JPS62254060A - Light measuring apparatus - Google Patents

Abstract

PURPOSE:To simplify the construction of the apparatus, by picking up a drop in voltage of a resistance for detecting an output current of a semiconductor light receiving element through a capacitor. CONSTITUTION:Current ILD flows through a light emitting element LD by way of a resistance Rl according to an output of an amplifier A and an emission output P1 of the element LD corresponding to the current ILD is inputted into a light receiving element D via an optical connector CN1, a voltage sensor S, an optical connector CN2 and the like. The input light P2 is converted into a photocurrent Ia with the element D to cause a drop in the voltage of a resistance R2 for detection. This voltage drop is applied to an LPF to pick up a DC component and then, inputted into the amplifier A to be compared with a reference voltage ES1. A control is made by increasing or decreasing the current ILD flowing through the element LD so that the mean of voltage drops caused in the resistance 2 will be kept constant. The voltage drop is applied to an capacitor CC to cut DC components therefrom and taken out at an output terminal OUT as output VOUT via an amplifier A3. This eliminates the need for a photodiode at an APC circuit, an avalanche photodiode at an AGC circuit or the like, thereby simplifying the construction.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is applicable to the voltage to be measured or 13! This invention relates to an optical 51 measurement device that measures the amount of light to be measured by measuring the intensity of light modulated in accordance with the amount to be measured, such as i9.

(Prior Art) FIG. 4 is a connection diagram of an example of a conventional optical 51 measurement device of this type. In the figure, 8PC is an auto power control circuit, AGC is an auto gain commer roll circuit, ]: I is an optical fiber, and S is a voltage (or magnetic field) sensor. Optical fiber F1 has optical connector CN1.C
N2 is set ('j).

A-to-power control [1-diode PD (in PC, a semiconductor light-emitting element such as a laser diode or a light-emitting diode, for rearward monitoring of part of the light emission amount of D) The photocurrent ip is supplied to the detection resistor R1, and the voltage drop (R1・Ip) and the reference voltage ESI are compared to the amplifier 1 to increase or decrease the current lid flowing through the light emitting element LD, so that Ip increases or decreases. υ1 part is set so that it is constant. In this case, the light emitting element D
Since the optical output P1 of is proportional to the photocurrent Ip of the monitoring photodiode PD, the optical output []1 is kept at a constant value. This optical output 1) 1G to optical connector CN
1. Optical fiber F1. Voltage sensor S, light = 1 connector C
Avalanche at 〇〇 to the auto gain control circuit via N2 1st diode △PD
is input. The optical output 1]1 of the optical element ID is modulated by the analog measured ff1Vx in the voltage sensor S, and as a result of A, the light from D changes as shown by the solid line in FIG. Therefore, the value of Vx can be measured by measuring the input light P2 of the APD.

By the way, in the device with this configuration, J3 has optical connector C.
N1. Poor river properties of CN2, mechanical distortion that the optical fiber -Fl receives, or 1. Due to optical instability of the i-voltage sensor S, the input light P2 to the APD fluctuates at a constant rate A as shown by the dotted line in FIG. This fluctuation is transferred to the auto gain control circuit AGC as follows.
3 and will be compensated. That is, the input light P2 to the APD is converted into a current (a) by the APD, and a voltage Y is applied to the detection resistor R2.
"Decrease 1・(R2・la> by 1". This change"J1
4. is 1-] - bus filter 1. ,,,, F)
1-' through its self-flow component (R2・l El l'equal f6R2-Ja) and quasi'1EiF, [1,,s
2 is compared, and the voltage difference between A and A is amplified by amplifier A2''C.

The amplified output of A is applied to the cathode of 8F3D and △ρ
1) by changing 11ff5-t'M, <R2''
The feedback Lll Zl works so that (a) becomes approximately equal to ES2. In this way, optical connector C
Even if the light h1 fluctuates due to NI, CN2, etc., by changing the multiplication factor M of △PD, (1(2・Ia) is controlled by υ directly at a constant j.(Fri2・la) The DC component (ff<2・Ia) is cut by the capacitor!J-CC, amplified by the 1j width amplifier △3, and then output from the −C output to the J voltage out.
It will be taken out as soon as possible. The voltage slope S is (ΔP2/P2)ccVx ・-41 near x=Q shown in the graph of Fig. 15.
)(, 'P2 is the DC component of R2, ΔP2 is the change in R2)), and since the photocurrent 1ai of API) is proportional to the input light P2 of this APD, (ΔIa/Ia) - (ΔP 2/P2)
-(2) (Δla is 1 minute change of la). Since vOutIctR2・Δia is amplified by amplifier A3, ■outocR2・ΔIa −(3)(+
> From formulas (2) and (3), VoutocR2・
Ia・(ΔP2/P2>0CR2-1a-Vx
−<4). As mentioned above, (R2・Ia) is the light m
Since the output voltage V OLJ t shown in equation (4) remains constant even when changing, the output voltage V OLJ t is not affected by the fluctuation of the light ffl and becomes proportional to the voltage to be measured VX.

The end 8111 device with such a configuration is well known as described above, but it is known that analog information transmission through nine fibers is possible.
As mentioned above, the M+ stage had a double Lit control circuit, that is, an APC circuit and a 〇〇 circuit as its constituent elements. This necessity is due to the circumstances of the light emitting element L-o. That is, the maximum current and maximum light emission output are specified for the light emitting element LD, and even if light emission is avoided with an output within the maximum light emission output, it is desirable to reduce the output as much as possible, taking X' into consideration for life.

However, compared to the noise of the entire system including the noise of the Rade diode itself, it is desirable to emit light with as large an optical output as possible in order to make the signal magnitude as enjoyable as possible. Therefore, it was natural to control the output of the ray 1f diode LD to an optimal constant value. On the other hand, semiconductor light emitting device 1. ．． If D is a light-emitting diode, the light output 11r1 is small to begin with, and the light-emitting area is also larger than that of a laser diode, so only a small portion behind the light-emitting output enters the thin core of the optical fiber. do not. Therefore, although the noise of the light emitting diode itself is small, the S of the entire system is
In order to improve the /N ratio, the light emission output needed to be as large as possible and constant.

Semiconductor light emitting device 1. , D for the reasons mentioned above, the optical output P2 will change by the amount of change in the light amount due to the optical connector CNI, CNI optical fiber FiyA or voltage sensor (J-S, etc.). In order to compensate for this, in FIG. 4 8u, an AG including an avalanche r photo diode
Since it is necessary to use an O circuit, there is a problem in that the overall configuration becomes complicated. Since there is an AI)C circuit in the circuit of FIG. Even if CN2 becomes disconnected, the semiconductor light emitting device ID continues to emit a constant amount of light, so there is no need to worry about damage.

(Problems to be Solved by the Invention) The present invention has been made to solve the above-mentioned problems. The purpose of the present invention is to provide an optical meter device with a simplified overall configuration that does not require an avalanche photo diode APD or the like in the OC circuit to compensate for sensitivity fluctuations due to fluctuations in It is something.

(Means for Solving the Problems) In order to achieve the above object, the present invention transmits the light emitting output of a semiconductor light emitting element through an optical fiber to an analog i! ! ! The light is input to the 14 full-circuit elements that undergo modulation depending on the measurement interval, and the light is input to the semiconductor light-emitting element via the 1 (9) conductor. The detection resistor detects the output current of the light receiving system.
By comparing the output voltage with the base IP7 through a bus filter and transmitting the difference output to the semiconductor light emitting device, the voltage Vt''F is controlled to be constant. !ζ Auto power - control [I-small circuit ↓-1
The above-mentioned electric current drop is combined in such a way that the DC component is taken out as an output via a capacitor. Examples will be explained below.

(Embodiment) Fig. 1 is a circuit diagram of an embodiment of the optical system according to the present invention. A is an amplifier.The cathode of light emitting element 1-D is resistor R1.
-C is connected to the output terminal of amplifier Δ via -C. [] is a light receiving element such as a diode, its cathode is connected to a bias power supply V13, and its anode is connected to the potential point A through a resistor R2, and the DC It is connected to the output terminal OUT through a series circuit of a capacitor Qc for component cutting and an operational amplifier A3, and is connected to the amplifier (±) through a low-pass filter LPF.
connected to the input terminal. A reference power source ESI is connected to the input terminal of the amplifier A. Dl is da, diode 11 is the power supply, and the cathode of diode D1 is jnn
It is connected to the connection point with the resistor cable R1 on the width scale, and the seven nodes are connected to a common potential point via the power supply v1. Fl is an optical fiber, S is a voltage (or magnetic field) sensor, and this sensor is provided in the middle of the optical fiber Fl as in FIG.

CNI and CN2 are optical connectors provided on the optical fiber F1. One end of the optical fiber Fl is a cliff blue body optical element LD.
The other end faces the semiconductor light receiving element. The operation of the device having such a configuration will be explained as follows.

Resistor R1 is applied to semiconductor light emitting device LD by the output of amplifier IA.
A current ILD flows through the optical connector CN1. The light emitting output P1 of the light emitting element 1-D corresponding to the current ILD is output from the optical connector CN1. Optical fiber fl, voltage sensor S.

The signal is input to the photo diode PD via the optical connector CN2. As explained in FIG. 2, the optical output P1 of the light emitting element LD is measured at the voltage sensor
As a result, the light from the LD changes as shown by the solid line in FIG.

Therefore, by measuring the input light P2 to be received, the value of VX can be measured.

The input light P2 to the light receiving unit is converted into light (a) in this element, and is sent to the detection unit 11 as a resistor (R2) under voltage (R2).
・Avoid I2). This 1 pressure drop is applied to the O bus filter LPF, and its DC component is taken out.

This DC component is added to the amplifier and is added to the reference voltage fEEs1
The voltage drop (R
iJI 1il so that the average value of 2.la) is constant.
IcX Reru. This voltage (R2・la) is added to the capacitor Cc to cut off its DC component, and is amplified by the amplifier A3 and output from the output terminal OLJ to VOLJ t.
is extracted as

In such a conjunctural tree 11 light, the light'necta CN
Even if any one of I, CN2, sensor+jS, or optical fiber I changes, and there is attenuation of light due to the dotted line J in Figure 5, it will be proportional to the input light of the light receiving element fl-). Since the system is controlled so that the average 1-turn (R2'' I a ) of the charge current 1a detection resistor R2's current LIE drop 1·(R2-1a>) is constant, in the case of the conventional example shown in Fig. In exactly the same way as (+
) to (4) are established. As a result, optical connector '7ta CN
1. The Ii:i degree of CN2, t:/It S d or the optical fiber [I is affected by the change in Lffi +-j
It is possible to accurately measure Vx without

It should be noted that while the circuit 45 in FIG. 1 is in operation, the optical connector CN1. If CN2 is disconnected, the input source of the light-receiving element becomes zero. be. In the present invention, in order to prevent the life of the light emitting element LD from being shortened even in such a case, 1 corresponding to the optical output P2 is
A current limiting circuit that prevents 1-D from becoming larger than the current is provided in stages. When the output J11) of the light-emitting element 1.-D becomes low, a current flows in the guide Δ-1 due to the voltage j1 drop (RL-ILD) at . , the current 11-, D does not increase to a predetermined value 11/iL, and the two-light beam 11) will not be destroyed or its life will be shortened. This is another embodiment of the inventive device.The circuit of FIG. 2 is the same as the circuit of FIG.
The circuit in Figure 3 is a combination of 1]-pass, filter L[], and amplifier △. Then, this output (1J) is applied to the L amplifier Δ5, and its output current is supplied to the light emitting element [1].
2 and 3. The basic operation of the unit in FIGS. 2 and 3 is the same as that in FIG. 1.

(Effect of the invention) As shown in FIG. 4, in the conventional device, the light emitting system is controlled by the A-1- power control circuit △PC, which includes the rear 72-taper die A-do PD. Since the output P1 of the child LD is kept constant 1n, sensitivity fluctuations occur. Therefore, auto
A gain control circuit was used to compensate for the sensitivity fluctuations. This makes the overall configuration complicated. In contrast, in the present invention, the amount of light passing through the entire system including the optical fiber, the light modulation element, etc. is detected, and the distance between the lights is controlled 117i to be constant (direct). After 1'3 was made an essential component of the device, the 7'7E dual diode was no longer necessary, and the avalanche J with gain = 1 control R capability was added to the light receiving line.
,・A photometer with a simplified overall configuration that allows you to freely select the light-receiving element by eliminating the need for a photodiode.
Can roam the L1 device.

4.L of the drawing! ! i 11 Explanation Figures 1 to 3 are connection diagrams of an embodiment of the optical measurement device related to Mokukomei, Figure 4 is a connection diagram of a conventional device, and Figure 5 is the output of this type of shoulder-side device. FIG. 3 is a diagram for explaining characteristics.

11)... Semiconductor light emitting element, D... Semiconductor light receiving element j
'-1R2...detection resistor, LPF...low-pass filter, S...light modulation element, += i...optical fiber, ESI...base t$electron 1, CC...・Capacitor for DC component cut.

Claims (1)

[Claims] The light emitting output of the semiconductor light emitting element is input through an optical fiber to an optical modulation element that is modulated according to an analog measured quantity, and the modulated output light of this optical modulation element is input to the semiconductor light receiving element through an optical fiber. , the voltage drop due to the detection resistor that detects the output current of this semiconductor light receiving element is compared with a reference voltage via a low-pass filter, and the output of the difference is given to the semiconductor light emitting element, so that the voltage drop is kept at a constant value. An optical measurement device comprising an auto power control circuit configured to control the voltage drop so as to output the voltage drop as an output via a capacitor for cutting a DC component.