JP2018013433A - Signal processing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a signal processing device that can effectively remove optical interference noise from a laser reception optical signal without providing an adjustment mechanism, implement a laser gas analyzer with a simple configuration, and cut down cost.SOLUTION: A signal processing device (70) is used in a laser gas analyzer (1) that converts laser light that has passed through a measurement space into laser reception optical signal (S), and extracts a signal component that has gone through light absorption by measurement object gas from the laser reception optical signal. The signal processing device includes a non-linear filter (73) to which a threshold value (ε) corresponding to optical interference noise that has occurred in an optical system the laser light has passed through is set.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a signal processing device used in a laser gas analyzer.

  2. Description of the Related Art Laser type gas analyzers that measure the presence or concentration of a measurement target gas existing in a measurement space using laser light are known. In the laser gas analyzer, a laser light source having the same emission wavelength band as the light absorption spectrum of the measurement target gas is used (see, for example, Patent Document 1). The measurement target gas is irradiated with laser light emitted from a laser light source, and the gas concentration is measured using absorption of the laser light by the measurement target gas.

  FIG. 9 is a schematic configuration diagram of a laser type gas analyzer described in Patent Document 1. In FIG. The laser gas analyzer 20 includes a light emitting unit 10 that emits laser light toward a measurement target space 30 in which a measurement target gas exists, a light receiving unit 20 that receives laser light that has passed through the measurement target space 30, and a light reception signal. And a signal processing unit 23 that extracts the amount of laser light absorbed by the measurement target gas and obtains the measurement target gas concentration by various arithmetic processes. The light emitting unit 10 includes a light source unit 11 on which a laser element is mounted, and a collimator lens 12 that converts laser light emitted from the light source unit 11 into a parallel beam. The light receiving unit 20 includes a condensing lens 21 that condenses the laser light that has passed through the measurement target gas, and a light detection unit 22 that detects the laser light collected by the condensing lens 21.

  The laser light is preferably completely transmitted through optical components such as the collimating lens 12 and the condenser lens 21 on the optical path, but may be slightly reflected by the optical components. For this reason, optical interference that causes multiple reflections between optical components is caused, and noise due to optical interference (hereinafter referred to as optical interference noise) is superimposed on the laser light reception signal of the light detection unit 22 to measure the measurement target gas concentration. There is a problem that an error occurs. In general, in order to prevent optical interference, a measure is taken to install the light source unit 11 and the optical component at a slight angle. Moreover, the influence of optical interference noise is reduced by preliminarily sealing the measurement target gas in the light emitting unit casing 17 and the light receiving unit casing 27 as a bias value of the measurement target gas concentration.

JP 2010-32422 A

  However, when the light source unit 11 and the optical component are installed at an angle, there is a problem that an angle adjustment mechanism is required and the apparatus configuration is complicated. In addition, when the dimensions of the adjusting mechanism change due to a change in ambient temperature, there is a problem that angle adjustment is not performed accurately and optical interference cannot be prevented. In addition, the method described in Patent Document 1 requires a mechanism for keeping the measurement target gas confidential in the light emitting unit housing 17 and the light receiving unit housing 27, which increases the cost.

  The present invention has been made in view of such problems, and an object of the present invention is to effectively remove optical interference noise from a laser light reception signal without providing an adjustment mechanism, and to simplify a laser gas analyzer. It is an object of the present invention to provide a signal processing device that can be realized with a simple configuration and can reduce costs.

  The signal processing apparatus of the present invention converts a laser beam that has passed through a measurement space into a laser light reception signal, and extracts a signal component that has received light absorption by the measurement target gas from the laser light reception signal. The apparatus is characterized by comprising a non-linear filter in which a threshold value corresponding to optical interference noise generated in the optical system through which the laser beam is transmitted is set.

  With this configuration, since the optical interference noise can be effectively removed using the threshold value determined from the optical interference noise by the nonlinear filter, the signal component in the light absorption wavelength region by the measurement target gas can be appropriately extracted. Can do.

  According to the present invention, there is provided a signal processing apparatus that can effectively remove optical interference noise from a laser light reception signal without providing an adjustment mechanism, can realize a laser gas analyzer with a simple configuration, and can reduce costs. Can be provided.

It is a functional block diagram which shows the signal processing process of the signal processing apparatus which concerns on 1st Embodiment. It is a block diagram which shows the structure of the nonlinear filter which concerns on 1st Embodiment. It is a block diagram which shows the structure of the light emission part and laser drive control circuit in 1st Embodiment. It is a figure which shows a response | compatibility with the scanning waveform of the laser beam in 1st Embodiment, and the absorption waveform of measurement object gas. The nonlinear function used by the noise analysis part in 1st Embodiment is shown. It is a figure which shows the signal waveform of the laser received light signal in the signal processing process of 1st Embodiment. It is a functional block diagram which shows the signal processing process of the signal processing apparatus which concerns on 2nd Embodiment. It is a figure for demonstrating the specific example of the signal processing process which concerns on 2nd Embodiment. It is a schematic block diagram of a laser type gas analyzer.

  Hereinafter, the signal processing apparatus of the laser type gas analyzer according to the first embodiment of the present invention will be described in detail. In the following description, the same components are denoted by the same reference symbols in all the drawings, and the description thereof is omitted as appropriate.

  FIG. 1 is a functional block diagram showing a signal processing process of the signal processing apparatus according to the first embodiment. The signal processing apparatus according to the present embodiment performs signal processing that takes in a laser light reception signal from the optical measurement unit of the laser gas analyzer 1 and extracts a signal component that has received light absorption by the measurement target gas. In the optical measurement unit of the laser gas analyzer 1, the laser beam emitted from the light emitting unit 40 passes through the measurement target gas and is received by the light receiving unit 50, and is output from the light receiving unit 50 as a current corresponding to the amount of received light. The The output current of the light receiving unit 50 is converted into a voltage signal by the IV converter 60 and taken into the signal processing device 70 as the laser light reception signal S. The signal processing device 70 according to the present embodiment includes a high pass filter (HPF) 71, an averaging filter 72, and a non-linear filter 73. These filters 71, 72, 73 cause various noises. After the removal, the measurement target gas concentration is calculated based on the signal component that has received light absorption by the measurement target gas. FIG. 2 shows a configuration example of the nonlinear filter 73. The nonlinear filter 73 includes a noise analysis unit 74, a threshold processing unit 75, and a noise removal unit 76.

  FIG. 3 is a block diagram showing the configuration of the light emitting unit and the laser drive control circuit in the optical measurement unit of the laser gas analyzer. The light emitting unit 40 includes the light source unit 40a on which the laser element 41 is mounted as described above. The light source unit 40a converts the laser drive signal generated by the laser element 41, the laser drive signal generation unit 42 that generates a laser drive signal for driving the laser element 41, and the laser drive signal generation unit 42 into a current. And a current control unit 43 that supplies the laser element 41. The laser drive signal generation unit 42 and the current control unit 43 constitute a laser drive control circuit.

  The laser drive signal generation unit 42 includes a wavelength scanning drive signal generation unit 42a, a high frequency modulation signal generation unit 42b, and a synthesis unit 42c. The wavelength scanning drive signal generator 42a scans the emission wavelength of the laser element 41 so as to cross the absorption wavelength of the measurement target gas. The high frequency modulation signal generation unit 42b frequency-modulates the wavelength with a sine wave in order to detect the absorption wavelength of the measurement target gas (see FIG. 4). A laser drive signal is generated by combining the output signals of the wavelength scanning drive signal generator 42a and the high frequency modulation signal generator 42b by a combiner 42c. The laser drive signal output from the laser drive signal generator 42 is converted into a current by the current controller 43 and supplied to the laser element 41.

  A thermistor 44 as a temperature detection element is disposed in the vicinity of the laser element 41, and a Peltier element 45 is disposed in the proximity of the thermistor 44. The Peltier element 45 is controlled by the temperature control unit 46 so that the resistance value of the thermistor 44 becomes a constant value, whereby the temperature of the laser element 41 is stabilized.

  Scanning in the laser light wavelength region will be described with reference to FIG. FIG. 4 is a diagram showing the correspondence between the scanning waveform of the laser beam and the absorption waveform of the measurement target gas. The wavelength scanning drive signal I1 (see FIG. 3) output from the wavelength scanning drive signal generation unit 42a is a substantially trapezoidal signal that is repeated at a constant period. The wavelength scanning drive signal I1 includes a portion i1 where the signal value is maintained at a constant value larger than zero, a portion i2 where the signal value increases linearly from a state higher than the i1 portion, and a portion where the signal value becomes zero. i3. The portion i1 of the wavelength scanning drive signal I1 is an offset portion that does not scan the absorption wavelength but causes the laser element 41 to emit light, and is equal to or higher than the threshold current of the laser element 41 in order to stabilize the light emission of the laser element 41. Set to a value. The portion i2 of the wavelength scanning drive signal I1 is a portion for gradually shifting the emission wavelength of the laser element 41 by linearly changing the magnitude of the current supplied to the laser element 41.

The wavelength scanning drive signal I1 from the wavelength scanning drive signal generation unit 42a and the high frequency modulation signal I2 from the high frequency modulation signal generation unit 42b are combined by the combining unit 42c, and the laser element 41 is driven according to the laser drive signal. . As a result, a laser beam that is scanned across the absorption wavelength band of the measurement target gas is emitted from the laser element 41 as shown in FIG. In FIG. 4, for example, the frequency of the high frequency modulation signal I2 is 50 kHz, the frequency of the wavelength scanning drive signal I1 is 0.2 kHz, λ ₁ is the wavelength corresponding to the offset, and λ ₂ and λ ₃ are the absorption wavelengths of the measurement target gas. The upper and lower limit values of the corresponding scanning range are shown.

  Next, the light receiving unit 50 will be described (see FIG. 1). A laser light reception signal S detected by a light detection unit (not shown) including a light receiving element in the light receiving unit 50 is converted into a current signal. The current signal is converted into a voltage signal by the IV converter 60 and input to the signal processing device 70.

  Next, the signal processing device 70 will be described. The laser light reception signal S is input to the averaging filter 72 via the high-pass filter 71 (see FIG. 1). The high-pass filter 71 removes an offset portion in the laser light reception signal S. In addition, a direct current component and a low frequency swell component (1 / f noise) can be removed. The averaging filter 72 receives the output of the high-pass filter 71 and reduces random noise. The laser light reception signal S from which the DC component, random noise, and the like have been removed by the high-pass filter 71 and the averaging filter 72 is input to the nonlinear filter 73.

  The non-linear filter 73 analyzes the amplitude of the optical interference noise superimposed on the laser light reception signal S in the noise analysis unit 74 (see FIG. 2). In addition to the optical interference noise, various noises may be superimposed on the laser light reception signal S. Here, the optical interference noise and noise having an amplitude similar to the optical interference noise are collectively referred to as small amplitude noise N. The noise analyzing unit 74 outputs the wavelength scanning drive signal i1 from the wavelength scanning drive signal generating unit 42a (see FIG. 4), that is, the timing before the signal waveform of the measurement target gas is generated (the signal of the measurement target gas is The amplitude of the small amplitude noise N is detected in the non-existing section b (see FIG. 6)). The threshold processing unit 75 sets the threshold ε based on the amplitude of the small amplitude noise N detected by the noise analysis unit 74. The noise removing unit 76 uses the threshold ε set by the threshold processing unit 75 to make the small amplitude noise N equal to or less than the threshold ε. Thereby, the small amplitude noise N can be removed from the laser light reception signal S.

  As the noise removal unit 76, for example, an ε-filter can be used. The ε-filter can effectively remove the small-amplitude noise N superimposed on the signal with a relatively large change without impairing the steepness of the signal. The input / output expression of the ε-filter is as shown in Expression (1), where x (n) is the input signal of the laser light reception signal S on which the small amplitude noise N is superimposed and y (n) is the output signal of the ε-filter. Can show.

は、非巡回型デジタルフィルタ（ＦＩＲ）である。ａ_ｉは非巡回型デジタルフィルタのフィルタ係数であり、フィルタ係数の直流ゲインを１とするために、その総和は式（３）のように示される。

Is a non-recursive digital filter (FIR). a _i is a filter coefficient of the acyclic digital filter, and in order to set the DC gain of the filter coefficient to 1, the sum is expressed as shown in Expression (3).

  F (x) is a non-linear function that limits the absolute value to ε, and is expressed as in Equation (4).

  FIG. 5 shows the nonlinear function F (x) used. FIG. 5 shows a non-linear function used in the noise analysis unit 74. As described above, the ε-filter can be derived by making the acyclic digital filter non-linear, and the laser light receiving signal is suppressed while keeping the difference between the input signal x (n) and the output signal y (n) below the threshold ε. The waveform of S can be smoothed. The ε-filter can remove small amplitude noise N that cannot be removed by a linear filter such as an analog circuit filter. Note that the ε-filter is an acyclic digital filter, and its phase characteristic does not change with frequency. In other words, since a constant phase (phase linearity) is guaranteed, even when a steep frequency characteristic is given, there is a feature that the waveform of the filter output waveform used in a general linear filter does not occur.

  The output signal of the noise removing unit 76 of the nonlinear filter 73 is sent to the gas concentration calculating unit 77 (see FIG. 1). The gas concentration calculator 77 calculates the measurement target gas concentration. The noise analysis unit 74 of the nonlinear filter 73 can easily detect the amplitude of the small amplitude noise N by detecting the noise at the timing before the signal waveform of the measurement target gas is generated. Using the threshold value ε determined from the amplitude of the small amplitude noise N in the threshold value processing unit 75, the noise removing unit 76 suppresses the small amplitude noise N to be equal to or less than the threshold value ε, thereby superimposing the small amplitude noise N superimposed on the laser light reception signal S. Can be effectively removed. Therefore, the gas concentration calculation unit 77 can calculate the measurement target gas concentration with high accuracy from the signal waveform of the measurement target gas from which the small amplitude noise N is removed.

  Further, since the small amplitude noise N can be removed from the laser light reception signal S using the non-linear filter 73, laser light generated in the optical system (between optical components) of the laser gas analyzer 1 in which the signal processing device 70 is used. It is not necessary to install a mechanism for preventing the reflection of light. Thereby, the structure of the laser type gas analyzer 1 can be simplified and cost reduction can be achieved.

  When impulsive noise (switching power supply noise or the like) larger than the laser light reception signal S is superimposed on the laser light reception signal S, median processing is performed after the nonlinear filter 73 or the gas concentration calculation unit 77. Median filters can be added.

Next, a specific example of the signal processing process in the first embodiment will be described.
FIG. 6 is a diagram illustrating a signal waveform of the laser light reception signal in the signal processing process of the first embodiment. 6A to 6C, the horizontal axis indicates the wavelength of the laser beam, and the vertical axis indicates the amplitude of the laser light reception signal S. The section a is the absorption wavelength band of the measurement target gas (corresponding to the portion i2 of the wavelength scan drive signal I1 output from the wavelength scan drive signal generation unit 42a (see FIG. 4)), and the signal waveform of the measurement target gas. It is shown. The section b is a wavelength band that is out of the absorption wavelength band of the measurement target gas (corresponding to the portion i1 (offset portion) of the wavelength scanning drive signal I1 output from the wavelength scanning driving signal generation unit 42a).

  As described above, the laser element 41 of the light receiving unit 50 is a laser beam frequency-modulated so as not to include the absorption wavelength band of the measurement target gas (the portion of the wavelength scanning drive signal I1 output from the wavelength scanning drive signal generation unit 42a). Corresponding to i1 (see FIGS. 3 and 4)) and a laser beam that is frequency-modulated so as to include the absorption wavelength band of the gas to be measured (the portion of the wavelength scanning drive signal I1 output from the wavelength scanning drive signal generator 42a) (corresponding to i2). The laser light reception signal S includes an offset portion (a portion i1 of the wavelength scanning drive signal I1), a small amplitude noise N due to multiple reflections between the optical components such as a collimating lens (see FIG. 1) and a condenser lens, a direct current component, and a low level. Frequency 1 / f noise, random noise, etc. are superimposed.

  In the high-pass filter 71 of the signal processing device 70, the offset portion, the direct current component, and the low frequency 1 / f noise in the laser light reception signal S are removed. FIG. 6A shows the waveform of the laser light reception signal S that has passed through the high-pass filter 71.

  The signal waveform in the absorption wavelength range of the measurement target gas is shown in the section a. The measurement target gas absorbs the laser beam in the wavelength range, and the output is reduced. The waveform corresponding to the offset portion of the laser light reception signal S appearing in the section b, the direct current component superimposed on the laser light reception signal S and 1 / f noise are removed, but the waveform of the laser light reception signal S has small amplitude noise N and Random noise remains superimposed. For this reason, it is difficult to directly extract the signal waveform of the measurement target gas from the section b. It is also difficult to detect only the small amplitude noise N.

  FIG. 6B shows the waveform of the laser light reception signal S that has passed through the averaging filter 72. Although it can be seen that the random noise appearing in the section a and the section b is greatly reduced by the averaging filter 72, the small amplitude noise N is still superimposed on the laser light reception signal S. In addition, since the section b is a place where the signal waveform of the measurement target gas is not originally generated, it can be seen that the waveform in the section b is one in which the small amplitude noise N remains. At this time, the amplitude of the small amplitude noise N can be easily detected in the section b.

  The noise analysis unit 74 of the non-linear filter 73 detects the amplitude of the small amplitude noise N at the interval b, that is, the timing before the signal waveform of the measurement target gas is generated. The threshold processing unit 75 sets the amplitude value of the small amplitude noise N detected by the noise analyzing unit 74 as the ε-filter threshold ε in the noise removing unit 76. The noise removing unit 76 uses the threshold ε set by the threshold processing unit 75 to make the small amplitude noise N equal to or less than the threshold ε. Since the switching of the laser light wavelength range corresponding to the section a and the section b is performed by the laser drive control circuit (see FIG. 3), the timing of the section b can be easily confirmed. Therefore, since the noise analysis unit 74 can detect the small amplitude noise N shown in the section b of FIG. 6B, it can stably detect the amplitude of the small amplitude noise N. Note that the noise analysis unit 74 can also detect the amplitude of the small amplitude noise N at a later timing when the signal waveform of the measurement target gas is generated.

  FIG. 6C shows the waveform of the laser light reception signal S that has passed through the nonlinear filter 73. In FIG. 6B, it can be seen that the small amplitude noise N remaining in the laser light reception signal S is removed. Thus, by using the nonlinear filter 73, the signal waveform of the measurement target gas can be appropriately extracted in the section b.

  The output signal of the noise removal unit 76 of the nonlinear filter 73 is input to the gas concentration calculation unit 77. The gas concentration calculation unit 77 can calculate the measurement target gas concentration with high accuracy from the signal waveform of the measurement target gas from which the small amplitude noise N in the section b is removed.

  In the noise analysis unit 74, the waveform of the laser light reception signal S shown in FIG. 6B is captured by the A / D converter, and the signal waveform of the measurement target gas is generated from the switching result of the section a and the section b by the laser drive control circuit. By checking the timing, it is possible to detect the amplitude of the small amplitude noise N from the interval b. It is also possible to detect the amplitude of the small amplitude noise N by short-time fast Fourier transform or wavelet analysis. In this case, since the time domain and the frequency domain of the laser light reception signal S can be analyzed simultaneously, the timing before the signal waveform of the measurement target gas is generated and the amplitude value of the small amplitude noise N can be obtained.

  Further, in the threshold processing unit 75, for example, by updating the threshold ε for each frequency of the wavelength scanning drive signal I1, a small change in response to a change in the optical system due to a change in the ambient temperature, that is, a change in the small amplitude noise N is small. The amplitude noise N can be removed. When the ambient temperature change is constant, the output of the averaging filter 72 may be directly input to the noise removing unit 76 without going through the noise analyzing unit 74 and the threshold processing unit 75. Thereby, the processing speed in the nonlinear filter 73 can be increased.

  According to the signal processing device 70 according to the first embodiment, by detecting the optical interference noise at the timing before the signal waveform of the measurement target gas is generated, the small amplitude noise outside the light absorption wavelength range of the measurement target gas. Since N can be detected, the amplitude ε of the small amplitude noise N can be easily detected. Since the small amplitude noise N can be effectively removed using the threshold value ε determined from the amplitude of the small amplitude noise N by the nonlinear filter 73, the signal waveform of the measurement target gas can be appropriately extracted. Further, by removing the small amplitude noise N using the non-linear filter 73, a mechanism for preventing the reflection of the laser light that occurs between the optical components is installed in the laser gas analyzer 1 in which the signal processing device 70 is used. There is no need. Thereby, the structure of the laser type gas analyzer 1 can be simplified and cost reduction can be achieved.

  Next, a signal processing apparatus according to the second embodiment will be described. In the second embodiment, a low-frequency component and a high-frequency component of the laser light reception signal S are separated by a band-pass filter (BPF: Band Pass Filter) and processed by the nonlinear filter 73. The difference from the first embodiment will be mainly described. Here, the high frequency component refers to the high frequency component of the laser light reception signal S, and the low frequency component refers to the low frequency component of the laser light reception signal S. .

  FIG. 7 is a functional block diagram illustrating a signal processing process of the signal processing device according to the second embodiment. A plurality of BPFs 81a to 81n are connected in parallel to the output end of the averaging filter 72, and a plurality of nonlinear filters 73a to 73n are connected to the output ends of the BPFs 81a to 81n. Further, compensators (delays) 82a to 82n are connected to the subsequent stages of the nonlinear filters 73a to 73n, respectively, and outputs from the compensators 82a to 82n are input to the waveform synthesis unit 83. The stage before the averaging filter 72 is as shown in FIG. For example, when the basic component of the laser light reception signal S is composed of a low frequency and a high frequency, the frequency components contained in the laser light reception signal S can be separated into a low frequency component and a high frequency component by the BPFs 81a to 81n. For this reason, the constant of the acyclic digital filter that is the basis of the threshold value ε or the ε-filter of the noise removing unit 76 can be set corresponding to the frequency components input to the nonlinear filters 73a to 73n.

  For example, when a low frequency is extracted from the frequency components included in the laser light reception signal S by the BPF 81a and is input to the nonlinear filter 73a, the constant of the acyclic digital filter of the nonlinear filter 73a is set so as to pass the low frequency component. Set. Then, a threshold value ε is set from the amplitude value corresponding to the small amplitude noise N level superimposed on the waveform of the low frequency component. Thereby, the small amplitude noise N can be effectively removed from the waveform of the laser light reception signal S while maintaining the waveform of the low frequency component of the laser light reception signal S. Similarly, when a high frequency is extracted from the frequency components included in the laser light reception signal S by the BPF 81b, the constant of the acyclic digital filter of the non-linear filter 73b is set so as to pass the high frequency component. A threshold ε is set from the amplitude value of the small amplitude noise N to be superimposed, and the small amplitude noise N is removed.

  The compensators 82a to 82n are set so that the delay times due to the filter processing are equalized by inputting the outputs of the nonlinear filters 73a to 73n to the compensators 82a to 82n. That is, the calculation processing time of the low frequency component of the laser light reception signal S input to the BPF 81a and the nonlinear filter a is equal to the calculation processing time of the high frequency component of the laser reception signal S input to the BPF 81b and the nonlinear filter b. So that the time compensation is delayed. The waveform synthesizer 83 synthesizes the outputs of the compensators 82a to 82n, re-synthesizes the laser light reception signal S separated into the low frequency component and the high frequency component as a waveform by addition, and reproduces the laser light reception signal S. By making the low frequency component calculation processing time and the high frequency component calculation processing time of the laser light reception signal S equal by the compensators 82a to 82n, the waveform synthesis unit 83 re-synthesizes the signal waveform of each component with high accuracy. be able to.

A specific example of the signal processing process in the second embodiment will be described with reference to FIG.
In FIG. 8, the horizontal axis indicates the wavelength of the laser light reception signal, and the vertical axis indicates the amplitude of the laser light reception signal. FIG. 8A shows a signal waveform of the laser light reception signal S that has passed through the averaging filter 72. The laser light reception signal S is composed of two components, a low frequency component L and a high frequency component H, and a state in which a small amplitude noise N is superimposed on the laser light reception signal S is shown.

  The output signal of the averaging filter 72 is input to the BPFs 81a to 81n, and the frequency component is separated into the low frequency component L and the high frequency component N. The separated laser light reception signals are input to the non-linear filters 73a to 73n, respectively, and the small amplitude noise N is removed (see FIG. 7). The laser light reception signal S is input to the BPF 81a that passes through the low frequency component L, the low frequency component L is separated, and input to the nonlinear filter 73a in which the acyclic digital filter constant corresponding to the low frequency component L and the threshold value ε are set. Thus, the small amplitude noise N is removed. Further, the laser light reception signal S is input to the BPF 81b that passes the high frequency component H, the high frequency component H is separated, and is input to the nonlinear filter 73b in which the acyclic digital filter constant corresponding to the high frequency component H and the threshold ε are set. Thus, the small amplitude noise N is removed.

  FIG. 8B shows the waveform of the laser light reception signal S that has passed through the BPF 81a that separates the low-frequency component L. FIG. FIG. 8C shows the waveform of the laser light reception signal S that has passed through the nonlinear filter 73a in which the acyclic digital filter constant corresponding to the low frequency component L and the threshold value ε are set. In FIG. 8B before the laser light reception signal S passes through the nonlinear filter 73a, the small amplitude noise N is superimposed on the waveform of the low frequency component L. In FIG. 8C after passing through the non-linear filter 73a, the small amplitude noise N is removed while the shape of the waveform of the low frequency component L is maintained. By setting the threshold value ε from the amplitude value in accordance with the small amplitude noise N level superimposed on the waveform of the low frequency component L, the low frequency component is effectively maintained while maintaining the waveform of the low frequency component L of the laser light reception signal S. It can be seen that the small amplitude noise N can be removed from the waveform.

  FIG. 8D shows the waveform of the laser light reception signal S that has passed through the BPF 81b that separates the high-frequency component H. FIG. 8E shows the waveform of the laser light reception signal S that has passed through the non-circular digital filter constant corresponding to the high frequency component H and the nonlinear filter 73b in which the threshold value ε is set. In FIG. 8B before the laser light reception signal S passes through the nonlinear filter 73a, the small amplitude noise N is superimposed on the waveform of the high frequency component H. In FIG. 8C after passing through the non-linear filter 73a, the small amplitude noise N is removed while the shape of the waveform of the high frequency component H is maintained. By setting the threshold value ε from the amplitude value in accordance with the small amplitude noise N level superimposed on the waveform of the high frequency component H, the waveform of the high frequency component H is effectively maintained while maintaining the waveform of the high frequency component H of the laser light reception signal S. It can be seen that the small amplitude noise N can be removed.

  The output signals of the nonlinear filters 73a to 73n are input to the compensators 82a to 82n so that the low frequency component L calculation processing time and the high frequency component H calculation processing time of the laser light reception signal S are equalized. The output signals of the compensators 82a to 82n are input to the wavelength synthesizer 83, and the low frequency component L and the high frequency component H are recombined to reproduce the laser light reception signal S. FIG. 8F shows the waveform of the laser light reception signal S recombined by the wavelength combining unit 83. It can be seen that the waveform of the low frequency component L and the waveform of the high frequency component H are recombined to reproduce the laser light reception signal S from which the small amplitude noise N is removed. As described above, even when the laser light reception signal S composed of a plurality of frequency components is re-synthesized, the small amplitude noise N is effectively reduced from the waveform of the laser light reception signal S while maintaining the waveform of the laser light reception signal S. It can be seen that it can be removed. Further, even if a plurality of nonlinear filters 73a to 73n are used, no signal distortion is caused. Thereby, since the signal waveform of the measurement target gas can be appropriately extracted, the gas concentration calculation unit 77 can calculate the measurement target gas concentration with high accuracy.

  According to the signal processing device 70 according to the second embodiment, since the threshold ε corresponding to the frequency component included in the laser light reception signal S can be set in the nonlinear filters 73a to 73n, the waveform of the frequency component The small amplitude noise N can be effectively removed from the waveform of the laser light reception signal S while maintaining the above. Since the laser light reception signal S from which the small amplitude noise N has been removed is reproduced when the waveform of each frequency component is recombined, the signal waveform of the measurement target gas can be appropriately extracted.

  The present invention is not limited to the embodiment described above, and can be implemented with various modifications.

1 Laser Gas Analyzer 70 Signal Processing Device 73 Nonlinear Filter N Small Amplitude Noise S Laser Light Received Signal ε Threshold

Claims (4)

It is a signal processing device in a laser gas analyzer that converts laser light transmitted through a measurement space into a laser light reception signal and extracts a signal component that has received light absorption by the measurement target gas from the laser light reception signal.
A signal processing apparatus comprising: a nonlinear filter in which a threshold value corresponding to optical interference noise generated in an optical system through which the laser beam is transmitted is set.   The non-linear filter sets a noise analysis unit that detects the optical interference noise from the laser light reception signal outside the light absorption wavelength range of the measurement target gas, and a threshold corresponding to the optical interference noise detected by the noise analysis unit. A threshold processing unit, and a noise removing unit that removes small amplitude noise corresponding to optical interference noise superimposed on a signal component that has received light absorption from the laser light reception signal, based on a threshold corresponding to the optical interference noise. The signal processing apparatus according to claim 1. The non-linear filter has a first non-linear filter corresponding to a low frequency component and a second non-linear filter corresponding to a high frequency component,
A first band-pass filter that extracts a low-frequency component from a signal component that has received light absorption by the measurement target gas, and a high-frequency component from the same signal component branched from the signal component that is input to the first band-pass filter A second bandpass filter that extracts the first non-linear filter that removes small amplitude noise corresponding to optical interference noise superimposed on a low-frequency signal output from the first bandpass filter; A waveform for combining the second nonlinear filter for removing small amplitude noise corresponding to the optical interference noise superimposed on the high-frequency signal output from the second band-pass filter and the outputs of the first and second nonlinear filters. The signal processing apparatus according to claim 1, further comprising a combining unit. The laser gas analyzer includes a laser drive control circuit that changes a wavelength range of the laser light so as to cross a light absorption wavelength range of the measurement target gas,
2. The noise analysis unit detects the optical interference noise from the laser light reception signal at a timing before or after the wavelength range of the laser beam crosses the light absorption wavelength range of the measurement target gas. The signal processing device according to claim 3.

Images