JP4889772B2 - Refractometer - Google Patents

Description

  The present invention relates to a refractometer used for measuring sugar content and concentration in a solution.

  As a refractometer used to measure sugar content and concentration in a liquid, light is irradiated to the boundary surface between the prism and the sample, and the light reflected by the boundary surface is detected by a photoelectric sensor. Refractometers that measure rate (sugar content, concentration) are known.

  The measurement principle of the refractometer is derived from the fact that the critical angle at which total reflection occurs at the interface between the prism and the sample depends on the refractive index of the sample. Therefore, such a refractometer assumes that only the reflected light at the boundary surface is incident on the photoelectric sensor.

  However, the place where the refractometer is used is not always indoors. For example, it may be more convenient to perform the measurement outdoors when juices from fruits and vegetables or antifreeze for automobiles are used as samples. In this case, external light that varies temporally and spatially passes through the prism from the sample side and is received by the photoelectric sensor together with the reflected light from the internal light source. For this reason, there was a problem that the refractive index could not be accurately measured outdoors.

Japanese Utility Model Publication No. 3-26443

  An object of the present invention is to provide a refractometer that can reduce the influence of external light and can accurately measure the refractive index even outdoors in order to solve the above problems.

The refractometer of the present invention makes light from a light source incident on a boundary surface of a prism that forms an interface with a sample, detects light reflected by the prism boundary surface by a photoelectric sensor, and outputs the light from the output signal of the photoelectric sensor. A refractometer for measuring the refractive index of a sample,
Filter means disposed between the prism boundary surface and the photoelectric sensor;
The filter means includes a wavelength filter that selectively transmits light in a predetermined wavelength range including the wavelength of light from the light source.

The wavelength filter is
A first filter that selectively blocks light in a wavelength range from a wavelength longer than a wavelength of light from the light source by a predetermined wavelength to a maximum value of a detection wavelength of the photoelectric sensor;
A second filter that selectively blocks light in a wavelength range from a wavelength shorter than a wavelength of light from the light source by a predetermined wavelength to a minimum value of a detection wavelength of the photoelectric sensor.

  Preferably, the filter means further includes a polarizing filter that selectively allows linearly polarized light to pass therethrough.

  The filter means may be integrally formed by laminating the wavelength filter and the polarizing filter in layers.

  The filter means may be adhered to the prism on a first surface and adhered to the photoelectric sensor on a second surface.

  The filter means may include a neutral density filter.

  Therefore, according to this invention, the influence of external light can be reduced and the refractometer which can measure a refractive index accurately also outdoors can be provided.

FIG. 1 is a cross-sectional view showing a main part of an embodiment of a refractometer according to the present invention. FIG. 2 shows the spectral transmittance of the filter means of the refractometer of FIG.

  FIG. 1 shows an embodiment of a refractometer according to the present invention.

  The refractometer 10 includes a frame 12, a sample stage 14 provided on the frame 12, and a prism 16 fixed inside the sample stage 14. The prism 16 includes a prism boundary surface 18 that forms an interface with the sample S dropped on the sample dropping window 15 formed on the sample stage 14, an incident surface 20 on which light enters the prism boundary surface 18, and a boundary surface And an emission surface 22 for emitting the reflected light from 18.

  A light source 24 is disposed on the incident surface 20 side of the prism 16. The light source 24 is preferably an LED that emits light having a wavelength of approximately 589 nm. Preferably, the light source 24 is a high brightness LED.

  Hereinafter, a plane defined by the incident light Ri incident on the prism boundary surface 18 from the light source 24 and the normal line N of the prism boundary surface 18 (a plane parallel to the paper surface of FIG. 1) is referred to as a refractive index measurement surface A.

  For example, a photoelectric sensor 28 including a line sensor in which a plurality of light receiving elements are arranged one-dimensionally is disposed on the emission surface 22 side of the prism 16.

  Filter means 30 is disposed between the prism boundary surface 18 and the photoelectric sensor 28. The filter unit 30 reduces the amount of light, wavelength filters 32 and 34 that selectively transmit light in a predetermined wavelength range including the wavelength of light from the light source 24, a polarization filter 36 that selectively transmits predetermined polarized light, and the like. A neutral density filter 38.

  The wavelength filters 32 and 34 include a first wavelength filter 32 that selectively transmits only light in a relatively short wavelength band, and a second wavelength filter 34 that selectively transmits only light in a relatively long wavelength band. Have.

  The first wavelength filter 32 blocks light in a wavelength range from a wavelength longer than the wavelength of light from the light source by a predetermined wavelength to the maximum value of the detection wavelength of the photoelectric sensor 28. Preferably, the first wavelength filter 32 is a near-infrared cut filter or a heat ray cut filter that cuts light in the near infrared region of approximately 700 nm or more and transmits light on the short wavelength side. Specifically, a glass filter (bandpass filter) “BG40” manufactured by Schott can be used as the first wavelength filter 32.

  Referring to FIG. 2, a curve Ta indicates the spectral transmittance of the first wavelength filter 32 using the filter “BG40” having a thickness of 1.0 mm. As illustrated, the first wavelength filter 32 transmits 70% or more of light in a short wavelength region of approximately 340 nm to 600 nm including the central wavelength L of light from the light source 24 of 589 nm.

  The second wavelength filter 34 blocks light in a wavelength range from a wavelength shorter than the wavelength of light from the light source by a predetermined wavelength to the minimum value of the detection wavelength of the photoelectric sensor 28. Preferably, the second wavelength filter 34 is a filter that cuts light in the visible region and ultraviolet region of approximately 550 nm or less and transmits light on the long wavelength side. Specifically, as the second wavelength filter 34, a sharp cut filter “O” whose transmission limit wavelength (the midpoint wavelength between the absorption limit wavelength of 5% transmittance and the high transmission limit wavelength of 72% transmittance) is 560 nm. -56 "(the symbol of JIS B7113 is SO56) can be used.

  In FIG. 2, a curve Tb shows the spectral transmittance of the second wavelength filter 34 using “O-56” having a thickness of 1 mm. As illustrated, the second wavelength filter 34 transmits 70% or more of light in a long wavelength region of approximately 570 nm or more including the center wavelength L = 589 nm of light from the light source 24.

  The spectral transmittance of the filter means 30 including the first wavelength filter 32 and the second wavelength filter 34 is indicated by a curve Tc in FIG. As shown in the figure, the filter means 30 transmits 70% or more of light in a wavelength range of approximately 570 nm to 600 nm.

  Next, the polarizing filter 36 is disposed so as to have a transmission axis in the refractive index measuring surface A, blocks S polarized light that vibrates in a direction perpendicular to the refractive index measuring surface A, and selectively passes only P polarized light. Let By transmitting only P-polarized light, most of the incident light from the outside can be blocked.

  The dimming (ND) filter 38 has a dimming rate corresponding to the luminance of the light source 24. As a result, the amount of light from the light source 24 can be reduced so that the amount of light received by the photoelectric sensor 28 is at an appropriate level, and at the same time, the amount of external light can be reduced. Accordingly, the higher the luminance of the light source 24 and the higher the light reduction rate of the light reduction filter 38 (lower transmittance), the lower the ratio of external light in the light that passes through the light reduction filter 38 and enters the photoelectric sensor 28. be able to.

  As shown in FIG. 1, it is preferable that the filter means 30 is integrally formed by laminating the wavelength filters 32 and 34, the polarizing filter 36, and the neutral density filter 38 in layers. Further, it is preferable that the first surface 30 a of the filter means 30 is bonded to the emission surface 22 of the prism 16 and the second surface 30 b is bonded to the light receiving surface 28 a of the photoelectric sensor 28. Thereby, the filter means 30 can be easily positioned and fixed with respect to the prism 12.

  In the example of FIG. 1, each of the filters 32, 34, 36, and 38 of the filter unit 30 is configured so that the reflected light from the prism boundary surface 18 is the first wavelength filter 32, the polarization filter 36, the second wavelength filter 34, and the neutral density filter. It arrange | positions so that it may permeate | transmit in order of 38. However, these filters 32, 34, 36, 38 may be arranged in any order.

  Hereinafter, the operation of the refractometer 10 will be described with reference to FIG.

  When the sample S is dropped on the sample dropping window 15 and a measurement start switch (not shown) is pushed, the light source 24 is turned on by the control means, and the light from the light source 24 passes through the condenser lens 26 and the prism boundary surface 18. Incident to Most of the incident light Ri is transmitted to the sample S side at an incident angle φ smaller than the critical angle φc (n) determined according to the refractive index n of the sample S, and is larger than the critical angle φc (n). In FIG. 2, the light is totally reflected toward the photoelectric sensor 28 (see FIG. 2).

  The light ray Rr reflected by the prism boundary surface 18 enters the filter means 30. Only the P-polarized light that is in a predetermined wavelength range (for example, 550 nm to 600 nm) including the wavelength of the light source 24 and vibrates in parallel with the refractive index measurement surface A is transmitted to the photoelectric sensor 28 by the filter unit 30. Further, the amount of light transmitted through the filter means 30 is reduced so as to be within an appropriate range of the amount of light received by the photoelectric sensor 28.

  The reflected light from the light source 24 is mainly composed of a wavelength of about 589 nm. On the other hand, incident light (external light) from the outside includes wavelength components covering the entire region from infrared rays to ultraviolet rays. Accordingly, by transmitting only light having a wavelength of around 589 nm by the filter means 30, most of the incident light from the outside is blocked, and most of the reflected light from the light source 24 is incident on the photoelectric sensor 28. be able to. Further, by allowing only the P-polarized light to pass through the filter unit 30 and reducing the amount of transmitted light, the external light component in the incident light to the photoelectric sensor 28 can be further reduced.

  An electrical signal corresponding to the amount of received light is output from each light receiving element of the photoelectric sensor 28, and this output is input to a calculation means (not shown) to obtain a light amount distribution curve. In this calculation means, the critical angle point Pc corresponding to the critical angle φc (n) is calculated based on the light quantity distribution curve, and the refractive index n of the sample S is obtained. More specifically, the critical angle point Pc is calculated by the following method.

  First, the range of the light quantity distribution curve used for calculating the critical angle point (position on the photoelectric sensor corresponding to the critical angle) Pc is determined. This range is an address range corresponding to a predetermined number (for example, 30) of data before and after the position (address) at which the differential value of the light amount distribution curve is maximized. Or when the measurement range of the refractive index of the refractometer 10 is very limited, it is good also as a predetermined range according to the range of the refractive index.

により、重心位置Ｐｃ’を算定する。式（１）において、Ｘｉは各受光素子の位置（アドレス）を表し、ＩｉはＸｉにおける受光量（Ｖ）を表す。式１から理解されるように、重心位置Ｐｃ’は、光量分布曲線の一次微分曲線（或いは一次差分曲線）の重心位置である。 Next, using m data in this range,

To calculate the center of gravity position Pc ′. In Formula (1), Xi represents the position (address) of each light receiving element, and Ii represents the amount of received light (V) at Xi. As understood from Equation 1, the barycentric position Pc ′ is the barycentric position of the primary differential curve (or the primary difference curve) of the light amount distribution curve.

  Finally, a constant C is added to the barycentric position Pc ′ to obtain a critical angle point Pc (= Pc ′ + C). The constant C is a value determined in advance by an experiment using a sample whose refractive index is known.

  When the light amount distribution curve includes a large amount of external light, the shape of the light amount distribution curve and the first derivative curve on the transmission region side changes with the temporal and spatial changes of the external light. Accordingly, the center of gravity position Pc 'varies greatly from measurement to measurement with respect to the true critical angle point, and a correct refractive index cannot be obtained.

  On the other hand, when the light amount distribution curve does not include outside light, it is possible to obtain a stable barycentric position Pc ′.

  Therefore, according to one embodiment of the refractometer according to the present invention, the critical angle point Pc can be obtained more accurately by the above-described method, and the refractive index can be measured with high accuracy.

  Even when the outside light is very strong, measurement can be performed without exceeding the dynamic range of the photoelectric sensor 28.

  In the above embodiment, the photoelectric sensor 28 may be configured to perform scanning when the light source 24 is turned on and off. In this case, a light amount distribution curve at the time of lighting and a light amount distribution curve at the time of turning off the light are detected, and the calculation means calculates the critical angle point Pc based on the light amount distribution curve obtained by subtraction thereof. As a result, the influence of outside light is almost eliminated, so that the refractive index n can be measured more accurately even in a very bright place such as outdoors.

  In short, an embodiment of the refractometer according to the present invention has the following characteristics.

1. The light from the light source (24) is incident on the boundary surface (18) of the prism (16) that forms an interface with the sample (S), and the light reflected by the prism boundary surface is detected by the photoelectric sensor (28). A refractometer (10) for measuring a refractive index of the sample from an output signal of the photoelectric sensor,
Filter means (30) disposed between the prism interface and the photoelectric sensor;
The filter means includes wavelength filters (32, 34) that selectively transmit light in a predetermined wavelength range including the wavelength (L) of light from the light source.

2. The wavelength filter is
A first filter (32) for selectively blocking light in a wavelength range from a wavelength longer than a wavelength of light from a light source (L) by a predetermined wavelength to a maximum value of a detection wavelength of the photoelectric sensor (28);
A second filter (34) for selectively blocking light in a wavelength range from a wavelength shorter than a wavelength (L) of light from the light source by a predetermined wavelength to a minimum value of a detection wavelength of the photoelectric sensor (28). .

  3. The filter means (30) includes a polarization filter (36) that selectively passes linearly polarized light.

  4). The filter means (30) is integrally formed by laminating the wavelength filters (32, 34) and the polarizing filter (36) in layers.

  5. The filter means (30) is bonded to the prism (16) on the first surface and is bonded to the photoelectric sensor (28) on the second surface.

  6). The filter means (30) includes a neutral density filter (38).

  In addition, this invention is not limited to the said embodiment, It can implement with a various other form. For example, the photoelectric sensor 28 and the filter unit 30 may be arranged apart from each other, and an objective lens may be provided between the photoelectric sensor 28 and the filter unit 30. Further, the light source 24 and the prism 16 may be arranged apart from each other, and a condenser lens may be provided between the light source 24 and the prism 16. The critical angle point can also be calculated by a method using the second derivative of the light amount distribution curve or both the first derivative and the second derivative.

  The refractometer has the following effects.

(1) Even in bright places such as outdoors, the influence of outside light can be reduced and the refractive index can be measured with high accuracy.
(2) Easy to manufacture.
(3) Manufacturing cost is low.
(4) Measurement can be performed easily and efficiently.

DESCRIPTION OF SYMBOLS 10 Refractometer 12 Frame 14 Sample stage 15 Sample dropping window part 16 Prism 18 Prism boundary surface 20 Prism entrance surface 22 Prism exit surface 24 Light source 28 Photoelectric sensor 30 Filter means 32 First wavelength filter 34 Second wavelength filter 36 Polarization filter 38 Reduction Light filter

Claims (5)

A prism (16) having an interface (18) forming an interface with the sample (S);
A light source (24) for causing light to enter the boundary surface (18) of the prism;
A photoelectric sensor (28) having a plurality of light receiving elements for detecting light reflected by the prism boundary surface;
A critical angle point (Pc), which is a position on the photoelectric sensor corresponding to the critical angle (φc), is calculated based on a light amount distribution curve obtained from the amount of light received by each light receiving element of the photoelectric sensor (28). Computing means for obtaining the refractive index (n) of the sample (S) based on the point (Pc);
With
The critical angle point (Pc) is
Formula (1)

as well as
Formula (2) Pc = Pc ′ + C
Calculated by
In the formula (1), Xi represents the position of the light receiving element, Ii represents the received light amount (V) in the light-receiving element in Xi, m is Ri number der of the light receiving element used in the calculation,
In the formula (2), C is a refractometer that is a constant determined in advance by an experiment using a sample having a known refractive index.   The refractometer according to claim 1, further comprising filter means (30) disposed between the prism interface and the photoelectric sensor. The refractometer according to claim 2 , wherein the filter means includes a wavelength filter (32, 34) that selectively transmits light in a predetermined wavelength range including a wavelength (L) of light from a light source. The wavelength filter is
A first filter (32) for selectively blocking light in a wavelength range from a wavelength longer than a wavelength of light from a light source (L) by a predetermined wavelength to a maximum value of a detection wavelength of the photoelectric sensor (28);
A second filter (34) for selectively blocking light in a wavelength range from a wavelength shorter than a wavelength (L) of light from the light source by a predetermined wavelength to a minimum value of a detection wavelength of the photoelectric sensor (28). The refractometer according to claim 3 . A refractometer according to claim 2 , wherein the filter means (30) comprises a polarizing filter (36) for selectively passing linearly polarized light.

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