JP5613974B2 - Temperature measurement method - Google Patents

Description

  The present invention relates to a temperature measurement method for measuring temperature using an optical fiber.

  In recent years, a large number of computers have been placed in the same room, such as data centers that manage and operate customer information and computer centers that handle a large amount of jobs (JOBs) (hereinafter collectively referred to as “data centers”). It is often installed and managed collectively. In a data center, a large number of racks are installed in a room, and a plurality of computers are stored in each rack. Under such circumstances, a large amount of heat is generated from the computer, and the temperature in the rack rises, causing malfunction. For this reason, a means for cooling the computers in the rack is required.

  Generally, the interior of a data center is separated into an equipment installation area in which racks are installed and a free access floor on which power cables, communication cables, and the like are arranged. Cold air is supplied from the air conditioner to the free access floor, and this cold air enters the equipment installation area via a vent (grill) provided on the floor separating the equipment installation area and the free access floor. Then, cool air is taken into the rack by a fan provided in the rack, and the computer is cooled.

By the way, the amount of heat generated from the computer varies greatly depending on the operating state of the computer. In order to reliably prevent a malfunction or failure of the computer due to heat, it is necessary to use a cooling device (such as an air conditioner and a fan) having a cooling capacity corresponding to the maximum amount of heat generated from the computer. In this case, it is not preferable to always operate a cooling device having a large cooling capacity at its maximum capacity, not only from the viewpoint of increasing the running cost but also from the viewpoint of energy saving and CO ₂ reduction. Therefore, it is necessary to measure the temperature of each rack installed in the data center in real time to optimize the cooling.

Conventionally, it has been proposed to use an optical fiber as a temperature sensor when measuring a temperature distribution in an area having a plurality of heat sources such as a data center.
JP 2003-14554 A JP 2003-57126 A JP-A-62-110160 JP-A-7-12655 JP-A-2-123304 JP 2002-267242 A Fujitsu Laboratories Ltd. PRESS RELEASE "Development of real-time multi-point temperature measurement technology for data centers" April 4, 2008

  In temperature measurement using an optical fiber, although it is relatively easy to measure a wide range of temperatures with high accuracy, a method for measuring a narrow range of temperatures with high accuracy has not been established. For example, in a data center, a large number of racks containing a plurality of computers are arranged close to each other. Therefore, simply laying the optical fiber so as to pass through each rack is affected by the temperature of the adjacent rack, and the temperature of each rack cannot be measured with high accuracy.

  In order to accurately measure the temperature in the rack, it is conceivable that an optical fiber having a sufficient length is wound around the temperature measurement point in the rack in a spiral shape. However, when there are a plurality of temperature measurement points in the rack, the length of the optical fiber required for one rack is remarkably increased. Therefore, in a data center where a large number of racks are arranged, the length of the required optical fiber becomes enormous, which is not realistic.

  Accordingly, it is an object of the present invention to provide a temperature measurement method capable of measuring the temperature distribution of a place having a plurality of heat sources such as a data center with good accuracy using an optical fiber.

According to one aspect, an optical fiber continuously laid over the first temperature measurement area and the second temperature measurement area , and 1 or 2 in the first temperature measurement area and / or the second temperature measurement area . in the temperature measuring method of measuring the temperature of a plurality of measurement points, passes within the optical fiber light fiber after introduction before and led to the first temperature measurement area from the end portion of each of the first temperature measurement area The optical fibers before and after being introduced into the second temperature measurement area are arranged close to each other over a length of ½ or more of the minimum heating length determined by the pulse width of the optical signal, respectively. the from end minimum heating length 1/2 or more is brought close over the length of the place, the first temperature measurement area and / or the temperature of the measuring points of the second temperature measurement area And measuring the temperature of the first temperature measurement area and / or the second prior to introduction into the temperature measurement area and proximity location which is disposed close to the optical fiber after deriving, based on the temperature of the proximity location Thus, a temperature measurement method for correcting the temperature of the measurement point is provided.

  According to the above aspect, the optical fiber before being introduced into the temperature measurement area and the optical fiber derived from the temperature measurement area are brought close to each other over a length of ½ or more of the minimum heating length determined by the pulse width of the optical signal. Arrange. Thereby, the influence of the crosstalk between each temperature measurement area can be excluded. In addition, according to the above aspect, the temperature of the proximity location where the optical fiber before and after introduction is placed in proximity to the temperature measurement area is measured, and each measurement point in the temperature measurement area is measured based on the temperature. Correct the temperature. Therefore, the temperature of the measurement point can be accurately measured without winding the optical fiber around the measurement point.

  Hereinafter, before describing the embodiment, a preliminary matter for facilitating understanding of the embodiment will be described.

  FIG. 1 is a schematic diagram showing a configuration of a temperature distribution measuring apparatus using an optical fiber. FIG. 2 is a diagram showing a spectrum of backscattered light, and FIG. 3 is a diagram showing a time-series distribution of the intensity of Raman scattered light detected by the photodetector 26.

  As shown in FIG. 1, the temperature distribution measuring apparatus includes a laser light source 21, lenses 22 a and 22 b, a beam splitter 23, an optical fiber 24, a wavelength separation unit 25, and a photodetector 26. .

  Laser light having a predetermined pulse width is output from the laser light source 21 at a constant cycle. This laser light enters the optical fiber 24 from the light source side end of the optical fiber 24 through the lens 22a, the beam splitter 23, and the lens 22b. In FIG. 1, 24 a indicates the core of the optical fiber 24, and 24 b indicates the cladding of the optical fiber 24.

  Part of the light that has entered the optical fiber 24 is backscattered by the molecules constituting the optical fiber 24. As shown in FIG. 2, the backscattered light includes Rayleigh scattered light, Brillouin scattered light, and Raman scattered light. Rayleigh scattered light is light having the same wavelength as incident light, and Brillouin scattered light and Raman scattered light are light having wavelengths shifted from the incident wavelength.

  The Raman scattered light includes Stokes light shifted to a longer wavelength side than incident light and anti-Stokes light shifted to a shorter wavelength side than incident light. The shift amount of Stokes light and anti-Stokes light depends on the wavelength of the laser light, the material constituting the optical fiber 24, and the like, but is usually about 50 nm. Moreover, although both the intensity of Stokes light and anti-Stokes light changes with temperature, the amount of change with temperature of Stokes light is small, and the amount of change with anti-Stokes light is large. That is, it can be said that the Stokes light has a small temperature dependency, and the anti-Stokes light has a large temperature dependency.

  As shown in FIG. 1, these backscattered light returns through the optical fiber 24 and exits from the light source side end. Then, the light passes through the lens 22 b, is reflected by the beam splitter 23, and enters the wavelength separation unit 25.

  The wavelength separator 25 includes beam splitters 31a, 31b, and 31c that transmit or reflect light according to the wavelength, optical filters 33a, 33b, and 33c that transmit only light of a specific wavelength, and optical filters 33a, 33b, and 33c. Condensing lenses 34a, 34b, and 34c for condensing the light that has passed through the light receiving portions 26a, 26b, and 26c of the photodetector 26, respectively.

  The light incident on the wavelength separator 25 is separated into Rayleigh scattered light, Stokes light, and anti-Stokes light by the beam splitters 31a, 31b, 31c and the optical filters 33a, 33b, 33c, and the light receivers 26a, 26b of the photodetector 26. , 26c. As a result, signals corresponding to the intensity of Rayleigh scattered light, Stokes light, and anti-Stokes light are output from the light receiving units 26a, 26b, and 26c.

  Note that the pulse width of the backscattered light input to the photodetector 26 is related to the length of the optical fiber 24. For this reason, the interval between the laser pulses output from the laser light source 21 is set so that the backscattered light from each laser pulse does not overlap. If the power of the laser beam is too high, a stimulated Raman scattering state occurs and correct measurement cannot be performed. For this reason, it is important to control the power of the laser light source 21 so as not to be in the stimulated Raman scattering state.

As described above, since the Stokes light has a small temperature dependency and the anti-Stokes light has a large temperature dependency, the temperature at the position where the backscattering can be evaluated by the ratio between the two. The intensity ratio of Stokes light and anti-Stokes light is as follows when the optical phonon angular frequency in the optical fiber is ω _k , the incident light angular frequency is ω ₀ , the Planck constant is h, the Boltzmann constant is k, and the temperature is T: Is expressed by the following equation (1).

すなわち、ストークス光及び反ストークス光の強度比がわかれば、（１）式から後方散乱が発生した位置の温度を算出することができる。

That is, if the intensity ratio between Stokes light and anti-Stokes light is known, the temperature at the position where backscattering occurs can be calculated from equation (1).

  By the way, the backscattered light generated in the optical fiber 24 is attenuated while returning through the optical fiber 24. Therefore, in order to correctly evaluate the temperature at the position where backscattering occurs, it is necessary to consider the attenuation of light.

  FIG. 3 is a diagram showing an example of a time-series distribution of the intensity of Raman scattered light, with time on the horizontal axis and the signal intensity output from the light receiving unit of the photodetector on the vertical axis. Stokes light and anti-Stokes light are detected by the photodetector for a certain period immediately after the laser pulse is incident on the optical fiber. When the temperature is uniform over the entire length of the optical fiber, the signal intensity decreases with the passage of time when the laser pulse is incident on the optical fiber. In this case, the time on the horizontal axis indicates the distance from the light source side end of the optical fiber to the position where backscattering occurs, and the decrease in signal intensity over time indicates the attenuation of light by the optical fiber.

When the temperature is not uniform over the length of the optical fiber, for example, when there are a high temperature portion and a low temperature portion along the length direction, the signal intensity of Stokes light and anti-Stokes light is not attenuated uniformly, As shown in FIG. 3, peaks and valleys appear on the curve indicating the change in signal intensity over time. In FIG. 3, the intensity of anti-Stokes light at a certain time t is I ₁ and the intensity of Stokes light is I ₂ .

4 calculates the I ₁ / I ₂ ratio for each time based on the time-series distribution of the intensity of Raman scattered light in FIG. 3, and the horizontal axis (time) in FIG. It is a figure which shows the result of having converted signal intensity | strength) into temperature. As shown in FIG. 4, the temperature distribution in the length direction of the optical fiber can be measured by calculating the intensity ratio (I ₁ / I ₂ ) between the anti-Stokes light and the Stokes light.

  Note that the intensity of Raman scattered light (Stokes light and anti-Stokes light) at the position where backscattering varies with temperature, but the temperature dependence of the intensity of Rayleigh scattered light is so small that it can be ignored. Therefore, it is preferable to specify the position where backscattering occurs from the intensity of Rayleigh scattered light, and to correct the intensity of Stokes light and anti-Stokes light detected by the photodetector according to the position.

  Hereinafter, the minimum heating length will be described with reference to FIGS.

The pulse width (ON time) t ₀ of laser light output from the laser light source 21 is 10 nsec, the speed c of light in vacuum is 3 × 10 ⁸ m / sec, and the refractive index n of the core 24 b of the optical fiber 24 is 1. Assuming 5, the pulse width W of the laser light in the optical fiber 24 is about 2 m as shown in the following equation (2).

W = t ₀ · c / n = 10 (nsec) · 3 × 10 ⁸ (m / sec) /1.5≈2 (m) (2)
The backscattered light of the laser beam corresponding to the pulse width is taken into the photodetector 26 as one signal, and the photodetector 26 detects the temperature from the integrated value of the signal corresponding to the pulse width. Therefore, accurate temperature measurement cannot be performed unless the length corresponding to the pulse width W of the optical fiber indicates a uniform temperature. Since the thermal conductivity of glass is two orders of magnitude smaller than that of metals such as iron, this is almost equivalent to the fact that heat must be uniformly applied to the length corresponding to the pulse width W of the optical fiber. Hereinafter, the minimum heating length necessary for accurate temperature measurement is referred to as Lmin.

  When the optical fiber is heated with the actual temperature distribution shown in FIG. 5A, that is, when only the portion of the length L of the optical fiber is uniformly heated (hereinafter, such temperature distribution is referred to as a step-type temperature distribution). The measured temperature distribution draws a Gaussian (normal distribution) curve as shown in FIG. As shown in FIG. 6, when the length L of the heating part is shorter than the minimum heating length Lmin, the peak of the measured temperature distribution becomes low, and when the length L of the heating part becomes long, the peak of the measured temperature distribution becomes high. . In order to make the difference between the measured temperature and the heating temperature within ± 5%, it is necessary to set the length L of the heating part to be equal to or greater than the minimum heating length Lmin.

  As shown in FIG. 6, when the length L of the heating unit is short, the measured temperature distributions do not overlap even if the two heating units are close to each other. However, when the length L of the heating part is equal to or longer than the minimum heating length Lmin, the measured temperature distributions are overlapped unless the distance between the two heating parts is longer than the minimum heating length Lmin. From this, in order to measure the temperature of the heating part with high accuracy, the minimum period LM of the heat distribution that can be measured is a value obtained by doubling the minimum heating length Lmin.

  In FIG. 7, the horizontal axis indicates the position of the optical fiber in the length direction, the vertical axis indicates the temperature, the optical fiber is disposed in an environment where the temperature is 25 ° C., and the temperature of the light source is about 80 ° C. at a position 5 m from the light source. It is a figure which shows measured temperature distribution at the time of applying heat so that it may become step type temperature distribution. Here, the length of the heating part is 40 cm, 1 m, 1.6 m, and 2.2 m, respectively. As can be seen from FIG. 7, when the length of the heating part is shorter than 2 m (minimum heating length Lmin), the peak of the measured temperature distribution is observed lower than the actual temperature, and the length of the heating part is 2 m or more. In this case, the peak of the measured temperature distribution almost coincides with the actual temperature.

  FIG. 8 is a diagram showing a transfer function (transfer function of the temperature measurement system) in the temperature distribution of FIG. 7 with the horizontal axis representing the distance from the heating center and the vertical axis representing the relative intensity. By convolving the transfer function of FIG. 8 with the step-type temperature distribution of FIG. 7, the measured temperature distribution of FIG. 7 is obtained. The transfer function in FIG. 8 is substantially equal to the impulse response characteristic of this temperature measurement system.

  The transfer function of the temperature measurement system changes according to the distance because the optical fiber has a group delay characteristic. Therefore, the transfer function cannot be uniquely defined over the entire length of the optical fiber. However, if the distance is short, the transfer function can be defined assuming that the loss and delay of the optical signal are uniform. The transfer function differs depending not only on the distance from the light source but also on the type of optical fiber. In the present embodiment, it is important to obtain a transfer function for each predetermined region in the length direction of the optical fiber in advance.

  On the other hand, the temperature measurement point (hereinafter, simply referred to as “measurement point”) can be determined in consideration of the sampling frequency of the measurement device, regardless of the minimum heating length. Considering a practical measurement time such as the time required for averaging in the measurement apparatus, the interval between measurement points can be set to a minimum of about 50 cm.

  Hereinafter, the laying of the optical fiber in the data center will be described.

  9 and 10 are schematic views showing a first example of laying optical fibers. FIG. 9 shows the laid state of the optical fiber when the rack is viewed from the side, and FIG. 10 shows the laid state of the optical fiber when the rack is viewed from above. In FIG. 10, a thick solid line indicates an optical fiber disposed in the equipment installation area (including the inside of the rack) 10, and a thick broken line indicates an optical fiber disposed on the free access floor 15. Further, the circles in FIG. 10 indicate the rising part or the falling part of the optical fiber.

  Here, the positions shown in FIGS. 9A to 9D, that is, the vicinity of the ventilation port (grill) for taking cold air into the rack 11 of the free access floor 15, the vicinity of the air inlet of the rack 11, the vicinity of the CPU of the computer c and the rack 11. The temperature in the vicinity of the exhaust port d is measured. FIG. 9 also shows an example of the path length of each part. The rack 11 has a height H of 2 m, a width W of 0.6 m, a depth D of 0.95 m, and a path length from the rack to the next rack of 0.7 m. In this case, the length of the optical fiber per rack is 6.8 m (= 0.3 + 2.1 + 0.6 + 1.6 + 0.3 + 1.2 + 0.7).

  FIG. 11 shows the actual temperature distribution (set value: solid line) when the optical fiber is disposed as shown in FIGS. 9 and 10 with the horizontal axis representing the length of the optical fiber and the vertical axis representing the temperature. It is a figure which shows an example and the measurement temperature distribution (predicted value: dashed-dotted line) using the Raman scattering assumed using the transfer function of FIG. As can be seen from FIG. 11, the actual temperature distribution and the measured temperature distribution almost coincide with each other in the vicinity of the intake port b of the rack 11, but in the vicinity of the exhaust port due to the influence of the temperature e between the rack 11 and the next rack 11. The temperature of d is measured about 3 ° C. lower than the actual temperature. Further, the temperature near the CPU c is also measured lower than the actual temperature.

  That is, when the optical fiber 24 is laid as shown in FIGS. 9 and 10, the length of the optical fiber 24 per rack can be as short as about 7 m, but due to the influence of the adjacent rack (crosstalk). The temperature distribution in the rack cannot be measured accurately.

  12 and 13 are schematic views showing a second example of laying optical fibers. FIG. 12 shows the laid state of the optical fiber when the rack is viewed from the side, and FIG. 13 shows the laid state of the optical fiber when the rack is viewed from above. Moreover, in FIG. 12, FIG. 13, the length of the optical fiber of each part is shown collectively. In FIG. 13, a thick solid line indicates an optical fiber disposed in the equipment installation area (including the inside of the rack) 10, and a thick broken line indicates an optical fiber disposed on the free access floor 15. Further, the circles in FIG. 13 indicate the rising part or the falling part of the optical fiber.

  In the second example, the optical fiber 24 introduced into the rack 11 from the free access floor 15 is returned to the free access floor 15 for each rack. A winding section 28 is provided between the rack 11 and the next rack 11 by winding an optical fiber of 3 m with a minimum bending radius, and the winding section 28 is disposed on the free access floor 15. . In this case, the length of the optical fiber per rack is about 13 m.

  FIG. 14 shows the actual temperature distribution (setting value: solid line) when the optical fiber is laid as shown in FIGS. 12 and 13, with the horizontal axis representing the length of the optical fiber and the vertical axis representing the temperature. It is a figure which shows measured temperature distribution (expected value: a dashed-dotted line). Here, the temperature of a part of the free access floor 15 is 5 ° C.

  As shown in FIG. 14, the optical fiber 24 is returned to the free access floor 15 for each rack, and a winding portion 28 is provided between the adjacent racks 11 by winding an optical fiber having a length of 3 m. In this case, the actual temperature and the measured temperature substantially coincide not only in the vicinity of the ventilation opening (grill) of the free access floor 15 but also in the vicinity of the intake opening b and the vicinity d of the exhaust opening.

  FIG. 15 is a schematic diagram illustrating a third example of laying an optical fiber. This third example is basically the same as the second example except that the winding portion 29 is formed by winding an optical fiber of 1 m. In this case, the length of the optical fiber per rack is about 11 m.

  FIG. 16 shows the actual temperature distribution (set value: solid line) and the measured temperature distribution when the optical fiber is laid as shown in FIG. 15 with the horizontal axis representing the length of the optical fiber and the vertical axis representing the temperature. (Expected value: one-dot chain line). As shown in FIG. 16, in the third example, not only in the vicinity of the vent (grill) of the free access floor 15 but also in the vicinity of the intake port b and the vicinity of the exhaust port d as in the second example. The actual temperature and the predicted temperature are almost the same.

  As can be seen by comparing FIG. 14 and FIG. 16 with FIG. 11, the optical fiber is not continuously laid from one rack to the next rack, but the temperature and temperature between the rack and the next rack are almost the same. By providing the winding part arranged on the fixed free-access floor 15, the influence of temperature distribution overlap (crosstalk) can be reduced. For example, in the example shown in FIG. 11, the difference between the actual temperature near the exhaust port d and the measured temperature is 3 ° C. or more, whereas in the examples shown in FIGS. The difference is within 2 ° C. Further, the length of the optical fiber per rack is relatively short, and the temperature of many racks can be measured with one optical fiber.

  In the temperature measurement using an optical fiber, the measurement accuracy decreases when the temperature difference between adjacent measurement points increases. This is because the optical fiber temperature measurement has only a low spatial frequency, so that a measurement error becomes large where the temperature difference between adjacent measurement points is large (where the spatial frequency is high). Moreover, in the example shown in FIG. 16, although the optical fiber length of the winding part is as short as 1 m, the influence of crosstalk is small like the example of FIG. For this reason, in order to suppress the influence of crosstalk, the portion where the temperature is constant between the rack and the next rack is longer than the length of the optical fiber between the rack and the next rack. It is thought that the effect of providing the is greater.

  FIG. 17 is a diagram showing an actual temperature distribution (set value: solid line) and a measured temperature distribution (predicted value: one-dot chain line) when an optical fiber is laid as shown in FIG. Here, the temperature of the free access floor is set to 15 ° C., and the winding portion of the optical fiber is arranged on the free access floor. Here, temperature measurement (sampling) is performed at intervals of 50 cm.

  FIG. 18 shows a transfer function at the position of the rack where the temperature is measured. This transfer function is obtained from the measured temperature distribution when a step-like temperature distribution is applied to the optical fiber as shown in FIGS. Here, this transfer function is approximately represented by five points (-1, 0.07), (-0.5, 0.54), (0, 1), (0.5, 0, 54), (1, 0.07). .

FIG. 19 shows the result of convolution of the transfer function with the actual temperature value (set value) at the measurement points every 50 cm in FIG. The measured temperature almost coincides with the value obtained by convolving the transfer function with the actual temperature. By calculating backward from this value (ie, deconvolution of the measured temperature), the original actual temperature should be reproducible. When T _i is the actual temperature of the i-th measurement point, the measurement temperature AP _{i at} the i-th measurement point is expressed by the following equation (3).

AP _i = (0.07 × T _i−2 + 0.54 × T _i−1 + T _i + 0.54 × T _{i + 1} + 0.07 × T _{i + 2} ) /2.22 (3)
Here, 2.22 is a constant for normalization. Specifically, five points (−1, 0.07), (−0.5, 0.54), (0, 1), (0.5, 0, 54) and (1, 0.07) are the sum of the values on the Y-axis. Assuming that values other than T _{i + 2} , that is, the values of T _i−2 , T _i−1 , T _i and T _{i + 1} are known, T _{i + 2} can be calculated by the following equation (4).

T _{i + 2} = (2.22 / 0.07) AP _i −T _i−2 − (0.54 / 0.07) T _i−1 − (1 / 0.07) T _i − (0.54 / 0.07) T _{i + 1} (4)
In the laying example shown in FIG. 15, as described above, an optical fiber winding portion is provided between the rack and the next rack, and this winding portion is disposed on a free access floor at a low temperature and a substantially constant temperature. . Therefore, the temperature of the free access floor can be measured with relatively good accuracy. If the measured temperatures at the four measurement points on this free access floor are T _i-2 , T _i-1 , T _i , T _{i + 1} , the temperature of T _{i + 2} (correction value) according to the above equation (4). ) Can be calculated.

Then, if T _i−1 , T _i , T _{i + 1} , T _{i + 2} , and AP _{i + 1} are T _i−2 , T _i−1 , T _i , T _{i + 1} , and AP _i , respectively, The temperature T _{i + 2} of the next measurement point can be calculated. In this way, the measured temperature AP _i can be sequentially corrected from the low temperature portions on both sides of the peak to obtain a temperature distribution (corrected temperature distribution) approximate to the actual temperature distribution.

Since the transfer function shown in FIG. 18 is a sharp function, when the error of T _i−2 , T _i−1 , T _i , and T _{i + 1} is large, the value of T _{i + 2} oscillates. Sometimes it cannot be determined. In order to avoid such problems, it may be necessary to change the bandpass bandwidth. That is, if the actual temperature distribution (set value) cannot be reproduced with good accuracy even if the measured value is corrected by the above-described method, the sample value is derived using a transfer function having a slightly higher band. Then, it is determined whether or not the actual temperature distribution is reproducible using this sample value, and when it is determined that the reproducibility is reproducible, data correction by weighted averaging is performed using this sample value. Thereafter, a process of confirming whether or not the original actual temperature distribution (set value) has been sufficiently reproduced is performed. Then, for example, if the error is less than ± 2 ° C. in each region, it is OK, and if the error is ± 2 ° C. or more, the transfer function sample value is changed again.

  For example, a step-type transfer function (−0.5, 1), (0, 1), (0.5, 1) is adopted as a transfer function having a higher bandwidth than before. When a moving average that becomes a high-pass filter is obtained using this transfer function, the following equation (5) is obtained.

AP _i −AP _i−1 = (T _{i + 1} −T _i−2 ) / 3
T _{i + 1} = 3 × (AP _i −AP _i−1 ) + T _i−2 (5)
Here, if T _i−2 is known, T _{i + 1} can be obtained. Thereafter, a similar temperature calculation (corrected temperature distribution) can be obtained by sequentially changing the value of i and performing the same calculation.

  As described above, in a data center with a free access floor, the temperature of the free access floor is maintained almost constant. Therefore, by placing the optical fiber between adjacent racks in the free access floor, The influence of talk can be eliminated. However, some data centers do not have a free access floor. The temperature measurement method in a data center without a free access floor will be described below.

(First embodiment)
Some data centers employ a row-by-row cooling (In Row) system that cools multiple racks row by row. In the present embodiment, a temperature measurement method in a data center employing such a cooling method will be described.

  20 and 21 are schematic views showing an example of laying optical fibers in the temperature measuring method according to the first embodiment. FIG. 20 shows the laid state of the optical fiber when the rack is viewed from the side, and FIG. 21 shows the laid state of the optical fiber when viewed from the intake side of the rack. In FIGS. 20 and 21, illustration of a computer and the like stored in the rack is omitted.

  As shown in FIG. 20, the rack 41 is provided with doors 42a and 42b on the intake side and the exhaust side, respectively. In the present embodiment, the optical fiber 45 is laid inside the intake door 42a on the intake side of the rack 41, and the temperature on the intake side in the rack 41 is measured.

  An optical fiber inlet / outlet port 43 is provided below the side surface of the rack 41, and the optical fiber 45 is introduced into the rack 41 through the optical fiber inlet / outlet port 43. The optical fiber 45 introduced into the rack 41 is laid so as to reciprocate from the bottom to the top of the open / close door 42a from the rack body side to the open / close door 42a side in the vicinity of the rotation shaft 44 of the open / close door 42a. Then, the optical fiber 45 is led out of the rack 41 from the optical fiber introduction / lead-out portion 43 in the vicinity of the rotary shaft 44 from the opening / closing door 42a side to the rack body side. In addition, a slack portion is provided between the optical fiber introduction / lead-out portion 43 and the opening / closing door 42a so that the optical fiber 45 is loosened so as not to hinder the opening / closing of the opening / closing door 42a.

  Outside the optical fiber introduction / lead-out part 43, a winding part 46 is provided, in which the optical fiber 45 before being introduced into the rack 41 and after being led out from the rack 41 is wound around the same winding jig.

  As described above, in order to avoid the influence of heat (crosstalk) due to the adjacent racks 41, the length of the optical fiber 45 between the racks is not less than the minimum heating length Lmin determined by the pulse width of the optical signal. is necessary. In the present embodiment, a winding portion 46 is provided for each rack 41 to wind the optical fiber 45 on the rack introduction side and the rack lead-out side. In this case, if the optical fiber 45 on the rack introduction side and the rack lead-out side is wound around the winding part 46 with a length of ½ or more of the minimum heating length Lmin, the influence of heat from the adjacent rack 41 (crosstalk) ) Can be avoided. Therefore, in the present embodiment, the optical fiber 45 before and after the rack is introduced around the winding portion 46 to a length equal to or more than ½ of the minimum heating length Lmin. That is, in the present embodiment, the optical fibers 45 before and after the rack introduction are arranged close to each other over a length of ½ or more of the minimum heating length. For example, if the minimum heating length Lmin is 2 m as described above, the optical fiber 35 before and after the rack introduction may be wound around the winding portion 46 by 1 m or more.

  Hereinafter, temperature measurement of an example in which an optical fiber is laid as in the first embodiment will be described in comparison with a comparative example.

  The temperature measurement when the optical fiber was laid (Example) as shown in FIG. 22 was compared with the temperature measurement when the optical fiber was laid (Comparative Example) as shown in FIG.

  In the embodiment, as shown in FIG. 22, the length of the optical fiber 45 between the front rack and the rear rack is 0.8 m, and the length of the optical fiber 45 of the winding portion 46 is 1.. 5 m (1.5 m for each of the introduction side and the extraction side), and the length of the optical fiber 45 at the slack portion between the optical fiber introduction / extraction port 43 and the open / close door 42 b is 0.4 m (each for the forward path and the return path is 0.4 m). The length of the rising portion and the falling portion of the optical fiber 45 laid inside the opening / closing door 42a is 1.8 m, and the length of the optical fiber 45 at the folded portion is 0.2 m. Moreover, the temperature of the winding part 46 is 16 degreeC. Further, as shown in FIG. 22, the inside of the rack 41 is divided into five regions in the height direction, and the temperature of each region is set to 18 ° C., 19 ° C., 22 ° C., 22 ° C., and 25 ° C. in order from the lower side.

  24 shows the actual temperature distribution when the optical fiber 45 is laid as shown in FIG. 22 with the position along the length direction of the optical fiber 45 on the horizontal axis and the temperature on the vertical axis. It is a figure which shows measured temperature distribution.

  In the embodiment, as shown in FIG. 24, the optical fiber 45 on the rack introduction side and the rack lead-out side is wound around the same place, so that the measured temperature on the rack introduction side in the winding portion 46 and the rack lead-out side are measured. The measured temperature is the same (16 ° C.). Further, in the embodiment, the optical fiber 45 is laid so that the temperature difference between the measurement points adjacent to each other in the length direction of the optical fiber 45 is small, and the rack introduction side and the rack lead-out side are further provided at places where the temperature is substantially constant. As described above, the influence (crosstalk) of adjacent racks can be ignored. Therefore, it can be considered that the measured temperature on the rack introduction side and the measured temperature on the rack outlet side in the winding section 46 indicate correct temperatures. As described above, the measured temperatures are sequentially corrected from the low temperature portions on both sides of the peak. Thus, a temperature distribution approximated to the actual temperature distribution (corrected temperature distribution) can be obtained.

  For the above correction, an inverse filter (such as a deconvolution filter) using an inverse correction function obtained from the impulse response is used. FIG. 26 shows an example of the inverse correction function. In FIG. 26, the horizontal axis indicates the distance, and the vertical axis indicates the coefficient. However, the inverse correction function shown in FIG. 26 improves the margin tolerance by cutting the high frequency response to the inverse correction function obtained from the impulse response.

  FIG. 27 shows an actual temperature distribution (step-type temperature distribution), a measured temperature distribution, and a temperature distribution (corrected temperature distribution) obtained by using an inverse filter for the measured temperature distribution. As shown in FIG. 27, a measured temperature distribution having a Gaussian curve shape is obtained with respect to the step-type temperature distribution (actual temperature distribution). When this measured temperature distribution is corrected using an inverse filter (deconvolved using an inverse correction function), a temperature distribution approximate to the actual temperature distribution (temperature distribution after correction) is obtained. In this case, undershoot occurs in the corrected temperature distribution on both sides of the peak (portions surrounded by broken circles in FIG. 27). This undershoot can be thought of as a product of deconvolution.

  In the present embodiment, the measured temperatures are the same at the positions of the winding portions 46 of the optical fiber 45 on the rack introduction side and the rack outlet side (positions of 0.7 m and 7 m), and the measured temperatures indicate the correct temperatures. Can be considered. Therefore, a more accurate temperature distribution can be obtained by replacing the temperature of the undershoot portion (the portion lower than the temperature of the winding portion 46) with the temperature of the winding portion 46 in the corrected temperature distribution.

  Further, when the optical fiber 45 is laid as shown in FIG. 22, the peak temperature (peak height) changes according to the operating state of the computer in the rack 41 under the condition that the air volume does not change greatly, but the temperature distribution It can be considered that the basic shape does not change. Therefore, the peak temperature can be calculated by comparing the integrated value of the temperature distribution assumed in advance (hereinafter referred to as “reference temperature distribution”) with the integrated value of the actually measured temperature distribution without using the inverse filter described above. It can also be estimated.

  In this case, the basic shape of the measured temperature distribution and the reference temperature distribution needs to be the same. In the embodiment shown in FIG. 22, the temperature (16 ° C.) at the position of the optical fiber winding portion 46 on the rack introduction side and the rack outlet side is the same, and thus the temperature of the winding portion 46 on the rack introduction side is indicated. A line connecting (a point indicated by A in FIG. 24) and a point indicating the temperature of the winding portion 46 on the rack outlet side (a point indicated by A ′ in FIG. 24) is parallel to the X axis in FIG. Therefore, if there is no significant change in the air volume, the integrated value of the curve indicating the measured temperature distribution (portion of 16 ° C. or more) can be considered as the total amount of heat generated in the rack, and the integrated value of the measured temperature distribution and the reference temperature distribution It is possible to estimate the peak temperature from the comparison with the integrated value of.

  Since the air volume can be considered in several stages depending on the inverter level of the air conditioner, etc., if these estimated values are switched in advance for several stages of air volume, good estimation is possible even for air volume changes. It becomes possible to do.

  On the other hand, in the comparative example, as shown in FIG. 23, the laying state of the optical fiber 45 in the rack 41 is the same as in the embodiment, but the winding portion 46a on the rack introduction side and the winding portion 46b on the rack outlet side are provided. They are located at different positions. In this example, the temperature at the arrangement position of the winding portion 46a on the rack introduction side is 16 ° C., and the temperature at the arrangement position of the winding portion 46b on the rack outlet side is 18 ° C.

  25, the horizontal axis indicates the position along the length direction of the optical fiber 45, the vertical axis indicates the temperature, and the actual temperature distribution (comparative example) when the optical fiber 45 is laid as shown in FIG. It is a figure which shows a continuous temperature) and measured temperature distribution (broken line). Here, the center of the optical fiber 45 wound around the winding portion 46a on the rack introduction side is positioned at 0.7 m, and the center of the optical fiber 45 wound around the winding portion 46b on the rack outlet side is positioned at 7 m. It is said.

  In the comparative example, the temperature of the winding portion 46a on the rack introduction side of the optical fiber 45 and the temperature of the winding portion 46b on the rack outlet side are different by 2 ° C. In this case, it is possible to correct the measured temperature from both sides of the peak with reference to the temperature of the winding portions 46a and 46b with respect to the measured temperature distribution, but the temperature of the winding portions 46a and 46b is the correct temperature. There is no guarantee and it may be affected by the temperature of the adjacent rack. For this reason, the reliability of the corrected temperature distribution is low. Further, even if undershoot occurs due to the correction, it is unclear whether the measured temperatures of the winding portions 46a and 46b are correct, so the undershoot cannot be removed.

  Further, since the temperature of the winding portion 46a on the rack introduction side and the temperature of the winding portion 46b on the rack outlet side are different, the point indicating the temperature of the winding portion 46a (the point indicated by A in FIG. 25) and the winding A straight line (indicated by a one-dot chain line in FIG. 25) connecting a point indicating the temperature of the portion 46b (a point indicated by A ′ in FIG. 25) is inclined with respect to the X axis in FIG. For this reason, simply integrating the measured temperature distribution at a portion of 16 ° C. or 18 ° C. or higher does not generate the amount of heat generated in the rack, but compares the measured temperature distribution with the reference temperature distribution to estimate the peak temperature. Can not be adopted.

(Second Embodiment)
Some data centers employ a system in which cool air blown from ceiling-mounted air conditioners is taken into the rack from the top of the rack to cool the computers in the rack. In the present embodiment, a temperature measurement method in a data center employing such a cooling method will be described.

  FIG. 28 is a schematic diagram illustrating an example of laying an optical fiber in the temperature measurement method according to the second embodiment. An optical fiber introduction / extraction port is provided in the upper portion of the rack 51, and the optical fiber 55 is introduced into the rack 51 through the optical fiber introduction / extraction port. The optical fiber 55 introduced into the rack 51 is laid so as to reciprocate from the top to the bottom of the open / close door 52a from the rack body side to the open / close door 52a side in the vicinity of the rotation shaft 54 of the open / close door 52a. The optical fiber 55 is led out from the opening / closing door 52a side to the rack body side in the vicinity of the rotary shaft 54 and to the upper side of the rack 51 through the optical fiber introduction / lead-out port.

  Above the rack 51, a winding portion 56 is disposed in which the optical fibers 55 before and after the rack are introduced are wound around the same winding jig. The optical fiber 55 before and after rack introduction is wound around the winding portion 56 with a length of 1.5 m. Cold air from the air conditioner is supplied above the rack 51. For this reason, the temperature of the place where the winding part 56 is arrange | positioned can be considered low temperature and substantially constant.

  Also in the present embodiment, as in the first embodiment, the optical fibers 55 before and after the rack introduction are wound around the same place, so that the rack introduction side and the rack extraction side in the winding portion 56 are arranged. The measured temperature is the same. Further, in the present embodiment, the optical fiber 55 is laid so that the temperature difference between adjacent measurement points is small, and the winding portion 56 is disposed at a place where the temperature is substantially constant. Therefore, as in the first embodiment, the temperature in the rack 51 can be measured with good accuracy.

(Third embodiment)
FIG. 29 is a schematic diagram showing an example of laying optical fibers in the temperature measurement method according to the third embodiment.

  In the present embodiment, the computer room is separated into an equipment installation floor 75 on which the rack 61 is installed and a free access floor 70 below it. The temperature of the free access floor 70 is maintained almost constant by an air conditioner (not shown). The optical fiber 65 passes from the free access floor 70 through the ventilation opening (grill) 71 and is introduced into the rack 61 from the optical fiber introduction / extraction opening provided at the lower portion of the rack 61.

  The optical fiber 65 introduced into the rack 61 is laid so as to reciprocate from the bottom to the top inside the open / close door 62a from the rack body side to the open / close door 62a side in the vicinity of the rotation shaft 64 of the open / close door 62a. The optical fiber 65 is led out of the rack 61 from the opening / closing door 62a side to the rack body side in the vicinity of the rotary shaft 64 through the optical fiber introduction / lead-out port.

  The optical fiber 65 after being led out of the rack enters the free access floor 70 from the ventilation port 71 and is laid on the next rack 61. However, in the present embodiment, between the free access floor 70 and the rack 61, the optical fiber 65 on the rack introduction side and the optical fiber 65 on the rack outlet side have a length (for example, 1.. 5m or more). Here, the optical fiber 65 on the rack introduction side and the optical fiber 65 on the rack exit side are not necessarily in close contact with each other. In short, the temperature of the optical fiber 65 on the rack introduction side and the temperature of the optical fiber 65 on the rack exit side are different. It may be arranged as close as possible. For example, if the distance between the optical fiber 65 on the rack introduction side and the optical fiber 65 on the rack lead-out side is set to be twice or less (for example, 30 mm or less) of the minimum bending radius of the optical fiber 65, the optical fiber 65 on the rack introduction side It can be said that the optical fiber 65 on the rack outgoing side is arranged close to the optical fiber 65.

  In this embodiment, no winding part is provided, but the optical fibers before and after the rack introduction are arranged at the same position as in the first embodiment. Accordingly, the temperatures of the optical fiber 65 before the rack is introduced and after the rack is led out are the same. Further, in the present embodiment, the optical fiber 65 is laid so that the temperature difference between the measurement points adjacent in the length direction becomes small, and the temperature of the optical fiber 65 before and after the rack introduction is substantially constant. It is arranged on the free access floor 70 that is maintained at the same time. Accordingly, as in the first embodiment, the temperature distribution in the rack 61 can be measured with good accuracy.

  In each of the above-described embodiments, the example in which the optical fiber is laid inside the intake door on the intake side of the rack has been described. However, the optical fiber may be laid on the inside of the door on the exhaust side. Further, an optical fiber may be laid outside the open / close door on the intake side or the exhaust side.

  Further, in each of the above-described embodiments, the temperature measurement in the rack arranged in the data center has been described. However, the disclosed technique can be applied to the temperature measurement in other locations. For example, the disclosed technology can be applied to temperature measurement in a factory or office building.

  Furthermore, in the first and second embodiments, the winding part is disposed in a place where the temperature is lowest, but the winding part is not necessarily disposed in a low temperature place. You may arrange in the place.

  The following additional notes are further disclosed with respect to various aspects including the above-described embodiment.

(Supplementary note 1) In a temperature measurement method for measuring the temperature of one or a plurality of measurement points in the temperature measurement area with an optical fiber laid in the temperature measurement area,
An optical fiber before being introduced into the temperature measurement area and an optical fiber after being derived from the temperature measurement area are arranged close to each other over a length of ½ or more of the minimum heating length determined by the pulse width of the optical signal,
Measure the temperature of the measurement point in the temperature measurement area and the temperature of the proximity placement location where the optical fiber before and after introduction into the temperature measurement area is placed in proximity,
A temperature measurement method, wherein the temperature of the measurement point is corrected with reference to the temperature of the close placement location.

  (Appendix 2) Using the transfer function of the temperature measurement system of the optical fiber, the temperature of the measurement point in the temperature measurement area is corrected in order from the temperature measurement point close to the proximity location based on the temperature of the proximity location. The temperature measuring method according to appendix 1, wherein:

  (Supplementary note 3) The integral value of the measured temperature in the temperature measurement area is compared with the integral value of a preset reference temperature distribution, and the peak temperature in the temperature measurement area is corrected based on the result. 2. The temperature measuring method according to 1.

  (Supplementary note 4) The supplementary note 1 is characterized in that the optical fiber before being introduced into the temperature measurement area and the optical fiber derived from the temperature measurement area are wound around the same jig and arranged at the close placement location. Temperature measurement method.

  (Additional remark 5) The temperature measuring method of Additional remark 1 characterized by maintaining the temperature of the said adjacent arrangement | positioning place constant.

  (Additional remark 6) The temperature measurement method of Additional remark 1 characterized by the temperature of the said adjacent arrangement | positioning place being lower than the temperature in the said temperature measurement area.

  (Supplementary note 7) The temperature measurement method according to supplementary note 1, wherein the temperature measurement area is in the vicinity of the surface of a rack which is arranged in a computer room and accommodates a plurality of computers or an area in the rack.

  (Supplementary note 8) The temperature measurement method according to supplementary note 7, wherein the rack is provided with an opening / closing door, and the optical fiber is disposed inside or outside the opening / closing door.

  (Additional remark 9) The optical fiber between the main-body part of the said rack and the said opening / closing door is provided with the slack part so that it may not interfere with the opening / closing of the said opening / closing door, The additional remark 8 characterized by the above-mentioned. Temperature measurement method.

  (Supplementary Note 10) The optical fiber introduced into the rack is laid so as to reciprocate in the vertical direction from the rack body side to the door side in the vicinity of the rotation axis of the door, and further to the rotation The temperature measuring method according to appendix 8, wherein the vicinity of the shaft is led out to the outside of the rack from the door side to the rack body side.

FIG. 1 is a schematic diagram showing a configuration of a temperature distribution measuring apparatus using an optical fiber. FIG. 2 is a diagram illustrating a spectrum of backscattered light. FIG. 3 is a diagram showing a time-series distribution of the intensity of Raman scattered light detected by the photodetector. FIG. 4 is a graph showing the result of calculating the I ₁ / I ₂ ratio for each time based on the time series distribution of the intensity of Raman scattered light in FIG. 3, and converting the horizontal axis to distance and the vertical axis to temperature. It is. FIG. 5 is a diagram (part 1) for explaining the minimum heating length. FIG. 6 is a diagram (part 2) for explaining the minimum heating length. FIG. 7 is a diagram showing a measured temperature distribution when an optical fiber is placed in an environment where the temperature is 25 ° C. and heat of 80 degrees is applied so as to form a step-type temperature distribution centering on a position 5 m from the light source. . FIG. 8 is a diagram showing a transfer function in the temperature distribution of FIG. FIG. 9 is a schematic side view showing a first example of laying optical fibers. FIG. 10 is a schematic top view showing a first example of laying optical fibers. FIG. 11 is a diagram showing an actual temperature distribution when an optical fiber is laid as shown in FIGS. 9 and 10, and a measured temperature distribution using Raman scattering assumed using the transfer function of FIG. FIG. 12 is a schematic side view showing a second example of laying optical fibers. FIG. 13 is a schematic top view showing a second example of laying an optical fiber. FIG. 14 is a diagram showing an actual temperature distribution and a measured temperature distribution when an optical fiber is laid as shown in FIGS. FIG. 15 is a schematic side view showing a third example of laying an optical fiber. FIG. 16 is a diagram (No. 1) showing an actual temperature distribution and a measured temperature distribution when an optical fiber is laid as shown in FIG. FIG. 17 is a diagram (part 2) illustrating an actual temperature distribution and a measured temperature distribution when an optical fiber is laid as illustrated in FIG. FIG. 18 is a diagram illustrating a transfer function at the position of the rack where the temperature is measured. FIG. 19 is a diagram showing a result of convolving a transfer function with the actual temperature value at the measurement points every 50 cm in FIG. FIG. 20 is a schematic diagram illustrating an example of laying an optical fiber in the temperature measurement method according to the first embodiment, and shows a laid state of the optical fiber when the rack is viewed from the side. FIG. 21 is a schematic diagram showing an example of optical fiber installation in the temperature measurement method according to the first embodiment, and shows an optical fiber installation state when viewed from the intake side of the rack. FIG. 22 is a diagram illustrating temperature measurement conditions of the example. FIG. 23 is a diagram illustrating temperature measurement conditions of a comparative example. FIG. 24 is a diagram illustrating an actual temperature distribution and a measured temperature distribution of the example. FIG. 25 is a diagram illustrating the actual temperature distribution and the measured temperature distribution of the comparative example. FIG. 26 is a diagram illustrating an example of the inverse correction function. FIG. 27 is a diagram illustrating an actual temperature distribution (step type temperature distribution), a measured temperature distribution, and a temperature distribution (corrected temperature distribution) obtained by using an inverse filter for the measured temperature distribution. FIG. 28 is a schematic diagram illustrating an example of laying an optical fiber in the temperature measurement method according to the second embodiment. FIG. 29 is a schematic diagram showing an example of laying optical fibers in the temperature measurement method according to the third embodiment.

Explanation of symbols

10 ... equipment installation area,
11, 31, 41, 51, 61 ... rack,
15 ... Free access floor,
21 ... Laser light source,
22a, 22b ... lenses,
23, 31a, 31b, 31c ... beam splitter,
24, 45, 55, 65 ... optical fiber,
25 ... wavelength separation part,
26 ... photodetector
28 ... winding part,
33a, 33b, 33c ... optical filter,
34a, 34b, 23c ... Condensing lens,
42a, 42b, 52a, 62a ... opening / closing doors,
43. Optical fiber introduction / extraction port,
44, 54, 64 ... rotating shaft,
46, 46a, 46b, 56 ... winding part,
70 ... Free access floor,
71 ... Ventilation opening (grill),
75: Equipment installation floor.

Claims (5)

The temperature of one or a plurality of measurement points in the first temperature measurement area and / or the second temperature measurement area by an optical fiber laid continuously over the first temperature measurement area and the second temperature measurement area In the temperature measurement method for measuring
1/2 from the end of the first respectively the first temperature measurement area prior to introduction into the temperature measurement area and the derived after the fiber-optic of minimal heating length determined by the pulse width of the optical signal passing through the said optical fiber It arranged close for more than a length,
The optical fibers before and after introduction into the second temperature measurement area are arranged close to each other over a length of ½ or more of the minimum heating length from the end of the second temperature measurement area,
The temperature of the measurement point in the first temperature measurement area and / or the second temperature measurement area and the light before being introduced into the first temperature measurement area and / or the second temperature measurement area and after being derived. Measure the temperature at the location where the fibers are placed close together,
A temperature measurement method, wherein the temperature of the measurement point is corrected with reference to the temperature of the close placement location. The temperature of the measuring points of the first temperature measurement area and / or the second temperature measurement area is corrected in order from the near measurement point the close location by using a transfer function of the temperature measurement system of the optical fiber The temperature measuring method according to claim 1. The integrated value of the measured temperature in the first temperature measurement area and / or the second temperature measurement area is compared with the integrated value of a preset reference temperature distribution, and the peak temperature in the temperature measurement area is calculated based on the result. The temperature measurement method according to claim 1, wherein correction is performed. To wind the optical fiber after supra and guide into the same jig to the first temperature measurement area, winding an optical fiber on the same jig after introduction before and led to the second temperature measurement area temperature measuring method according to claim 1, characterized in that the times. 2. The first temperature measurement area and the second temperature measurement area are each located in the vicinity of the surface of a rack that is arranged in a computer room and houses a plurality of computers, or an area in the rack. The temperature measuring method described.

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