JPH04198844A - Liquid concentration sensor - Google Patents

Abstract

PURPOSE:To accurately measure the concn. of a liquid by holding the measured voltage of a detection part obtained when an LED emits light and the measured voltage thereof when the LED emits no light to a sample hold circuit and subtracting both voltages to remove the effect of an external disturbance light component. CONSTITUTION:A part of the laser beam reflected from a reflecting film 12a is transmitted through a liquid 7 to be measured at a sensing part 1A and the remainder thereof is totally reflected from an inner surface to be incident to a photosensor 14b. The quantity of the laser beam generating total reflection becomes the function of the refractive index of the liquid 7 and, since there is definite correlation between the concn. and refractive index of the liquid 7, the quantity of laser beam, that is, the quantity of the beam incident to the photosensor 14b is detected to make it possible to measure the concn. of the liquid 7. At the time of measurement, an LED 14a intermittently emits beam and the output VA of the sensor 14b at the time of the emission of beam is held to a sample hold circuit 18 and the output VB thereof at the time of the non-emission of beam is held to a sample hold circuit 19. Subsequently, the operation of VA-VB is performed by a subtraction circuit 20 and signal voltage not affected by a disturbance light component is calculated. Next, the concn. of the liquid is calculated by an operation circuit 21 to be displayed on a display part 22.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a liquid concentration sensor that determines the concentration of a liquid to be measured by utilizing the reflection characteristics in a detection section or changes depending on the concentration value of the liquid to be measured. .

(Prior Art) It has been known that there is a certain correlation between the concentration (volume fraction) of a liquid and the refractive index of that liquid. Taking advantage of this correlation, a liquid concentration sensor as shown in FIG. 10 is used.

In the figure, 1 is a first optical fiber, one end of this optical fiber 1 is connected to an optical splitter 2, and the other end has a crat part 1a peeled off and a core part 1b with a refractive index of ncO exposed. , is considered to be the detection section.

The exposed core portion 1b of the detection portion is curved, and a reflective film 1c is formed at the tip. 3 is a light emitting part with a built-in light emitting diode that emits a light beam to the detection part 1;
is connected to the optical splitter 2 via an optical fiber 4 . Reference numeral 5 denotes a photodetection section with a built-in photosensor, which is connected to the optical splitter 2 via a third optical fiber halo. The core portion 1b, which is the detection portion of the first optical fiber 1, is placed in the liquid to be measured 7 having a refractive index of nM. 8 is an A/D converter that converts the analog data of the photosensor light detection unit 5 into digital data; 9 is an A/D converter that takes in the output data from the A/D converter 8 and the information written in the ROM10; The cPU 11 that performs calculations is a display unit that displays the calculation results of the CPU 9.

Next, the operation of the above configuration will be explained. The light beam emitted from the light emitting section 3 is sent to the second optical fiber 4. It reaches the core portion 1b of the first optical fiber 1 via the optical splitter 2. here,
Since the propagation mode in the optical fiber 1 is multimode, the angle of the light beam with respect to the inner surface of the core portion 1b includes various components.

Therefore, a part of the light beam is transmitted to the measurement liquid on the exposed inner surface of the core portion 1b, but the remaining light beam is totally reflected on the exposed inner surface of the core portion 1b. Then, the totally reflected light beam is reflected by the reflective film 1c, branched into an optical path by the optical splitter 2, and then passed through the third optical fiber 6 to the photodetector 5.
incident on the photo sensor.

The light beam incident on the photodetector 5 is converted into an analog electrical signal here. This analog electrical signal is converted into digital data by an A/D converter 8. Next, the concentration of the liquid to be measured 7 is calculated by the CPU 9, which has read various comparison data from the ROM 10, using this digital data, and the calculation result (a degree) is displayed on the display section 11.

According to the above configuration, the exposed core portion 1b of the light beam
The proportion of the amount of light that is totally reflected on the inner surface is a function of the refractive index nM of the liquid 7 to be measured. On the other hand, since there is a certain correlation between the concentration of the liquid to be measured 7 and the refractive index of the liquid to be measured 7, the amount of light beam that causes total reflection, that is, the photo sensor in the photodetector 5 By detecting the amount of light incident on the
It is also possible to measure the concentration of the liquid 7 to be measured. and,
By arbitrarily selecting the curvature of the core portion 1b, all liquids 7 to be measured whose refractive index or nkl<nco
It is possible to measure the concentration of Further, according to the second configuration, there is no generation of electrical sparks and no influence of electromagnetic induction, so it is possible to realize a liquid concentration sensor suitable for chemical plants that require safety and explosion-proof properties.

(Problem to be solved by the invention) However, in the conventional example with the above configuration, light from the outside (indoor lighting light, disturbance light such as sunlight) enters the core part 1b, and the detection voltage of the light detection part 5 This may cause measurement errors. In such a case, since the detection voltage of the photodetector 5 is not accurate, there is a problem that the determined liquid concentration is also inaccurate.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a liquid concentration sensor that can accurately measure concentration without being affected by ambient light.

(Means for Solving the Problems) The present invention that solves the above problems includes a detection section that has an end face on which a reflective film is formed and is disposed in a liquid to be measured, and a light beam is emitted to the detection section. a light-emitting section that drives the light-emitting section intermittently; a light-emitting section drive means that drives the light-emitting section intermittently; a detection section that detects the light reflected by the detection section and generates a voltage corresponding to the intensity of the reflected light; a first sample hold means for holding the detection voltage of the detection means when the light emitting section is driven by the light emitting section driving means; and a detection voltage of the detection means when the light emitting section is not driven by the light emitting section driving means. and a subtraction means for subtracting the voltage held by the first sample and hold means and the voltage held by the second sample and hold means. It is something to do.

(Function) In the liquid concentration sensor of the present invention, the light beam emitted from the light emitting section to the detecting section is reflected by the reflective film, and then a part of it is totally reflected on the inner surface of the detecting section, and then enters the detecting section. Then, this incident light is converted into a voltage according to the light amount in the detection section, and the first
sample hold means. Further, the output of the detection section when the light emitting section is not driven is held by the second sample hold means. Then, the voltage held by the first sample hold means and the voltage held by the second sample hold means are subtracted by the subtraction means, and the influence of the disturbance light component is removed according to the concentration of the liquid to be measured. You can get a signal.

(Example) Next, one embodiment of the present invention will be described using the drawings.

FIG. 1 is a block diagram showing an embodiment of the present invention.

In the figure, reference numeral 11 is a glass rod made of quartz and having a refractive index of nco. One end side (tip side) of this glass rod 12 is used as a detection part, and has a so-called beveled cylindrical shape with an end face cut obliquely at an angle α with respect to the axis. The end face is coated with a reflective film 12a. On the other end side (base end side) of the glass rod 12,
A holder 13 is provided. This holder 13 includes a light emitting diode 14a as a light emitting part whose light emitting surface abuts on the other end side end surface of the glass rod 12, and a photosensor 1 as a light detecting section whose light receiving surface abuts on the other end side end surface.
4b is also provided. Note that the glass rod 12 is disposed in the liquid to be measured 7 having a refractive index of nM.

Reference numeral 15 denotes a light emitting unit driving device that intermittently drives the light emitting diode 14a, and 16 an oscillation circuit that intermittently drives the light emitting unit driving device and switches the switch 17. ] 8 is a light emitting diode] 4 Sample and hold circuit that holds the output voltage of the photosensor 14b when the light emitting diode 14a is not emitting ■4, 19 is holding the output voltage VB of the photosensor 14b when the light emitting diode 14a is not emitting light A sample hold circuit, 20 is a subtraction circuit that subtracts 8 from 2, 21 is an arithmetic circuit that calculates the concentration of the liquid to be measured 7 from the subtraction result of the subtraction circuit 20, and 22 is an arithmetic circuit 21
This is a display unit that displays the concentration of the liquid to be measured 7 based on the calculation result.

Next, the operation of the above configuration will be explained. Light emitting diode-F'
14a or is driven by the light emitting unit driving device 15 to emit a light beam. The light beam emitted from the light emitting diode 14a propagates inside the crow rod 12, and passes through the reflective film 12a.
reflect. Since this light beam has multiple modes, part of the light beam is transmitted to the liquid to be measured 7 at the sensing part A, and the remaining light beam is totally reflected by the inner surface of the sensing part A. The totally reflected light beam then enters the photosensor 14b.

According to this configuration, the amount of light beam that causes total reflection on the inner surface of the sensing portion A of the glass rod becomes a function of the refractive index nM of the liquid 7 to be measured. On the other hand, since there is a certain correlation between the concentration of the liquid to be measured 7 and the refractive index n2 of the liquid to be measured 7, the amount of light beam that is totally reflected on the inner surface of the glass rod, that is, the amount of light that is incident on the photosensor 14b. By detecting this, the concentration of the liquid to be measured 7 can be measured.

Note that the light emitting diode 14g emits light intermittently due to the oscillation output of the oscillation circuit 16. And light emitting diode 1
The sample and hold circuit 18 holds the output V^ of the photosensor 14b when the light emitting diode 14a emits light.
4 Output V of photosensor 14b when no light is emitted
B is held by the sample hold circuit 19. For this purpose,
The switch 17 performs switching in synchronization with the oscillation circuit 16. Then, the subtraction circuit 20 subtracts VA-VB to obtain a signal voltage that is not affected by the disturbance light component. After that, the arithmetic circuit 21 calculates the concentration of the liquid to be measured 7, and the display unit 2
Display on 2.

FIG. 2 is a waveform diagram showing this situation. Here, FIG. 2(A) shows the detection signal waveform of the photodetector 5 of the conventional device. In this way, it is impossible with the conventional method to separate the signal component and the disturbance light component. On the other hand, in the liquid concentration sensor of the present invention shown in FIG. 2(B), it is possible to independently detect the voltage VB of the disturbance light component and the voltage 6 of the disturbance light component and signal component. . Therefore, VA-■8
By subtracting , it is possible to extract only the signal components (VA VB).

Note that by arbitrarily selecting the cut angle α of the end face coated with the reflective film 12a, it is possible to measure the concentration of all liquids 7 to be measured whose refractive index satisfies nM<nco.

Further, according to such a configuration, there is no generation of electrical sparks and there is no influence of electromagnetic induction, so a liquid concentration sensor suitable for chemical plants that require safety and explosion-proofness can be realized. Furthermore, since the glass rod 12 is made of quartz, it has excellent chemical resistance.

Furthermore, compared to the conventional example described above, since the glass rod 12 is used as the detection section, the detection section is more durable. Furthermore, since the diameter of the glass rod 12 used as the detection section is large, the light emitting/receiving integrated element 14, in which the light emitting diode 14a as the light emitting section and the photosensor 14b as the light detecting section are integrally provided, is mounted on the holder 13. Since it is provided on the end face of the glass rod 12 via the holder, the structure becomes simple.

Furthermore, since there is no need to use a CPU or ROM, the configuration becomes simple and inexpensive.

FIG. 3 is a circuit diagram showing a specific circuit of a main part of an embodiment of the device of the present invention. Here, FIG. 3(A) shows the integrated light/receiver element 14. The sample and hold circuit and the subtraction circuit are shown, and FIG. 3B shows the light emitting unit driving device 15 and the oscillation circuit 16. In this figure, A1-A4 are operational amplifiers, for example, LF3478F can be used. STI and Sr1 have a Schmitt trigger C, for example, CMO3409B can be used.

SR is a shift register, for example CMO34015
can be used. 3AND is a three-person AND circuit, and can be achieved by using, for example, CMO3407B. X1 to X3 are reed relays.

Also, FIG. 4 shows pulses A, B, and C created by the shift register SR, and pulses X created based on these.
I, X2. It shows X3. In addition, pulses A, B,
C and pulses XI, X2. The relationship of X3 can be expressed by the following formula.

Xl-C X2-C-B-A X3-C-B-A The operation will be explained below with reference to FIGS. 3 and 4.

Trl is driven by a pulse C generated by shift register SR, and reed relay X1 is intermittently driven. As a result, the light emitting diode '14a emits light intermittently. Of this light emission output, only the reflected light from the glass rod 12 is detected by the photosensor 14b. This detected voltage is amplified by the operational amplifier A1 and then sampled and held by the operational amplifier A2. Here, since X2 is driven when Xl is off, the hold value of operational amplifier A2 is VB of the disturbance light component. On the other hand, the operational amplifier A3 performs subtraction processing, and the operational amplifier A4 samples and holds the result. Since X3 is driven during the on period of Xl, the hold value of operational amplifier A4 becomes V, -V8. Therefore, only the signal component from which the disturbance light component has been removed is extracted.

Here, FIG. 5 shows the relationship between the alcohol concentration of the liquid to be measured 7 and the output voltage of the photosensor 14b when the apparatus having the above configuration was actually tested under the following conditions.

■Glass lot 12 Material: quartz glass Size φ3 +n+n, length 30mm α-79゜■Receiving/emitting integrated element 14 TLP907 (manufactured by Toshiba) ■Measurement liquid 7 Mixed liquid of distilled water and whiskey with an alcohol concentration of 40% ■Room temperature: 20° C. In this way, it was confirmed that there is a linear relationship between the alcohol concentration and the output voltage of the photosensor 14b.

In the above embodiment, the tip of the glass rod 12 is shaped like a beveled cylinder, but the shape is not limited thereto.

For example, as shown in FIG. 6, a reflective film 30a may be provided on the cut surface of a glass rod 30 whose tip is cut into a ■ shape, or as shown in FIG. 7, whose tip is cut into a conical shape. A reflective film 31a is applied to the cut surface of the glass rod 31.
may be provided. Furthermore, as shown in FIG. 8, in the collar slot 12, part of the light beam is transmitted to the liquid to be measured 7, and the remaining light beam is reflected on the glass surface other than the part A (sensing part) where it is totally reflected. A coating 12b (eg aluminum vapor deposition) may also be applied. By doing so, the performance of the sensor can be improved.

FIG. 9 is an external view showing the external appearance of the liquid concentration sensor according to the present invention. The same numbers are given to the parts that have already been explained, and the explanation will be omitted. In this figure, SW is a main switch, and each part starts its operation by operating this switch SW. Further, D1 to D5 are light emitting diodes that constitute the display section 22. This light emitting diode DI~D
The density is displayed by the number of lights emitted or turned off. Also,
The number of light emitting diodes in FIG. 9 is not limited to this example. That is, it is possible to display the concentration with a desired resolution by adjusting the number of light emitting diodes.

In the above-mentioned embodiments, a glass rod is used as the detection section disposed in the liquid to be measured, but the present invention is not limited to this. That is, it may be made of transparent resin or the like, and various types of rotary fibers may be used.

(Effects of the Invention) As explained in detail above, in the present invention, after sample-holding the voltage measured by the detection unit when the light emitting diode emits light and the voltage measured by the detection unit when the light emitting diode does not emit light, , the two mold pressures are subtracted to obtain measurement results that are not affected by disturbance light components. Therefore, it is possible to realize a liquid concentration sensor that can accurately measure concentration without being affected by ambient light.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram showing an embodiment of the present invention, FIG. Figure 3 is a timing chart showing the signal timing of each part of the circuit, Figure 5 is a characteristic diagram showing the relationship between the light reception output and alcohol concentration in Figure 1, and Figures 6 to 8 are other examples of glass rods. FIG. 9 is an external view showing the appearance of a liquid concentration sensor, and FIG. 10 is a configuration diagram showing the configuration of a conventional example. 7...Liquid to be measured 12.Ear slot 12a...
Reflective film 13, holder 14, light emitting and receiving integrated element 14a, light emitting diode 14b, photosensor 15, light emitting unit drive device 16, oscillation circuit 17, switch 18, 19,
...Sample hold circuit 20...Subtraction circuit 21
...Arithmetic circuit 22...Display section

Claims (1)

[Claims] A detection section having an end surface on which a reflective film is formed and disposed in the liquid to be measured; a light emitting section that emits a light beam to the detection section; and a light emitting section that emits a light beam to the detection section; a light emitting unit driving means for driving; a detecting means for detecting reflected light at the detection unit and generating a voltage according to the intensity of the reflected light; a first sample hold means for holding the detection voltage of the detection means; a second sample hold means for holding the detection voltage of the detection means when the light emitting section is not driven by the light emitting section driving means; A liquid concentration sensor comprising: a subtraction means for subtracting a voltage held by the first sample hold means and a voltage held by the second sample hold means.