JPS6259247B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a flow meter using an optical fiber as a sensor.

BACKGROUND ART Conventionally, a vortex flowmeter is known in which a vortex generator is placed in a pipe and the number of vortices generated by the vortex generator is counted. In the case of such a vortex flowmeter, the frequency of the generated vortex corresponds to the flow rate, so the flow rate can be determined by measuring the frequency. FIG. 1 is a diagram showing a conventional example of a vortex flowmeter. In the figure, 1 is a flow tube. 2 is a vortex generator placed in the channel of the flow tube. When fluid flows through the pipeline shown in the figure in the direction of the arrow, a vortex is generated in the direction shown in the figure.

The present invention realizes a flow meter that utilizes interference fringes caused by changes in the optical path length of an optical fiber. Hereinafter, the present invention will be explained in detail with reference to the drawings.

FIG. 2 is a configuration diagram showing an embodiment of an optical fiber flowmeter showing an embodiment of the present invention. In the figure, 3 is a light source. The light source may be of any type, such as a laser or a light emitting diode. 4 and 5 are optical fibers that receive the light output from the light source 3. 6
is a fluid pipe as shown in FIG. 3, through which fluid flows. In FIG. 3, the same parts as in FIG. 2 are given the same reference numerals. Returning to FIG. 2 again, 7 is a sensor section installed inside the flow tube 6. The optical fibers 4 and 5 run through the sensor section 7. 8 is a photoelectric conversion circuit that receives the output of the optical fiber that has passed through the flow tube. For example, a photodiode is used as the photoelectric conversion element.

Reference numeral 9 denotes an amplifier that receives the output of the photoelectric conversion circuit 8 and amplifies it to an appropriate level.
10 is a rectifier circuit that rectifies the output of the amplifier. C ₁ and C ₂ are capacitors connected between the photoelectric conversion circuit 8 and the amplifier 9, and between the amplifier 9 and the rectifier circuit 10, respectively. 11 is a comparison circuit that compares the output of the rectifier circuit 10 with a certain constant voltage. 12
is a frequency stabilization circuit for stabilizing the pulse frequency taken out from the comparator circuit 11. For example, a PLL circuit or the like is used as the stabilizing circuit. The operation of the device configured in this way will be explained below.

The light emitted from the light source 3 is transmitted through optical fibers 4 and 5.
It is divided into two parts and enters the sensor section 7. Since the sensor section 7 is placed in the fluid, the optical path length of the two optical fibers inside the sensor section changes due to the stress generated inside them. If interference is caused at the input part of the photoelectric conversion circuit 8, the optical path length will be modulated by the vibration of the fluid, and the interference fringes will move. That is, if we focus on one point on this interference fringe, it will be seen that the intensity modulation of light has occurred at that point. The movement of the interference fringes mentioned above can be extracted as a change in frequency, so
The device shown in FIG. 2 can be used as a flowmeter. The photoelectric conversion circuit 8 converts the movement of the interference fringes into an electrical signal. This electrical signal is transmitted to the subsequent amplifier 9
is amplified by

The amplified signal is rectified by a rectifier circuit 10 and converted into direct current. The output of this rectifier circuit 10 is
It is a pulsating flow with a certain offset. Comparison circuit 11 compares the output of rectifier circuit 10 with a certain constant voltage and converts it into a pulse output without offset. The output of the comparison circuit 11 is input to the frequency stabilization circuit 12 that follows. The frequency stabilization circuit is
It operates to keep the frequency constant even when sudden disturbances occur in the input signal. A PLL circuit or the like is usually used for this purpose. The output V _OUT of the frequency stabilization circuit 12 becomes the output of the fiber optic flow meter shown in FIG. The output V _OUT corresponds to the vibration frequency of the fluid, and by measuring this vibration frequency, the flow rate of the fluid can be determined. By modulating the light source at a frequency higher than the vortex frequency, a frequency band that can be easily handled as an electrical signal can be used. It is also possible to use synchronous detection or the like.

In order to increase the sensitivity of the sensor section 7, it is sufficient to increase the effective length of the optical fiber embedded in the sensor section. Alternatively, the sensitivity can be improved even if it is bent to a permissible bending radius. As the effective length increases, the loss increases, so sensitivity can be increased. Moreover, the smaller the bending radius, the higher the sensitivity becomes. FIG. 4 is a diagram showing various shapes of optical fibers embedded in the sensor section 7. FIG. Both are processed into optical fibers to increase sensitivity.

According to the present invention, the following effects can be obtained.

The optical fiber flowmeter according to the present invention is a transmission type flowmeter that measures the flow rate based on light transmitted through the fluid. For this reason, compared to a reflective flow meter that reflects light in the fluid and measures the flow rate based on the reflected light, the optical system is closed, so there is less light leakage and high measurement accuracy can be achieved.

Since two optical fibers are inserted into the sensor section, disturbances occurring simultaneously in these optical fibers can be canceled by canceling each other out.

As described above in detail, according to the present invention, a flowmeter that utilizes the features of optical fibers can be realized.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the configuration of a conventional vortex flowmeter. FIG. 2 is a configuration diagram showing an embodiment of the present invention;
FIG. 3 is a diagram showing the main part of FIG. 2. Figure 4 shows
It is a figure showing the shape of an optical fiber. 3... Light source, 4, 5... Optical fiber, 6... Flow tube, 7
...Sensor part, 8...Photoelectric conversion circuit, 9...Amplifier, 1
0... Rectifier circuit, 11... Comparison circuit, 12... Frequency stabilization circuit.

Claims (1)

[Scope of Claims] 1. A light source, two optical fibers that receive light output from the light source, these optical fibers are immersed in a fluid part, and stress is generated inside the two optical fibers by vibrations caused by the fluid. , a sensor unit that changes the optical path length of the optical fiber, and a photoelectric conversion unit that causes interference in the light transmitted by the two optical fibers and outputs a signal in accordance with the movement of interference fringes due to stress generated in the optical fiber. An optical fiber flowmeter comprising: a circuit; an amplifier that receives the output of the conversion circuit; and a comparison circuit that pulses the output of the amplifier.