JP2000292351A - Optical interference type fluid characteristic measuring device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enlarge a measuring range and a dynamic range without elongation of an image sensor. SOLUTION: This device is equipped with an image sensor 14 for receiving an image of an interference fringe generated by a light beam passing through a measuring cell composed so that a phase change of the interference fringe does not exceed ±πduring the period of one sampling cycle and a reference cell juxtaposed therewith, a Fourier analysis means 24 for calculating the phase θ of a fundamental wave component included in an interference fringe signal from the image sensor 14, and a shifted cycle number detection means 25 and an addition and subtraction means 26, for judging whether the phase θ calculated by the Fourier analysis means 24 satisfies a physical restriction that a phase change caused by a fluid characteristic of the measuring cell does not exceed ±π during one sampling cycle or not, and for outputting the phase θ as a phase changing quantity in the case of satisfying the restriction, and for outputting the value obtained by adding or subtracting 2 π. as the phase changing quantity in the case of not satisfying it. And, a contradiction of a solution of the Fourier analysis means 24 is removed by utilizing positively the fluid characteristic of the measuring cell.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention detects a difference in the refractive index of light between a fluid to be measured and a standard fluid as a change in interference fringes, and measures characteristics such as the concentration of the fluid to be measured based on the change. More specifically, the present invention relates to a technique for detecting a displacement amount of an interference fringe using an image sensor.

[0002]

2. Description of the Related Art An apparatus for measuring a fluid characteristic by interference of light has two optical cells arranged side by side, irradiates two cells with light emitted from the same light source, and irradiates each cell with two light beams. An interference fringe is generated by the transmitted light, and a displacement amount of a specific region of the interference fringe, for example, a portion showing the highest brightness, that is, a displacement amount of a so-called zero-order interference fringe, is read by an image sensor such as a CCD which can read out digitally. It has been proposed to detect and detect the optical density.

[0003]

However, since the resolution is governed by the cell density of the CCD, there is a problem that the measurement accuracy is limited. In order to eliminate such a limitation by the CCD, it is conceivable to obtain the phase difference by performing a Fourier transform on the envelope of the interference fringe detected by the image sensor. In the case where it exceeds, there is a problem that the amount of phase change cannot be determined and the dynamic range is limited. The present invention has been made in view of such a problem, and the object thereof is to:
It is an object of the present invention to provide an optical interference type fluid characteristic measuring device capable of detecting a fluid characteristic in a wide dynamic range from a phase difference of an envelope of an interference fringe regardless of a change form of the fluid characteristic.

[0004]

In order to solve such a problem, according to the present invention, there is provided a measuring cell configured so that a phase change of an interference fringe does not exceed ± π during one sampling period. And an image sensor receiving an image of interference fringes generated by the light beam passing through each cell, and a phase θ of a fundamental wave component included in an interference fringe signal from the image sensor. Fourier analysis means, and determines whether the phase θ calculated by the Fourier analysis means satisfies a physical constraint that a phase change due to fluid characteristics of the measurement cell does not exceed ± π during one sampling period. , The phase θ is regarded as the amount of phase change when satisfied, and 2π when not satisfied.
Means for outputting a value obtained by adding or subtracting as a phase change amount, and eliminating inconsistencies in phase from the Fourier analysis means by positively utilizing the fluid characteristics of the measurement cell.

[0005]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be described below with reference to the illustrated embodiments. FIG. 1 shows an embodiment of the present invention, in which reference numeral 1 denotes a measurement chamber, and reference numerals 2 and 3 denote reference chambers disposed on both sides of the measurement chamber 1. The ends 2 and 3 are sealed at both ends by light-transmitting plates 4 and 4 and have fluid inlets and outlets H1, H2, H3, H4,
H5 and H6 are provided.

The measuring chamber 1 is connected to a buffer tank, a throttle, and the like (not shown). The optical characteristics of the fluid flowing into the measuring chamber 1 change the phase of the interference fringe during one sampling period, for example, several tens of milliseconds. Does not exceed 2π, that is, is changed only within the range of -π ≦ θ <π.

[0007] The reference chambers 2 and 3 are connected to through holes H3 and H6 provided at the ends thereof by flow paths (not shown) so that the same standard gas can be supplied from one standard gas source. Is configured. A parallel plane mirror 5 forming a beam splitter is disposed on one side of each of the chambers 1, 2, and 3, and a main prism 6 is disposed on the other side.

Reference numeral 10 denotes a light source. In this embodiment, a light emitting diode having a center wavelength of 660 nm is used. The light source is mounted on a housing 11 of the measuring apparatus main body so as to irradiate a predetermined position P0 near one side of the parallel plane mirror 5. Have been.

The light beam L0 from the light source 10 is split into two beams L1 and L2 by the plane-parallel mirror 5, and one beam L1 passes through an optical path near one side of the measuring cell 1 and enters the main prism 6. Then, the beam L3 again passes through the optical path on the other side of the measurement cell 1 and is incident on the parallel plane mirror 5.

The other beam L2 passes through one reference cell 2 and is emitted from the other reference cell 3 by the prism 6 as a beam L4.
Out of the same point P1 as the irradiation point of the beam L3 emitted from the measurement cell 1 to generate interference fringes, and the objective lens 16
Then, the image is enlarged to a size suitable for detection by an enlargement optical system formed by the optical member 18 on the front surface of the cylindrical body 13 and forms an image on an image detection surface of a line image sensor 14 such as a CCD described later. In this embodiment, the line image sensor 14 having 256 pixels is used, and an optical path is set in the detection area so that six cycles of interference fringes are formed.

Reference numeral 14 denotes the aforementioned line image sensor.
As shown in FIG. 2, the plurality of photoelectric conversion elements S1, S2, S
3 ‥‥ Sn are arranged in a line, and the arrangement direction of the photoelectric conversion elements S1, S2, S3 ‥‥ Sn is arranged so as to coincide with the moving direction of the interference fringes, and the output is measured. It is input to the circuit 20.

FIG. 2 shows an embodiment of the measuring circuit 20 described above. The reading control means 21 synchronizes with each of the photoelectric conversion elements S1, S2 in synchronization with a clock of a constant frequency of a clock signal generating means 22. , S3 {intensity of the light incident on Sn as an address, that is, each photoelectric conversion element S1, S2, S3}.
読 み 出 す The data is read out in the arrangement order of Sn.

Each of the photoelectric conversion elements S1, S2, S3 ‥‥ Sn
Is converted into a digital signal by the analog-digital conversion means 23 and output to the Fourier analysis means 24,

(Equation 1) (Note that N represents the number of pixels of the image sensor 14, and 256 in this embodiment. M represents the number of stripes that can be captured by the image sensor by the number of periods of the basic sine wave. In this embodiment, 6 is used. Data (j) indicates the output value of each pixel of the image sensor 14 at the address j.), And the phase P of the basic sine wave component sin (2πmj / N) is mathematically solved. Is detected as

The data from the Fourier analysis means 24 is output to the displacement cycle number detection means 25. The displacement cycle number detecting means 25 determines that the phase change amount of the interference fringes during one sampling cycle by the measurement cell 1 is minus π from the phase one sampling cycle ago due to its structure or the flow characteristic of the test gas. , Or a physical limitation that it does not change more than plus π minutes (FIG. 4);
The inconsistency with the simple mathematical solution is solved by incrementing or decrementing the integer M by an integer M, and the total phase change P from the start of the measurement is output from the addition / subtraction means 26 as θ + 2πM (M is an integer).

Next, the operation of the above-configured apparatus will be described with reference to the flowchart shown in FIG. The time when the standard gas is present in the reference cell 5 and the gas to be measured is present in the measuring cell 1 in a steady state is defined as an initial state.
= 0 (step a), and the initial phase P0 of the interference fringe formed on the image sensor 14 as shown in FIG.
Is calculated by the Fourier analysis means 24 (step
B). When the fluid characteristics of the gas under measurement change in this state,
The interference fringes described above begin to move.

The sum P 'of the phase .theta. (-.Pi..ltoreq..theta. <. Pi.) Obtained by the Fourier analysis means 24 and 2.pi.M (where M is set to 0 in the above-described step) is calculated as an assumed value. (Step c), the difference {P ′ − (P (−1))} between this assumed value and the previous total phase change amount (P (−1)).
Is in the range between -π and + π.

That is, {P ′ − (P (−1))} and −
and π first (step d), and ΔP ′ − (P
If (−1))｝> − π, the process proceeds to step (e), where {P ′ − (P (−1))} is compared with π (step E), and {P ′ − ( If P (−1))｝ ≦ π, the assumed value P ′ is set as the current detection value P (step f), and this value P is set to 1 in the next sampling cycle.
It is stored as the total phase change amount P (-1) before the current time (step G), and the value P−P0 is output as the amount of movement of the interference fringe from the start of the measurement (step H). Wait for the sampling period of.

On the other hand, the assumed value P and the previous total phase change amount (P
(P) − (P (−1))} <− in a comparison of the difference {P ′ − (P (−1))} with (−1)) and minus π.
If π holds, it is a physically impossible solution that is inconsistent with the above-described replacement characteristic of the test gas in the cell 1, and therefore, a value P obtained by adding 2π to P ′ is used as a detection value. Increment M (step re) and step (c)
And waits for the next sampling cycle to arrive.

On the other hand, the assumed value P and the previous total phase change amount (P
(P)-(P (-1))} and a difference {P '-(P (-1))}>-
Although π holds (step d), ｛P '-(P
(-1)) When｝ ≧ π is satisfied, it is a physically impossible solution that is inconsistent with the above-described replacement characteristic of the test gas in the cell 1, and thus a value obtained by subtracting 2π from P ′. P is set as a detection value, M is decremented (step nu), and the procedure returns to step (c) to wait for the next sampling period.

As described above, even if a value that can exist in Fourier analysis is calculated, a solution showing physical conditions that clearly contradicts the replacement characteristic of the test gas in the cell 1 is: The assumed value P and the previous total phase change amount (P (−
1)) and the difference {P ′ − (P (−1))},
Since 2π is added or subtracted, the total phase change amount from the measurement start point can be calculated.

It is apparent that the interference fringe measuring technique of the present invention can be applied to a measuring apparatus for detecting a calorific value, a pressure, a density, a concentration, etc. of a gaseous fuel by a displacement amount or a phase change amount of the interference fringe.

[0022]

As described above, according to the present invention, the measuring cell configured so that the phase change of the interference fringe does not exceed ± π during one sampling period, and the reference cell attached thereto. A cell, an image sensor receiving an image of an interference fringe generated by a light beam passing through each cell, a Fourier analysis means for calculating a phase θ of a fundamental wave component included in an interference fringe signal from the image sensor, and a Fourier analysis means It is determined whether or not the calculated phase θ satisfies a physical constraint that a phase change due to fluid characteristics of the measurement cell does not exceed ± π during one sampling period. Means for outputting a value obtained by adding or subtracting 2π as a phase change amount when the value is not satisfied. Phase inconsistency can be eliminated,
A large dynamic range can be ensured regardless of the size of the image sensor.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing one embodiment of the present invention.

FIG. 2 is a block diagram showing one embodiment of a measuring circuit in the device.

FIG. 3 is a diagram illustrating an output from each photoelectric conversion element and a sine signal formed based on the output when an interference fringe is imaged on a line image sensor.

FIG. 4 is a diagram showing, by a phase, a measurement cell and conditions for changing characteristics of a fluid flowing into the measurement cell.

FIG. 5 is a flowchart showing an operation of the above device.

[Explanation of symbols]

 Reference Signs List 1 measurement cell 2, 3 reference cell 5 parallel plane mirror 6 main prism 10 light source device 14 line image sensor 20 measurement circuit S1, S2, S3 ‥‥ Sn photoelectric conversion element

Claims (1)

[Claims] 1. A measuring cell configured so that a phase change of an interference fringe does not exceed ± π during one sampling period, a reference cell attached to the measuring cell, and a light beam passing through each of the cells. An image sensor that receives an image of an interference fringe generated by, a Fourier analysis unit that calculates a phase θ of a fundamental wave component included in the interference fringe signal from the image sensor, and the phase θ calculated by the Fourier analysis unit, It is determined whether or not a phase change due to the fluid characteristics of the measurement cell satisfies a physical constraint that does not exceed ± π during one sampling period. If so, the phase θ is regarded as a phase change amount and not satisfied. A means for outputting a value obtained by adding or subtracting 2π as a phase change amount in such a case.