JPH059732B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention employs a unique method that has not been seen before, called a multi-fluid modulation method (this is the name given by the inventors). This is a completely new technology that allows two (or split into two systems) sample fluids to be analyzed simultaneously, continuously, and with great precision using only one detector. This was done to provide a fluid analysis device.

[Conventional technology]

For example, when analyzing the concentration (and thus the amount) of harmful components (such as NO _x , H _y C _z , or CO _x ) contained in the atmosphere, which is an example of a sample fluid, such as automobile exhaust gas or factory exhaust gas. Conventionally, the fluid analysis devices used in this case are those equipped with a chemical luminescence detector (CLD), a flame ion detector (FID), or a condenser microphone. Alternatively, various types of detectors (sensors) such as pneumatic detectors using a microflow method or non-dispersive infrared analyzers (NDIR) equipped with thermopiles or solid state detectors such as semiconductors, etc.
A fluid analysis device that employs the following is used.

By the way, when performing the above-mentioned fluid analysis, it is necessary to analyze various substances in the sample fluid, such as NO and NO ₂ , methane (CH ₄ ) and HC other than methane (NMHC), or CO and CO ₂ . It is often necessary to measure the concentration of two components simultaneously and continuously, but in order to achieve this with conventional fluid analyzers, two detectors (sensors) are required. It was hot.

In other words, when simultaneously and continuously measuring NO and NO ₂ , the sample fluid is divided into two measurement systems, and one system is equipped with a first NO detector to independently measure the NO concentration in the sample gas. and the other system is equipped with a second NO detector to measure the total NO concentration in the processing fluid generated by converting NO ₂ in the sample gas to NO. (The NO ₂ concentration is obtained as the difference between the total NO concentration detected by the second NO detector and the NO single concentration detected by the first NO detector, and this method is called the difference method.) In addition, when simultaneously and continuously measuring methane and HC other than methane (NMHC), the sample fluid is divided into two measurement systems, and one system measures the total HC concentration (THC) in the sample fluid. A first HC detector is installed to detect methane in the sample fluid, and the other system is equipped with a first HC detector to detect
A second HC detector is installed to measure the methane concentration in the treated gas generated by catalytic combustion of HC to remove it.
A detector is required (again, the differential method is used, and NMHC is obtained as the difference between the THC concentration detected by the 1st HC detector and the methane concentration detected by the 2nd HC detector), and the sample in fluid
When measuring CO and CO ₂ simultaneously and continuously, the sample fluid is divided into two measurement systems, and one system is
Two different detectors, a CO detector and a CO ₂ detector, are required: one system has a CO detector and the other system has a CO ₂ detector.

By dividing the same sample fluid into two systems as described above, it is possible to analyze not only the simultaneous and continuous analysis of two components in the sample fluid but also the components contained in each of the two different sample fluids. It is clear that two detectors (sensors) are similarly required when simultaneously and continuously analyzing a specific component.

However, as mentioned above, simultaneous and sequential analysis of two components in the same sample fluid, or
When performing simultaneous and continuous analysis of specific components contained in two different sample fluids,
The need to use two detectors as in the conventional device has the following problems: (a) The analyzer becomes larger and the manufacturing cost increases, as well as (b) Since adjustments such as zero and span adjustments are required, measurement requires a lot of effort and is very troublesome. (c) Each detector is not adjusted sufficiently, and there may be zero adjustment errors or sensitivity between the two detectors. If a difference exists, it causes various problems such as very large measurement errors.

Therefore, in order to avoid such problems, two components in the same sample fluid can be measured alternately using an analyzer equipped with only one detector, or alternatively, two components in the same sample fluid can be measured alternately. It is also possible to use a so-called batch analysis method in which measurements are taken at different times, but in that case, there is a disadvantage that the measurement data becomes discontinuous because simultaneous and continuous measurements cannot be performed. When performing analysis using the difference method, there is a risk of significant deterioration in measurement accuracy. Therefore, adopting such a batch analysis method simply to save the number of detectors may greatly sacrifice the original purpose of fluid analysis, and is not a good idea. .

Therefore, in view of the conventional situation, the present inventors, as a result of intensive research, have adopted an innovative method called a multi-fluid modulation method, which allows the use of only one detector. , we have developed a completely new fluid analysis method and fluid analysis device that can simultaneously and continuously analyze multiple sample fluids (or divided into multiple systems), and the basic concept is as follows: , 1986
Patent application filed on December 11th and December 12th, 1988
This has already been proposed through earlier applications such as patent applications filed on the same date.

That is, the fluid analysis device using the multi-fluid modulation method (the method is applied in this device) is shown in the basic conceptual diagram shown in Fig. 10 and the main part specific configuration diagram shown in Fig. 11. As is clear from the above, multiple (two in this example) sample fluids S1,
S2 (which may be originally different or may be a single sample fluid divided into two systems) is fluid-modulated at different frequencies F1 and F2 (Hertz) by reference fluids R1 and R2, respectively. an analysis section A having only one detector D and to which the fluid-modulated sample fluids S1 and S2 are simultaneously and continuously supplied; The output signal O from the detector D at is suitably frequency separated and signal rectified.
Using a smoothing means (conceptually shown in FIG. 10), the signal components O1,
a signal processing means B for obtaining analysis values for each of the sample fluids S1 and S2 by rectifying and smoothing the sample fluids S1 and S2; 1
As specifically shown in the figure, from the output signal O from the detector D, there are two bandpass filters a1 and a that respectively pass only signals in bands around the respective modulation frequencies F1 and F2.
2 are provided in parallel with each other, and at the subsequent stage of each of the bandpass filters a1 and a2, the band pass filters are arranged in synchronization with the actual fluid modulation operation by the fluid modulation means V1 and V2 corresponding to the pass band frequencies F1 and F2. Pass filter a1,a
Synchronous detection rectifiers b1 and b2 are provided to detect and rectify the output signals from the synchronous detection rectifiers b1 and b2, and a smoothing element c is provided after each of the synchronous detection rectifiers b1 and b2 to smooth the output signals therefrom.
1 and c2 are provided.

In other words, in a fluid analysis device using a multi-fluid modulation method having such a configuration, an appropriate fluid modulation means V1 consisting of, for example, a rotary valve, a three-way switching solenoid valve, a four-way switching solenoid valve, etc.
V2 is used to analyze two sample fluids S1 and S2 (or separated into two systems) fluid-modulated by reference fluids R1 and R2 at different frequencies F1 and F2, respectively, with only one detector D. By simultaneously and continuously supplying the sample fluids to section A, first, the individual measurement signal components (O1, O2) corresponding to all sample fluids S1, S2 are superimposed all at once from that single detector D. In addition to adopting a unique method that was completely unthinkable in the conventional common sense of obtaining a single measurement signal O (=O1 + O2),
For example, as illustrated in FIG. 10, the output signal O from the . Fluid S
Analytical values for each of the sample fluids S1 and S2 are obtained by performing signal processing of separating signal components O1 and O2 of each modulation frequency F1 and F2 for each of the sample fluids S1 and S2, and rectifying and smoothing the signal components, respectively. Therefore, even when performing simultaneous and continuous analysis of two components in the same sample fluid, or simultaneous and continuous analysis of specific components contained in two different sample fluids, only one detector ( Therefore, compared to conventional fluid analysis devices that required two detectors, the entire device can be made smaller and simpler, and costs can be reduced. The basic advantage is that it can be adjusted easily and quickly, and that zero adjustment errors and sensitivity differences between multiple detectors cannot occur as in conventional methods, ensuring good measurement accuracy at all times. have.

Moreover, as the signal processing means B, a computer capable of performing numerical analysis processing such as Fourier analysis (corresponding to frequency separation processing) and absolute value averaging processing (corresponding to rectification/smoothing processing) is used. Alternatively, it is possible to configure appropriate means using various software or hardware, such as using an electric circuit such as a lock-in amplifier. and,
A smoothing element c composed of synchronous detection rectifiers b1 and b2 and a low-pass filter or a capacitor, for example.
1 and c2 are connected in series.
Since the series is arranged in parallel, it is not only much simpler and cheaper to construct than the above-mentioned means using a computer or a lock-in amplifier, but also a bandpass filter a.
1 and a2 alone may be insufficient, but is supplemented by synchronous detection rectifiers b1 and b2 to achieve even more accurate frequency separation. For example, simply bandpass There is also the advantage that it is possible to obtain significantly superior signal processing performance (S/N ratio) compared to a configuration in which absolute value rectification is performed immediately after frequency separation using only a filter.

[Problem that the invention seeks to solve]

However, even in the fluid analysis device using the multi-fluid modulation method, which has various useful advantages as described above, the following problems still remain.

That is, as explained using FIG. 11 above,
In the signal processing means B, the measurement signal O input from the detector D is first passed through band pass filters a1 and a2 to both sample fluids S1,
The measurement signal components O1 (frequency F1) and O2 (frequency F2) corresponding to S2 are separated into individual measurement signal components O1 (frequency F1) and O2 (frequency F2). Unless practical measures are taken, such as using high-grade pass filters a1 and a2 with fairly sharp frequency cut characteristics, reliable frequency separation results cannot be obtained. Therefore, in addition to the signal O1 of the original frequency F1 (F2), the signal passing through each bandpass filter a1, a2 inevitably contains a noise component due to the other fluid modulation frequency F2, F1. Interference effects will occur.

In this way, each bandpass filter a1, a
If noise components of the other fluid modulation frequencies F2 and F1 due to mutual interference are mixed into the signal that has passed through the two fluid modulation frequencies F2 and F1, the following problems will occur.

In other words, both fluid modulation frequencies F1 and F2 are
Normally, it can be set arbitrarily, but in that case, generally the signal is
1 and b2, the signal corresponding to the interference noise component remains as a measurement error factor (that is, its smoothed value does not become 0).

This means, for example, that one fluid modulation frequency F
It will be easily understood from FIGS. 12A and 12B, which show an example where F1 is 1Hz and the other fluid modulation frequency F2 is 3Hz.

Furthermore, as is clear from Figure 12A, the measurement error factor due to mutual interference effects as described above appears to be very large especially in systems where the measurement signal is a lower frequency signal, but from Figure 12B, As is clear, it does not appear as much in the system where the higher frequency signal is the measurement signal (in other words, the difference between the system where the higher frequency signal is the measurement signal and the system where the lower frequency signal is the measurement signal) It has been experimentally found that there is a tendency for the interference between

Further, the above-mentioned problem is not limited to noise components due to mutual interference effects, but also due to other system frequencies F2 and F1 caused by other factors such as a deviation in the mechanical duty of the fluid modulation means V1 and V2. A similar problem occurs when a noise component is mixed in.

The present invention has been made in view of the above circumstances, and its purpose is to maintain various advantages of the fluid analysis device using the multi-fluid modulation method according to the earlier application, while also maintaining both fluid modulation frequencies. Without resorting to measures that are difficult in practice, such as setting sufficiently large differences, or using high-grade filters with sharp frequency cut characteristics as both bandpass filters in the signal processing means,
In order to reliably reduce measurement errors caused by interference noise components of the other frequency signal in a system where one frequency signal is the measurement signal as described above, by using a practical means that can be implemented extremely easily. It's about trying.

[Means for solving problems]

In order to achieve the above object, a fluid analysis device using a multi-fluid modulation method according to the present invention is provided as shown in the basic conceptual diagram shown in FIG. As such, the two sample fluids S1 and S2 (also split into two systems) are compared to the comparison fluids R1 and R2, respectively.
Different frequencies F1 and F2 (Hertz)
fluid modulation means V1, V2 for modulating the fluid with
an analysis section A having only one detector D and to which each of the fluid-modulated sample fluids S1 and S2 is supplied simultaneously and continuously; and an output signal from the detector D in the analysis section A. O is the signal component O1, O2 of each modulation frequency F1, F2 for each sample fluid S1, S2.
In order to obtain analysis values regarding the respective sample fluids S1 and S2 by separating them into rectifying and smoothing processing, the bands around the respective modulation frequencies F1 and F2 are extracted from the output signal O from the detector D. Two band pass filters a1 and a2 are provided in parallel with each other to pass only the signals of , respectively, and fluid modulation means V1 and V1 corresponding to the pass band frequencies F1 and F2 are provided downstream of each of the band pass filters a1 and a2, respectively. In synchronization with the actual fluid modulation operation by V2, the bandpass filter a1,
Synchronous detection rectifiers b1 and b2 are provided to detect and rectify the output signal from a2, and smoothing elements c1 and c2 are provided downstream of each of the synchronous detection rectifiers b1 and b2 to smooth the output signal therefrom. Further, the fluid modulation means V1 and V2 are set so that the ratio of the fluid modulation frequencies F1 and F2 thereof is an even number or a fraction of an even number. It has the following characteristics.

[Effect]

The effects exhibited by the above characteristic configuration are as follows.

That is, since the overall basic configuration is the same as the fluid analysis device using the multi-fluid modulation method according to the earlier application, the same various advantages are sufficiently maintained, and the present invention has the following advantages. In particular, both fluid modulation means V1 and V2 are arranged such that the ratio of the fluid modulation frequencies F1 and F2 by them is an even number or a fraction of an even number (for example, when h is an integer,
For example, the two fluid modulation frequencies may be set to be sufficiently different, or the signal processing means may Noise in the other frequency signal in a system where one frequency signal is the measurement signal as described above can be eliminated without using practically difficult means such as using a high-grade bandpass filter with sharp frequency cut characteristics. It has become possible to reliably and easily reduce measurement errors caused by components.

In other words, for example, if one (lower) fluid modulation frequency F1 is 1 Hz and the other (higher) fluid modulation frequency F2 is an even multiple (twice) of that, 2 Hz, as shown in Figure 3A, In addition to the original signal O1 (1Hz), there is interference noise of the higher fluid modulation frequency (2Hz) in the signal that has passed through bandpass filter a1 in a system where the lower frequency signal (1Hz) is the measurement signal. Even if the noise component (2Hz) is mixed in, if the signal is synchronously detected and rectified by the synchronous detection rectifier b1, the noise component (2Hz) can be removed.
is synchronously detected and rectified so that the subsequent smoothing value by smoothing element c1 is canceled out by plus/minus and becomes 0. Therefore, smoothing element c1
, a correct measurement signal corresponding only to the original signal O1 (1 Hz) is obtained. Contrary to the above, even in a system where the higher frequency signal (2Hz) is the measurement signal, the smoothed value of the interference noise component of the lower frequency signal (1Hz) is similarly canceled out by plus/minus. It becomes 0, and as expected,
It will be easily understood from FIG. 3B that a correct measurement signal without measurement errors can be obtained.

〔Example〕

Hereinafter, specific embodiments of a fluid analysis device using a multi-fluid modulation method according to the present invention will be described with reference to the drawings (FIGS. 4 to 9).

FIG. 4 shows the overall schematic configuration of a fluid analysis device using a multi _- fluid modulation method according to the first embodiment. _y C _z
It is used when analyzing the concentration of etc.

Now, as shown in the figure, two sample fluids S1 and S2 (which may be originally different or, as will be explained in detail later, a single sample fluid divided into two systems) ) at different frequencies F1, F by means of comparison fluids R1, R2 (generally zero gas is used) using fluid modulation means V1, V2, respectively.
2 (hertz) (i.e., passing the sample fluid and the reference fluid alternately at a predetermined frequency), each fluid-modulated sample fluid S1, S2, R1, R2 is Detector D
The sample is configured to be simultaneously and continuously supplied to an analysis section A having a sensor (sensor).

The fluid modulation means V1 and V2 are set so that the ratio of their fluid modulation frequencies F1 and F2 is an even number or a fraction of an even number. In other words, if one frequency (F1 or F2) is lHz, the other frequency (F2 or F1)
is set to 2hlHz (h is an integer).
The specific values of this example are F1=1Hz, F2=2Hz
(l=1, h=1).

By the way, in the case of this embodiment, the detector D in the analysis section A is generally a chemical luminescence detector (CLD) for NO detection or a flame ion detector for methane (CH ₄ ) detection. Since a type such as a detector (FID) through which the sample fluid directly passes is used, both the fluid-modulated sample fluids S1 and S2 are supplied to the detector D in a mixed state.

Therefore, the signal O output from the detector D via the preamplifier 2 has individual measurement signal components (O1, O2) corresponding to both sample fluids S1 and S2, as schematically shown in the figure. are obtained as a single measurement signal (O=O1+O2) in which these are collectively superimposed.

Therefore, as conceptually illustrated in FIG. By using means B, signal processing is performed to separate signal components O1 and O2 of modulation frequencies F1 (1 Hz) and F2 (2 Hz) for each of the sample fluids S1 and S2, and rectify them, respectively. Analytical values regarding sample fluids S1 and S2 are obtained.

The specific circuit configuration of the signal processing means B is as shown in FIG.

That is, the signal O output from the detector D via the preamplifier 2 is branched into a plurality of signal processing series (two series in this example) provided in parallel with each other, and one signal processing series has a sample Fluid S1
A band pass filter a1 is provided for separating and extracting (passing) only the signal O1 having a modulation frequency (1 Hz) for the sample fluid S1, and a synchronizing signal generator 1a attached to the fluid modulation means V1 for the sample fluid S1 is provided at the subsequent stage. The synchronization signal from (signal representing the actual fluid modulation operation by the fluid modulation means V1: F1 = 1Hz) supplements the frequency separation effect, which may not be sufficient with the bandpass filter a1 alone, and improves accuracy. A synchronous detection rectifier b1 is provided for synchronously rectifying the output signal O1 from the bandpass filter a1 so that the separated alternating current can be converted into direct current at the same time as good separation of the two currents can be performed. A low pass filter (LPF) is provided as a smoothing element c1 for smoothing the output signal from the synchronous detection rectifier b1 and removing high frequency noise, and
The other signal processing line is provided with a bandpass filter a2 for separating and extracting (passing) only the signal O2 of the modulation frequency (2 Hz) for the sample fluid S2, and at the subsequent stage, a bandpass filter a2 for separating and extracting (passing) only the signal O2 at the modulation frequency (2 Hz) for the sample fluid S2. A synchronization signal from the synchronization signal generator 1b attached to the means V2 (a signal representing the actual fluid modulation operation by the fluid modulation means V2:
F2 = 2Hz), it is possible to supplement the frequency separation effect that may not be sufficient with the bandpass filter a2 alone, and to achieve even more accurate separation, and at the same time, it is possible to convert the separated alternating current into direct current. , a synchronous detection rectifier b for synchronously rectifying the output signal O2 from the bandpass filter a2.
2, and a low-pass filter (LPF) as a smoothing element c2 for smoothing the output signal from the synchronous detection rectifier b2 and removing high frequency noise is further provided at the subsequent stage.

According to the fluid analysis device using the multi-fluid modulation method configured as described above, as is clear from the detailed explanation in the [Operation] section above, in a system where one frequency signal is the measurement signal, the other frequency signal is used as the measurement signal. The measurement error caused by the interference noise component of the frequency signal can be reliably and easily reduced.

FIG. 6 shows a schematic configuration of main parts of a fluid analysis device using a multi _- fluid modulation method according to the second embodiment. It is used when analyzing the concentration of

In this case, the analyzer section A is generally composed of a non-dispersive infrared analyzer (NDIR), and the detector D (sensor) is a pneumatic type using a condenser microphone method or a microflow method. A type of detector, such as a thermopile or a solid state detector such as a semiconductor, through which the sample fluid does not directly pass, is used. However, as shown in this figure, analysis section A
When configured with a so-called single-cell type NDIR using only one cell C, both sample fluids S1, S2, R1, R2 which are fluid-modulated are similar to the case of the first embodiment described above. are supplied to the cell C in a mixed state, and the absorbance of measurement infrared rays passing through the cell C is measured by a detector D.

The other configurations of this embodiment are the same as those of the first embodiment, so members having the same functions are designated by the same reference numerals, and the explanation thereof will be omitted.

FIG. 7 shows a schematic configuration of main parts of a fluid analysis device using a multi-fluid modulation method according to a third embodiment, and this is also used when analyzing the concentration of CO _x or the like.

In this case, the analysis section A is divided into two cells C1,
Since it is configured with a so-called double cell type non-dispersive infrared analyzer (NDIR) having C2, both sample fluids S1, S2, R1, R
2 are each separate cell C without being mixed with each other.
The absorbance of each measuring infrared ray that has passed through both cells C1 and C2 is simultaneously measured by one detector D.
Although not shown, the two cells C
1 and C2, for example, a solid filter for CO measurement is attached to one side, and a solid filter for CO ₂ measurement is attached to the other side.

Further, since the other configurations of this embodiment are the same as those of the first and second embodiments, members having the same functions are given the same reference numerals, and the description thereof will be simplified. Omitted.

By the way, the two sample fluids S1 and S2
may be originally different, for example, when they are introduced separately from two exhaust channels, or, as illustrated in FIG. 8, a single sample fluid S0 may be introduced into two systems It may also be a branched stream. This is generally applied when simultaneously and continuously measuring CO and CO ₂ , NO and NO ₂ , methane and HC other than methane (NMHC) in the same sample fluid S0. ,
As shown, in at least one system,
For converting NO ₂ to NO or CO
Although not shown, a converter 5 for converting the CO ₂ to CO 2 is normally provided, as is a non-methane removal device or a necessary filter. Incidentally, as illustrated in FIG. 8, the comparison fluids R1 and R2 also have a common fluid R
0 (for example, zero gas) may be used.

Further, each of the fluid modulation means V1 and V2 may have any configuration as long as it can alternately switch between the sample fluids S1 and S2 and the comparison fluids R1 and R2 at a predetermined frequency. It may be configured with a rotary valve as shown in Figure 9A, or it may be configured with a four-way switching solenoid valve as shown in Figure 9B, or a three-way switching valve, although not shown. There is no problem in configuring it using a solenoid valve.

〔Effect of the invention〕

As is clear from the above detailed description, the fluid analysis device using the multi-fluid modulation method according to the present invention fully provides the same various advantages as the fluid analysis device using the multi-fluid modulation method according to the earlier application. Moreover, in particular, it is only necessary to use the easily implemented practical means of setting both fluid modulation means such that the ratio of the fluid modulation frequencies by them is an even number or a fraction of an even number. However, in a system in which one frequency signal is used as a measurement signal, it is possible to reliably reduce measurement errors caused by interference noise components of the other frequency signal.

[Brief explanation of the drawing]

FIGS. 1 and 2 show the basic concept of a fluid analysis device using a multi-fluid modulation method according to the present invention, and explanatory diagrams (diagrams corresponding to claims) of the specific configuration of its main parts. Figures A and B show explanatory diagrams of their effects, respectively. 4 to 9 show various specific embodiments of the fluid analysis device using the multi-fluid modulation method according to the present invention.
5 is a schematic diagram of the overall configuration of the first embodiment, FIG. 5 is a specific circuit diagram of the main part thereof, FIG. 6 is a schematic diagram of the main part of the second embodiment, and FIG. 7 is a diagram of the main part of the third embodiment. FIG. 8 is a schematic diagram of the main part of the embodiment, and FIG. 9 is a schematic diagram of the main part for supplementary explanation of each embodiment, and FIGS. FIG. 2 is a schematic configuration diagram of main parts. Furthermore, FIGS. 10 to 12 are for explaining the technical background of the present invention and problems in the prior art, and FIGS. 10 and 11 illustrate the multi-fluid modulation system according to the prior art. 12A and 12B show explanatory diagrams of the basic concept of a fluid analyzer and the specific configuration of its main parts, and FIGS. 12A and 12B respectively show explanatory diagrams of the problems. S1, S2: Sample fluid, R1, R2: Comparison fluid, F1, F2: Fluid modulation frequency, V1, V
2: fluid modulation means, A: analysis section, D: detector,
B: Signal processing means, O: Output signal from detector D, O1, O2: Signal components of each modulation frequency F1, F2 for each sample fluid S1, S2, a1,
a2: band pass filter, b1, b2: synchronous detection rectifier, c1, c2: low pass filter.

Claims (1)

[Claims] 1. Fluid modulation means for fluid modulating two sample fluids (also divided into two systems) at mutually different frequencies by a comparison fluid, and having only one detector, and , an analysis section to which each of the fluid-modulated sample fluids is simultaneously and continuously supplied, and an output signal from the detector in the analysis section is separated into signal components of each modulation frequency for each of the sample fluids. two bandpass filters that respectively pass only signals in bands around the respective modulation frequencies from the output signal from the detector in order to obtain analytical values regarding the respective sample fluids through rectification and smoothing processing, respectively; are provided in parallel with each other, and the output signal from the bandpass filter is detected and rectified in synchronization with the actual fluid modulation operation by the fluid modulation means corresponding to the pass band frequency at the subsequent stage of each of the bandpass filters. A signal analysis means comprising a synchronous detection rectifier and a smoothing element provided at a subsequent stage of each of the synchronous detection rectifiers for smoothing the output signal therefrom; A fluid analysis device using a multi-fluid modulation method, characterized in that the ratio of the fluid modulation frequencies thereof is set to be an even number or a fraction of an even number.