and a bandwidth of the second signal pass band are variable depending on the type of gas to be measured.

8. the ΔΣ modulator operates in phase synchronization with modulation of the laser light; A gas analyzer according to any one of claims 1 to 7.

9. The ΔΣ modulator operates in phase synchronization with the frequency of a power supply.

9. A gas analyzer according to any one of claims 1 to 8.

10. The output of the subtraction unit is supplied to the band-pass filter unit.

10. A gas analyzer according to any one of claims 1 to 9.

11. The bandpass filter section has a maximum gain in a region including at least a frequency twice the modulation frequency.

11. A gas analyzer according to any one of claims 1 to 10.

12. The subtraction unit calculates a difference between the light receiving signal and the output of the DA conversion unit.

12. A gas analyzer according to any one of claims 1 to 11.

13. The bandpass filter section has a maximum gain at a frequency that is one time the modulation frequency and a frequency that is twice the modulation frequency.

11. A gas analyzer according to any one of claims 1 to 10.

Images