JPH10160842A - Electronic distance meter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an electronic distance meter which measures the level of a liquid surface inside a tank containing an inflammable liquid such as, e.g. gasoline, LPG or the like. SOLUTION: An electronic distance meter is provided with a light-emitting element 12 by which radiant light carrying a modulation signal is radiated to a target 18, with a light-receiving element 20 which receives incident light reflected by the target 18 so as to obtain a measured value, with a changeover means, i.e., an automatic disphragm device 28, through which calibration light carrying the modulation signal is received by the light-receiving element 20 via an internal calibration passage having a prescribed length so as to obtain a calibration value and with a control circuit 32 containing a microcomputer which is operated at a low voltage and which computes a distance up to the target 18 on the basis of the measured value and the calibration value. In order to adjust the quantity of incident light from the target 18, an automatic dispphragm device 24 which is operated at a low voltage is used. The automatic diaphragm device 28 is replaced by a second light-emitting element and an electric changeover means. The automatic diaphragm device 24 is replaced by a multiplier which makes the output to the light-emitting element 12 variable.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light wave level meter installed in a tank of a flammable liquid such as gasoline or LPG, and operates a control circuit at a low voltage to measure a distance to a liquid level. It relates to an explosion-proof lightwave distance meter.

[0002]

2. Description of the Related Art A lightwave distance meter for measuring a distance to a target by using a phase difference of modulated light is disclosed in U.S. Pat. No. 3,619,058.
No. JP-A-60-21380 to JP-A-60-2113
No. 82.

In these lightwave distance meters, a calibration path having a predetermined length is formed inside, and an external measurement value up to a target is calibrated with a measurement value obtained by the calibration path, thereby improving measurement accuracy. As a member for alternately switching the internal calibration path and the external measurement path, a DC motor for rotating a perforated disk or a blade, or a liquid crystal element which becomes transparent or opaque by applying a voltage has been used.

Further, a DC motor for rotating a variable ND filter or a liquid crystal element whose density changes when an analog voltage is applied has been used as a member for controlling the light amount of the external measurement path to a specified value.

[0005]

However, in a conventional lightwave distance meter, a DC motor for rotating a shutter plate or a variable ND filter generates a high voltage whose winding inductance is, for example, 15 volts or more. Sparks may occur between brushes. Therefore, the conventional lightwave distance meter is not suitable for an explosion-proof lightwave level meter for measuring the liquid level of a flammable liquid.

Further, in the method using a liquid crystal element for the shutter and the filter, an AC voltage having an effective value of 5 to 20 volts is required for the applied voltage. It is very difficult to obtain a given performance in a circuit. Therefore, when manufacturing an explosion-proof type distance meter, it is necessary to satisfy an intrinsically safe explosion-proof standard which defines the use range of the capacitance-voltage of the capacitor, the inductance-current of the coil, and the current-voltage.

SUMMARY OF THE INVENTION In view of the above-mentioned problems, the present invention provides a mechanical shutter or an automatic aperture device which operates at a low voltage of, for example, 5 volts or less and satisfies the intrinsic safety standard without using a motor or a liquid crystal element. It is an object of the present invention to provide a lightwave distance meter having the same.

[0008]

In order to solve these problems, an electro-optical distance meter according to the present invention comprises a light-emitting element which emits a radiated light carrying a modulation signal to a target, and an incident light reflected by the target. A light-receiving element that receives a measurement value by receiving light, and a switching unit that receives a calibration light that carries the modulation signal from the light-emitting element to the light-receiving element via an internal calibration path having a predetermined length to obtain a calibration value, A control circuit including a microcomputer that operates at a low voltage and calculates a distance to the target based on the measured value and the calibration value; and a low voltage for adjusting the light amount of the incident light from the target. The automatic iris (auto iris) which operates with the feature is used.

In another aspect of the present invention, there is provided an electro-optical distance meter which emits a radiated light carrying a modulated signal to a target.
A light-emitting element, a light-receiving element that receives incident light scattered by the target object to obtain a measurement value, and a calibration light that carries the modulation signal is received by the light-receiving element via an internal calibration path having a predetermined length. A second light-emitting element that obtains a calibration value, and operates based on the measured value and the calibration value obtained by alternately switching the modulation signal to the first and second light-emitting elements while operating at a low voltage. A control circuit including a microcomputer for calculating a distance to the target. For adjusting the light quantity of the incident light, an automatic diaphragm operating at a low voltage is used.

The switching means includes a second automatic stop which operates at a low voltage, and a glass or an objective lens on which a non-reflection film for light is deposited is hermetically disposed on the front surface of the light receiving element and the light emitting element. Is done. The amplitude of the signal supplied to the first light emitting element is adjusted so that the level of the signal reaching the light receiving element is constant, and the signal is adjusted so that the phase is constant when the amplitude is varied.

Therefore, in a small and lightweight metal case, the distance to the target is calculated based on the phase difference between the light-emitting and light-receiving elements that emit the modulated light to the target and receive the reflected light, and the signals transmitted to and received from these optical elements. A microcomputer operating at low voltage is hermetically incorporated. An automatic aperture device that operates at a low voltage is used for light amount adjustment. Instead of mechanically switching between the internal calibration path and the external measurement path, the light emitting elements may be separately provided for external measurement and internal calibration, and the modulation signal may be switched alternately under the control of the microcomputer.

[0012]

FIG. 1 is a schematic block diagram of a first embodiment of a lightwave distance meter according to the present invention. The basic operation of this lightwave distance meter is well known, but the main points will be described.

In FIG. 1, a light emitting element 12 is composed of a semiconductor laser, a light emitting diode or a super luminescent diode. The light emitting element 12 radiates the radiated light carrying the modulation signal to the target 18 via the internal calibration path mirror 14 and the objective lens 16.

On the other hand, the light receiving element 20 is a P which operates at a low voltage.
It consists of an IN diode. The light receiving element 20 receives the incident light reflected by the target 18 and condensed by the objective lens 22 via the automatic diaphragm 24 and the optical filter 26, and measures a signal whose phase is shifted from the first modulation signal. Get the value.

The automatic diaphragm 24 continuously controls the diaphragm with a low analog voltage of, for example, 5 volts or less for each external measurement, and continuously adjusts the amount of incident light that has reciprocated to the target 18. The automatic aperture device 24 maintains this state until the next external measurement. On the other hand, the radiated light carrying the modulated signal from the light emitting element 12 is reflected and branched by the mirror 14 into calibration light.

The calibration light is received by the light receiving element 20 via the switching means 28 and an internal calibration path having a predetermined length.
A calibration value with a slight phase shift is obtained. This switching means 28
Includes an automatic aperture 28 that continuously controls the internal calibration path formed by the mirror 14 and the prism or mirror 30 from fully closed to an intermediate aperture. Therefore, the automatic iris 2
Under the control of 8, the external measuring path and the internal calibration path are switched mechanically.

The feature of this first embodiment is that it has automatic diaphragms 24 and 28 which operate at a low voltage of, for example, 5 volts or less and satisfy the intrinsic safety standards of capacity vs. voltage, inductance vs. current, and current vs. voltage. That is. At the time of external measurement, the automatic aperture device 28 is closed, and the aperture of the automatic aperture device 24 is controlled so that the voltage photoelectrically converted by the light receiving element 20 becomes a specified value. At the time of internal calibration, the automatic aperture device 24 is closed, and the aperture of the automatic aperture device 28 is controlled such that the voltage photoelectrically converted by the light receiving element 20 becomes a specified value.

The automatic aperture devices 24 and 28 use a moving magnet method such as EP4605 manufactured by NISKA used for a video camera. The control circuit 32 operates at a worst-case low power supply voltage of 7 volts or less to satisfy the intrinsic safety standard and calculate the distance to the target 18 based on the measured value and the calibration value (not shown). including.

In the preferred embodiment, the automatic diaphragms 24 and 28
Indicates that the resistance of the drive coil is 136 ohms, the resistance of the braking coil is 875 ohms,
It can be controlled with an operating voltage of ~ 4 volts. Also, the automatic squeezers 24 and 28 are set to 100 to 100
It requires a time of about 300 milliseconds.

Although the automatic diaphragm 24 is arranged on the incident side in the embodiment shown in FIG. 1, it may be arranged on the radiation side. On the front surfaces of the light receiving element 12 and the light emitting element 20, glass (not shown) on which an anti-reflection film is deposited or objective lenses 16 and 22 are arranged in an airtight manner. Airtight or waterproof plugs and jacks are used for the power connector 34 and the signal connector 36.

FIG. 2 shows a second embodiment of the present invention in which measurement data can be obtained at a higher speed than the embodiment shown in FIG. FIG. 2 shows an explosion-proof light wave in which a first light emitting element 12 and a second light emitting element 42 are provided instead of the mirror 14 and the mechanical switching means 28, and the modulation signals applied to these light emitting elements are electrically switched. It is a schematic block diagram of a distance meter.

In FIG. 2, members corresponding to those shown in FIG. 1 are denoted by the same reference numerals. First, as the first light emitting element 12 and the second light emitting element 42, a semiconductor laser, a light emitting diode or a super luminescent diode is used.

The first light-emitting element 12 emits a radiated light carrying a modulation signal to a target 18, and an incident light scattered by the target 18 is received by a light-receiving element 20 to obtain an external measurement value.
On the other hand, the second light emitting element 42 transmits the calibration light carrying the modulation signal to an optical fiber 44 and an optical filter 46 having a predetermined length.
Through the light receiving element 20 to obtain a calibration value.

The control circuit 32 operates at a low voltage of, for example, 3.3 volts, and alternately supplies a modulation signal to the first light emitting element 12 or the second light emitting element 42 by switching.
It includes an OS type multiplexer and a CMOS type microcomputer which calculates the distance to the target 18 based on the obtained measured value and calibration value.

Next, an outline of the operation will be described. First,
The light emitting element 12 is selected, and the light emitted from the light emitting element 12 is emitted to the target 18 substantially parallel by the objective lens 16. The incident light reflected by the target 18 is condensed by the objective lens 22 and received by the light receiving element 20 via the automatic diaphragm 24 and the optical filter 26.

The feature of the second embodiment is that the automatic aperture
4 and the light-emitting element 42, and the aperture of the automatic aperture device 24 is controlled so that the voltage obtained by the photoelectric conversion becomes a specified value at the time of external measurement. The automatic aperture device 24 maintains this state until the next external measurement.

Next, the light emitting element 42 is selected, and the internal calibration of the distance meter is performed. The calibration light of the light emitting element 42 having the modulation signal in phase with the modulation signal of the emitted light is transmitted through the optical fiber 44 and the ND filter 46 of a predetermined length to the light receiving element 20.
To obtain a calibration value. In this case, the light amount of the calibration light is adjusted by the fixed ND filter 46 in which various densities are arranged stepwise.

As described above, by repeatedly performing the measurement up to the target 18 and the measurement of the internal calibration path by switching the electric signal carrying the modulation signal to the light emitting elements 12 and 42, the switching of the signal is instantaneous. As a result, high-speed measurement can be performed.

Further, Japanese Patent Publication No. 8-726 by the present applicant
When the ratio of the number of times of external measurement and the number of times of internal calibration is set to N / 1, the measurement speed can be further increased.

In this embodiment, two objective lenses 16 and 2
2 was used, but one objective lens was
The present invention can also be applied to an optical system of a modification in which light is divided and used for incident light.

Although the present invention has been described with an emphasis on the explosion-proof type lightwave distance type, there is no problem even in normal use, and handling is easy because of the low voltage.

FIG. 3 is a schematic block diagram of an explosion-proof lightwave distance meter provided with a variable amplifier 50 capable of changing the amplitude or the degree of modulation of the modulation signal supplied to the first light emitting element 12 instead of the automatic diaphragm 24. It is. 3, members corresponding to those shown in FIG. 2 are denoted by the same reference numerals.

The variable amplifier 50 includes modulation amplifiers D1 to Dn having a constant amplification degree, and the outputs of these amplifiers are connected via coupling capacitors C1 to Cn and resistors R1 to Rn having various resistance values. The light is supplied to the light emitting element 12. A grounding resistor R11 is connected to a connection point of each resistor to form a voltage dividing resistor having various degrees of attenuation.

Therefore, the applied input modulation signal is turned on / off by the control signal applied to each amplifier, and the synthesized modulation signals having various amplitudes are supplied to the light emitting element 12.

FIG. 4 is a partial detailed view of the control circuit of FIG. In FIG. 4, internal calibration is first performed by a calibration / measurement selection signal from the microprocessor 52. The light emitting element 42 is activated, the calibration light is guided and output by the optical fiber 44, and the ND film 46, the filter 2
The light 6 enters the light receiving element 20. Since the ND film 46 is adjusted so that the output level of the frequency conversion circuit 54 becomes an appropriate value in advance, the internal calibration phase at this time is measured and stored by the phase meter 52.

Next, the mode is switched to the external measurement. Light emitting element 1
2 emits light that is 100% modulated by the modulation signal of the variable amplifier 50. The emitted light is radiated substantially parallel by the objective lens 16 and passes through the filter 26 to the light receiving element 20.
Is collected and photoelectrically converted.

The level of the output signal of the frequency conversion circuit 54 varies greatly depending on the material of the target object and the distance to the object to be measured (target object). The modulation amplifiers D1 to Dn of the variable amplifier 50 are on / off controlled such that the difference between the modulation amplifiers D1 and D2 is within a certain range. Therefore, an appropriate level is input to the phase meter 52, and the external phase is measured. This external phase value is calibrated by its internal calibration phase value, then calculated and displayed as a distance value.

The great advantage of digitally variably controlling the amplitude or the degree of modulation is obtained when the amplitude or the degree of modulation is switched. Even if subtle differences in circuit components possessed by each modulation amplifier cause a phase error, which may cause an error in the distance measurement value, the modulation amplifier D1
Since the address of Dn is known, the distance measurement value can be corrected.

The variable width of the modulation degree is 1, 2, 4, 8, 16
The step may be a step suitable for a distance meter such as dB or a fixed width of 6 dB × 10.

Instead of the variable amplifier 50, a multiplier in which a modulation signal is applied to the X input and a controlled analog voltage is applied to the Y input may be used. In this case, the voltage dividing resistors of various attenuations are omitted.

In a circuit in which a constant current flows from the low power supply to the light emitting element 12 through the resistor R11, the modulation degree of the modulation amplifier for supplying the modulation signal is determined by the light receiving level signal.
Digitally controlled while comparing with the reference voltage.

The variation value of the phase that changes by the combination of the modulation amplifiers D1 to Dn is corrected for each address indicating the combination, and no error occurs in the measurement distance even if the modulation degree is changed.

[0043]

As described above, according to the present invention,
There is an advantage that the explosion-proof lightwave distance meter can be easily configured.

[Brief description of the drawings]

FIG. 1 is a schematic view of a first embodiment of a lightwave distance meter using two automatic diaphragms according to the present invention.

FIG. 2 shows one automatic aperture device and two light emitting elements according to the present invention.
It is the schematic of the 2nd Example of the lightwave distance meter which used this.

FIG. 3 is a schematic view of a third embodiment of a lightwave distance meter according to the present invention.

4 is a partial detailed block diagram of a control circuit of the lightwave distance meter shown in FIG.

[Explanation of symbols]

 REFERENCE SIGNS LIST 12 light emitting element 14 mirror 18 target 20 light receiving element 24 automatic stop 28 automatic stop 32 control circuit 42 light emitting element 44 optical fiber 46 fixed ND filter

Claims (6)

[Claims] 1. A light-emitting element for emitting a radiation signal carrying a modulation signal to a target, a light-receiving element for receiving incident light reflected by the target to obtain a measurement value, and a modulation signal from the light-emitting element. Switching means for receiving a calibration light for carrying the light through the internal calibration path of a predetermined length to the light receiving element to obtain a calibration value, operating at a low voltage, and operating the target object based on the measurement value and the calibration value. And a control circuit including a microcomputer for calculating a distance to the target, wherein an automatic diaphragm operated at a low voltage is used for adjusting the amount of the incident light from the target. 2. A first light emitting element for emitting radiation light carrying a modulation signal to a target, a light receiving element for receiving incident light scattered by the target to obtain a measurement value, and carrying the modulation signal. A second light-emitting element for receiving a calibration light to be received by the light-receiving element via an internal calibration path of a predetermined length to obtain a calibration value, and operating at a low voltage and transmitting the calibration light to the first and second light-emitting elements. A control circuit including a microcomputer for calculating a distance to the target based on the measured value and the calibration value obtained by alternately switching a modulation signal, and adjusting a light amount of the incident light from the target. A light rangefinder using an automatic diaphragm operated at a low voltage. 3. An electro-optical distance meter according to claim 1, wherein said switching means includes a second automatic stop which operates at a low voltage. 4. A first light emitting element for emitting a radiation signal carrying a modulation signal to a target, a light receiving element receiving incident light scattered by the target to obtain a measurement value, and carrying the modulation signal. A second light-emitting element for receiving a calibration light to be received by the light-receiving element via an internal calibration path of a predetermined length to obtain a calibration value, and operating at a low voltage and transmitting the calibration light to the first and second light-emitting elements. A control circuit including a microcomputer that calculates a distance to the target based on the measured value and the calibration value obtained by alternately switching the modulation signal, and a signal supplied to the first light emitting element. Wherein the amplitude is adjusted so that the level of the signal reaching the light receiving element is constant. 5. A signal supplied to the first light emitting element,
5. The lightwave distance meter according to claim 4, wherein the phase is adjusted to be constant when the amplitude is changed. 6. An electro-optical distance meter according to claim 1, wherein glass having an anti-reflection film deposited thereon is hermetically disposed in front of said light receiving element and said light emitting element.