JPH06109843A - Measuring instrument by making use of doppler effect - Google Patents

Abstract

PURPOSE:To calibrate the title instrument with high accuracy by a method wherein a mode changeover means which changes over between a measuring mode and a calibration mode is provided, a reference frequency signal for calibration is input to a frequency/voltage conversion means and the signal is compensated according to a deviation from a proper value. CONSTITUTION:In a calibration mode, a range is selected by a range selection switch SW3a. The SW3a is interlocked with a range changeover switch 231 and with an output frequency from a first transmitter 31. The switch 231 is changed over to a target range according to a range selected by the SW3a, and a reference frequency generated by the transmitter 31 is changed over to a frequency corresponding to it. A compensation-voltage generation circuit 38 is provided with a buffer amplifier A5 and a differential amplifier A4, and the reference signal is input to a negative-side input terminal for the amplifier A4 via the amplifier A5. A compensation reference voltage is applied to the positive-side input terminal for the amplifier A4. Consequently, the difference between the compensation reference voltage and an analog voltage is output from the amplifier A4 as a compensation voltage.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a measuring instrument for converting a beat frequency obtained from a laser beam to which a Doppler effect has been applied and a reference laser beam into a voltage signal for measurement, and particularly to a measuring instrument having a plurality of measuring ranges. The present invention relates to a method of switching and using.

[0002]

2. Description of the Related Art FIG. 3 is a block diagram showing the configuration of a measuring instrument utilizing the Doppler effect, for explaining the conventional technique. The prior art will be described below with reference to this figure.

The illustrated apparatus includes a laser light source 11, a power source 111 for the laser light source, first and second polarization beam splitters (hereinafter referred to as PBS) 12a and 12b.
, A wave plate 13, a lens system 14, an acousto-optic device (hereinafter referred to as AOM) 15, and an AOM for driving this AOM.
An optical system 1 including a driver 151, a reflection mirror 16, and a beam splitter (hereinafter referred to as BS) 17, an optical / electrical signal converter (hereinafter referred to as O / E converter) 21, a frequency conversion circuit 22, and a frequency / A voltage converter (hereinafter referred to as F / V converter) 23, a changeover switch 231 connected to the F / V conversion circuit 23 for switching the output range of the F / V conversion circuit, and an offset as a correction means and a compensation voltage generation means. Electrical system 2 consisting of circuit 3 and amplifier 24
It has and.

The laser light emitted from the laser light source 11 is split into laser light for measurement (hereinafter referred to as measurement light) and laser light for comparison reference by the first PBS 12a. The laser light for comparison and reference is first incident on the AOM 15. Here, the frequency of this laser light is shifted by a predetermined amount and adjusted to a desired frequency. This predetermined amount is determined based on the excitation signal from the driver 151. After that, the laser light is incident on the O / E converter 21 via the BS 17 and is used as reference light that serves as a reference.

Further, the measurement light is transmitted to the second PBS 12b,
The DUT 4 through the wave plate 13 and the lens system 14 in order.
Is irradiated. The measurement light with which the DUT 4 is irradiated is affected by the moving speed of the DUT (Doppler effect), and is reflected in a state in which the frequency of the measurement light is shifted by the amount corresponding to this influence. This reflected laser light (hereinafter referred to as reflected light) is used for the lens system 14, the wave plate 13, and the second PBS.
12b, the reflecting mirror 16 and the BS 17 in order
The light enters the / E converter 21.

The O / E converter 21 converts these two incident lights into electric signals. What is converted into an electric signal here is the beat (swell) component of the two laser beams. That is, the frequency difference between these two reference lights and the reflected light is detected and converted as a beat frequency.

If the DUT 4 is in a stationary state, the frequency shift amount in the AOM 15 described above becomes a difference in frequency between the reflected light and the measurement light, and this difference is converted as a beat frequency. . On the other hand, when the DUT 4 is in the moving state, the beat frequency is a frequency in which the shift amount due to the Doppler effect is superimposed in addition to the difference between the reflected light and the measurement light. The converted electric signal is further converted by the frequency conversion circuit 22 into a signal in a relatively low frequency range that is easy to handle as an electric signal. This signal is converted to F / V converter 2
At 3, the voltage signal is converted into a voltage signal according to the frequency, further amplified by the amplifier 24, and subjected to predetermined processing to obtain the moving speed and vibration frequency of the DUT 4.

In the measuring instrument using the Doppler effect configured as described above, the object to be measured 4 is measured in order to perform highly accurate measurement.
The detection sensitivity is switched according to the moving speed (vibration frequency) of the F / V conversion circuit 23 as well as the range of the frequency conversion circuit 22 is switched. Was there.
For example, when the frequency of the output signal from the frequency conversion circuit 22 is close to a certain reference frequency f1, the range change switch 231 is set to the range 1 side, and when it is close to another reference frequency f2, the range change switch 231 is set. Connect to Range 2 side. And in both measurements, F /
The V conversion circuit 23 is configured to output a predetermined voltage when the reference frequency signal arrives. However, since these output voltages may deviate from the expected values due to some factors, the offset for compensation shown in FIG. 4 is provided between the F / V converter 23 and the amplifier 24 in such a device. The circuit 3'was arranged and this difference was calibrated. Here, the conventional offset circuit is set to 3'to distinguish the conventional offset circuit from the offset circuit disclosed by the present invention. In the following, what is shown with a suffix "'" indicates the configuration of the conventional offset circuit.

[0009]

Offset circuit 3 '
Has a first amplifier 31 'as a correction means and a power supply circuit 32' as a compensation voltage generation means connected to the negative side input terminal of the amplifier 31 '. Further, the power supply circuit 32 'has a voltage e for compensation having an appropriate value.
1'and e2 'are switched by a changeover switch SW1' which operates corresponding to the changeover switch 231.
The output of the F / V conversion circuit 23 is connected to the positive input terminal of the amplifier 31 ', and the output of the amplifier 31' is connected to the amplifier 24.

The offset circuit 3'constituted in this way
In the configuration, the compensating voltages e1 ′ and e2 ′ are set to predetermined values, and a signal of 0 [V] is output from the first amplifier 31 ′ when a signal having the reference frequency is input. ing. Therefore, when the conversion rate of the F / V conversion circuit 23 changes due to an illegal factor such as a change in ambient temperature,
Since this variation is output in the form of being amplified by the first amplifier 31 ', there is a problem that the accuracy of the calibration is deteriorated. The present invention has been made in view of this point, and an object of the present invention is to provide a measuring instrument using the Doppler effect, which can perform accurate and highly accurate calibration even when an incorrect factor occurs. It is in.

[0011]

For this reason, the measuring apparatus utilizing the Doppler effect of the present invention makes the difference in frequency between the reflected laser light to which the Doppler effect of the moving object to be measured is added and the reference laser light O / E converter is used as a measurement frequency signal, and based on the measurement frequency signal, a measuring instrument utilizing the Doppler effect for measuring physical quantities such as vibration and velocity of the object, wherein the measurement frequency signal is converted into a measurement voltage signal. A Doppler effect having at least a frequency / voltage converting means for converting and a compensating voltage generating means for generating a compensating voltage for compensating a deviation from a proper value of the measured voltage signal outputted from the frequency / voltage converting means is utilized. In the measuring instrument,
It has a mode switching means for switching between the measurement mode and the calibration mode of the device when switching the measurement range, or according to an operator's instruction or predetermined timing, and in the calibration mode, a reference for calibration generated from the reference frequency source. The frequency signal is input to the frequency / voltage converting means instead of the measured frequency signal, and the compensating voltage generating means is set so as to generate a compensating voltage according to a deviation of the output of the frequency / voltage converting means from an appropriate value. It is characterized by doing.

[0012]

Function: The calibration is automatically performed when the measurement range is switched. It can also be performed at any timing according to an instruction from the operator. During calibration, the reference frequency voltage from the reference frequency voltage source is input to the frequency / voltage conversion means instead of the measured frequency voltage. If the output of the frequency / voltage converting means at this time deviates from the proper value, the compensating voltage generating means is calibrated so as to generate a compensating voltage for compensating for this deviation. At this stage, the calibration mode ends and the measurement mode is automatically switched to. The above-mentioned compensation voltage is added to the output voltage related to the measurement signal of the aforementioned frequency / voltage conversion means. Therefore, even when the output from the frequency / voltage conversion means changes due to the above-mentioned incorrect factors, the calibration operation is appropriately performed, so that it is possible to cope with this change and highly accurate calibration can be performed.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a block diagram showing a first circuit configuration of a main part centering on an offset circuit 3 in a measuring instrument utilizing the Doppler effect of the present invention. Other configurations in the present invention are the same as those shown in the prior art, and therefore the description thereof is omitted here to avoid duplication.

In FIG. 1, the offset circuit 3 has a first amplifier A1 as the correction means, while a first oscillator 31, a controller 32, and a second oscillator 33 as the compensation voltage generation means. , The first gate circuit 34, D
/ A converter 35, up-down (U / D) counter 3
6, a second gate circuit 37, a compensation voltage generating circuit 38, a second amplifier A2, a comparator A3 and the like.

The apparatus shown in FIG. 1 has a measurement mode and a calibration mode. In the measurement mode state, as described above, the optical signal from the optical system 1 is input to the O / E converter 21, the F / V conversion circuit 23, and the first amplifier A are input.
1 and the desired output signal via the amplifier 4.

The calibration mode is performed, for example, when the measurement range is changed, and is intended to set the offset value in the range. First, the range is selected by the range selection switch SW3a. The range selection switch SW3a is linked to the output frequencies of the range changeover switch 231 and the first oscillator 31. According to the range selected by the range selection switch SW3a, the range changeover switch 231 is switched to the target range (for example, range 2), and the reference frequency emitted by the oscillator 31 is the corresponding frequency (for example, f2).
Switch to. At this point, the controller 32 sends the signal tc
To connect SW1 to the side of the first oscillator 31 (CAL) and open the gate of the first gate circuit 34 to apply a signal of frequency f3 to the second gate circuit 37. Further, when the operator performs this calibration operation at an arbitrary timing, the calibration switch SW3b is connected. At this time, similarly to the above, SW1 is connected to the first oscillator 31 side while the measurement range and the output frequency of the oscillator 31 are maintained in the state when the switch is pressed down, and the first gate circuit 34 is used. And the signal of frequency f3 is applied to the second gate circuit described later.

In the calibration mode, the first oscillator 3
The reference frequency signal emitted from the No. 1 is input to the F / V conversion circuit 23. The F / V conversion circuit 23 outputs a reference voltage signal having a predetermined value according to the conversion range and the input frequency. In the apparatus of the embodiment, a device having two ranges is shown for ease of explanation, but there are cases where the device has more ranges.

The output of the F / V conversion circuit 23 is input to the positive side input terminal of the first amplifier A1 and the compensation voltage, which will be described later, is input to the negative side input terminal thereof, and the difference value between these two input voltages is input. Is amplified with an amplification factor of about 1 to 10 times and output to the amplifier 24. The same signal as that of the first amplifier A1 is input to the positive and negative input terminals of the second amplifier A2, and the difference value between these two input voltages is amplified by an amplification factor of about several tens to several hundreds. And output.

The output of the second amplifier A2 is input to the positive input terminal of the comparator A3. Since the ground level (0 [V]) is input to the negative side input terminal of the comparator A3, the comparator A3 is a zero-cross comparator, that is,
When the output from the amplifier A2 is 0 [V] or less, the L level is output, and when the output exceeds 0 [V], the H level is output 2
Operates as a digitization circuit. Therefore, the signal at TP1 on the output end side of the comparator 3 is 0 [V] at L level,
A predetermined voltage (for example, 5 [V]) is output at the H level, and matching with a connected digital circuit is achieved.

This signal is input to the second gate circuit 37. The second gate circuit 37 is an inverter 371,
It is composed of a first NAND gate 372 and a second NAND gate 373. Here, the signal is branched into two, one is input to the positive side input terminal of the first NAND gate 372 via the inverter 371, and the other is input to the second N
It is directly input to the positive input terminal of the AND gate 373. A signal from the second oscillator 33 is input to the negative input terminals of both NAND gates. As described above, the second oscillator 33 outputs the predetermined frequency signal f3 during the calibration time tc by the first gate circuit 34 arranged between the second oscillator 33 and the second gate circuit 37. It is designed to output. Therefore, when the signal at TP1 is at H level, the second NAND gate 373 sends an electric signal, and when it is at L level, the first NAND gate 372 sends an electric signal corresponding to the frequency f3. The output from the first NAND gate 372 is input to the U / D counter 36 as the UP clock f5, and the output from the second NAND gate 373 is input to the DOWN clock f4.

The U / D counter 36 increases or decreases the instruction value according to these two clocks and sends the instruction value to the D / A converter 35. The D / A converter 35 outputs a voltage with an analog value to a compensation voltage generating circuit 38 described later according to the instruction value from the U / D counter 36, but this output has its output range limited by resistors R9 and R12. ing. This range limitation is made to improve the resolution of the D / A converter. If the D / A converter 35 has a variable range of 0 to 6 [V], the variable range is set to 0 to 2 [V] by setting the resistors R9 and R12 to appropriate values. Can be restricted. In this way, the control voltage per clock can be reduced to 1/3, and the substantial resolution can be improved three times.

The compensating voltage generating circuit 38 includes a buffer amplifier A5 and a differential amplifier A4, and the D / A converter 3 is provided.
The output analog voltage of 5 is input to the negative side input terminal of the differential amplifier A4 via the buffer amplifier A5. The compensation reference voltage e1 is applied to the positive input terminal of the differential amplifier A4. Therefore, from this differential amplifier A4,
The difference between the compensation reference voltage e1 and the analog voltage is output as the compensation voltage.

This compensation voltage is input to both the negative side input terminal of the second amplifier A2 and the negative side input terminal of the first amplifier A1. Therefore, the second amplifier A
2 forms a feedback loop, and the voltage input to the positive side input terminal of the comparator A3 is 0 during the calibration time tc.
The compensation voltage is varied by increasing or decreasing the indicated value of the U / D counter 36 until it becomes [V]. When the compensation voltage is determined in this way, the instruction value of the U / D counter 36 is fixed and the configuration mode by the controller 32 ends. Since the second amplifier A2 has an amplification factor of several tens to several hundreds, the difference between the reference voltage and the compensation voltage output from the input F / V conversion circuit 23 is amplified, Calibration with higher accuracy is performed. In the first amplifier A1, the difference between the compensation voltage calibrated with high accuracy and the reference voltage output from the F / V conversion circuit 23 is amplified by an amplification factor of about 1 to 10 times, and Amplifier 2
Output to 4. In short, in this configuration, the compensation voltage is determined by the second amplifier having a high amplification factor, and this compensation voltage is utilized by the first amplifier having a low amplification factor, resulting in high calibration accuracy.

FIG. 2 is a block diagram showing the second circuit configuration of the present invention. The difference from the above-described first circuit configuration is in the following points. A point that the reference frequency signal for configuration is input to the subsequent stage of the O / E converter 21. The positive input of the second amplifier A2 is the output of the first amplifier A1. The compensation reference voltage connected to the positive side input terminal of the differential amplifier A4 of the compensation voltage generation circuit 38 is switched according to the range of the F / V conversion circuit 23. A capacitor C1 is connected between a positive input terminal and an output terminal of the differential amplifier A4 and is controlled by a switch SW5.
Point.

The above is configured so that the variation of the frequency conversion circuit 22 can also be compensated. In the device of the second embodiment, the F / F in the latter stage of the O / E converter 21 is
The circuit configuration of the V converter 23 will be generically referred to as frequency / voltage conversion means. This is done to correct the offset voltage of the first amplifier A1 itself. In this configuration, since the output of the first amplifier A1 becomes the reference voltage, the output voltage is corrected including the offset voltage of the first amplifier itself. The above description is made to perform calibration with higher accuracy, and the control range of the D / A converter 35 is widened due to a slight output difference caused by the range switching of the frequency / voltage conversion means. It was made to. With this configuration, when the range is switched, the compensating reference voltage is switched according to the output from the frequency / voltage converting means, so that the control range of the D / A converter can be narrowed and highly accurate calibration can be performed. It will be possible. The above is made to reduce noise at the time of measurement and improve the response at the time of calibration. SW5 is cut off at the time of calibration to improve the response, and SW5 is connected at the time of measurement to increase the high frequency. It reduces noise. Due to these, it is possible to perform more accurate calibration.

In the above embodiment, the case where the calibration mode is changed is explained when the measurement range is switched and when the user operates. However, the calibration mode execution program is provided in the apparatus in advance to start the measurement. It is also possible to automatically execute the calibration operation at a certain time or at a predetermined timing during measurement.

[0027]

As described above in detail, the measuring instrument utilizing the Doppler effect of the present invention has an advantage that accurate and highly accurate calibration can be performed even when external factors change.

[Brief description of drawings]

FIG. 1 is a block diagram showing a first embodiment device of the present invention.

FIG. 2 is a block diagram showing a second embodiment device of the present invention.

FIG. 3 is a block diagram of a measuring instrument using the Doppler effect to which the present invention is applied.

FIG. 4 is an explanatory diagram showing a conventional device.

[Explanation of symbols]

 21 O / E converter 22 Frequency conversion circuit 23 F / V conversion circuit 24 Amplifier 3 Offset circuit 35 D / A converter 36 U / D counter 37 Second gate circuit 38 Offset voltage generation circuit A1 First amplifier

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Takuyuki Kobayashi 503-1 Shinanomachi, Totsuka-ku, Yokohama, Kanagawa Prefecture Graftech Co., Ltd.

Claims (1)

[Claims] 1. A difference in frequency between a reflected laser beam to which the Doppler effect of a moving measured object is added and a reference laser beam is taken out as a measurement frequency signal by an O / E converter,
A measuring instrument utilizing the Doppler effect for measuring a physical quantity such as vibration or velocity of the object based on the measurement frequency signal, wherein a frequency / frequency for converting the measurement frequency signal into a measurement voltage signal
In a measuring instrument utilizing the Doppler effect, which has at least a voltage converting means and a compensating voltage generating means for generating a compensating voltage for compensating the deviation of the measured voltage signal output from the frequency / voltage converting means from an appropriate value, It has a mode switching means for switching between the measurement mode and the calibration mode of the device when switching the measurement range, or according to an operator's instruction or predetermined timing, and in the calibration mode, the reference for calibration generated from the reference frequency source. A frequency signal is input to the frequency / voltage conversion means instead of the measured frequency signal,
A measuring instrument utilizing the Doppler effect, characterized in that the compensating voltage generating means is set so as to generate a compensating voltage according to a deviation of the output of the voltage converting means from an appropriate value.