JPH0731060B2 - Optical interference angular velocity meter for piping - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an optical interference angular velocity meter for piping, and particularly to piping for measuring azimuth and vertical angle of gas, water, electric piping and other installed piping. The present invention relates to an optical interference gyro.

“Prior Art” A mechanical gyro was used to obtain angular velocity information to measure the azimuth and vertical angle of gas, water, electric pipes and other pipes buried underground in the city. FIG. 6 is a diagram showing the situation. In FIG. 6, the measuring unit 11 is composed of a gyro sensor 12 and a control circuit 13 as shown in FIG. Then, the control circuit 13 controls each power source 1 that drives the gyro sensor 12.
4, 15 and a signal processing unit 16 for synchronously detecting signals obtained from the gyro sensor 12. The monitor panel 17 receives the power source 18 for the measuring unit 11 and the angular velocity information obtained by the measuring unit 11 and performs an arithmetic operation in the arithmetic circuit 19 for displaying on the display 21 or outputting a signal to the recorder 22. As shown in FIG. 6, the drive vehicle 23 pulls the measuring unit 11 through the pipe 24. The measurement unit 11 detects the angular velocity in the azimuth direction and the vertical direction while being pulled, and transmits the signal to the monitor panel 17 via the cable 25. Monitor panel 17
Integrates the angular velocity information obtained by the measuring unit 11 to obtain the azimuth angle and the vertical angle, and displays or transmits it to the recorder 22.

The conventional example of the optical interference angular velocity meter for piping as described above is
The control circuit 13 of 11 cannot be housed in the monitor panel 17. The reason is as follows.

First, a mechanical gyro requires a two-phase or three-phase 400Hz 26V power supply of several watts to rotate a spin motor, and a 12.8kHz power supply for exciting a signal generator. Here, if the gyro sensor 12 and the control circuit 13 are connected by a long cable of several hundred meters, the spin motor and the signal due to the voltage drop in the cable, the fluctuation of the stray capacitance due to the fluctuation of the cable and other causes. The power supply voltage for exciting the generator fluctuates, which deteriorates the function and performance of the gyro, which is not preferable. If the electric resistance in the cable is to be suppressed to be small, the cable becomes thick, and if the cable becomes thick, the weight of the cable increases. Therefore, it is necessary to enlarge the driving vehicle 23 to further increase the traction force. The drive vehicle 23 becomes large and costly.

Then, it is difficult to transmit a minute signal at a minute input angular velocity of about several degrees / hour through a cable of several hundred meters without performance deterioration because it is disturbed by external noise.

The conventional example of the optical interference angular velocity meter for piping as described above is the measuring unit 11
Can not be downsized, and can only be applied to measurement of thick pipes of 100 mmφ or more. It was not possible to measure the azimuth angle and vertical angle of the smaller tubes.
The moving vehicle 23 is required to move the measuring unit 11, and the driving vehicle 23 also needs a large traction force.

On the other hand, an optical interference gyro that can detect an angular velocity like a mechanical gyro has been proposed. To describe the optical interference gyro with reference to FIG. 8, the light 27 emitted from the light source 26 reaches the optical distribution coupler 31 through the optical distribution coupler 28 and the polarizer 29, and here the left and right sides are reversed. Light propagating in the direction
It is branched into 33 and 34 and supplied to the optical fiber coil 32 for angular velocity detection wound one or more times. These left and right lights,
The phase is modulated by the phase modulator 35 arranged at one end of the angular velocity detecting optical fiber coil 32. These two lights 33 and 34 are then again combined by the light distribution coupler 31 and interfere with each other.
The interference light reaches the photoelectric conversion circuit 36 through the polarizer 29 and the light distribution coupler 28. The interference light I ₀ that has reached the photoelectric conversion circuit 36 is I ₀ = C {1-cosΔφ (J ₀ (x) + 2J ₂ (x) cos2ωt ′ + ... + 2J _2m (x) cos2mωt ′ + ...) + sin Δφ (2J ₁ (X) sin ωt '+ 2J ₃ (x) sin 3ωt' + ... + 2J _2m-1 (x) sin (2m-1) ωt '+ ...)} ...
(1)

Where C; constant J _n ; Bessel function of the nth order (n = 0,1,2,3 ...) x; 2Asinπf ₀ τ A; modulation index τ; propagation time f of light passing through the optical fiber coil 32 for angular velocity detection ₀ ; Drive frequency of phase modulator 35 t ′; t−τ / 2 Δφ; Phase difference between both lights 33 ′ and 34 ′ propagating in the optical fiber coil 32 for angular velocity detection in opposite directions. R: Radius of optical fiber coil 32 for angular velocity detection L; Optical fiber coil for angular velocity detection configured in a loop
Length of 32 C; speed of light λ; wavelength of light As is apparent from the equation (1), the interference light I ₀ includes a term proportional to cos Δφ and a term proportional to sin Δφ.
The interference light I ₀ is photoelectrically converted in the photoelectric conversion circuit 36.
The signal converted into the electric signal is synchronously detected by the output of the oscillator 39 in the synchronous detection circuit 38 in order to take out the signal V ₁ proportional to J ₁ (x) sin Δφ to the terminal 37. The oscillator 39 supplies a modulation signal to the phase modulator 35.

Here, the optical path of the optical coherence gyro is usually composed of an optical fiber. As this optical fiber, in order to reliably transmit the phase information of the light, a constant polarization optical fiber having a property of retaining the polarization plane of the light is usually used. Another technique is to make the light emitted from the light source 26 unpolarized and use a single mode optical fiber in the optical path of the optical coherence gyro. In this case, the polarizer 29 is unnecessary.

The present invention makes it possible to measure the azimuth angle and the vertical angle of a thin tube by reducing the size and weight of the measuring unit, reduce the size of the driving vehicle or eliminate the need for the driving vehicle, and receive the influence of external noise. The present invention provides an optical interference gyro for pipes.

"Means for Solving the Problems" A control circuit having a light source 26, an optical distribution coupler 28, and an optoelectric conversion circuit 36 for detecting the light intensity of the interference light as an electric signal.
An optical cable 43 that includes the first optical fiber 44 and the second optical fiber 47, which are protected by a coating material, is transmitted from the light source 26 through the long first optical fiber 44. To the angular velocity detecting optical fiber coil 32, and a polarizer 29 that selectively passes one polarized light of the polarized light, an angular velocity detecting optical fiber coil 32 that makes at least one round, and a polarized light emitted from the polarizer 29 to the angular velocity detecting optical fiber coil 32. Right-handed light 33 and left-handed light
It has a light distribution coupler 31 that interferes with the clockwise light and the counterclockwise light that have propagated through the angular velocity detection optical fiber coil 32 while branching into 34, and the polarizer 29 is arranged immediately before the light distribution coupler 31. , An angular velocity provided with a phase modulator 35 arranged in cascade between the optical distributor / coupler 31 and one end of the angular velocity detecting optical fiber coil 32 to apply a phase change to the clockwise light and the counterclockwise light. In the optical interference velocimeter for piping provided with the detection unit 42, the control circuit 41 further, an oscillation circuit 45 for driving the phase modulator 35, and a modulation signal output from the oscillation circuit 45 to change the light intensity. And a changing electro-optical conversion circuit 46, the angular velocity detection unit 42 further detects the intensity of light emitted from the electro-optical conversion circuit 46 as an electric signal and generates a drive signal for the phase modulator 35. Having a photoelectric conversion circuit 48, and the electro-optical conversion circuit 46 and Serial photoelectric conversion circuit 48 and the second elongate
And the angular velocity detecting section 42 is housed in a spherical angular velocity detecting section housing 63, which constitutes an optical interference angular velocity meter for piping.

Then, a piping optical interference angular velocity meter including a plurality of pairs of the angular velocity detection unit 42 and the control circuit 41 is configured.

[Embodiment] First, with reference to FIG. 1, a circuit configuration of the present invention will be described. FIG. 1 illustrates the circuit configuration of the optical interference angular velocity meter for piping of the present invention. In FIG.
The control circuit 41 includes a light source 26, a light distribution coupler 28, and a photoelectric conversion circuit.
36 and a synchronous detection circuit 38. Angular velocity detector 42
Is composed of a polarizer 29, an optical distribution coupler 31, an angular velocity detecting optical fiber coil 32, and a phase modulator 35. The control circuit 41 and the angular velocity detector 42 are the optical fibers in the long optical cable 43.
Connected by 44.

A modulation signal for driving the phase modulator 35 is generated by an oscillator 45 in a control circuit 41, which is converted into a light intensity change in an electro-optical conversion circuit 46, and then an optical fiber 47 in an optical cable 43.
Is transmitted to the angular velocity detecting section 42 via the signal, is converted into an electric signal again by the photoelectric conversion circuit 48, and is applied to the phase modulator 35. Since the optical fiber 47 used here is for transmitting a change in the intensity of light, it does not need to be a constant polarization optical fiber or a single mode optical fiber, but a multimode optical fiber. be able to. Here, the battery 49 is for driving the photoelectric conversion circuit 48, and the voltage applied to the phase modulator 35, which is a load, is about 0.7 Vrms and consumes almost no power. Can be used.

FIG. 2 is a diagram showing an example of a cross section of the optical cable 11. A plurality of optical fibers 53 are arranged on the outer circumference of the tensile strength member 51 via the buffer layer 52, a buffer layer 55 is arranged on the outer circumference of these optical fibers 53 via the inclusions 54, and a jacket 56 is provided on the outer circumference thereof. . By bundling the optical fibers 53 and protecting them with a covering material,
Since the optical fiber 53 can be drawn over a long length, the azimuth angle and the vertical angle of a long pipe can be measured.

Looking at the optical transmission loss of a long optical fiber, the polarization loss of a constant polarization optical fiber having a cladding diameter of 125 μm is about −2 db / km, and the transmission loss does not pose a problem even if it is run for several hundred meters. Since it is not necessary to bend the fixed polarization optical fiber in the optical cable 43 into a small diameter, it is not necessary to use a fixed polarization optical fiber having a small diameter and a high relative refractive index described later.

Next, the size of the angular velocity detector 42 will be described. The angular velocity detecting optical fiber coil 32 is formed by winding a plurality of optical fibers around a winding frame, and the diameter and the optical fiber length thereof determine the size of the angular velocity detecting section 42 and the angular velocity detecting sensitivity. The optical fiber used for the optical fiber coil 32 for angular velocity detection is a constant polarization optical fiber having a polarization plane of light in order to reliably transmit phase information of the light. In the polarization-maintaining optical fiber, as shown in FIG. 3, the stress imparting portions 58 provided on both sides of the core 57 impart birefringence to the core 57 to enhance the polarization maintaining property of the propagating light. . Stress applying part 58
Is in the clad 59, a silicon resin layer 61 is formed on the outer circumference of the clad 58, and an ultraviolet curable resin layer 62 is formed on the outer circumference thereof.

To reduce the size of the angular velocity detector 42 as much as possible and coil the optical fiber without compromising the angular velocity detection sensitivity, the optical fiber is wound into a small diameter to reduce transmission loss and polarization-maintaining of the polarization-maintaining optical fiber. It is necessary that the performance of the optical fiber such as crosstalk and other optical fibers does not deteriorate so much that it significantly affects the functional performance of the optical interference angular velocity diameter. Table 1 shows that a normal polarization-maintaining optical fiber (clad diameter 125 μm is used so that the performance deterioration is small even if the optical fiber is wound in a small diameter.
m, core / cladding relative refractive index difference of 0.3 to 0.4%), with a smaller diameter (cladding diameter 80 μm), high relative refractive index difference (0.8%)
The characteristic data of the polarization-maintaining optical fiber is shown.

According to the characteristic data of Table 1, even if the winding diameter is 20 mmφ, the increase in transmission loss is 0.3 db after winding 1 km, which is hardly a problem. On the other hand, crosstalk hardly deteriorates when the winding diameter is 50 mmφ, but increases when the winding diameter is further reduced. However, the above-mentioned fixed polarization optical fiber wound around 20 mmφ is a conventional fixed polarization optical fiber wound around 200 mmφ (clad diameter 125 μm, core / clad relative refractive index difference 0.3 to
It is about the same as the crosstalk in 0.4). By the way, in the past, an optical interference angular velocity meter was prototyped using a conventional polarization-maintaining optical fiber having a crosstalk similar to that when wound around the above 20 mmφ, and a high sensitivity of 0.01 ° / hour of angular velocity detection was obtained. Since the optical interference angular velocity meter has a prototype, the increase in crosstalk in Table 1 is not a problem for the optical interference angular velocity meter.

FIG. 4 and FIG. 5 are views for explaining an example of the shape and structure of the angular velocity detecting section in the optical interference angular velocity meter for piping according to the present invention.

Depending on the application, the angular velocity detecting section 42 may detect the input angular velocity not only in one direction but in three orthogonal directions. In this case, three pairs of the angular velocity detecting section 42 and the control circuit section 41 are required, and correspondingly, three pairs of the optical cables 43 are required. The optical interference angular velocity meter for piping shown in FIGS. 4 and 5 shows a case where the directions of the input angular velocity to be detected are two directions orthogonal to each other. FIG. 4 shows a cross section of the angular velocity detecting section and the pipe in the Y-axis direction, and FIG. 5 shows a cross section of the angular velocity detecting section in the X-axis direction.

In FIGS. 4 and 5, a spherical angular velocity detector housing
An optical fiber coil 32y for detecting the Y-axis angular velocity is arranged coaxially with the coil 63 within the bobbin of the coil 32y, and an optical fiber coil 32x for detecting the X-axis angular velocity whose axis is perpendicular to the coil is formed inside the bobbin. The bobbin is provided with a phase modulator 35 coaxially therewith. The angular velocity detector housing 63 is movably arranged in the pipe 24 via wheels 64,
The optical cable 43 is led out in the rear direction with respect to the traveling direction.

If the casing of the angular velocity detecting unit 42 as described above is a spherical casing, even if the pipe 24 is bent at 90 °, it can pass therethrough relatively easily. When the winding diameter of the inner X-axis angular velocity detecting optical fiber coil 32x is 20 mmφ, the outer shape of the angular velocity detecting section 42 can be about 50 mmφ.

[Advantages of the Invention] As described above, measurement of the azimuth angle and vertical angle of a pipe using a mechanical gyro was possible for a pipe having a diameter of about 100 mmφ or more. However, most of the gas pipes have a diameter of about 50 mmφ, and it has been required to construct a measuring unit capable of measuring the azimuth angle and the vertical angle of the pipe having that diameter. The optical interference angular velocity meter for piping according to the present invention can make the outer shape of the spherical casing of the angular velocity detecting portion have a diameter of about 50 mmφ, which makes it easy to measure the azimuth angle and the vertical angle of the 50 mmφ piping. Can be executed.

The gas, water, electric pipes, and other pipes buried in the underground of the city are generally buried in places exposed to the external electromagnetic field, and the angular velocity detection unit of the optical interference angular velocity meter for pipes running inside the pipes is installed. Will also be exposed to this electromagnetic field. However, since the optical interference angular velocity meter for piping of the present invention transmits an optical signal by an optical fiber cable, it is not affected by noise caused by electromagnetic interference from the outside, which is a problem when using an ordinary electric wire cable. It became nothing.

Further, the optical interference angular velocity meter for piping according to the present invention is configured such that the circuit parts constituting the same are moved from the angular velocity detecting portion 42 side moving in the pipe to the control portion 41 side as much as possible, and the angular velocity detecting portion 42 is configured to have a small diameter and light weight. In addition, by replacing the electric wire cable with the optical fiber cable as the signal medium, it was possible to significantly reduce the weight of the towed object,
It has become possible to use a small towing vehicle 23 having a small traction force. Alternatively, a driving method in which the angular velocity detecting section 42 is pushed into the pipe with a thick steel wire without using a towing vehicle can also be adopted.

Further, the present invention is an optical distribution coupler that splits the optical fiber coil 32 for angular velocity detection into right-handed light and left-handed light.
A polarizer 29 is arranged immediately before 31 so that one of the polarized lights of the light propagated from the light source 26 through the long optical fiber 44 is selectively passed. Therefore, the right-handed light and the left-handed light sent to the angular velocity detecting optical fiber coil 32 via the optical distributor / coupler 31 are completely in the same polarization state in the same deflection mode, and the optical fiber gyro performance is secured. Very convenient above.

[Brief description of drawings]

FIG. 1 is a block diagram showing an example of an optical interference gyro according to the present invention, FIG. 2 is a sectional view showing an example of an optical cable, FIG. 3 is a sectional view showing an example of a constant polarization optical fiber, and FIG. FIG. 5 is a sectional view showing an example of the structure of the angular velocity detecting portion of the optical interference angular velocity meter of the invention, FIG. 5 is a sectional view taken along the line AA in FIG. 4, and FIG. 6 is a diagram showing the direction and vertical angle of the pipe using the conventional mechanical gyro. FIG. 7 is a schematic diagram showing a measurement system, FIG. 7 is a block diagram showing the functional configuration of FIG. 6, and FIG. 8 is a block diagram showing an example of a conventional optical interference angular velocity meter.

Claims (2)

[Claims] 1. A control circuit having a light source, a light distribution coupler, and a photoelectric conversion circuit for detecting the light intensity of interference light as an electric signal, comprising a long first optical fiber and a second optical fiber. An optical cable having an optical fiber protected by a covering material is provided, and at least one round is made with a polarizer that selectively passes one polarized light of the light propagated from the light source through the long first optical fiber. The optical fiber coil for angular velocity detection and the right-handed light that has propagated through the optical fiber coil for angular velocity detection while branching the polarized light emitted from the polarizer into the clockwise light and the counterclockwise light with respect to the optical fiber coil for angular velocity detection. A light distributing coupler for interfering with the counterclockwise light is arranged, and a polarizer is arranged immediately before the light distributing coupler, and the light distributing coupler and one end of the optical fiber coil for angular velocity detection are cascaded between them. Arranged clockwise In piping optical interference gyro comprising an angular velocity detecting portion disposed to a phase modulator for changing the phase of light and the counterclockwise light, the control circuit further includes an oscillation circuit for driving the phase modulator,
The electro-optical conversion circuit that changes the modulation signal output from the oscillation circuit into a change in light intensity, and the angular velocity detection unit further detects the intensity of light emitted from the electro-optical conversion circuit as an electrical signal It has a photoelectric conversion circuit that generates a drive signal for the modulator, and the electro-optical conversion circuit and the photoelectric conversion circuit are connected by a long second optical fiber, and the angular velocity detection unit is housed in a spherical angular velocity detection unit housing. An optical interference angular velocity meter for piping, characterized in that 2. An optical interference angular velocity meter for piping according to claim 1, comprising a plurality of pairs of angular velocity detectors and control circuits.