JP5467521B2 - Temperature distribution measuring instrument - Google Patents

Description

  The present invention relates to a temperature distribution measuring instrument that measures temperature distribution using Raman scattered light generated when pulsed light is incident on an optical fiber.

  2. Description of the Related Art A temperature distribution measuring device that measures temperature distribution using Raman scattered light generated when pulsed light is incident on an optical fiber is known. FIG. 6 is a block diagram showing a configuration of a conventional temperature distribution measuring device. As shown in the figure, the temperature distribution measuring device 300 includes a sensor optical fiber 200, a pulse generator 310, a light source 320, a directional coupler 330, a filter 340, a light receiver 350, a light receiver 351, an amplifier 352, an amplifier 353, An AD converter 354, an AD converter 355, an averaging circuit 360, and a calculation unit 370 are provided.

  In the temperature distribution measuring device 300, based on the pulse signal generated by the pulse generator 310, a light pulse is emitted from the light source 320 to the sensor optical fiber 200, and backscattered light of the light pulse returns from the sensor optical fiber 200. come.

As shown in FIG. 7, the back-scattered light of the incident light of wavelength lambda _0, Rayleigh scattered light having a wavelength lambda _0, the Raman scattered light having a wavelength lambda ₀ ± several 10 nm, the wavelength lambda ₀ Brillouin scattered light ± several nm such Is included. The temperature distribution measuring device 300 uses Raman scattered light having high temperature dependency among these back scattered light.

  As shown in this figure, Raman scattered light includes anti-Stokes light generated on the short wavelength side and Stokes light generated on the long wavelength side with respect to the wavelength of the light pulse. Proportionally changes. Using this characteristic, the temperature distribution measuring device 300 measures the temperature distribution of the object using the sensor optical fiber 200.

  The temperature distribution measuring device 300 extracts Stokes light and anti-Stokes light using the directional coupler 330 and the filter 340, and receives them by the light receiving unit 350 and the light receiving unit 351. The Stokes light is converted into an electric signal by the light receiving unit 350 and input to the averaging circuit 360 via the amplifier 352 and the AD converter 354. The anti-Stokes light is converted into an electric signal by the light receiving unit 351 and input to the averaging circuit 360 through the amplifier 353 and the AD converter 355.

  Since the backscattered light is weak, the Stokes light and the anti-Stokes light are measured repeatedly by emitting a light pulse, and the measurement result is averaged by the averaging circuit 360, thereby increasing the temperature measurement resolution. I am doing so. Then, the calculation unit 370 calculates the intensity ratio of the averaged Stokes light and anti-Stokes light.

  The temporal change in the intensity of the Stokes light and the anti-Stokes light with respect to the pulsed light corresponds to the path length of the sensor optical fiber 200, so that the temperature distribution detected by the sensor optical fiber 200 by the calculation of the calculation unit 370 can be obtained. .

JP 2001-349792 A

  The analog signals corresponding to the Stokes light intensity and the anti-Stokes light intensity are digitized by the AD converter 354 and the AD converter 355, respectively, but the AD converter 354 and the AD converter 355 have linearity errors. Then, an error occurs in the temperature of the measurement result, and in particular, a problem occurs when measuring a temperature difference between two points with high accuracy.

  FIG. 8 shows an example of measurement results when an object having a uniform temperature distribution is affected by the linearity error of the A / D converter. Originally, it should have a uniform temperature distribution at all distances, but the measurement results vary in temperature.

  Therefore, an object of the present invention is to reduce the influence of linearity error of an AD converter in a temperature distribution measuring device.

  In order to solve the above problems, a temperature distribution measuring device of the present invention includes a light source that emits an optical pulse to an optical fiber, a light receiving unit that receives Raman scattered light from the optical fiber and converts it into an electrical signal, and the electrical An offset voltage generator that generates an offset voltage to be added to the signal; an AD converter that converts an analog signal corresponding to the electrical signal to which the offset voltage has been added to a digital signal; and a plurality of signals converted by the AD converter An averaging circuit that averages the digital signals, and an arithmetic unit that calculates a temperature distribution of the optical fiber based on the averaged signal are provided.

  In the present invention, since the value obtained by digital conversion using the signal to which the offset voltage is added is averaged, the influence of the linearity error of the AD converter is dispersed. Therefore, the influence of the AD converter linearity error is reduced.

  Here, the light receiving unit and the AD converter may be provided corresponding to Stokes light and anti-Stokes light of Raman scattered light.

  Further, when the light pulse emitted from the light source is a single light pulse, the offset voltage generation unit sets the offset voltage so that the sum is zero during the averaging period of the averaging circuit. To occur. As a result, the averaged value is not affected by the offset voltage.

  The optical pulse emitted from the light source may be an optical pulse train that is code-modulated using a Golay code. In this case, the total offset voltage need not be zero.

  According to the present invention, in the temperature distribution measuring instrument, the influence of the linearity error of the AD converter can be reduced.

It is a block diagram which shows the structure of the temperature distribution measuring device which concerns on this embodiment. It is a figure explaining the offset voltage which an offset voltage generation part generates. It is a figure explaining the effect at the time of using an offset voltage. It is a figure which shows the example of a measurement result of the temperature distribution measuring device of this embodiment. It is a figure which shows the modification of this embodiment. It is a block diagram which shows the structure of a temperature distribution measuring device. It is a figure explaining backscattered light. It is a figure which shows the example of a measurement result received to the influence of the linearity error of an A / D converter.

  Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing a configuration of a temperature distribution measuring device according to the present embodiment. As shown in the figure, the temperature distribution measuring device 100 includes a sensor optical fiber 200, a pulse generation unit 110, a light source 120, a directional coupler 130, a filter 140, a light receiving unit 150, a light receiving unit 151, and an amplifier, as in the prior art. 152, an amplifier 153, an AD converter 154, an AD converter 155, an averaging circuit 160, and an arithmetic unit 170, and further, an offset voltage generator 180, an adder 190, and an adder 191 are included as characteristic parts of the present embodiment. I have.

  In the present embodiment, the sensor optical fiber 200 is a GI-type quartz multimode optical fiber, and is laid so that the temperature from the object can be efficiently transmitted.

  As shown in FIG. 2A, the offset voltage generator 180 generates an offset voltage whose value changes every time a light pulse is emitted. The offset voltage can be an arbitrary value that changes as randomly as possible. However, as shown in FIG. 2B, when calculating the average value of the light intensity by N times of pulse emission, in order to prevent the offset value from appearing in the average value of the light intensity, the offset is calculated in the average value calculation period. Generate so that the sum (average value) of the values becomes zero.

  The offset value generated by the offset voltage generation unit 180 is added to the Stokes optical signal output from the light receiving unit 150 by the adder 190, and is added to the anti-Stokes optical signal output from the light receiving unit 151 by the adder 191. As a result, even if the AD converter 154 and the AD converter 155 have linearity errors, the influence is dispersed.

  Note that the offset voltage generated by the offset voltage generation unit 180 may be different from the value for the Stokes light and the value for the anti-Stokes light as long as each sum is zero.

  With this configuration, the temperature distribution measuring device 100 performs the following operation. That is, a light pulse is emitted from the light source 120 to the sensor optical fiber 200 based on the pulse signal generated by the pulse generator 110, and backscattered light of the light pulse continuously returns from the sensor optical fiber 200.

  The backscattered light is guided to the filter 140 by the directional coupler 130, and is separated into Stokes light and anti-Stokes light by the filter 140. The Stokes light is converted into an electric signal by the light receiving unit 150, and the offset voltage output from the offset voltage generation unit 180 is added by the adder 190. Then, it is amplified by the amplifier 152, digitally converted by the AD converter 154, and input to the averaging circuit 160.

  The anti-Stokes light is converted into an electrical signal by the light receiving unit 151, and the offset voltage output from the offset voltage generating unit 180 is added by the adder 191. Then, it is amplified by the amplifier 153, digitally converted by the AD converter 155, and input to the averaging circuit 160.

  Since the backscattered light is weak, the measurement of the Stokes light and the anti-Stokes light by the emission of the light pulse is repeated N times, and the averaging circuit 160 averages the measurement results of N times. At this time, every time an optical pulse is emitted, the offset voltage generator 180 randomly changes the offset voltage value so that the sum is finally zero. Note that the number N of measurement repetitions can be set to a large value, for example, about 2 to the 17th power.

  Then, the calculating unit 170 calculates the intensity ratio of the averaged Stokes light and anti-Stokes light for each distance, and can obtain the temperature distribution of the object on which the sensor optical fiber 200 is laid.

  As described above, in the temperature distribution measuring instrument 100 of the present embodiment, signals obtained by adding various values of offset voltages to the Stokes optical signal and the anti-Stokes signal are used as input signals to the AD converter 154 and the AD converter 155. As a result, the influence of the linearity error of the AD converter 154 and the AD converter 155 is dispersed. As a result, the influence on the temperature distribution measurement due to the linearity error of the AD converter 154 and the AD converter 155 can be reduced.

  For example, when Stokes light or anti-Stokes light as shown in FIG. 3B is obtained by emission of the optical pulse signal shown in FIG. 3A, the voltage range indicated by the region a in FIG. Assuming that a linearity error of the AD converter 154 or the AD converter 155 occurs, even if the temperature distribution is uniform, the measurement result varies.

  Therefore, when digital conversion is performed and averaged using a signal to which an offset voltage as shown in FIG. 3C is added, the linearity of the AD converter 154 and AD converter 155 is obtained as shown in FIG. The effect of error will be dispersed. Moreover, since the sum of the offset voltages is zero, the averaged value is not affected by the offset voltage.

  As a result, when an object having a uniform temperature distribution is measured, a highly accurate temperature distribution measurement result with little variation can be obtained as shown in FIG.

  Next, a modification of this embodiment will be described. In the above-described embodiment, the case where the backscattered light is measured by emitting a single light pulse has been described. In recent years, in order to increase the temperature resolution of the measurement results, an optical pulse train that has been code-modulated using a Golay code is emitted to the sensor optical fiber, and the backscattered light from the sensor optical fiber is received and obtained. A temperature distribution measuring device that performs correlation processing (demodulation) on a received light signal to calculate a temperature distribution has been put into practical use. The present invention can also be applied to such a temperature distribution measuring device.

In the temperature distribution measuring instrument in the modification of the present embodiment, the pulse generator 110 outputs a pulse signal to the light source 120 so that the optical pulse train becomes an optical pulse train that is code-modulated using a Golay code. Here, n bits (e.g., 64 bits) Golay code, the two code sequences _{A 0: a 1, a 2} , a 3 ... a n, B 0: b 1, b 2, b 3 ... b n These are bipolar correlation codes each consisting of (-1) and (+1) elements.

However, since light does not have negative power, the temperature distribution measuring device modulates using four types of code strings A +, A−, B +, and B−. Here, A + = (1 + A ₀ ) / 2, B + = (1 + B ₀ ) / 2, A − = (1−A ₀ ) / 2, and B − = (1−B ₀ ) / 2. Then, using the signals S (A +), S (A−), S (B +), S (B−) received at the time of each modulation and the code string (A ₀ , B ₀ ) of the modulation code, “ The signal intensity is calculated by taking the cross-correlation according to the equation shown in Equation (1).
For more detailed contents of the Golay code, if necessary, Nazarathy Moshe, Newton Steven A., Giffard RP, Moberly DS, Sischka F., Trutna WR Jr., Foster S., "Real-time long range complementary correlation optical time domain reflectometer ", Journal of Lightwave Technology, January 1989, Vol. 7, p. See 24-38. In addition to the Golay code, for example, a Barker code can be used.

  When the temperature distribution measuring device emits an optical pulse train that is code-modulated using a Golay code, even if an offset value is added to the received signal S (X ±) in “Equation 1”, four types of pulse train transmissions are performed. If the offset value is the same, the offset is subtracted as derived from “Equation 1”, and the final result is not affected.

  For this reason, in the above-described embodiment, the sum of offset values needs to be zero. However, when an optical pulse train that is code-modulated using a Golay code is emitted, the sum of offset values needs to be zero. Disappear.

  Therefore, as shown in FIG. 5, it is sufficient to arbitrarily change the offset voltage in synchronism with an optical pulse train of four types of code sequences as one unit.

DESCRIPTION OF SYMBOLS 100 ... Temperature distribution measuring device, 110 ... Pulse generation part, 120 ... Light source, 130 ... Directional coupler, 140 ... Filter, 150 ... Light receiving part, 151 ... Light receiving part, 152 ... Amplifier, 153 ... Amplifier, 154 ... AD conversion 155 ... AD converter, 160 ... averaging circuit, 170 ... arithmetic unit, 180 ... offset voltage generator, 190 ... adder, 191 ... adder, 200 ... optical fiber for sensor, 300 ... temperature distribution measuring device, DESCRIPTION OF SYMBOLS 310 ... Pulse generation part, 320 ... Light source, 330 ... Directional coupler, 340 ... Filter, 350 ... Light receiving part, 351 ... Light receiving part, 352 ... Amplifier, 353 ... Amplifier, 354 ... AD converter, 355 ... AD converter 360 ... Averaging circuit, 370 ... Calculation unit

Claims (2)

A light source that emits light pulses to an optical fiber;
A light receiving unit that receives Raman scattered light from the optical fiber and converts it into an electrical signal;
An offset voltage generator for generating an offset voltage to be added to the electrical signal;
An AD converter that converts an analog signal corresponding to the electrical signal to which the offset voltage is added into a digital signal;
An averaging circuit for averaging a plurality of the digital signals converted by the AD converter;
A calculation unit for calculating a temperature distribution of the optical fiber based on the averaged signal ,
The light pulse emitted from the light source is a single light pulse,
The temperature distribution measuring instrument , wherein the offset voltage generator generates the offset voltage so that the sum is zero during the averaging period of the averaging circuit .   The temperature distribution measuring device according to claim 1, wherein the light receiving unit and the AD converter are provided corresponding to Stokes light and anti-Stokes light of Raman scattered light.