JPH06331660A - Optical sensor - Google Patents

Abstract

PURPOSE:To enable measurement at a high response characteristic by enabling the noise component of light input to an optical fiber from a light source to be eliminated, enabling detection using an optical fiber sensor at high accuracy, and eliminating the necessity of passing a detection signal from the optical fiber sensor through a band-pass filter. CONSTITUTION:Part of light input to an optical sensor portion 1 from a light source 8 is separated by a polarizer 2, guided to a monitoring light receiver 18 by means of an optical fiber 6, amplified by a light-receiving amplifier 19, and input to a comparator 11. The comparator 11 outputs a level difference between the output of a reference voltage generator 12 which generates a driving reference voltage and the output of the light-receiving amplifier 19; to set this output to zero, a light-source driving level control portion 10 outputs an appropriate voltage to a light source driving portion 9, which in turn controls the output level of the light source 8. A detection signal from the optical sensor portion 1 is received by the light receiver 14 of a signal detecting system.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel optical type sensor, and more particularly to an optical type sensor which eliminates fluctuations of input light to an optical fiber sensor and has high sensitivity and high response speed.

[0002]

2. Description of the Related Art Optical sensors that detect AC signals include optical current sensors and optical voltage sensors. Here, the optical system current / voltage sensor is an optical fiber sensor to which a magneto-optical effect such as the Faraday effect or an electro-optical effect such as the Pockels effect is applied. Since the optical fiber sensor is measured by using light, it can be measured in a state of being electrically insulated from the system under measurement, and thus can be used as a monitoring sensor of the power system. Since this optical fiber sensor modulates the intensity of light in proportion to the measured current / voltage, the measurement result is obtained as a light intensity signal proportionally modulated based on the measured value. Therefore, the measured values of current and voltage can be obtained by examining the modulation intensity of the light output from the optical fiber sensor. Then, in order to investigate such a modulation intensity of light, an electro-optical conversion (E / O conversion) circuit and a photoelectric conversion (O / E conversion) circuit are provided in an optical system sensor circuit using an optical fiber sensor. You will be prepared.

Conventionally, an optical sensor having a structure shown in FIG. 3 is generally used. The optical sensor unit 1 of the optical sensor takes out one polarization component of the polarization components of light and arranges a polarizer 2 and an analyzer 5 arranged to detect the polarization state of light, a Faraday element, a Pockels element, and the like. Sensor element 4 and a quarter wavelength plate 3 provided when the sensor element 4 is a voltage sensor using a Pockels element.

Further, the sensor circuit 7 is provided with a light source drive section 9 for driving a light source 8 such as a light emitting diode,
The light source drive unit 9 is a light receiver 14 such as a pin photodiode.
The light source 9 is driven so that the received light amount becomes constant. Therefore, after the output of the light receiver 14 is amplified by the light receiving amplifier 15, the light emission level of the light source 8 is feedback-controlled by using the value obtained by removing the modulation component of the detection signal from the output of the light receiving amplifier 15.

The above-mentioned constant control of the received light intensity is performed by converting the electric signal obtained by the light receiver 14 into the light receiving amplifier 15 as shown in FIG.
After being amplified by, the DC component is extracted through the low-pass filter 13 (average value processing), this level is compared with the output from the reference voltage generator 12 by the comparator 11, and this result is compared with the light source drive level control unit (error convergence). Circuit) 10. The light source drive level control unit 10 outputs a certain voltage value to the light source drive unit 9 so that the output from the comparator 11 becomes zero or the difference becomes constant.

In this way, the amount of light received by the light receiver 14 is made constant, thereby stabilizing the detection signal level and performing high-sensitivity detection. On the other hand, when receiving a signal, the output from the light receiving amplifier 15 is extracted through the high-pass filter 16 to obtain only the AC component, and then the band-pass filter 17 cuts unnecessary frequency components and outputs the AC component. Here, the pass frequency of the band pass filter 17 is determined by the signal component to be detected and the response characteristic. A general bandpass filter having a characteristic of passing only the commercial frequency component is used, and the response characteristic is adjusted by the Q value.

[0007]

However, in the above optical sensor, the direct current component (strictly speaking, the average value level) is taken out from the light receiving amplifier 15 through the low pass filter 13, and the intensity of the light source 8 is controlled by the level. However, fluctuations due to components below the cutoff frequency of the low-pass filter 13 occur, affecting the output signal of the light source 8. In addition, the noise component generated in the feedback group, that is, the noise of the power source and the transistor noise give a slight change in the light amount to the light source 8. In particular, the influence of the noise of the power supply for applying the voltage to the light source 8 is large, and the time constant is large in order to detect the direct current component in the feedback circuit, so that the fluctuation of the frequency due to the noise cannot be removed. Therefore, if it is attempted to remove the noise by making the response of the feedback circuit fast, the fluctuation component due to the detection signal is also removed, and the signal cannot be detected.

For the above reasons, the fluctuation of the output of the light source 8 due to the power source noise cannot be completely removed, and as a result, the detection signal is affected by the error and causes an error. As a result, the signal detection sensitivity is affected and the detection accuracy is reduced, and when the bandpass filter 17 having a high Q value is used in the output stage to improve the accuracy, the response characteristic deteriorates. there were.

An object of the present invention is to eliminate the above-mentioned conventional drawbacks, remove noise components due to minute fluctuations in the output level of a light source, measure a detection signal with high accuracy, and remove noise components. An object of the present invention is to provide an optical sensor that can relax the limitation of the signal frequency band of the output stage of the detection signal system and improve the response characteristics.

[0010]

An optical sensor of the present invention includes a light source for supplying light to an optical fiber sensor, an optical signal from the optical fiber sensor, and an electric signal corresponding to the intensity of a received light signal. And a receiver for monitoring the input light for branching the input light from the light source to the optical fiber sensor, receiving the light, and outputting an electric signal corresponding to the intensity of the received light signal. The output of
And a control circuit for feedback controlling the output level of the light source.

In this case, the means for branching the input light to the optical fiber sensor may be a polarizer provided in the optical fiber sensor for branching after being input to the optical fiber sensor, or between the light source and the optical fiber sensor. It may be an optical coupler that is provided and branches before inputting to the optical fiber sensor.

[0012]

A part of the input light from the light source to the optical fiber sensor is branched and received by the monitor light receiver, and the electric signal corresponding to the received light signal intensity is input to the control circuit. The control circuit feedback-controls the output level of the light source so as to remove the noise component contained in the input light to the optical fiber sensor based on the electric signal input from the monitor light receiver.

[0013]

An embodiment of the present invention will be described in detail below with reference to the accompanying drawings.

As shown in FIG. 1, the optical sensor is installed when the polarizer 2, the analyzer 5, the sensor element 4 provided between the polarizer 2 and the analyzer 5, and the sensor element 4 is a Pockels element. Optical sensor unit 1 including a quarter wavelength plate 3
And a sensor circuit 7 for supplying light to the optical sensor unit 1 and obtaining a detection signal from the output light from the optical sensor unit 1, and an optical fiber for transmitting an optical signal between the optical sensor unit 1 and the sensor circuit 7. 6 and 6.

The sensor circuit 7 includes a light source 8 such as a light emitting diode, a light source driving section 9 for driving the light source 8, and an optical sensor section 1.
A photodetector 14 such as a pin photodiode for receiving an optical signal from the photodetector and outputting the photodetection signal, a photodetector amplifier 15 for amplifying the photodetection signal output from the photodetector 14, and an AC component from the output of the photodetection amplifier 15. High pass filter 1
6, a photodetector 18 for monitoring such as a pin photodiode that receives the light branched by the polarizer 2 that is input to the optical sensor unit 1 and outputs a photodetection signal, and a photodetection signal that is output from the photodetector 18. A light receiving amplifier 19 for amplification, and a reference voltage generator 1 for generating an output of the light receiving amplifier 19 and a drive reference voltage.
A comparator 11 for detecting the difference between the output levels of 2 and the comparator 11
It mainly comprises a light source drive level control unit 10 having an error converging function for outputting an appropriate voltage to the light source drive unit 9 so that the output from the comparator 11 becomes zero. .

The optical sensor unit 1 is attached to an object to be measured for measuring current and voltage, and the light passing through the sensor element 4 is subjected to light intensity modulation in proportion to the measured amount of current, voltage and the like. The optical signal intensity-modulated in proportion to the measured amount is photo-electrically converted into a light receiving signal by the light receiver 14, and the output of the light receiving amplifier 15 is input to the high-pass filter 16 to extract an AC detection signal. The output of the high-pass filter 16 is the output of the sensor circuit 7. By measuring the degree of amplitude modulation of this output, measured values such as current and voltage can be obtained.

The monitor light receiver 18 monitors the light that is input from the light source 8 to the optical sensor unit 1 and is branched by the polarizer 2. The monitor light from the polarizer 2 is an unnecessary polarization component other than the linearly polarized light input to the sensor element 4, and the amount of light input to the sensor element 4 does not change. The output of the monitor light receiver 18 is amplified by the light receiving amplifier 19 and input to the comparator 11. Here, the dominant factor in the variation of the light input to the optical sensor unit 1 is power source noise mixed in the voltage applied to the light source 8.

By monitoring the light having a heavy noise component directly by the monitor light receiver 18 and using the monitor signal as a feedback control signal, the light source 8 is modulated in a direction in which the noise component is canceled. You can As a result, the light input to the optical sensor unit 1 becomes a direct-current light without fluctuation, and the output of the sensor circuit 7 becomes a signal which is purely modulated by the current / voltage value applied to the sensor element 4. Here, the response speed of the feedback control circuit for the output of the light source 8 is set sufficiently higher than the commercial frequency to remove the commercial power source noise component. As described above, since the response speed on the light source 8 side is fast and the detection light from the optical sensor unit 1 has no noise component, it is not necessary to provide the bandpass filter 17 having a high Q value as in the conventional example of FIG. A signal with good response can be detected. Another embodiment of the present invention will be described with reference to FIG. When attaching the optical sensor unit 1 to the measurement target, the optical sensor unit 1 is downsized or the optical sensor unit 1 is
There are cases where it is desired to reduce the number of cores of the optical fiber 6 to the. Therefore, in this embodiment, the optical sensor unit 1 as in the above embodiment is used.
Instead of branching the input light from the polarizer 2 for monitoring, an optical coupler 20 is provided in the optical fiber 6 between the light source 8 and the optical sensor unit 1 to input the light from the light source 8 to the optical sensor unit 1. Before that, a part of the light is branched by the optical coupler 20 and introduced into the monitor light receiver 18.

[0019]

The optical sensor of the present invention has the following remarkable effects.

(1) Since the input light to the optical fiber sensor is monitored and the output of the light source is controlled so that the input light to the optical fiber sensor does not fluctuate due to noise components, highly accurate measurement is possible. Become. Further, since the detection light from the optical fiber sensor has no noise component, it is not necessary to pass a bandpass filter having a high Q value to the detection side to improve the accuracy, and the detection light output from the optical fiber sensor does not have to pass through. However, since the input light is monitored and the output of the light source is controlled, the response speed on the light source side can be made sufficiently fast, so that a sharp change in the signal can be detected and excellent response characteristics can be measured.

(2) Since the optical coupler is provided between the light source and the optical fiber sensor so that the input light is branched before being input to the optical fiber sensor, downsizing of the sensor portion and the optical fiber core wire are prevented. Reduction can be achieved.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of an optical sensor according to the present invention.

FIG. 2 is a block diagram showing a configuration of an optical transmission unit in another embodiment of the optical sensor according to the present invention.

FIG. 3 is a block diagram showing a configuration of a conventional optical sensor.

[Explanation of symbols]

 1 Optical Sensor Section 2 Polarizer 3 1/4 Wave Plate 4 Sensor Element 5 Analyzer 6 Optical Fiber 7 Sensor Circuit 8 Light Source 9 Light Source Driving Section 10 Light Source Driving Level Control Section 11 Comparator 12 Reference Voltage Generator 14 Photoreceptor 15, 19 Receiver amplifier 16 High-pass filter 18 Monitor receiver 20 Optical coupler

Claims (2)

[Claims] 1. A light source for supplying light to an optical fiber sensor,
A light receiver for receiving an optical signal from the optical fiber sensor and outputting an electric signal corresponding to the intensity of the received light signal, and a light receiving signal for receiving the branched light obtained by branching the input light from the light source to the optical fiber sensor An optical sensor, comprising: a monitor light receiver for input light that outputs an electric signal corresponding to the intensity; and a control circuit that feedback-controls the output level of the light source by the output of the monitor light receiver. 2. The means for branching the input light to the optical fiber sensor is an optical coupler provided between the light source and the optical fiber sensor to branch the light before it is input to the optical fiber sensor. Optical sensor described in.