JPS5915089Y2 - Laser output monitoring device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a laser output monitoring device for monitoring the intensity of a signal caused by a laser beam.

Generally, in online systems and the like, a laser beam is used as a light source, but in this case, a decrease in the output intensity of the laser beam has a large effect on the analysis of the received signal as a laser beam.

Particularly when a laser beam is discriminated based on an on/off signal, a decrease in the output intensity of the laser beam directly causes malfunction.

Therefore, in order to avoid malfunctions and ensure reliability of conventional online systems, means have been adopted to monitor the output intensity of laser beams.

One means for this purpose is to use a laser oscillator 1 as shown in FIG.
A laser beam emitted from the laser beam is split into two by a beam splitter 2, and one of the transmitted laser beams is incident on a measurement field 3, where samples are placed on a belt conveyor at predetermined intervals and passes through the belt conveyor while stopping intermittently. Ru.

That is, the laser beam passes through the measurement field 3 and is extracted as an on/off signal, which is converted into an electric signal by the photoreceiver 4 and subjected to desired signal processing by the signal processing circuit 5.

On the other hand, the other laser beam reflected by the beam splitter 2 is converted into an electrical signal by the receiver 6, and this signal is measured as the output intensity of the laser beam by the intensity measurement circuit 7, and the measured value is Based on this, a compensation signal is given to the signal processing circuit 5.

8 is a compensation circuit.

With this means, it is possible to measure the intensity of the laser output, but it is difficult to measure a decrease in signal intensity due to a change in the measurement system (for example, a change in the sensitivity of a photomultiplier tube).

Furthermore, dividing the laser beam into two using the beam splitter 2 causes loss in the laser beam as a signal source, making it impossible to accurately measure the signal intensity.

Also, there is a problem in terms of space associated with beam splitter 2.
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Another conventional means employs a configuration as shown in FIG.

That is, the laser beam from one output side of the laser oscillator 1 is guided to the signal processing circuit 5 through the same route as shown in FIG. The signal is converted into an electrical signal and calibrated by a comparison/calibration circuit 9, and a compensation signal is given to the signal processing circuit 5 based on the electric signal.

However, in the configuration shown in Figure 2, the signal intensity caused by one laser beam is measured using the laser beam on the high reflection side, but since the output ratio of these two laser beams is not constant, the signal intensity The control of the processing circuit 5 is not accurate, and each time the laser tube is replaced, a sufficient amount of time must be spent to adjust the correlation, making it unsuitable for monitoring and controlling signal strength.

This idea was made to eliminate the above drawbacks.
A laser beam oscillated from one side of the laser oscillator is received by a light receiver, a part of the output signal of the light receiver is taken out and compared with a predetermined reference voltage, and the intensity of the signal is measured, To provide a laser output monitoring device that accurately measures intensity, eliminates the need for a beam splitter that causes signal loss, and eliminates the complexity of adjustment based on the correlation between two laser beams. .

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

Figure 3 is a systematic block diagram of the laser output monitoring device.
The laser beam emitted from the laser oscillator 11 is transmitted to the measurement field 1.
2.

This measurement field 12 is a place from which data is taken out as a signal source for the online system, and for example, on/off signals suitable for the online system are taken out from this measurement field 12.

Now, the laser beam as an on/off signal obtained from the measurement field 12 enters the light receiver 13, is converted into an electric signal, and is supplied to the signal processing circuit 14.

Further, the signal taken out from the light receiver 13 is supplied to an intensity measurement circuit 15 that measures signal intensity and a drift measurement circuit 16 that monitors dark current, drift, etc.

The intensity measuring circuit 15 gives an operating signal to the alarm circuit 17 when the signal obtained from the light receiver 13 becomes lower than a predetermined reference voltage, and the drift measuring circuit 16 detects the drift state with an indicator 18. I try to give instructions.

Next, FIG. 4 shows the light receiver 13, signal processing circuit 14, and
FIG. 2 is a diagram specifically showing an intensity measurement circuit 15, a drift measurement circuit 16, and the like.

Note that FIG. 4 is a specific example as one embodiment, and the internal configuration is not particularly limited to this.

First, the light receiver 13 is composed of a light receiving element 13a and an amplifier 13b, and converts the on/off signal input from the measurement field 12 into a signal as shown in FIG. 5a at an output point 20 and takes it out.

In the signals shown in the figure, the O level is when no laser beam is incident on the photoreceptor 13, and 1' is a value determined by the intensity of the incident laser beam and the detection sensitivity of the photodetector 13a.

Therefore, if this ■1' is taken as the Lebel, if the intensity is the Lebel when it is always on, no error will occur in the signal processing circuit 14, etc. However, the intensity of the laser beam varies depending on various causes, and therefore the intention of the present application is Monitoring is required.

In particular, in the case of a signal as shown in FIG. 5a, the level cannot be determined simply by comparing it with a comparison signal.

Therefore, the intensity measuring circuit 15 and drift measuring circuit 16 described below are used to reliably determine the level and notify it by means such as an alarm.

That is, in the intensity measurement circuit 15, a transistor 15a constituting an emitter follower circuit is used on the input side to lower the signal impedance, and this transistor 15a
A signal obtained from the emitter side of the capacitor 15C is charged with a voltage corresponding to v1' through the diode 15b.

As a result, even if a 0 level signal appears at the output point 20, the diode 15b prevents the diode 15b from discharging.

Furthermore, since the transistor 15d in the latter stage also constitutes an emitter follower circuit, it is maintained at a high input impedance. Therefore, the voltage charged in the capacitor 15C is connected almost as is, and the voltage as shown in Fig. 5 is input from the emitter side of the transistor 15d. It is possible to extract a DC voltage of 1".

Therefore, this voltage 1'' is compared with the reference voltage obtained by the reference voltage setter 15e, and as a result of this comparison, the voltage Vl
' is lower than the reference voltage, comparator circuit 1
It outputs a signal of 1 at 5f to issue a so-called alarm.

On the other hand, the drift measurement circuit 16 monitors dark current and zero drift during line running, and the signal at the output point 20 is transmitted to the transistor 16 that constitutes the emitter follower circuit.
a, and is converted into an integral waveform by an integrating circuit composed of a resistor 16b and a capacitor 16C.

At this time, if the integration time constant is set sufficiently larger than the pulse width, the rising voltage will be delayed as shown in FIG. 5C, and only a small voltage will be obtained across the capacitor 16C.

Further, when the output point 20 becomes 0 level, the voltage charged in the capacitor 16C is discharged by the diode 16d, so the voltage V charged in the capacitor 16C, /// is as shown in FIG. As shown in FIG.
A drift voltage as shown in FIG. 1 can be monitored with an indicator 18.

That is, if the zero adjustment circuit 16i initially sets the indicator 18 to zero, when the input signal drifts, the amount of drift can be directly indicated to the indicator 18.

18a is a span adjuster of the indicator 18. Therefore, when performing signal processing using the ON/OFF signal of the measurement field 12, by adding the intensity measurement circuit 15 and the drift measurement circuit 16, the laser beam can be adjusted. The intensity of the signal caused by this can be easily measured, and based on this, an alarm may be issued and signal processing may be stopped, or a feedback signal may be provided to the signal processing circuit 14 (not shown).

As described above, this invention makes it possible to eliminate the need for a beam splitter, which has a particularly large signal loss, by adding an intensity measurement circuit, etc. to the output side of the photoreceiver.This allows the original signal level to be extracted with almost no attenuation. Therefore,
Accurate monitoring becomes possible.

Furthermore, since there is no need to provide measuring equipment such as a beam splitter around the laser oscillator, space can be improved compared to the conventional method.

Furthermore, there is no problem with the configuration shown in FIG. 2, that is, the correlation between the two laser beams, and in this respect, there is no need to make adjustments by exchanging laser tubes.

In addition, this circuit of one embodiment uses an intensity measurement circuit and a drift measurement circuit in combination, so it can be determined whether the signal strength is decreasing due to the laser beam or the S/N ratio of the measurement field is deteriorating. Measures can be taken.

[Brief explanation of drawings]

1 and 2 are schematic configuration diagrams showing a conventional laser output monitoring device, FIG. 3 is a schematic configuration diagram showing a laser output monitoring device according to the present invention, and FIG. 4 is a specific diagram showing a part of the device. FIG. 5 is a waveform diagram illustrating the operation of this device. 11... Laser oscillator, 12... Measurement field, 13... Light receiver, 14... Signal processing circuit, 15... Intensity measurement Circuit, 15e...
... Reference voltage setting device, 16 ... Drift measurement circuit, 17 ... Alarm circuit, 18 ... Indicator.

Claims (1)

[Scope of utility model registration request] A device that makes a laser beam oscillated from a laser oscillator enter a measurement field, extracts a laser beam as an ON/OFF signal from the measurement field, receives the light with a light receiver, and performs signal processing using the received light signal; A part of the received light signal is added,
This light reception signal is compared with a predetermined reference voltage, and an intensity measuring circuit and an alarm circuit that issue an alarm when the light reception signal is below the reference voltage, and a part of the light reception signal is added to detect the drift voltage of this light reception signal. A drift measurement circuit and an indicator are provided, and the indicator is initially set to zero, and when the received light signal drifts, the zero drift is monitored so that the amount of drift can be directly indicated by the indicator. A laser output monitoring device featuring: