JP3063037B2 - Distributed optical fiber sensor - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a distributed optical fiber sensor capable of measuring one signal simultaneously and in parallel with different resolutions and greatly reducing the measurement time.

[Prior Art] FIG. 3 shows a block diagram of a distributed optical fiber temperature sensor which is a kind of a conventional optical fiber sensor. A laser pulse oscillated from a laser pulser 30 such as a semiconductor laser of a light source unit is incident on an optical fiber 32 to be measured, and backward Raman scattered light generated in the optical fiber 32 returns to an incident end. The backward Raman scattered light is guided to the measurement device by the optical directional coupler 31, and first, Stokes light and anti-Stokes light in the Raman scattered light are separated and detected by the filter 33, and the separated light is detected by the photoelectric conversion units 34 and 34 '. It is converted into an electric signal proportional to the intensity. The electric signals are amplified by preamplifiers 35 and 35 ', respectively, and converted into digital signals by AD converters 36 and 36'. The digitized signals are transmitted to a signal processing unit 37, which performs an averaging process and a Stokes processing. Processing such as taking the ratio of the signal of the light and the anti-Stokes light and converting it to a temperature distribution is performed.

The AD converter 36 or 36 'and the signal processing section 37 shown in FIG. 3 are shown in detail in FIG. 1 is an AD preamplifier, 2 is an AD converter, 3 is an AD memory, 4 is an adder,
Reference numeral 5 denotes an addition memory, and reference numeral 6 denotes a control circuit for designating a start-end address of the AD memory 3 by a sampling clock signal. The data added to the addition memory 5 for a predetermined number of measurements is further transmitted to a computer or the like and averaged, and a temperature distribution is calculated by taking a ratio with the averaged data of the anti-Stokes optical signal.

Conventionally, measurement was performed by a single system (one AD converter, one AD memory, one adder, and one addition memory for each electric signal). To increase the optical fiber distance, increase the memory capacity to cope with the problem.To measure the entire physical quantity distribution, thin out sampling points with low-speed sampling.For local and steep physical quantity distribution, use high-speed sampling. Two methods of switching are proposed.

[Problems to be Solved by the Invention] Problems of the former two methods are as follows.

1. Since the amount of data to be subjected to the averaging process increases, the calculation time increases, the effective repetition period becomes longer, and the measurement time becomes longer. If the measurement length is 10km and the sampling interval is m,
10,000 × 10 (nsec) = 100 μsec for data recording and 10,000 × 80 (nsec) if the adder cycle time is 80 nsec
= 800 μsec, and the repetition period is at least 900 μs
ec required.

2. Inefficient use of memory. The problems of the latter method are as follows.

1. Since measurement is switched in a time-sharing manner, real-time performance is lacking. That is, when the high resolution side determination is being performed, there is no possibility of seeing any other area at all, and a sudden temperature change may be missed.

2. In order to perform highly accurate measurements, it is necessary to make corrections based on the attenuation rate of the optical fiber, but this correction requires an accurate temperature at the correction start point. For example, in order to perform high-resolution sampling on 1km between 6km and 7km from the light source out of a total length of 10km, an accurate temperature of 6km is required. Therefore, in this method, correction is performed using the latest temperature data of the low-speed sampling. However, even if the above-mentioned temperature data is refreshed at regular time intervals, a sudden temperature change causes a measurement error. .

[Means for Solving the Problems] The present invention has been made to solve the above-described problems, and includes a light source unit for injecting a laser pulse into an optical fiber to be measured, and a return light from the optical fiber to be measured. An optical directional coupler for guiding light to the device, a photoelectric conversion unit for photoelectrically converting the return light into an electric signal, and a signal processing unit for calculating a physical quantity distribution related to the distance of the measured optical fiber from the photoelectrically converted electric signal. In the distributed optical fiber sensor provided, the signal processing unit includes a plurality of A / D converters for performing the A / D conversion on the electric signals in parallel at different sampling frequencies,
A distributed optical fiber sensor, comprising: a plurality of adders corresponding to the plurality of AD converters, each of which adds a plurality of types of converted digital signals to a previous addition result.

For example, in the measurement of a temperature distribution of 10 km, it is not always necessary to measure at the highest resolution over the entire area. Rather, the area where high-resolution measurement is required is limited, and the area where high-resolution measurement is required is known in advance depending on the object to which the optical fiber is attached, or can be inferred to some extent after data has been collected for a certain period of time. For example, when used for monitoring the temperature of a power transmission cable, a joint portion of the cable or the like corresponds.

In order to reduce the amount of data and the processing time by focusing on the above points, there have been the above two methods, but they have the above-mentioned problems. Therefore, the present invention solves the problem without impairing the merits of the technology by operating and processing a system for sampling and averaging the entire region at a low resolution and a system for measuring a specific region at a high resolution in parallel. doing.

Further, the sensor of the present invention can be used not only for measuring temperature distribution but also for measuring defects such as disconnection and damage of an optical fiber and pressure.

[Operation] The system using the present invention operates as follows. First, a high-resolution measurement region is specified in advance so that the measurement length is 2 km or less. However, the number of high-resolution measurement regions may be two or more. Next, AD conversion and averaging are performed at two kinds of sampling frequencies. 20MS for one measurement system
Using the average data of the Mega Sampling Per sec. (PS), measure the temperature distribution over a total length of 10 km. At this time, the temperature correction is sequentially performed as usual from the temperature at the incident end. The other measurement system converts the temperature based on the averaging data of 100 MSPS and the specified start-end address (distance from the incident end). At this time, the temperature at the starting point is known from the temperature data of 10 km, and the attenuation rate is corrected.

Since the temperature distribution of 10km is 5m sampling, if this data is used as the starting point temperature of the high resolution data, an error may occur. That is, the case where the starting point has a steep temperature peak. In this case, an error can be avoided by correcting the flat part closest to the start point as a new start point.

[Embodiment] Fig. 1 shows an embodiment. To apply to a temperature sensor, a similar system for anti-Stokes optical signal is provided for another channel.
2ch.) Required. 19 is an input signal which is a Stokes optical signal, 7 is an input buffer amplifier, 8 is a pre-filter for a low-speed AD converter, 9 and 10 are AD pre-amplifiers (odd numbers are for low-speed sampling), 11 and 12 are AD converters, and 11 is 20MSP
S and 12 are 100 MSPS. Reference numerals 13 and 14 denote AD memories whose outputs are controlled by 24 memory control circuits. The memory control circuit outputs a write pulse, a read pulse, and an address to the memory according to each sampling clock (low speed, high speed) and the measurement area designation signal 23 (only high speed). 22 is an output data bus.

In this embodiment, the memory capacity is 2 kw (kiloword). If this addition cycle is 80nsec,
2000 × 50nsec = 100μsec, 2000 × 80nsec = 160μsec,
Totally 260 μsec.

[Effects of the Invention] The present invention has an excellent effect of greatly reducing the measurement time using a general-purpose adder. Moreover, a low-cost system can be configured without deteriorating the real-time property and accuracy.

[Brief description of the drawings]

FIG. 1 is a block diagram of an embodiment of the present invention, and FIGS. 2 and 3 are block diagrams of a conventional example. 11,12 AD converter 13,14 AD memory 15,16 Adder 17,18 Addition memory 19 Input signal 20 Low-speed clock 21 High-speed clock 22 Output data bus 23 …… Measurement area designation signal 24 …… Memory control circuit

Continued on the front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) G01J 1/02 G01J 1/42-1/44 G01J 5/02-5/08 G01M 11/00-11/02 G01K 11 / 12 G01L 1/24 G08C 15/02

Claims (3)

(57) [Claims] 1. A light source unit for injecting a laser pulse into an optical fiber to be measured, a light directional coupler for guiding return light from the optical fiber to be measured to a measuring device, and photoelectrically converting the return light into an electric signal. In a distributed optical fiber sensor including a photoelectric conversion unit and a signal processing unit that calculates a physical quantity distribution related to the distance of the measured optical fiber from the photoelectrically converted electric signal, the signal processing unit differs in parallel with the electric signal. A plurality of AD converters for performing AD conversion at a sampling frequency; and a plurality of adders corresponding to the plurality of AD converters each of which adds a plurality of types of digital signals subjected to AD conversion to a previous addition result. Characteristic distributed optical fiber sensor. 2. A method according to claim 1, wherein the plurality of A / D converters are a first A / D converter for performing A / D conversion at a certain sampling frequency in order to measure the entirety of the measured optical fiber, and locally convert a part of the measured optical fiber. A second AD converter for performing AD conversion at a higher sampling frequency for measuring at a high resolution, and a control circuit for designating a measurement area of the second AD converter. Distributed optical fiber sensor. 3. The return light is backward Raman scattered light, and has a spectroscope for dispersing Stokes light and anti-Stokes light in the backward Raman scattered light, and photoelectrically converts the Stokes light and anti-Stokes light, respectively. A photoelectric conversion unit; and a signal processing unit that calculates a temperature distribution with respect to the distance of the optical fiber to be measured from a ratio of the two electrical signals obtained by the photoelectric conversion, the signal processing unit including the two of the Stokes light and the anti-Stokes light. Electrical signals in parallel with different sampling frequencies
2. A system according to claim 1, further comprising a plurality of AD converters for performing AD exchange, and a plurality of adders corresponding to the plurality of AD converters, each of which adds a plurality of types of digital signals subjected to AD conversion to a previous addition result.
The distributed optical fiber temperature sensor as described.