JP5333179B2 - Refractometer - Google Patents

Description

  The present invention relates to a refractometer used for measuring the sugar content and concentration of a liquid, and more particularly to a technique for reducing the influence of ambient light.

  As shown in FIG. 4, the conventional refractometer for measuring the sugar content and concentration of the liquid has a sample portion 1 that protects the liquid sample S dropped on the prism 4, and a boundary surface between the sample S and the prism 4. A light source 2 that emits incident light Ro, a light-receiving element array that is arranged in the increasing / decreasing direction of the reflection angle, a photoelectric detector 3 that receives light totally reflected at the boundary surface, and light to the photoelectric detector 3 The polarizing plate 25 is disposed on the incident side and cuts P-polarized light.

The total reflected light Rc and the critical angle θc at which total reflection occurs are read from the output signals of the respective light receiving elements of the photoelectric detector 3, and the refractive index n of the sample S is calculated from the following equation.
n = no × sin θc (1)
Here, no is the refractive index of the prism 4.

  However, this type of refractometer is often used for simple measurements such as measuring the juice of fruits and vegetables mainly in the field or workplace, and it is preferable that the state of the sample S can be visually observed from the outside. The sample part 1 is open to the outside. For this reason, in addition to the total reflected light Rc to be measured, extra disturbing light incident on the prism 4 from the outside enters the photoelectric detector 3, which hinders accurate measurement of the refractive index.

  The polarizing plate 25 disposed between the prism 4 and the photoelectric detector 3 cuts the P-polarized light Rp having a large proportion of disturbance light. When light is incident obliquely on the medium, the transmittance of the P-polarized light Rp is higher than that of the S-polarized light Rs. By cutting the P-polarized light Rp by the polarizing plate 25, disturbance light can be greatly reduced, The rate can be accurately measured (see, for example, Patent Document 1).

JP 2004-271360 A

  In the conventional refractometer shown in FIG. 4, for example, if the constituent material of the prism 4 is BK7 glass and the disturbance light incident on the prism 4 is non-polarized light having a wavelength of 589 nm incident at an incident angle of 56 °, the P-polarized component It can be calculated from Fresnel's well-known formula that 100% and S-polarized light components enter the prism 4. The P-polarized light Rp is cut immediately before the photoelectric detector 3. However, when disturbance light is diffusely reflected and repeatedly scattered inside the prism 4, the strong P-polarized light Rp is converted into light having an S-polarized component, and the polarizing plate 25. And enters the photoelectric detector 3 as noise light. The amount of noise light that enters the photoelectric detector 3 increases in proportion to the absolute amount of disturbance light that enters the prism 4, which is an obstacle to obtaining an accurate refractive index.

  The present invention includes a sample portion having a through-hole into which a liquid sample is dropped, a sample surface in contact with a lower surface opening of the through-hole, an incident surface on which light from a light source is incident on the sample surface, A prism having a detection surface on which a photoelectric detector for detecting reflected light from the sample surface is disposed, the light source for emitting light incident on the sample surface, and detecting reflected light from the sample surface In the refractometer including the photoelectric detector, a polarizing plate that cuts P-polarized light so as to be openable and closable is disposed at the upper surface opening of the through hole. Furthermore, a polarizing plate that cuts S-polarized light may be disposed between the photoelectric detector and the detection surface. Therefore, there is little noise light incident on the photoelectric detector, and the state of the dropped liquid sample can be observed.

  The disturbance light incident on the prism is removed from the strong P-polarized light and becomes only the weak S-polarized light, the scattered light inside the prism is also greatly reduced, and the noise light incident on the photoelectric detector is reduced and accuracy is reduced. A good refractive index can be measured. In addition, it is possible to observe the state of the sample dropped by the S-polarized light that passes through the polarizing plate as before. Furthermore, by disposing a polarizing plate that cuts S-polarized light between the photoelectric detector and the detection surface of the prism, the S-polarized component of the disturbance light can be removed, and the refractive index can be measured with higher accuracy. it can. In this case, the light incident on the photoelectric detector is light having P-polarized light component generated by repeated irregular reflection of P-polarized light reflected by the prism-sample interface and S-polarized light incident on the prism. The light having is weak light generated from weakly polarized S-polarized light and has little adverse effect on accuracy.

It is a figure which shows schematic structure of the refractometer by the Example of this invention. It is a light quantity distribution curve obtained from the output signal of a photoelectric detector. It is a figure which shows schematic structure of the modification of the refractometer by the Example of this invention. It is a figure which shows schematic structure of the conventional refractometer.

  A refractometer according to an embodiment of the present invention includes a sample surface in contact with a dropped liquid sample, an incident surface that allows light from a light source to enter the sample surface, and photoelectric detection that detects reflected light from the sample surface. A prism having a detection surface on which a vessel is disposed and a polarizing plate that cuts P-polarized light on the upper surface are disposed to be openable and closable. And a calculation control system for calculating the refractive index from the output signal of the photoelectric detector.

  An embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a diagram showing a schematic configuration of a refractometer according to an embodiment of the present invention. FIG. 2 is a light amount distribution curve Vp obtained from the output signal of the photoelectric detector 3.

  As shown in FIG. 1, the refractometer according to the embodiment of the present invention includes a sample surface 4b in contact with the dropped liquid sample S, and an incident surface on which light from the light source 2 enters the sample surface 4b as incident light Ro. 4a, a prism 4 having a detection surface 4c on which a photoelectric detector 3 for receiving total reflection light Rc from the sample surface 4b, and the like are in contact with the sample surface 4b, and a dropping portion of the liquid sample S It comprises a sample part 1 in which a mortar-shaped through-hole is formed and an arithmetic control system for calculating a refractive index from the output signal of the photoelectric detector 3. Note that no is the refractive index of the prism 4 and n is the refractive index of the sample S. The critical angle θc is a critical angle at which total reflection occurs.

  A polarizing plate 5 that cuts P-polarized light Rp is held on a top surface of the sample unit 1 via a hinge 6 so as to be opened and closed. “Openable / closable” means that the operator can switch between a state in which the upper surface of the opening of the sample unit 1 is covered with the polarizing plate 5 and a state in which the sample is not covered. The photoelectric detector 3 is composed of a light receiving element array arranged in the increasing / decreasing direction of the reflection angle. The arithmetic control system is stored with a light receiving element switching means 10 for sequentially selecting the light receiving elements in the light receiving element array, and a light quantity reading storage means 11 for digitizing the amount of light incident on the selected light receiving elements and storing it for each light receiving element number. The critical angle point detecting means 12 for detecting the critical angle θc from the distribution of the amount of light corresponding to the light receiving element number, and the refractive index calculating means 13 for calculating the refractive index by applying the detected critical angle θc to the equation (1). Consists of.

  In FIG. 2, the relationship of the light quantity (V) stored corresponding to the light receiving element number (I) is shown by a light quantity distribution curve Vp. The critical angle point detection means 12 obtains a differential curve Vd of the light quantity distribution curve Vp, and when the peak value of the differential curve Vd exceeds a predetermined value, the light receiving element number corresponding to the peak value is set as the critical angle point Ic. The relationship between the critical angle point Ic and the critical angle θc can be specified from the critical angle point Ic when a liquid sample having a known critical angle θc at which total reflection occurs is measured, and conversion for converting the critical angle point Ic to the critical angle θc Find the formula. The critical angle θc of the unknown sample calculated by the conversion formula is transmitted to the refractive index calculating means 13, and the refractive index of the unknown sample is calculated from the formula (1).

  Since the present invention has the above-described configuration, the disturbance light incident on the prism 4 is removed from the high-intensity P-polarized light Rp, and becomes only the low-intensity S-polarized light Rs, and the scattered light inside the prism 4 is also greatly reduced. Then, the noise light incident on the photoelectric detector 3 is reduced, the light quantity distribution curve Vp is clearly separated from the low value to the high value around the critical angle point Ic, and the differential curve Vd having a clear peak is obtained. A good refractive index can be measured. Moreover, the state observation of the sample S can be performed from the outside by the S-polarized light Rs transmitted through the polarizing plate 5 as usual.

  In the embodiment shown in FIG. 1, a polarizing plate that cuts S-polarized light is not provided, but as shown in FIG. 3, polarized light that cuts S-polarized light between the photoelectric detector 3 and the detection surface 4c of the prism 4. A plate 15 may be provided. By removing the S-polarized light component of the disturbance light with the polarizing plate 15, it is possible to expect a more accurate refractive index measurement. In this case, the light incident on the photoelectric detector 3 is light having P-polarized light components generated by repeated irregular reflection of the P-polarized light reflected at the interface between the prism 4 and the sample S and the S-polarized light incident on the prism 4. The light having the P-polarized light component is weak light generated by the weak S-polarized light, and has little adverse effect on accuracy. 3 are the same as those in FIG. 1 and are not described here. As described above, the present invention is not limited to the illustrated examples and includes various modifications.

  The present invention relates to a refractometer used for measuring the sugar content, concentration, and the like of a liquid, and may be used particularly for a technique for reducing the influence of ambient light.

DESCRIPTION OF SYMBOLS 1 Sample part 2 Light source 3 Photoelectric detector 4 Prism 4a Incidence surface 4b Sample surface 4c Detection surface 5 Polarizing plate 6 Hinge 10 Light receiving element switching means 11 Light quantity reading storage means 12 Critical angle point detection means 13 Refractive index calculation means 15 Polarizing index 25 Polarizing plate θc Critical angle Ic Critical angle point Rc Total reflected light Ro Incident light Rp P-polarized light Rs S-polarized light S Sample Vd Differential curve Vp Light distribution curve

Claims (2)

  A sample portion having a through-hole into which a liquid sample is dropped, a sample surface in contact with a lower surface opening of the through-hole, an incident surface on which light from a light source is incident on the sample surface, and from the sample surface A prism having a detection surface provided with a photoelectric detector for detecting reflected light, the light source for emitting light incident on the sample surface, and the photoelectric detection for detecting reflected light from the sample surface A refractometer comprising: a polarizing plate that cuts P-polarized light so as to be openable and closable at an upper surface opening of the through hole.   2. The refractometer according to claim 1, wherein a polarizing plate for cutting S-polarized light is disposed between the photoelectric detector and the detection surface.

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