JPH10135509A - Photosensor using photovoltaic element and method for making its output current constant - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make the output current of photovoltaic elements, such as pin photodiode, constant even with temperature change. SOLUTION: An optical path to a pin photodiode for measurement 2, generates output current in response to the irradiation quantity from a LED 1, is enclosed in a case 3, scattered light and reflecting light of the light projected from the LED 1 in the case 3 are received by a pin photodiode for feed-back 5 provided in a hole 4 of the case 3. For the pin photodiodes 2 and 5, the diodes having the same or almost equivalent light quantity/output current characteristic are used. The output current of the pin photodiode 5 varies by the change of the ambient temperature. The driving current of the LED 1 is varied by the output current of the pin photodiode 5, and the output current of the pin photodiode 2 having the same characteristic that varies by the change of the ambient temperature is made constant.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical sensor using an element whose output current fluctuates due to a temperature change, such as a photodiode or a phototransistor, particularly a pin photodiode, and a method for stabilizing the output current value.

[0002]

2. Description of the Related Art An optical sensor using a pin photodiode generally generates an LED 1 as a light source and an output current corresponding to the amount of light emitted from the LED, as shown in FIG. A measurement pin photodiode 2 and a case 3 surrounding these to limit an optical path from the LED 1 to the measurement pin photodiode 2 are arranged.
And a circuit for taking out the output current of the measurement pin photodiode 2 and measuring the current value.

Of course, in an optical sensor having such a configuration,
LED1 regardless of changes in environmental conditions, especially temperature conditions
It is desirable that the output current value of the measuring pin photodiode 2 be constant when the light emitting drive is performed under a constant condition. However, in a pin photodiode used in this type of optical sensor, a change in the ambient temperature causes a change in the light absorption coefficient, which is the main cause, for example, as shown in FIG. Has become. 7A shows the temperature characteristics of the sensitivity of various two-element pin photodiodes manufactured by Hamamatsu Photonics KK, and FIG. 7B shows the sensitivity temperature characteristics of various four- and six-element pin photodiodes manufactured by Hamamatsu Photonics. Is shown. In any case, as shown in the drawing, a positive temperature coefficient is shown in a long wavelength region, and a negative temperature coefficient is shown in a short wavelength region.

In an optical sensor for position detection using such a pin photodiode, for example, a position detection value calculated based on an output current value of the pin photodiode is affected by a change in ambient temperature. In particular, there is a problem that a large error may occur in a detection result in a sensor for detecting a minute position change.

For this reason, conventionally, measures have been taken to make the value of the current (hereinafter referred to as LED current) flowing through the LED which is the light emitting source constant. For example, resistance control is performed using a variable resistor, or an IC and an operational amplifier are controlled. To try to make the LED current value constant. However, in the former method,
The LED current itself fluctuates due to a temperature change, and accordingly, the light emission amount of the LED and the output current of the pin photodiode also fluctuate, and the effect of stabilizing the LED current is not so much obtained. Further, in the latter method, although the LED current can be kept constant irrespective of the temperature change, there is a problem that the light emission amount of the LED fluctuates, and therefore the output current of the pin photodiode also fluctuates.

SUMMARY OF THE INVENTION In view of the above-mentioned conventional problems, the present invention provides an optical sensor capable of stabilizing an output current value of a photovoltaic element such as a pin photodiode with a simple configuration even when there is a temperature change, and a method of stabilizing the same. The purpose is to provide.

[0007]

In order to achieve the above object, an optical sensor using a photovoltaic element according to the present invention generates a light source and an output current corresponding to the amount of light emitted from the light source. In an optical sensor comprising a photovoltaic measuring element and surrounding means such as a case or a cover for limiting an optical path from the light source to the measuring element, the light emitted from the light source is enclosed in the surrounding means. A feedback element having the same or almost the same light quantity-output current characteristic as a photovoltaic element of the same type as the measuring element is provided at a portion in the surrounding means capable of receiving the scattered light and reflected light at And a means for varying the drive current of the light source in accordance with the output current of the feedback element.

According to a second aspect of the present invention, there is provided a method for stabilizing an output current value of an optical sensor, wherein a photovoltaic type measuring device for generating an output current corresponding to an amount of light emitted from a light source is provided to achieve the above object. The measuring element in which an optical path to the element is limited by surrounding means such as a case or a cover, and scattered light or reflected light of the light emitted from the light source in the surrounding means is provided in a separate part in the surrounding means. Receiving light by a feedback element having the same or almost the same light quantity-output current characteristic as that of a photovoltaic element of the same type as that described above, and varying the drive current of the light source according to the output current of the feedback element. It is characterized by.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. In the following, only parts common to the related art will be given the same reference numerals, and duplicate description will be omitted.

FIG. 1 is a sectional view conceptually showing one embodiment of an optical sensor according to the present invention. The optical sensor according to the present embodiment is provided with a hole 4 extending in a direction substantially perpendicular to the optical path from the LED 1 to the measuring pin photodiode 2 at an intermediate portion of the case 3, and a feedback pin photo is provided in an opening outside the hole 4. A diode 5 is provided so that scattered light and reflected light in the case 3 can be received. The feedback pin photodiode 5 separately measures the light quantity-output current characteristic in advance, and the measurement pin photodiode 2
Use the same or almost the same one. Not only the position of the feedback pin photodiode 5 but also the hole 4
And the present invention is not limited to the illustrated example.

FIG. 2 is a diagram showing a circuit configuration of the embodiment of FIG. In the figure, reference numeral 6 denotes an emission control IC for the LED 1;
Is an operational amplifier, 8 is a gate transistor, and IC6
Is connected to the inverting input terminal of the operational amplifier 7.
The output of the feedback pin photodiode 5 is connected to the non-inverting input terminal of the operational amplifier 7.

With such a configuration, of the light emitted from the LED 1, a part of the light scattered and reflected in the case 3 enters the feedback pin photodiode 5, and an output current corresponding thereto is output from the operational amplifier 7. Input to the inverted input terminal. In this state, even if the ambient temperature changes and the relationship between the light quantity of the measuring pin photodiode 2 and the output current changes, the LED current and the LED light quantity are controlled so as to fluctuate according to this change. The output current of the measuring pin photodiode 2 is kept almost constant.

If the temperature characteristic relating to the current-light amount of the LED 1 is corrected by using a temperature sensor, the output current of the measuring pin photodiode 2 can be more accurately made constant.

[0014]

EXPERIMENTAL EXAMPLES AND COMPARATIVE EXAMPLES Hereinafter, the operation of the above-described embodiment of the optical sensor according to the present invention for stabilizing the output current, the case where resistance control is performed using the above-described variable resistor, and the case where an LED is performed using an IC and an operational amplifier The operation will be described in comparison with the operation when the current value is made constant.

[0015]

First Comparative Example FIG. 3 is a circuit diagram (A) showing a first comparative example.
7 is a graph (B) showing the relationship between the ambient temperature T, the LED current Lc, and the output current Io of the measurement pin photodiode. In this example, the resistance control is performed using a variable resistor, and the output current Io of the pin photodiode increases by a maximum of 9.3 mV with respect to a rise of the ambient temperature T of a maximum of 1.2 degrees during the measurement for about 30 minutes. And the temperature coefficient is 7.75 mV
/ ° C.

[0016]

FIG. 4 is a circuit diagram (A) showing a second comparative example.
7 is a graph showing a relationship between the ambient temperature T, the LED current Lc, and the output current Io of the measurement pin photodiode.
In this example, the LED current Lc is obtained by using the IC 6 and the operational amplifier 7 and feeding back the emitter current of the transistor 8 for the gate to the non-inverting input terminal of the operational amplifier 7.
Is constant, and the output current Io of the pin photodiode increases by a maximum of 8 mV with respect to the rise of the ambient temperature T by a maximum of 1 degree during the measurement of about 1 hour, and the temperature coefficient is 8 mV / ° C. Was.

[0017]

Experimental Example of the Present Invention FIG. 5 is a graph showing the relationship between the ambient temperature T, the LED current Lc, and the output current Io of the measuring pin photodiode in the experimental example of the present invention having the configuration shown in FIG. In this example, the output current Io of the pin photodiode increased by a maximum of 1.6 mV and the temperature coefficient was 0.8 mV / ° C. with respect to a rise in the ambient temperature T of a maximum of 2 degrees during the measurement of about one hour. .

In the above description, only the case of a pin photodiode is described, but the present invention is not limited to this, and a photovoltaic type such as a photodiode or a phototransistor whose output current fluctuates due to a temperature change. It is needless to say that the present invention can be applied to an optical sensor using the above element. Further, the configuration of the light emission drive circuit of the measurement pin photodiode 2 and the circuit used for feedback of the output current of the feedback pin photodiode 5 are not limited to the illustrated example, and various types can be employed.

[0019]

As described above, the method of stabilizing the output current value of the optical sensor using the photovoltaic element and the method of stabilizing the output current value of the optical sensor using the photovoltaic element according to the present invention are as described above. A photovoltaic element of the same type as the measuring element, which receives the scattered light and reflected light in the surrounding means of the light emitted from the light source by the feedback element having the same or almost the same light quantity-output current characteristic. Since the drive current of the light source is varied by the output current of the feedback element, the output current of the photovoltaic element for measurement can be made constant regardless of the fluctuation of the ambient temperature. There is an effect that precise position measurement can be performed without errors.

[Brief description of the drawings]

FIG. 1 is a sectional view conceptually showing one embodiment of an optical sensor according to the present invention.

FIG. 2 is a diagram showing an electric circuit configuration of the embodiment of FIG.

FIG. 3 is an electrical circuit diagram (A) of a first comparative example and a graph (B) showing a relationship among an ambient temperature, an LED current, and an output current of a measurement pin photodiode.

FIG. 4 is an electric circuit diagram (A) of a second comparative example, and a graph (B) showing a relationship among an ambient temperature, an LED current, and an output current of a measurement pin photodiode.

5 is a graph showing a relationship between an ambient temperature, an LED current, and an output current of a measurement pin photodiode in an experimental example of the present invention having the configuration of FIG. 2;

FIG. 6 is a cross-sectional view illustrating a configuration of a conventional optical sensor using a pin photodiode.

FIG. 7 is a diagram showing temperature characteristics of sensitivity of a pin photodiode.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 LED 2 pin photodiode for measurement 3 case 4 hole 5 pin photodiode for feedback 6 IC for LED light emission drive control 7 operational amplifier 8 transistor for gate

Claims (2)

[Claims] 1. A light source, a photovoltaic measuring element for generating an output current corresponding to an amount of light emitted from the light source, and a case and a cover for limiting an optical path from the light source to the measuring element. In the optical sensor including the surrounding means, the light emitted from the light source can be scattered or reflected in the surrounding means. A power-type element having a feedback element having the same or substantially the same light quantity-output current characteristic, and a means for varying a drive current of the light source according to an output current of the feedback element; An optical sensor comprising: 2. An optical path to a photovoltaic type measuring element for generating an output current corresponding to an amount of light emitted from a light source is limited by surrounding means such as a case or a cover, and the surrounding of light emitted from the light source is defined by the surrounding means. A scattered light or reflected light in the means is a photovoltaic element of the same kind as the measuring element provided in a separate part in the surrounding means, and has the same or almost the same light quantity-output current characteristic. Received by the element for
A method for stabilizing an output current value of an optical sensor, wherein a drive current of the light source is varied according to an output current of the feedback element.