JPH0547391Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical power meter, and more particularly to an optical power meter that eliminates erroneous measurements due to errors in offset operation to eliminate errors caused by dark current of a light receiving element in a photodetector.

<Prior Art> (Fig. 2) Generally, when measuring optical power, an optical power meter is used.

The light receiving element used in the photodetector of this optical power meter has dark current. This dark current is a current that flows even when no light is incident on the light receiving element, and is one of the causes of measurement errors. Therefore, in measurement, it is necessary to offset the dark current component. This offset operation must be performed each time the optical power is measured, or at regular intervals if the measurement is to be continued for a long time, since the dark current changes depending on the temperature and other factors.

FIG. 2 shows the configuration of a conventional optical power meter equipped with such an offset function. In FIG. 2, 1 is a photodetector equipped with a photodetector such as a photodiode, 2 is an amplifier circuit that amplifies the detection output from the photodetector 1, and 3 is an A/R converter that converts the output of the amplifier circuit 2 into a digital value. 4 is an offset switch, and 5 is a measurement switch.

Reference numeral 6 denotes a control circuit that controls the output value of the A/D converter 3 to be sent to the offset storage circuit 7 when it receives the input from the offset switch 4, and to the arithmetic circuit 8 when it receives the input from the measurement switch 5. .

Reference numeral 7 denotes an offset storage circuit that updates and stores the output value from the A/D converter 3 as an offset value via the control circuit 6. 8 is an arithmetic circuit that outputs a value obtained by subtracting the offset value of the offset storage circuit 7 from the output value of the A/D converter 3 via the control circuit 6 as a measured value. Reference numeral 9 denotes a display device that displays the measured values from the arithmetic circuit 7.

With this configuration, before measuring optical power, the light receiving section of the photodetector 1 is first shielded from light (for example, by covering the light receiving connector of the light receiving section with a cap).
Operate offset switch 4. At this time, an output is generated from the photodetector 1 due to the dark current of the photodiode of the photodetector 1 in a state where no light is received. This output passes through the amplifier circuit 2 to the A/D converter 3.
It becomes a digital value and is stored as an offset value in the offset storage circuit 7 via the control circuit 6.

Next, the cap is removed from the light receiving section of the photodetector 1 so that it can receive light, and the measurement switch 5 is operated to measure the optical power. A detection output from the photodetector 1 is input to an arithmetic circuit 8 via an amplifier circuit 2, an A/D converter 3, and a control circuit 6. Arithmetic circuit 8
Then, the offset value in the offset storage circuit 6 is subtracted from this value, output as a measured value, and displayed on the display device 9.

<Problems to be Solved by the Present Invention> However, in the conventional optical power meter with such a configuration, after operating the offset switch 4 to store the offset value before measurement, the offset value is stored during the optical power measurement operation. In some cases, the offset switch 4 may be operated by mistake. However, if the offset switch 4 is operated by mistake in this way, the detected output value from the photodetector 1, which has received much larger external light than the dark current that does not completely block the light receiving part, will be offset as an offset value. The data will be updated and stored in the memory circuit 7.

Therefore, if a measurement is performed without realizing that the offset switch has been operated by mistake, a completely random value will be output as the measured value, which is a problem. Furthermore, even if it is realized that the offset switch has been operated by mistake, the correct offset value has already been erased, so there is a problem in that the light receiving section must be shielded from light again and the operation for storing the correct offset value must be performed again.

The present invention aims to provide an optical power meter that solves these problems.

<Means for solving the above problems> In order to solve the above problems, the optical power meter of the present invention includes a photodetector that detects optical input, and an output value based on the dark current of a light receiving element of the photodetector. A reference value setter offset switch is set to a larger reference value, and the output value of the photodetector when the offset switch is operated is compared with the reference value of the reference value setter. a comparison circuit that outputs an error signal when the output value of the photodetector is larger than the offset switch; and an output from the photodetector when the error signal from the comparison circuit is not output when the offset switch is operated. The offset storage circuit includes an offset storage circuit that stores a value, and an arithmetic circuit that outputs a value obtained by subtracting the offset value stored in the offset storage circuit from the output value of the photodetector as a measured value.

<Function> As described above, in the optical power meter of the present invention, even if the offset switch is operated by mistake during measurement operation, the light receiving part is not blocked, so
The output of the photodetector becomes a much larger value than the reference value set in the reference setting circuit, and as a result, an error output is output from the comparison circuit, and the offset value in the offset storage circuit is not erased but is stored as is. .

<Embodiment of the present invention> (FIG. 1) Hereinafter, an embodiment of the present invention will be described based on the drawings.

FIG. 1 shows an embodiment of the present invention.
In the figure, 1 is a photodetector, 2 is an amplifier circuit, 3 is an A/D converter, 4 is an offset switch, 5 is a measurement switch, 7 is an offset storage circuit, 8 is an arithmetic circuit, and 9
2 is a display device, which is the same as the conventional device shown in FIG. 2, so the explanation thereof will be omitted.

10 is configured to send the output of the A/D converter 3 to the comparator circuit 12 when the operation input of the offset switch 4 is received, and to the arithmetic circuit 8 when the operation input of the operation switch 5 is received. This is a control circuit that controls the

Reference numeral 11 denotes a reference value setting device for presetting a reference value of a digital value larger than the output value due to the dark current of the light receiving element of the photodetector 1.

12 compares the output value from the A/D converter 3 via the control circuit 10 with the reference value from the reference value setter 11 when an operation input is made to the offset switch 4, and determines whether the output value is smaller than the reference value. In this case, the content of the offset storage circuit 7 is rewritten to the output value of the A/D converter 3, and if the value exceeds the reference value, the comparator circuit outputs an error signal.

13 is an error display device that displays the error signal from the comparator 12, and 14 is a buzzer that sounds in response to the error signal.

Next, the operation of the above embodiment will be explained.

First, in order to store the offset value before measurement, the light receiving section of the photodetector 1 is shielded from light and the offset switch 4 is operated. The photodetector 1 generates an output due to the dark current of the photodiode, and the amplifier circuit 2,
The signal is sent via the A/D conversion circuit 3 to the comparison circuit 12 by the control circuit 10. This value is compared with the reference value of the reference value setter 11, but since it is much smaller than the reference value due to dark current, the A/D conversion circuit 3
The digital value from is stored in the offset storage circuit 7 as an offset value.

Next, when the light-receiving part of the photodetector 1 is unblocked for measurement and the measurement switch 6 is operated to start the measurement operation, the detection output from the photodetector 1 is transferred to the amplifier circuit 2, A/D converter. The signal is sent via the circuit 3 to the arithmetic circuit 8 by the control circuit 10. In the arithmetic circuit 8, the offset value stored in the offset storage circuit 7 is subtracted from this detected output value, and this subtracted value is displayed on the display device 9 as a device value.

However, if the offset switch 4 is operated by mistake during this measurement operation, the light-receiving section of the photodetector 1 is not shielded from light, so that a much larger output value is output than the dark current when the light is shielded. Since this value is larger than the reference value of the reference value setter 11, an error signal is output from the comparison circuit 12, so the contents of the offset storage circuit are not rewritten and the previous correct offset value is saved. Then, an error message is displayed on the display 13, and the buzzer 14 also sounds. Therefore, by mistake, offset switch 4
Correct measurements can be continued regardless of the offset operation, and there is no need to repeat the offset operation.

<Effects of the Present Invention> Since the optical power meter of the present invention has the above configuration, even if the offset switch is operated by mistake, the previous correct offset value is saved and measurement can be continued. This is extremely useful in practice, as it eliminates the need to redo the offset operation.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention.
FIG. 2 is a block diagram showing a conventional optical power meter. 1...Photodetector, 2...Amplification circuit, 3...A/
D converter, 4... Offset switch, 5... Measurement switch, 7... Offset storage circuit, 8...
Arithmetic circuit, 9... display device, 10... control circuit,
11... Reference value setter, 12... Comparison circuit, 13
...Error display device, 14...buzzer.

Claims (1)

[Claims for Utility Model Registration] A photodetector 1 that detects optical input; a reference value setting device 11 that is set with a reference value larger than an output value due to dark current of a light-receiving element of the photodetector; The set switch 4 compares the output value of the photodetector when the offset switch is operated with the reference value of the reference value setter, and if the output value of the photodetector 1 is larger than the reference value, a comparison circuit 12 that outputs an error signal; and when the error signal from the comparison circuit is not output when the offset switch is operated,
An offset storage circuit 7 that stores an output value from the photodetector; and an arithmetic circuit 8 that outputs a value obtained by subtracting the offset value stored in the offset storage circuit from the output value of the photodetector as a measured value. Equipped with an optical power meter.