JPH0474937A - Distribution-type optical fiber sensor and processing method of signal - Google Patents

Abstract

PURPOSE:To read out a plurality of kinds of measured data as measured data in one time series by providing a timing generator which generates a memory specification signal synchronously with a plurality of kinds of trigger signals for a light source. CONSTITUTION:In a timing generator 3, four (n= 4) kinds of trigger signals for a light source, phases of which are shifted by periods of 0/4, 10X1/4, 10X2/4 and 10X3/4 (n sec) of the period of 10 n sec of a sampling clock of an A/D converter 9 for a clock for trigger of a laser pulser 4 which is the light source and oscillates at 8 kHz, are generated sequentially. In synchronization with these four kinds of trigger signals for the light source, four kinds of measured data are stored sequentially in four addition memories in a signal processing element. A high distance resolution can be obtained easily by using inexpensive A/D converters.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a distributed optical fiber sensor such as a distributed optical fiber temperature sensor and a Confucian code processing method thereof.

[Prior Art] A block diagram of a conventional distributed optical fiber temperature sensor is shown in FIG. A laser pulse emitted from a laser pulser 40 in the light source section is input to an optical fiber 42 to be measured, and the Raman scattered light generated in the optical fiber 42 returns to the input end. The light is guided to the measuring device by the coupler 41, and first passes through the filter 43.
Stokes light and anti-Stokes light in the Raman scattered light are separately detected, and each is converted into an electric signal proportional to its intensity by a photoelectric conversion unit 44.44°. The electric signals are amplified by preamplifiers 45 and 45 degrees, respectively, and converted into digital signals by A/D converters 46 and 46 degrees. The A/D converted signal is transmitted to the signal processing unit 47, which performs averaging processing, takes the ratio of the Stokes light and anti-Stokes light signals, and calculates the delay time of the signal, that is, the temperature distribution with respect to the distance from the light source. Processing such as conversion is performed. Here, the trigger signal for conventional laser pulse driving is the A/D converter 4.
A signal synchronized in phase with a 6.46° sampling clock signal was used.

[Problems to be Solved by the Invention] FIG. 2 shows the relationship between temperature distribution and sampling clock in a conventional example. 11 is a temperature distribution, 12 is a sampling clock, and 13 is a laser pulse. 14 is a Raman scattered optical signal converted into a time series by a laser pulse, and the rise is proportional to the laser pulse. For simplicity, attenuation due to optical fiber loss is ignored. 15 is an analog value of data sampled by this clock. As described above, when the width of the laser pulse becomes four times or less than the sampling period, the rising edge of the signal cannot be reproduced, and when the width becomes less than twice the sampling period, the rising edge becomes dull and the distance resolution deteriorates significantly.

Usually, a laser pulse width of about 1 onsec is used, so a clock of 2.5 nsec is required.

However, such an AD converter is very expensive and requires advanced circuit technology.

[Means for Solving the Problems] The present invention has been made to solve the above-mentioned problems, and includes a light source that injects a laser pulse into an optical fiber to be measured, and a detector that detects the return light from the optical fiber. an optical directional coupler that guides light to the optical fiber, a detector that photoelectrically converts the returned light into an electrical signal, an AD converter that converts the electrical signal into a digital signal, and a physical quantity distribution related to the distance of the optical fiber from the digital signal. In a distributed optical fiber sensor, a distributed optical fiber sensor includes a clock that generates a sampling clock of an AD converter, and a light source trigger that oscillates at a predetermined frequency, assuming that the period of the sampling clock of the AD converter is 1. O to the clock for
≦XO<x+ <...< x n < 1 and 0 <
x +-+ -x +≦0.5 (n is an integer of 1 or more,
(i is an integer of O≦i<n) A plurality of types of light source trigger signals are sequentially generated with their phases shifted in a cycle, and multiple types of light source trigger signals corresponding to the plurality of types of light source trigger signals are stored in the memory in the signal processing unit. A timing generator that generates a memory designation signal in synchronization with the trigger signals for the plurality of types of light sources in order to sequentially store the measurement data, and a process that reads out the plurality of types of measurement data in the memory as one time series measurement data. A distributed optical fiber sensor is characterized in that it has a signal processing section, and a laser pulse is input from a light source to an optical fiber to be measured, photoelectrically converts the return light from the optical fiber, and the photoelectrically converted electricity is generated. In a signal processing method in which a signal is converted into a digital signal by an AD converter, and the digital signal is processed by a signal processing unit to calculate a physical quantity distribution regarding the distance of the optical fiber, the clock pulse of the sampling clock of the AD converter and the The relative position of the analog value of the returned light is measured by shifting it multiple times within the period of the sampling clock at least 172 cycles or less, and the obtained multiple types of measurement data are measured as one time series. The present invention provides a signal processing method characterized by reading out data.

FIG. 1 shows an embodiment of the present invention, where ■ is a system clock, 2 is a frequency divider, 3 is a timing generator as a timing generator, 4 is a laser pulser as a light source, and 5 is an optical fiber coupler or an acousto-optic element. 5° is a filter that separates Stokes light and anti-Stokes light, 6, 6° is a detector such as a photoelectric converter, 7
, 7° is the amplifier, 8 is the optical fiber to be measured 9,9
° is an AD converter, and lO is a digital signal processing unit.

The timing generator 3 creates a phase-controlled laser pulse trigger signal based on the system clock. The phase information at this time is sent to the digital signal processing section 1O, and areas determined for each phase on the addition memory are accessed and the addition results are stored. By interleaving the data that has been subjected to averaging processing for each phase as one time series signal at a predetermined position as shown in Figure 3,
Reproduce the rise of the signal.

[Operation] A case will be described in which the clock 1 generates a predetermined clock signal of, for example, 200 MHz, and the frequency divider 2 generates a 100 MHz sampling clock signal for an AD converter. 1
The clock interval of 00MHz sampling clock is 10
Although the interval is the same as the laser pulse width of nsec, a clock of 10/4=2.5 nsec is required to accurately reproduce the change in the Raman scattered light signal generated by the laser pulse. Here, assuming that the refractive index of the optical fiber is approximately 1.5, the speed of light is 3 x 10' (m/5ecl), and the laser pulse makes one round trip through the optical fiber, the laser pulse width of 1 Onsec is 2 Xl, 5 /
(3X10') = IOX 10-" (see/m)
= 10 (n5ec±0), which corresponds to a distance resolution of 1I11.

In the timing generator 3, the 8K light source
The period of the sampling clock of the AD converter is 1 with respect to the trigger clock of the laser pulser 4 which oscillates at Hz.
0nsec 0/4.10x 1/410x 2/4
, IOX sequentially generates 4 (n 4) types of light source trigger signals whose phases are shifted with a period of nsecl. In synchronization with these 4 types of light source trigger signals, 4 types of light source trigger signals in the signal processing section are generated. Four types of measurement data are sequentially stored in the addition memory.The four types of measurement data each have a phase of 2.5n.
This was obtained based on laser pulses shifted by sec, and when converted to distance, this is equivalent to shifting the measurement point by 25 cm. Therefore, these measurement data are
If 5 cm (2.5 nsec) is plotted as one time series of measurement data (interleaving), measurement with a distance resolution of 25 cm (4 times) becomes possible.

In the above case, the light source is triggered with four phases (four types), but as long as there are two or more phases, three phases, eight phases, etc. are also possible, and the same phase may be used. Also, the interval x of each phase
1° and −X may be constant or undefined, but it is preferable to keep them constant in terms of timing control.

It is also possible to provide multiple memories in the signal processing section, and add and average the multiple types of data corresponding to each of the above phases until the end of the measurement, and read them out as one time series data. However, a plurality of types of data may be stored as one time series data, and the averaging process may be performed by the end of the measurement.

In addition, as another embodiment of the present invention, a configuration may be adopted in which four-phase clocks having a phase difference of 90 degrees are used, or four AD converters are placed in parallel in front of the signal processing section to change the phase by 90 degrees. It is also possible to perform sampling by shifting the measurement data by degrees and read out four types of measurement data as one time series. in this case,
Needless to say, it is not limited to four phases.

[Example] No. 4b is an example of a timing generator. 16
1 is a 200 MHz clock generator, which is the same as the system clock 1 in FIG. 1, and 17 is a frequency divider, which divides the laser repetition period to 8 kHz. 18-20 are each 2.5.5.0.7.5 n5ec
Delay lines of ±0.1 nsec, 21 to 24 are buffers. Buffers 21 to 24 are unnecessary if they do not affect the characteristics. 25 is an inverter, 26 is 2 bi
The binary counter 27 of t is a multiplexer controlled by this 2-bit data. 28 is the trigger signal output of the laser pulser, and 29 is phase information for specifying the addition memory.

Figure 5 is a timing chart, and 30 is 17/8.
KH2 output, 31.32 is 26 output, 33 is 4
It is a kind of trigger signal. The second trigger pulse at 33 has the same phase as the second pulse at 30, but
3rd is 2.5nsec, 4th is 5n5ec, 5
The 7th n5ec phase is delayed, and the 6th is in phase. Also, when 31 is L (low) and 32 is L, the multiplexer 27 selects the output of 21, and the 31st
When is H (high) and 32 is L, output 22 is selected; when 31 is and 32 is H, output 23 is selected;
is H and 32 is H, output 24 is selected.

The above functions can also be achieved with a 400 MHz system clock and sequencer, but the higher frequency may increase costs.

Further, phase control can also be performed from outside (computer or digital signal processing unit). In this case, 25.
26 is unnecessary. The system becomes more flexible and reliable.

The above is an example in which one sequence has four phases, but if higher resolution is required, the number of phases can be easily increased.

In this configuration, the delay lines 18 to 20 are connected in parallel, so if the number of delay lines is p, the number of phases is p+1. If the connection method between the delay line and the multiplexer or SW (switch) is devised, it is possible to realize the number of phases of p+2 or more. The rotation direction of the phase and the sequence order may be arbitrary.

C Effects of the Invention] The present invention has an excellent effect in that high distance resolution can be easily obtained using an inexpensive AD converter.

[Brief explanation of the drawing]

1 and 3 to 5 show embodiments of the present invention, and FIG. 1 is a block diagram of a distributed optical fiber temperature sensor,
Figure 2 is a waveform diagram showing the relationship between the temperature distribution and the sampling clock of the AD converter in the conventional example, Figure 3 is a waveform diagram showing interleaving of four types of measurement data, and Figure 4 is a waveform diagram showing the relationship between the temperature distribution and the sampling clock of the AD converter in the conventional example. Fig. 5 is a block diagram of the timing generator, Fig. 5 is a timing chart of the main signals of the timing generator, and Fig. 6 is a block diagram of a conventional distributed optical fiber temperature sensor.・Timing generator 8...Optical fiber 9...AD converter lO...Digital signal processing unit

Claims (5)

[Claims] (1) A light source that injects a laser pulse into an optical fiber to be measured, an optical directional coupler that guides the return light from the optical fiber to a detector, and a detector that photoelectrically converts the return light into an electrical signal. , a distributed optical fiber sensor comprising an AD converter that converts the electric signal into a digital signal, and a signal processing unit that calculates a physical quantity distribution regarding the distance of the optical fiber from the digital signal, generating a sampling clock for the AD converter. If the period of the sampling clock of the AD converter is 1, then 0≦x_0<x_1<...<x_n<1 and 0 with respect to the light source trigger clock oscillated at a predetermined frequency.
＜x_i_+_1−x_i≦0.5 (n is an integer of 1 or more, i is an integer of 0≦i<n), and sequentially generates multiple types of light source trigger signals whose phases are shifted in a period of a timing generator that generates a memory designation signal in synchronization with the plurality of types of light source trigger signals to sequentially store a plurality of types of measurement data corresponding to the plurality of types of light source trigger signals in the memory; and a plurality of the memories. 1. A distributed optical fiber sensor comprising: a signal processing unit that performs processing to read out various types of measurement data as one time series measurement data. (2) Inject a laser pulse from a light source into an optical fiber to be measured, photoelectrically convert the return light from the optical fiber, convert the photoelectrically converted electrical signal into a digital signal with an AD converter, and convert the digital signal into a signal. In a signal processing method in which a physical quantity distribution related to the distance of the optical fiber is calculated by processing in a processing unit, the relative position of the clock pulse of the sampling clock of the AD converter and the analog value of the returned light is calculated based on the period of the sampling clock. 1. A signal processing method, comprising: performing measurements at a plurality of times within a range with a period of at least 1/2 or less of the period, and reading out a plurality of types of obtained measurement data as one time series of measurement data. (3) Inject a laser pulse from a light source into the optical fiber to be measured, photoelectrically convert the return light from the optical fiber, convert the photoelectrically converted electric signal into a digital signal with an AD converter, and convert the digital signal into a signal. In a signal processing method that calculates a physical quantity distribution related to the distance of the optical fiber by processing in a processing unit, if the period of the sampling clock of the AD converter is 1, then 0≦ with respect to the light source trigger clock oscillated at a predetermined frequency. x_0<x_1<...<x_n
<1 and 0<x_i_+_1−x_i≦0.5 (n is 1
The above integer, where i is 0≦i<n, sequentially generates multiple types of light source trigger signals whose phases are shifted at a period of 0≦i<n, and stores multiple types of light source trigger signals corresponding to the multiple types of light source trigger signals in the memory in the signal processing unit. A memory designation signal is generated in synchronization with the plurality of types of light source trigger signals in order to sequentially store the plurality of types of measurement data, and the plurality of types of measurement data in the memory in the signal processing section are read out as one time series measurement data. A signal processing method featuring (4) A light source that injects a laser pulse into the optical fiber to be measured, a light directional coupler that guides the backward Raman scattered light from the optical fiber to the detector, and Stokes light contained in the backward Raman scattered light. a detector that photoelectrically converts the and anti-Stokes light into electrical signals, an AD converter that converts the electrical signals into digital signals, and a signal processing unit that calculates the temperature distribution with respect to the distance of the optical fiber from the digital signals. In the distributed optical fiber temperature sensor equipped with the above-mentioned distributed optical fiber temperature sensor, if the clock that generates the sampling clock of the AD converter and the period of the sampling clock of the AD converter are 1, then 0≦ with respect to the light source trigger clock that is oscillated at a predetermined frequency. x_0<x_1<...<x_
Sequentially generating multiple types of light source trigger signals whose phases are shifted at a period of n<1 and 0<x_i_+_1−x_i≦0.5 (n is an integer of 1 or more, i is an integer of 0≦i<n),
and a timing generator that generates a memory designation signal in synchronization with the plurality of types of light source trigger signals in order to sequentially store a plurality of types of measurement data corresponding to the plurality of types of light source trigger signals in the memory in the signal processing unit. 2. The distributed optical fiber temperature sensor according to claim 1, further comprising: a signal processing section that sequentially reads out a plurality of types of measurement data from the memory as one time series of measurement data. (5) Inject a laser pulse from the light source into the optical fiber to be measured, photoelectrically convert the Stokes light and anti-Stokes light contained in the backward Raman scattered light from the optical fiber, and AD the photoelectrically converted electrical signal. In a signal processing method in which a converter converts the digital signal into a digital signal and a signal processing unit processes the digital signal to calculate a temperature distribution with respect to the distance of the optical fiber, when the period of the sampling clock of the AD converter is 1, a predetermined frequency 0≦x_0<x_1<... for the light source trigger clock oscillated by
・<x_n<1 and 0<x_i_+_1−x_i≦0.
5 (n is an integer of 1 or more, i is an integer of 0≦i<n) for multiple types of light sources, and sequentially generates trigger signals for multiple types of light sources whose phases are shifted at a cycle of A memory designation signal is generated in synchronization with the trigger signals for the plurality of light sources in order to sequentially store the plurality of types of measurement data corresponding to the trigger signals for the light source, and the plurality of types of measurement data in the memory in the signal processing section are sequentially stored in the memory. The signal processing method according to claim 2, wherein the signal processing method is read out as time-series measurement data.