JPS6130169Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to an optical physical quantity measuring device that measures a physical quantity by changing the intensity of two lights of different wavelengths.

A conventional example of this type of measuring device is shown in FIG. According to the time chart shown in FIG. 2, light beams with wavelengths λ ₁ and λ ₂ enter the multiplexer 3 from the light source 1 with the wavelength λ ₁ and the light source 2 with the wavelength λ ₂ , and are transmitted through the optical fiber 4 and sent to the detection unit 5. leading to. In the detector 5, the λ ₁ and λ ₂ lights are given differential changes in intensity. If the detection unit 5 detects displacement, for example, a filter that transmits the light of λ ₁ and a filter that transmits the light of λ ₂ are arranged on the plate 5a so as to be symmetrical to the optical path when the displacement is zero. Then, the intensities of the λ ₁ and λ ₂ lights transmitted through the plate 5a are equal when the displacement is zero, and when a displacement occurs, one of them becomes large and the other becomes small. The light emitted from the detection unit 5 is demultiplexed by a demultiplexer 7, and then sent to a photoreceiver 8, respectively.
The signal is converted into an electric signal at 9, differentially amplified at a differential amplifier 10, and the amount of displacement at the detection section 5 is measured.

However, the optical physical quantity measuring device described above has the following drawbacks.

[1] The power of the light passing through the optical fiber is about several μW when an LED is used as the light source, and in order to detect minute changes in the signal, it is necessary to detect weak light of 0.1% or less. As a result, noise such as shot noise and thermal noise becomes noticeable, making highly accurate measurement difficult.

[2] In order to improve the accuracy of differential detection, increasing the gain of the amplifier after the photoreceiver makes it impossible to obtain a large dynamic range and increases noise. In other words, amplifier errors directly affect the measurement results.

The present invention was made in order to eliminate the above-mentioned drawbacks, and in order to solve the above-mentioned drawback [2], a closed system is constructed to reduce the influence of the amplifier.
To solve the problem in item [1], pulse width modulation is used to make the total amount of light within the pulse period of λ ₁ and λ ₂ equal in the light receiving part, and the signal is detected by the pulse width, so shot noise, Reduce the effects of thermal noise. Furthermore, in order to improve the followability of pulse width modulation, current A/D conversion techniques (successive approximation, follow-up comparison, etc.) are incorporated.

Embodiments of the present invention will be described below with reference to the drawings. FIG. 3 shows the basic configuration of the present invention. In Fig. 3, two 14 are light emitters of λ ₁ and λ ₂ ,
12 and 13 are respective drive circuits. The light is guided to a detection section 17 by an optical fiber 16. In FIG. 3, the optical fiber 16 has one wavelength per wavelength.
Although the optical fiber is used, it is also possible to transmit the signal using a single optical fiber using a demultiplexer and a multiplexer as in the conventional example.
Now, if the detection unit 17 is a displacement sensor, the sensor is equipped with filters for wavelengths λ ₁ and λ ₂ , and the light of wavelength λ ₁ is (1+Δ) for displacement Δ.
The light of wavelength λ ₂ is given a transmittance proportional to (1-Δ), and the output is differential. The differentially changed light is converted into an electrical signal by the photoreceiver 15, and then passed through a filter, an amplifier,
It enters a comparison section 18 consisting of a comparator. Reference numeral 19 is a register operated by a signal from the comparator 18. When configured by successive approximation, it is a successive approximation register, and when configured by tracking comparison, it is an up-down counter.
The output 20 of this register 19 is the output of this system and is a digital output. Reference numeral 11 is a part that converts the digital output of the register 19 into analog, and is a pulse width modulation type D/A converter.
3 is controlled.

Next, an embodiment of the present invention for a displacement sensor having a successive approximation type configuration based on the above basic configuration will be described with reference to FIG.
2 and 23 are light source driving circuits, 24 is an inverter,
5 is a light source of wavelength λ ₁ , 26 is a light source of wavelength λ ₂ ,
Reference numeral 7 denotes a multiplexer/demultiplexer, 28 denotes an optical fiber, 29 denotes a detector for providing a differential change, which in this case is a displacement sensor, 30 and 31 denote photodetectors for the light of λ ₁ and λ ₂ , respectively, 32 and 33 denote first filter amplifiers,
The reference numeral 34 denotes a comparator, 35 denotes a successive approximation register, 36 denotes a register, 37 denotes a control logic, 38 denotes a control signal, and 39 denotes a digital output.

In the optical applied physical quantity measuring device of the embodiment of the present invention configured as described above, the differential output type displacement sensor is initially in a balanced state, and after passing through the first and second filter amplifiers 32 and 33, The outputs are adjusted to equal values. At this time, the wavelengths λ ₁ and λ ₂
The input optical pulse is in the state shown in FIG. 2, and the duty ratio is 1:1. Now, when the displacement sensor 29 detects the displacement amount Δ, the optical output also changes λ ₁ accordingly.
The light at λ2 undergoes a change of (1 + Δ) times, and the light at λ ₂ undergoes a change of (1 - Δ) times. These optical outputs are converted into electrical signals by photodetectors 30 and 31, respectively. Light receiver 30
The output is converted into an average value of the DC component within the pulse period of the pulsed light by the first filter amplifier 32, and the signal is amplified and outputted as _E1 . The output of the photoreceiver 31 is converted by the second filter amplifier 33 into an average value of the DC component within the pulse period of the pulsed light of _λ2 , and the signal is amplified and outputted as _E2 .

These two outputs E ₁ and E ₂ enter a comparator 34 and are compared. The successive approximation register 35 switches on the highest digit and sends a digital signal to the pulse width modulation circuit 21 and the register 36 according to a command from the control logic 37. The pulse width modulation circuit 21 D/A converts the input digital signal and outputs it as an analog signal.The output signal controls the light source drive circuits 22 and 23, and the pulse width modulation circuit ₂₁ controls the light source drive circuits 22 and 23 according to the signal value. The pulse width is shortened, and the pulse width of the optical pulse with wavelength λ ₂ is increased. Then, the total amount of input light of λ ₁ within its pulse period decreases, and the output E ₁ of the first filter amplifier 32 decreases. On the other hand, for the input light of λ ₂ , the total amount of light within the pulse period increases, and the second
The output E ₂ of the filter amplifier 33 increases. These are compared by a comparator 34, and if E ₁ >E ₂ , the successive approximation register 35 directly advances to the next digit. If E ₁ > E ₂ , the highest digit is switched off and the next digit is switched on. According to the digital output output from the successive approximation register 35 by this switched-on digit, the pulse width modulation circuit 21 outputs the λ 1 light source 25 and the λ ₂ light source 25 via the light source drive circuits 22 and ₂₃ .
The pulse width of the light pulse of the light source 26 is changed. below,
Try the same way up to the lowest digit until E ₁ =E ₂ . Then, λ when E ₁ = E ₂ holds true
₁ and λ ₂ input light as shown in FIG _.
The pulse width of λ 2 is small, and the pulse width of λ ₂ is large. At this time, if the on/off state of each digit is read out, a digitized output of the difference between the pulse widths of the λ ₁ and λ ₂ lights can be obtained. When the comparison operation is completed, a signal indicating that the comparison result has been output is sent from the successive approximation register 35 to the control logic 37, and the control logic 37 sends a signal to the register 36.
A command to read the comparison result is sent to register 36.
The difference in pulse width when E ₁ =E ₂ is established is output digitally. Since this pulse width difference is a function of displacement, this causes the detection unit 29
The displacement at can be measured.

As is clear from the above explanation, the optical applied physical quantity measuring device according to the present invention does not measure signals by amplitude, but by pulse width. By appropriately lengthening the reference pulse width, noise can be canceled by the integrating circuit in the filter stage, and when measuring the pulse width, an accurate clock signal can be easily obtained using a crystal, etc. This pulse width is not affected by the noise. Furthermore, since a feedback circuit is configured, the requirement for accuracy of the amplifiers 32 and 33 can be reduced, and digital signals can be directly taken out as outputs. This is because this device itself has a detection section 29.
This is because the A/D converter is configured to include the following. As described above, according to the present invention, it is possible to ignore the influence of noise and amplifier errors in the measurement of minute changes, which are the shortcomings of the conventional technology, with a simple circuit, and it is possible to use optical applied physical quantities that can easily obtain digital output. A measuring device can be provided.

Note that in the above embodiment, the pulse widths of the lights with wavelengths λ ₁ and λ ₂ were changed during a certain period of time to change the duty ratio, but it is also possible to fix the pulse width of one light and use it as a reference light. , only the pulse width of the other light may be changed. In this case, the driving circuit for one of the light sources may be separated from the pulse width modulation circuit to fix the pulse width of the light source. Also,
In the embodiment described above, the pulsed lights of wavelengths λ ₁ and λ ₂ are alternated, but the pulsed lights may start at the same time.

[Brief explanation of the drawing]

Figure 1 is a block diagram showing a conventional example of an optical physical quantity measuring device, Figure 2 is a time chart showing the waveform of input light to the detection section, and Figure 3 is the basic configuration of the optical physical quantity measuring device according to the present invention. FIG. 4 is a block diagram showing an optical physical quantity measuring device according to an embodiment of the present invention, and FIG. 5 shows the waveform of pulse width modulated input light to the detection unit in the device of FIG. 4. It is a time chart. 11... Pulse width modulation circuit, 12, 13... Light source drive circuit, 14... Light source, 15... Light receiver, 1
6... Optical fiber, 17... Detection section, 18...
Comparator, 19...Register, 21...Pulse width modulation circuit, 22, 23...Light source drive circuit, 24...
Inverter, 25... Light source with wavelength λ ₁ , 26...
Light source with wavelength λ ₂ , 27... Multiplexer/demultiplexer, 28...
. . . Optical fiber, 29 . . . Detection unit that gives differential change, 30, 31 .
...Comparator, 35...Successive approximation register, 36...
Register, 37... Control logic, 38
...Control signal, 39...Digital output.

Claims (1)

[Claims for Utility Model Registration] (1) A light source with a wavelength of λ ₁ and a light source with a wavelength of λ ₂ that are driven at a constant cycle through their respective light source drive circuits, and pulsed light from each of these light sources caused by changes in physical quantities. a detection unit that differentially changes the intensity of light in response; a light receiver with a wavelength λ ₁ and a light receiver with a wavelength λ ₂ that output electrical signals proportional to the intensity of each output light from the detection unit; A first filter amplifier that converts the output signal from the photoreceiver with the wavelength λ ₁ into an average value of the DC component within the pulse period of the pulsed light with the wavelength λ 1 and amplifies the signal, and an output from the photoreceiver _with the wavelength λ ₂ A second filter amplifier that converts the signal into the average value of the DC component within the pulse period of the pulsed light of wavelength λ ₂ and amplifies the signal, and a digital output of the successive approximation register that compares these two signals and makes the difference zero. and a pulsed light that controls each of the light source drive circuits according to the digital output of the successive approximation register to change the duty ratio of the pulse width of the pulsed light of wavelength λ ₁ and the pulsed light of wavelength λ ₂ . a width modulation circuit;
and a register that outputs the digital output of the successive approximation register as a measured value of a change in the physical quantity in the detection section when the difference between the two signals becomes zero. (2) The optical applied physical quantity measuring device according to claim 1, wherein a light source with a wavelength λ ₁ and a light source with a wavelength λ ₂ are driven alternately within a certain period of time. (3) The optical applied physical quantity measuring device according to claim 1, wherein a light source with a wavelength λ ₁ and a light source with a wavelength λ ₂ are driven simultaneously. (4) Utility model registration claim 1, characterized in that one of the light source driving circuits is separated from the pulse width modulation circuit to fix the optical pulse width and change the optical pulse width of only the other light source. The optical applied physical quantity measuring device described above.