JP4257438B2 - Temperature sensor - Google Patents

Description

  The present invention relates to a temperature sensor, and more particularly to a temperature sensor using laser interferometry.

  Conventionally, as a method for measuring a temperature change of a gas in a non-contact manner, a measurement method by a laser interferometry using a Mach-Zehnder interferometer is known (for example, see Non-Patent Document 1).

  In this temperature measurement by laser interferometry, one of the two laser beams is used as a reference beam to pass through a space in which the gas state is kept constant, and the temperature is detected using the other laser beam as a test beam. The interference light is generated by causing the reference light and the test light to interfere with each other, and the change in the interference fringe is detected to detect the temperature change in the measurement space.

  That is, in the measurement space, when the temperature changes, the density of the gas in the measurement space changes, and the refractive index of the laser light changes due to this change in density. The interference fringes fluctuate with the fluctuation of the refractive index of the laser beam, and the temperature change can be detected by detecting the fluctuation state. Note that the object to be measured is not limited to gas, and a temperature measurement method based on a laser interference method can be used for an object to be measured that can pass laser light like liquid.

  Note that this temperature measurement by laser interferometry does not directly measure the temperature of the object to be measured like a thermocouple, but detects temperature fluctuations that occur in the object to be measured. Although direct temperature measurement is not possible, it is extremely responsive compared to temperature detection means such as thermocouples by detecting density fluctuations of the measurement object, and it takes a long time to detect instantaneous temperature fluctuations. It has the feature of having resolution.

  On the other hand, in temperature measurement by laser interferometry, temperature fluctuations are detected by detecting the phase difference of the laser beam using interference, so it is weak against vibration and must be used with vibration suppressed as much as possible. there were.

  In view of this, the present inventor has provided an optical fiber between the interference unit that detects the phase difference by causing the reference light and the test light to interfere with each other, and the sensing unit that guides the test light and traverses the measurement space. Then, with this optical fiber, the test light is guided from the interference part to the sensing part, and the test light reflected by an appropriate reflector provided in the sensing part is guided from the sensing part to the interference part.

  Then, a temperature measuring method has been proposed in which the sensing unit is arranged in the space to be measured, while the interference unit is arranged on a vibration control table in which vibration is suppressed to make it less susceptible to vibration (for example, Patent Documents). 1).

  That is, in the temperature sensor based on this temperature measurement method, as shown in FIG. 9, the interference unit 100 emits from a stabilized He—Ne laser output device 110 that is a light source and from this stabilized He—Ne laser output device 110. The heterodyne acoustooptic device 120 which emits two types of P-polarized and S-polarized laser beams by shifting the laser beam to a predetermined frequency, and the S-polarized laser beam emitted from the heterodyne acoustooptic device 120 A first mirror 130 that reflects light, and a first beam that combines S-polarized laser light reflected by the first mirror 130 and P-polarized laser light emitted from the heterodyne acoustooptic device 120 into a single beam. A polarization beam splitter 140, a first half mirror 150 that separates the laser beam emitted from the polarization beam splitter 140 into two beams, and a laser beam that has passed through the first half mirror 150 is P It provided a second polarizing beam splitter 160 for separating the light and S 2 kinds of laser light polarization.

  The laser light reflected by the first half mirror 150 passes through and interferes with the first polarizing plate 170 whose polarization plane is inclined by 45 degrees, and then enters the first light receiving element 180, and this first light receiving element 180. The interference beat signal was detected as a reference signal.

  The P-polarized laser beam separated by the second polarization beam splitter 160 is test light, passes through the first quarter-wave plate 190 and becomes circularly polarized light, and is provided at the end of the optical fiber 200. The light is incident on the optical fiber 200 through the Selfoc® microlens 210, is emitted from the second Selfoc® microlens 220 provided at the other end of the optical fiber 200, and is incident on the sensing unit 300. .

  The sensing unit 300 is provided with a reflecting mirror 310 that reflects incident test light. In particular, the reflecting mirror 310 is arranged so that the test light reaching the reflecting mirror 310 crosses the measurement target region 320.

  The test light incident on the sensing unit 300 crosses the region to be measured 320 and reaches the reflecting mirror 310, is reflected by the reflecting mirror 310, crosses the region to be measured 320 again, and enters the second self-foc (registered). Trademark) was incident on a microlens 220.

  The test light reflected by the sensing unit 300 is incident on the interference unit 100 through the optical fiber 200, passes through the first quarter-wave plate 190, and enters the second polarizing beam splitter 160 as S-polarized light. .

  On the other hand, the S-polarized laser beam separated by the second polarization beam splitter 160 is reference light, passes through the second quarter-wave plate 230 and becomes circularly polarized light, and is reflected by the second mirror 240 and reflected by the second mirror 240. The second quarter-wave plate 230 passes again and enters the second polarizing beam splitter 160 as P-polarized light.

  The test light and the reference light incident on the second polarizing beam splitter 160 are caused to interfere with each other by passing through the second polarizing plate 250 whose polarization plane is inclined by 45 degrees, and then incident on the second light receiving element 260. An interference beat signal was detected by the two light receiving elements 260 and used as a test signal.

Then, the phase difference is calculated from the difference between the beat frequencies of the reference signal and the test signal to detect the density fluctuation in the measurement target region 320, and the temperature fluctuation can be detected based on the density fluctuation.
JP 2002-39870 A Hamamoto et al., Measurement of Gas Temperature Change by Laser Interferometry, Transactions of the Japan Society of Mechanical Engineers (B), Vol. 53, No. 496, pp. 3798-3802, December 1987

  However, when an optical fiber is provided between the separation unit that separates the laser beam into the test beam and the reference beam and the sensor unit, the test beam is affected by the optical fiber and the connection with the optical fiber. Therefore, it is difficult to conclude that the obtained result is only a result of the influence of density fluctuation in the sensitive part, and the reliability of the result may not be sufficient.

  That is, for example, when a change in phase is detected between the reference light and the test light using interference, the change in the phase difference reflects the temperature change generated in the space under measurement, or It was extremely difficult to determine whether it was caused by other factors generated in the optical fiber.

  In particular, the inventors of the present application wanted to measure the temperature in the combustion chamber of the internal combustion engine. However, the internal combustion engine vibrates as it is driven and generates heat, and the influence of this vibration and heat generation results in the temperature fluctuation measurement result. It is difficult to determine how much the influence is exerted, and there is no temperature sensor that can withstand practical use.

  In view of the present situation, the present inventors have conducted research to develop a temperature sensor capable of accurately measuring the temperature in the combustion chamber of an internal combustion engine, and have achieved the present invention.

In the temperature sensor of the present invention, a light source unit that emits laser light, a separation unit that separates the laser light emitted from the light source unit into test light and reference light, and a measurement target whose temperature is measured on the optical path of the test light A temperature provided with a sensing unit arranged across the space, and a detection unit that detects a change in temperature by detecting a change in the interference state by causing the test light and the reference light to cross the measurement target space to interfere with each other. In the sensor, the sensing part is provided at the tip of a cylindrical casing parallel to the optical path of the test light, and a separation part is provided at the base end of the casing. The casing includes a transparent member that allows the test light to pass through, and a reference light. It has a feature that a tip wall provided with a reflector to be reflected is provided at the tip portion, and the test light that has passed through the transparent member reaches the sensing part and is reflected by the reflector provided in the sensing part. .

  In the temperature sensor of the present invention, the casing includes a transparent member that allows the test light and the reference light to pass therethrough, and the test light and the reference light that have passed through the transparent member reach the sensing unit to receive the light. Reflected by a reflector provided in the sensing part and either the crossing distance of the test light that crosses the measurement space in the sensing part or the crossing distance of the reference light that crosses the measurement space, the other crossing distance The transparent member is also characterized in that a step is provided on the reflector-side surface and the crossing distance of the test light and reference light measurement space is adjusted. .

  In the temperature sensor of the present invention, the casing directs the first reflector that changes the irradiation direction of the test light and the irradiation direction of the test light whose irradiation direction has been changed by the first reflector to the separation unit. A second transparent body is provided at the tip portion, a measurement space is provided between the first reflector and the second reflector, and the reference light is reflected by the second reflector to cross the measurement space. And then reflecting the reflected light to the first reflector, and making either the crossing distance of the test light crossing the measurement space or the crossing distance of the reference light crossing the measurement space shorter than the other crossing distance The first reflector is disposed on the first support made of a transparent material through which the test light and the reference light can pass, and the second reflector is formed of the test light and the reference light. Is disposed on a second support made of a transparent material that can pass through, and a space to be measured is defined between the first support and the second support. In addition, the crossing distance of the measurement space of the test light and the reference light is adjusted by providing a step on at least one surface of the first support body and the second support body facing the measurement space. It is what has.

  According to the present invention, the sensing part is provided at the tip of the cylindrical casing, and the separation part is provided at the base end of the casing, so that the sensing part and the separation part are substantially identically oscillated through the casing. It can be in a state, and the influence of vibration can be suppressed.

  In addition, since the test light and the reference light can shorten the respective optical paths, it is possible to eliminate the possibility that a fluctuation factor other than the sensing part intervenes in the measurement result, and it is possible to detect temperature fluctuation with higher accuracy. .

  The temperature sensor of the present invention separates the laser beam emitted from the light source unit that emits the laser beam into the test beam and the reference beam at the separation unit, and traverses the measurement space in which the temperature is measured to pass the optical path of the test beam Is provided, and interference fringes are generated by causing the test light and the reference light to interfere with each other, and fluctuations in the interference fringes are detected to detect temperature fluctuations in the measurement space.

  In particular, in the temperature sensor, a cylindrical casing is provided, a separation part is provided at the base end of the casing, and a sensing part is provided at the tip of the casing.

  As described above, by providing the casing with the separation part and the sensing part, the vibration state of the separation part and the sensing part can be made substantially the same, and the performance against vibration can be improved. Furthermore, since the distance from the separating unit to the sensing unit can be shortened, it is possible to make it difficult to intervene with an uncertain factor that may affect the measurement result.

  In addition, in the case where the tip wall provided with the transparent member that allows the test light to pass through and the reflector that reflects the reference light is provided at the tip portion of the casing, the reference light also passes through the casing together with the reflector, The temperature difference between the optical path of the reference light and the optical path of the test light can be almost ignored, temperature correction can be made unnecessary, and the temperature sensor can be made compact.

  Alternatively, a transparent member that allows the test light and the reference light to pass therethrough is provided at the tip of the casing, and the test light and the reference light that have passed through the transparent member reach the sensing part, and the reflector provided in the sensing part. When either one of the crossing distance of the test light that crosses the measurement space in the sensing part and the crossing distance of the reference light that crosses the measurement space is shorter than the other crossing distance The effects of temperature and vibration, which are factors that cause measurement errors, can be made substantially the same between the test light and the reference light, and these effects can be offset to improve measurement accuracy.

  Alternatively, a first reflector that changes the irradiation direction of the test light at the tip portion of the casing, and a second transparent body that directs the irradiation direction of the test light whose irradiation direction has been changed by the first reflector toward the separation unit Is provided at the tip portion, a measurement space is provided between the first reflector and the second reflector, and the reference light is reflected by the second reflector to cross the measurement space. Even if one of the crossing distance of the test light that crosses the measurement space and the crossing distance of the reference light that crosses the measurement space is made shorter than the other crossing distance, Effects such as temperature and vibration, which are factors causing measurement errors, can be made substantially the same between the test light and the reference light, and the measurement accuracy can be improved by canceling these influences.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic diagram of a temperature sensor A1 according to the first embodiment.

  The temperature sensor A1 of the present embodiment includes a light source unit 10 that emits a required laser beam, a first optical fiber 20 that guides the laser beam emitted from the light source unit 10, and the first optical fiber 20 through the first optical fiber 20. The incident laser light is separated into the test light L1 and the reference light L2, and only the test light L1 is reflected across the measurement space T in which the temperature is measured, and the reference light L2 is appropriately reflected and further reflected. Sensor unit 30 for emitting the test light L1 and the reference light L2 together, a second optical fiber 40 for guiding the test light L1 and the reference light L2 emitted from the sensor unit 30, and the test light L1 The detection unit 50 is configured to detect a temperature change by detecting a change in the interference state when the light L2 is caused to interfere.

  The light source unit 10 uses a He—Ne laser device that emits laser light having an output of 1 mW and a wavelength of 632.8 nm as a light source, and the laser light emitted from the He—Ne laser device is described in the section of the related art. The frequency shift is performed by separating the frequency into P-polarized light and S-polarized light having different frequencies such as 80.0 MHz and 79.975 MHz by using an acoustooptic device for heterodyne (Bragg cell type). Laser light is collectively emitted into one beam by a polarization beam splitter (not shown).

  In the present embodiment, the He—Ne laser is used as described above. However, the interference state change may be detected using an interference semiconductor laser, and any interference may be used as long as the interference can be detected. .

  The laser beam emitted from the light source unit 10 is separated into two laser beams by the half mirror 11, one laser beam is incident on the first light receiving element 12, and the first light receiving element 12 interferes with the laser light. A beat signal is detected and output as a reference signal. The reference signal is input to the detection unit 50. In FIG. 1, 13 is a half-wave plate, and 14 is a first interference filter.

  In FIG. 1, 21 is a first Selfoc® microlens (hereinafter simply referred to as “SML”) provided at one end of the first optical fiber 20, and 22 is provided at the other end of the first optical fiber 20. Second SML. In the present embodiment, a polarization-maintaining optical fiber is used for the first optical fiber 20.

  The second optical fiber 40 is also a polarization-maintaining optical fiber, and a third SML 41 and a fourth SML 42 are connected to both ends of the second optical fiber 40, respectively, and the test light L1 and the reference light L2 are detected by the second optical fiber 40. Guide to part 50. The second optical fiber 40 may be a plastic fiber having a relatively large diameter. In this case, the third SML 41 and the fourth SML 42 can be omitted.

  In the detection unit 50, the temperature change is detected from the reference signal detected by the first light receiving element 12 and the test signal detected by the second light receiving element 51 in the same manner as the conventional temperature sensor.

  The sensor unit 30, which is the main part of the present invention, includes a separation unit 31 at one end that separates the laser light incident through the first optical fiber 20 into the test light L1 and the reference light L2. A sensing part 32 that reflects the separated test light L1 across the measurement space T in which the temperature is measured is constituted by a cylindrical casing 33 provided at the other end.

  In this embodiment, the separation unit 31 includes a first mirror 31a that bends the irradiation direction of the laser light incident via the first optical fiber 20 by 90 degrees, and the laser light that is bent by the first mirror 31a. The S-polarized light is bent 90 degrees and the P-polarized light is transmitted to separate the test light L1 and the reference light L2, and the irradiation direction of the P-polarized laser light transmitted through the beam splitter 31b is bent 90 degrees. 2 mirrors 31c.

  In particular, in the present embodiment, the first mirror 31a, the beam splitter 31b, and the second mirror 31c have a cubic shape having the same outer dimensions. As described above, by making the first mirror 31a, the beam splitter 31b, and the second mirror 31c into cubic shapes having the same dimensions, it is possible to facilitate the assembling work of the separation portion 31 portion. If possible, a beam splitter in which the first mirror 31a, the beam splitter 31b, and the second mirror 31 are integrally formed may be used.

  The casing 33 is provided with a hollow longitudinal cavity 33a parallel to the optical path of the test light L1 separated by the beam splitter 31b. The casing 33 is not limited to a cylindrical shape, and may be a rectangular tube shape. Similarly, the hollow portion 33a that is the internal space of the casing 33 is not limited to a cylindrical shape, and has a prismatic shape. May be.

  The tip portion of the casing 33 is provided with a tip wall 33c provided with a passage port 33b for allowing the test light L1 to pass therethrough. A quartz glass 35, which is a transparent member for allowing the test light L1 to pass, is attached to the passage port 33b. is doing. A sapphire glass can be used instead of the quartz glass 35, or a light-transmitting material having a high transmittance and a low thermal expansion coefficient can be used.

  In particular, the front end wall 33c of the casing 33 is provided with an accommodation recess 33d for accommodating the quartz glass 35 in the passage port 33b. The quartz recess 35d is accommodated in the accommodation recess 33d, and the accommodation recess 33d. The sensor part 32 is mounted using the inner peripheral surface of the sensor.

  That is, the sensing part 32 is configured by a cylindrical wall 32a that can be fitted into the housing recess 33d, and a flat support plate 32b is provided at one end of the cylindrical body 32a, and a test light is provided on the support plate 32b. The reflector M1 is attached to reflect the test light L1 that has passed through the quartz glass 35.

  The cylindrical wall body 32a is provided with a through-hole at a predetermined position so that gas or liquid can freely flow inside and outside the cylindrical wall body 32a, and is formed by an inner space of the cylindrical wall body 32a. The measurement space T is in the same temperature state as the outer space of the cylindrical wall body 32a.

  The test light reflector M1 may be configured by mounting an appropriate mirror on the support plate 32b, or the test light reflector M1 may be formed by mirror-finishing the surface of the support plate 32b.

  In the present embodiment, the cylindrical wall body 32a is formed with a male screw, the housing recess 33d is formed with a female screw, and the cylindrical wall body 32a is screwed into the housing recess 33d so as to be attached to the tip of the casing 33. The sensing part 32 is attached.

  Further, the quartz glass 35 is provided with an insertion convex portion 35a that is inserted into the cylindrical wall body 32a, and the cylindrical wall body is inserted while the insertion convex portion 35a of the quartz glass 35 is inserted into the cylindrical wall body 32a. By attaching 32a to the casing 33, the quartz glass 35 can be stably attached. In FIG. 1, 36a is an O-ring-shaped first elastic material, and 36b is an O-ring-shaped second elastic material.

  In the present embodiment, the reference light L2 separated by the beam splitter 31b is bent 90 degrees by the second mirror 31 and passes through the cavity 33a of the casing 33 in parallel with the test light L1.

  Thus, by arranging the optical path of the reference light L2 close to the optical path of the test light L1, the temperature difference between the optical path of the reference light L2 and the optical path of the test light L1 can be almost ignored, and temperature correction is performed. Can be made unnecessary.

  In particular, the reference light L2 is reflected by a reference light reflector M2 provided on the inner surface of the tip wall 33c of the casing 33.

  In this way, by reflecting the reference light L2 with the reference light reflector M2 provided on the inner side surface of the tip wall 33c, the difference between the reference light L2 and the test light L1 can be only the sensitive part 32, It is possible to improve the measurement accuracy by eliminating the possibility that factors such as temperature in parts other than the sensing part 32 affect the measurement result.

  In the present embodiment, the reference light reflector M2 is composed of a mirror attached to a flat metal plate 37 attached to the inner surface of the tip wall 33c of the casing 33, but the surface of the metal plate 37 is mirror-finished. Thus, the reference light reflector M2 may be used. Further, the reference light reflector M2 is attached to the tip of a screw rod (not shown) screwed to the tip wall 33c of the casing 33, and the reference light reflector M2 is moved back and forth by moving the screw rod forward and backward. It may be moved back and forth along the optical axis.

  In FIG. 1, 34 is a collar provided for fixedly mounting the metal plate 37 on the inner side surface of the tip wall 33c of the casing 33, and 36c is a third elastic material in the form of an O-ring. Particularly, the scattering of laser light can be suppressed by setting the inner peripheral surface of the collar 34 to black. In the case where the collar 34 is not provided, the scattering of laser light can be suppressed by setting the inner peripheral surface of the casing 33 to be black.

  Further, in FIG. 1, reference numeral 38 denotes a quarter wavelength plate, and the S-polarized test light L1 separated by the beam splitter 31b passes through the quarter wavelength plate 38 and becomes circularly polarized light. Passes through the cavity 33a and the quartz glass 35, reaches the sensing part 32, crosses the measurement space T, is reflected by the test light reflector M1, crosses the measurement space T again, quartz glass 35, and The light passes through the cavity 33a of the casing 33, passes through the quarter-wave plate 38, becomes P-polarized light, passes through the beam splitter 31b, and is incident on the second optical fiber 40.

  On the other hand, the P-polarized reference light L2 separated by the beam splitter 31b is bent by the second mirror 31c, passes through the quarter-wave plate 38, becomes circularly polarized light, and passes through the cavity 33a of the casing 33. Then, it is reflected by the reference light reflector M2 provided on the inner side surface of the tip wall 33c of the casing 33, passes through the cavity 33a of the casing 33 again, and passes through the quarter-wave plate 38, thereby becoming S-polarized light. After being bent by the mirror 31 c, it is bent by the beam splitter 31 b and is incident on the second optical fiber 40.

  As described above, in the temperature sensor A1, the sensing part 32 is provided at the distal end of the casing 33, and the separation part 31 is provided at the base end of the casing 33, so that the vibration state between the sensing part 32 and the separation part 31 is substantially reduced. They can be the same, and can be made less susceptible to vibrations.

  Moreover, since the optical path of the test light L1 can be made relatively short, it is possible to eliminate the possibility of interfering with fluctuation factors of the test light L1 other than the sensor 32, and to detect temperature fluctuations with higher accuracy. Can do.

  In the above-described embodiment, for convenience of explanation, the casing 33 has been described as being integrated from the proximal end to which the first optical fiber 20 and the second optical fiber 40 are connected to the distal end wall 33c. The casing 33 includes a cylindrical base composed of a tip wall 33c and a cavity 33a, a quarter-wave plate support base on which a quarter-wave plate 38 is mounted, a first mirror 31a, a beam splitter 31b, and a second mirror 31. Is composed of four parts, a separation part support base to which the optical fiber is mounted and an optical fiber connection base to which the first optical fiber 20 and the second optical fiber 40 are connected, each being detachably coupled via a fixing screw. is doing.

  If the beam splitter 31b can be reduced to a size of several millimeters, an integral casing 33 can be used.

  In the present embodiment, the light source unit 10 and the detection unit 50 are configured separately from the sensor unit 30, but the light source unit 10 and the detection unit 50 are also integrally mounted on the proximal end side of the casing 33. It can also be miniaturized.

  As another embodiment, as shown in FIG. 2, the sensing part 32 'may be configured as follows. In the following description, the same components as those of the above-described temperature sensor A1 will be denoted by the same reference numerals, and redundant description will be omitted, and the sensitive part 32 'different from the above-described temperature sensor A1 will be described in detail.

  That is, a passage port 33b ′ that allows the test light L1 ′ and the reference light L2 ′ to pass therethrough is provided at the tip of the casing 33 ′, and the test light L1 ′ and the reference light L2 ′ are passed through the passage port 33b ′. A quartz glass 35 ', which is a transparent material to be passed, is attached.

  At the front end portion of the casing 33 ′, an accommodation recess 33d ′ for accommodating the quartz glass 35 ′ is formed in the passage port 33b ′, and the quartz glass 35 ′ is accommodated in the accommodation recess 33d ′. The sensing part 32 ′ is mounted using the inner peripheral surface of the housing recess 33d ′.

  The sensing part 32 ′ is composed of a cylindrical wall 32a ′ that can be fitted into the accommodating recess 33d ′, and a flat support plate 32b ′ is provided at one end of the cylinder 32a ′. “Reflector M” is attached to “and the test light L1 ′ and the reference light L2 ′ that have passed through the quartz glass 35 ′ are reflected.

  The cylindrical wall body 32a ′ is provided with a through hole at a predetermined position so that gas or liquid can freely flow inside and outside the cylindrical wall body 32a ′, and is configured by an inner space of the cylindrical wall body 32a ′. The measured space T ′ to be measured is in the same temperature state as the outer space of the cylindrical wall body 32a ′.

  The reflector M ′ may be configured by mounting an appropriate mirror on the support plate 32b ′, or may be the reflector M ′ by mirror-finishing the surface of the support plate 32b ′.

  Also in the present embodiment, the cylindrical wall body 32a ′ is formed with a male screw, the housing recess 33d ′ is formed with a female screw, and the cylindrical wall body 32a ′ is screwed into the housing recess 33d ′. The sensing part 32 ′ can be attached to the tip of the casing 33 ′. Furthermore, the quartz glass 35 ′ is provided with an insertion convex portion 35a ′ to be inserted into the cylindrical wall body 32a ′, and the insertion convex portion 35a ′ of the quartz glass 35 ′ is inserted into the cylindrical wall body 32a ′. On the other hand, by attaching the cylindrical wall body 32a ′ to the casing 33 ′, the quartz glass 35 ′ can be stably attached. In FIG. 1, 36a ′ is an O-ring-shaped first elastic material, and 36b ′ is an O-ring-shaped second elastic material.

  Also in this embodiment, the reference light L2 ′ separated by the beam splitter 31b is bent by 90 degrees by the second mirror 31 and passes through the cavity 33a ′ of the casing 33 ′ in parallel with the test light L1 ′.

  Thus, by arranging the optical path of the reference light L2 ′ close to the optical path of the test light L1 ′, the temperature difference between the optical path of the reference light L2 ′ and the optical path of the test light L1 ′ can be almost ignored. Temperature correction can be made unnecessary.

  In particular, the reference light L2 ′ passes through the quartz glass 35 ′ provided at the tip of the casing 33 ′ and reaches the sensitive part 32 ′, and is reflected on the reflector M ′ provided on the support plate 32b ′ of the sensitive part 32 ′. Reflected.

  Therefore, not only the test light L1 ′ but also the reference light L2 ′ crosses the measured space T ′, and the temperature difference between the optical path of the reference light L2 ′ and the optical path of the test light L1 ′ can be further reduced. Since the influence of the temperature boundary layer on the surface of the quartz glass 35 ′ and the surface of the reflector M ′ can be canceled by the test light L1 ′ and the reference light L2 ′, the temperature measurement accuracy can be improved. .

  Here, the temperature boundary layer is a layer that occurs along the wall surface when there is a temperature difference between the wall surface and the fluid when the fluid moves along the wall surface, and the test light that crosses the temperature boundary layer. When the temperature of the fluid is measured by the above method, the measurement result has an error corresponding to the temperature boundary layer.

  Specifically, the ratio of the calculated temperature error when measuring the temperature of water at a flow rate of 0.13 m / s with a temperature sensor with the crossing distance of the measurement space being 2 mm, 4 mm, 6 mm, 8 mm, 10 mm is as follows: As shown in FIG. The test light is reflected by the reflector, so that the distance between the quartz glass provided at the tip of the casing and the reflector is half of the transverse distance of the space to be measured.

  As shown in FIG. 3, the longer the crossing distance of the space to be measured, the smaller the influence of the temperature boundary layer. On the other hand, when the crossing distance of the space to be measured is short, the influence of the temperature boundary layer It can be seen that is large.

  Further, when measuring the temperature in the combustion part of the internal combustion engine that we intend to apply, that is, for example, when measuring the temperature of hot air with a flow rate of 10 m / s, the ratio of the calculated temperature error 4 is as shown in FIG. 4 when the crossing distance of the space to be measured is 2 mm, 4 mm, 6 mm, 8 mm, and 10 mm, respectively.

  In other words, when the temperature of the fluid being the subject is extremely high and moves at a high speed, and the temperature of the temperature sensor is low, it is clear that the influence of the temperature boundary layer cannot be ignored by increasing the thickness of the temperature boundary layer. is there. In particular, for example, when the crossing distance of the measurement space is 6 mm, there is an error of 10% or more at a temperature of about 2000 K. When measuring the temperature of a fluid moving at a high temperature and high speed, Therefore, it is necessary to use a temperature sensor in consideration of the temperature boundary layer. As shown in FIG. 2, the test light L1 ′ and the reference light L2 ′ also cross the measurement space T ′ to cancel the influence of the temperature boundary layer. Is desirable.

  It should be noted that the actual combustion part of the internal combustion engine is in a high pressure state of about several MPa during combustion, and it has been confirmed that the influence of the temperature boundary layer is mitigated when this pressure is taken into consideration.

  That is, FIG. 5 shows the result of calculating the calculated temperature error ratio while changing the crossing distance of the measurement space, assuming that the temperature of the subject air is 900K, the pressure is 4.0 MPa, and the flow velocity is 10 m / s. As shown in FIG. 5, if the subject has a high pressure, the error can be reduced to 1% or less even if the crossing distance of the measurement space is about 10 mm, and the influence on the measurement is mitigated. I understand.

  The sensing unit 32 ′ is positioned on the optical path of the reference light L2 ′ in order to shorten the crossing distance of the measurement light T2 of the reference light L2 ′ and the crossing distance of the measurement light T1 of the test light L1 ′. A step 39 is provided by bulging the surface of the quartz glass 35 ′ on the reflector M ′ side.

  As described above, the step distance 39 is provided at a required position in the quartz glass 35 ′, whereby the transverse distance of the measurement space T ′ of the test light L1 ′ or the reference light L2 ′ can be adjusted. The step 39 may be formed at the time of processing the quartz glass 35 ', or a transparent member such as a flat plate-like quartz glass having a required size at a predetermined position of the quartz glass 35' having a flat surface without a step. May be used as a step, and the crossing distance of the measured space T ′ may be shortened. Further, the step 39 may not be provided on the optical path of the reference light L2 ′, but may be provided on the optical path of the test light L1 ′, and the test light L1 ′ and the reference light L2 ′ cross the measured space T ′. It is sufficient if the distance is different.

  The casing 33 ′ of the present embodiment has a black inner surface and is not mounted with the collar 34 described above.

  When the sensor unit 32 ′ is configured in this manner, the S-polarized test light L1 ′ separated by the beam splitter 31b passes through the quarter-wave plate 38 and is circularly polarized, as in the case described above. Passes through the cavity 33a 'of the casing 33' and the quartz glass 35 ', reaches the sensing part 32', is reflected by the reflector M 'across the measurement space T', and is measured Is crossed again, passes through the quartz glass 35 'and the cavity 33a' of the casing 33 ', passes through the quarter-wave plate 38, becomes P-polarized light, passes through the beam splitter 31b, and passes through the second optical fiber 40. Is incident on.

  On the other hand, the P-polarized reference light L2 ′ separated by the beam splitter 31b is bent by the second mirror 31c, then passes through the quarter-wave plate 38 to become circularly polarized light, and becomes a cavity 33a ′ of the casing 33 ′. , And the quartz glass 35 ′ and the auxiliary light projecting material 39 to reach the sensitive part 32 ′, cross the measurement space T ′, are reflected by the reflector M ′, and cross the measurement space T ′ again. After passing through the auxiliary light projecting material 39, the quartz glass 35 ′, and the cavity 33a ′ of the casing 33 ′ and passing through the quarter-wave plate 38, it becomes S-polarized light and is bent by the second mirror 31c. The light is bent by the beam splitter 31 b and is incident on the second optical fiber 40.

  As described above, in the temperature sensor A1 ′, the sensing part 32 ′ is provided at the distal end of the casing 33 ′, and the separation part 31 is provided at the proximal end of the casing 33 ′. Can be made substantially the same, and can be made less susceptible to vibration.

  Moreover, since the optical path of the test light L1 'can be made relatively short, the possibility of interfering with the fluctuation factors of the test light L1' other than the sensor 32 'can be eliminated, and temperature fluctuations can be detected with higher accuracy. It can be.

  Next, the temperature sensor A2 of the second embodiment will be described. FIG. 6 is a schematic diagram of a temperature sensor A2 according to the second embodiment.

  The temperature sensor A2 of the present embodiment includes a light source unit 60 that emits a required laser beam, an optical fiber 70 that guides the laser beam emitted from the light source unit 60, and a laser that is incident through the optical fiber 70. The light is separated into the test light L1 "and the reference light L2", crossed the measurement space T "respectively, and then combined into a single sensor 80, and the signal output from the sensor 80 is analyzed And an analysis unit 90 for detecting a temperature change.

  The light source unit 60 uses a He—Ne laser device that emits laser light having an output of 10 mmW and a wavelength of 632.8 nm as a light source. The light source is not limited to the He—Ne laser device, and any light source may be used as long as interference can be detected.

  A fifth SML 71 is provided at one end of the optical fiber 70, and laser light emitted from the light source unit 60 is incident on the optical fiber 70 from the fifth SML 71, and is emitted from a sixth SML 72 attached to the other end of the optical fiber 70. Yes. In the present embodiment, a polarization plane preserving optical fiber is used as the optical fiber 70.

  The sixth SML 72 is attached to the proximal end of the sensor unit 80, and laser light is incident on the sensor unit 80.

  The sensor unit 80 includes a first beam splitter unit 81 serving as a separation unit for separating the laser light emitted from the sixth SML 72 into the test light L1 ″ and the reference light L2 ″, and the test separated by the first beam splitter unit 81. A sensing unit 83 that guides the light L1 "and the reference light L2" to the measurement space T "and crosses the measurement space T", and the test light L1 "and the reference light L2" that have passed through the measurement space T ". A second beam splitter unit 82 that causes interference light to generate interference light, a photodiode 84 that is irradiated with the interference light emitted from the second beam splitter unit 82, and a casing 85 that is disposed at a predetermined position. It is composed.

  The sensing unit 83 is provided at the distal end of a cylindrical casing 85 that is parallel to the irradiation direction of the test light L1 ″ and the reference light L2 ″ emitted from the first beam splitter unit 81, and is provided on the proximal end side of the casing 85. A first beam splitter unit 81 that is a separation unit is provided.

  The analysis unit 90 receives a signal output from the photodiode 84 of the sensor unit 80, and the analysis unit 90 detects a temperature variation based on this signal.

  In the first beam splitter 81, the incident laser light is separated into test light L1 "and reference light L2", and in this embodiment, the reference light L2 "goes straight ahead and is emitted, and the test light L1" A beam splitter 81a that emits in a direction that forms an angle of 90 ° with respect to the reference light L2 ", and a mirror that emits the test light L1" emitted from the beam splitter 81a in a direction parallel to the emission direction of the reference light L2 " It consists of 81b.

  Therefore, the test light L1 "and the reference light L2" are parallel to each other, and the sensor unit 83 guides the test light L1 "and the reference light L2" while maintaining the parallel state, and the second beam. The light is emitted toward the splitter unit 82.

  Similarly to the first beam splitter unit 81, the second beam splitter unit 82 includes a beam splitter 82a and a mirror 82b. The beam splitter 82a causes interference between the test light L1 "and the reference light L2". Generated and emitted. The mirror 82b reflects the test light L1 "toward the beam splitter 82a. The test light L1" reflected by the mirror 82b is incident on the beam splitter 82a, and the reference light L2 "directly incident on the beam splitter 82a. Is interfering with.

  The sensing part 82 is integrally formed of quartz glass, and a mounting base 83a for mounting on the front end of the casing 85 of the temperature sensor A2, and a first beam splitter section on the mounting base 83a. A longitudinal column 83b erected parallel to the traveling direction of the test light L1 "and reference light L2" incident from 81, and parallel to each other along the longitudinal direction of the column 83b at the tip of the column 83b The first support body 83c and the second support body 83d are provided upright.

  In this embodiment, the mounting pedestal 83a has a rectangular shape, but the mounting pedestal 83a is not limited to a rectangular shape, and may have any shape as long as it can stably support the column 83b. May be.

  The column part 83b is arranged on the optical path of the test light L1 "and the reference light L2" so that the test light L1 "and the reference light L2" pass through the column part 83b.

  The first support 83c and the second support 83d are arranged in parallel with each other at a predetermined interval, and the space between the first support 83c and the second support 83d is a measured space T ″.

  Test light L1 "and reference light L2", which are emitted from the first beam splitter 81 and pass through the mounting base 83a and the support post 83b, are incident on the first support 83c, and the first support 83c is provided at the tip portion. The test light L1 "and the reference light L2" are reflected by one mirror surface m1 and emitted toward the second support 83d. The first mirror surface m1 is a reflector that directs the irradiation directions of the test light L1 "and the reference light L2" to the second support 83d.

  The tip of the second support 83d is provided with a second mirror surface m2 that reflects the test light L1 "and the reference light L2" incident from the first support 83c, and the test light reflected by the second mirror surface m2. L1 "and reference light L2" are emitted toward the second beam splitter unit 82, which is a separation unit. The second mirror surface m2 is a reflector that directs the irradiation directions of the test light L1 "and the reference light L2" toward the second beam splitter unit 82, and the test light L1 "and the reference light L2" reflected by the second mirror surface m2 are The second support 83d, the support post 83b, and the mounting base 83a are incident on the second beam splitter 82.

  That is, the test light L1 "and the reference light L2" are reflected by the first mirror surface m1 of the first support 83c, cross the measurement space T ", and reflected by the second mirror surface m2 of the second support 83d. The inside of the sensing unit 83 proceeds toward the second beam splitter unit 82.

  In particular, in the first support 83c and the second support 83d, a step 83e is formed by bulging the passage region of the reference light L2 "on the side surface facing the measurement space T" to the measurement space T "side, The crossing distance of the reference light L2 "crossing the measurement space T" is shorter than the crossing distance of the test light L1 "crossing the measurement space T".

  In the present embodiment, the step 83e is formed by sticking a flat quartz glass plate to the side surfaces of the first support 83c and the second support 83d facing the measurement space T ″. The reference light L2 "traversing the measured space T" is defined by setting the crossing distance of the test light L1 "traversing the measured space T" to 5 mm and the thickness of the quartz glass plate constituting the step 83e to 1 mm. The crossing distance is set to 3 mm. The crossing distance of the test light L1 "and the crossing distance of the reference light L2" crossing the measurement space T "are not limited to these values, but as appropriate dimensions according to the measurement object. Good. Alternatively, the crossing distance of the test light L1 "may be shorter than the crossing distance of the reference light L2".

  Further, the step 83e may be provided not only on both the first support 83c and the second support 83d, but also on only one of the first support 83c and the second support 83d. The level difference 83e can adjust the optical path length of the reference light L2 "traversing the measurement space T" by adjusting the thickness dimension of the quartz glass plate. In the present embodiment, the step 83e is formed by sticking a quartz glass plate at a predetermined position of the first support 83c and the second support 83d, but the step 83e is formed by the first support 83c and the second support. It may be formed integrally with 83d in advance.

  In this way, the reference light L2 "is irradiated in parallel with the test light L1" so that not only the test light L1 "but also the reference light L2" traverses the measured space T ", so that the temperature in the test light L1" Since the influence of the boundary layer can be canceled, the temperature measurement accuracy can be improved.

  The photodiode 84 is irradiated with the interference light between the test light L1 "and the reference light L2" emitted from the second beam splitter unit 82, and converts the intensity of this interference light into an electrical signal and outputs it.

  In the temperature sensor A2 of the present embodiment, when a temperature variation occurs in the measured space T ", the variation in the refractive index of the measurement target that occurs in the region corresponding to the difference in the crossing distance between the test light L1" and the reference light L2 " As a result, the phase difference fluctuates between the test light L1 "and the reference light L2", and the intensity of the interference light resulting from the interference between the test light L1 "and the reference light L2" fluctuates due to the fluctuation in the phase difference.

  The photodiode 84 detects the intensity fluctuation of the interference light emitted from the second beam splitter section 82, and outputs an electrical signal corresponding to the intensity fluctuation.

  The analysis unit 90 detects the presence and degree of temperature change by analyzing the electrical signal output from the photodiode 84.

  FIG. 7 is a temperature change graph when the water temperature is measured with a thermocouple while heating water and when the temperature sensor A2 of the second embodiment is used, and the temperature sensor A2 of the second embodiment measures the temperature. It can be seen that if the temperature serving as a reference for the temperature can be specified, the temperature can be measured to the same extent as a thermocouple.

  In FIG. 6, for convenience of explanation, the casing 85 is formed in a longitudinal shape, the first beam splitter unit 81 and the second beam splitter unit 82 are arranged apart from the sensing unit 83, and the sixth SML 72 is disposed in the first beam splitter unit 81. The photodiode 84 is arranged apart from the second beam splitter unit 82, but the first beam splitter unit 81 and the second beam splitter unit 82 are as close as possible to the sensing unit 83. The sixth SML 72 is arranged close to the first beam splitter unit 81, and the photodiode 84 is arranged close to the second beam splitter unit 82, thereby making it less susceptible to vibration. .

  As shown in FIG. 8, the temperature sensors A1, A1 ′, and A2 described above are configured integrally with the spark plug, so that the temperature in the combustion chamber of the internal combustion engine can be measured very easily.

  That is, the spark plug P with the temperature sensor A shown in FIG. 8 is provided with an electrode p1 that generates a spark discharge when a high voltage current is applied, and a socket p3 for connecting to the energization wiring p2 on the base end side. It is attached detachably.

  Further, the spark plug P includes a screwing portion p4 that is screwed into a mounting portion of the spark plug P provided in a cylinder head (not shown).

  An insertion hole (not shown) into which the temperature sensor A is inserted is provided in the screwing portion p4, and the temperature sensor A is inserted into the insertion hole and fixed to the screwing portion p4 through the casing a33. Wearing. In FIG. 5, b is a fixing nut used for fixing the temperature sensor A to the screwed portion p4 via the casing a33. In FIG. 8, a20 is a first optical fiber connected to the temperature sensor A, and a40 is a second optical fiber connected to the temperature sensor A.

  The temperature sensor A that is integrally attached to the screwing part p4 is arranged with the sensing part a32 close to the electrode p1 of the spark plug P. Therefore, the temperature sensor A can measure the temperature change near the electrode p1 of the spark plug P with high accuracy.

  In particular, the temperature sensor A is adjusted by appropriately moving the mounting position in the longitudinal direction of the temperature sensor A by the fixing nut b so that ignition by the spark plug P is not hindered. The sensitive part a32 of the temperature sensor A can be positioned at a position where the temperature change in the room can be measured.

  The temperature sensor of the present invention is resistant to vibration and can measure a temperature change in a vibrating object such as a temperature in a combustion chamber of an internal combustion engine with extremely high accuracy.

It is a schematic diagram of the temperature sensor which concerns on 1st Embodiment of this invention. It is a schematic diagram of the modification of the temperature sensor which concerns on 1st Embodiment of this invention. It is a graph which shows the analysis result of the temperature error which originates in the temperature boundary layer at the time of making fluid into water. It is a graph which shows the analysis result of the temperature error resulting from the temperature boundary layer at the time of making a fluid into high temperature and high-speed gas. It is a graph showing the analysis result of the temperature error caused by the temperature boundary layer when the fluid is temperature: 900K, pressure: 4.0MPa, flow velocity: 10m / s and the crossing distance of the measurement space is changed . It is principal part explanatory drawing of the temperature sensor which concerns on 2nd Embodiment of this invention. It is a temperature change graph obtained by measuring the temperature of the water during heating with the temperature sensor which concerns on 2nd Embodiment of this invention. It is explanatory drawing of the temperature sensor with which the spark plug was mounted | worn. It is a schematic diagram of the conventional temperature sensor.

Explanation of symbols

A1 Temperature sensor
L1 test light
L2 Reference light T Measurement space
M1 test light reflector
M2 reference reflector
10 Light source
11 Half mirror
12 First light receiving element
13 1/2 wavelength plate
14 First interference filter
20 First optical fiber
30 Sensor section
31 Separation part
31a First mirror
31b beam splitter
31c Second mirror
32 Sensory part
32a Tubular wall
32b support plate
33 Casing
33a Cavity
33b Passage
33c Tip wall
33d receiving recess
34 colors
35 quartz glass
36a 1st elastic material
36b Second elastic material
36c 3rd elastic material
37 Metal plate
38 1/4 wave plate
50 detector
51 Second light receiving element
52 Second interference filter

Claims (5)

A light source unit that emits laser light;
A separation unit that separates the laser light emitted from the light source unit into test light and reference light;
A sensing unit that arranges the optical path of the test light across a measurement space in which the temperature is measured; and
A detecting unit for detecting a change in temperature by causing interference between the test light crossing the measurement space and the reference light to detect a change in an interference state;
In the temperature sensor with
The sensing part is provided at the distal end of a cylindrical casing parallel to the optical path of the test light, and the separation part is provided at the base end of the casing,
The casing is provided with a tip wall provided with a transparent member that allows the test light to pass through and a reflector that reflects the reference light at a tip portion,
Said passing through the transparent member to test light to reach the sensitive part, temperature sensor you, characterized in that it is reflected by the reflector provided on the sensing part. A light source unit that emits laser light;
A separation unit that separates the laser light emitted from the light source unit into test light and reference light;
A sensing unit that arranges the optical path of the test light across a measurement space in which the temperature is measured; and
A detecting unit for detecting a change in temperature by causing interference between the test light crossing the measurement space and the reference light to detect a change in an interference state;
In the temperature sensor with
The sensing part is provided at the distal end of a cylindrical casing parallel to the optical path of the test light, and the separation part is provided at the base end of the casing,
The casing includes a transparent member that allows the test light and the reference light to pass therethrough at a tip portion, and causes the test light and the reference light that have passed through the transparent member to reach the sensitive part, and to the sensitive part. While reflecting with the reflector provided,
One of the crossing distance of the test light that crosses the measured space and the crossing distance of the reference light that crosses the measured space in the sensing part is shorter than the other crossing distance. temperature sensor shall be the. 3. The temperature sensor according to claim 2 , wherein the transparent member is provided with a step on a surface on the reflector side to adjust a transverse distance of the measurement space of the test light and the reference light. A light source unit that emits laser light;
A separation unit that separates the laser light emitted from the light source unit into test light and reference light;
A sensing unit that arranges the optical path of the test light across a measurement space in which the temperature is measured; and
A detecting unit for detecting a change in temperature by causing interference between the test light crossing the measurement space and the reference light to detect a change in an interference state;
In the temperature sensor with
The sensing part is provided at the distal end of a cylindrical casing parallel to the optical path of the test light, and the separation part is provided at the base end of the casing,
The casing includes a first reflector that changes an irradiation direction of the test light, and a second transparent body that directs the irradiation direction of the test light, the irradiation direction of which is changed by the first reflector, toward the separation unit. At the tip,
The measurement space is provided between the first reflector and the second reflector, and the reference light is reflected by the second reflector to traverse the measurement space, and then the first 1 to reflect on the reflector,
Wherein the transverse distance of the test light traversing the measured space, said one of the transverse distance of the reference beam to traverse the measured space, temperature characterized in that it is shorter than the other transverse distance Sensor. The first reflector is disposed on a first support made of a transparent material through which the test light and the reference light can pass.
The second reflector is disposed on a second support made of a transparent material through which the test light and the reference light can pass.
The space between the first support and the second support is used as the measurement space, and a step is provided on the surface of at least one of the first support and the second support that faces the measurement space. The temperature sensor according to claim 4 , wherein a transverse distance of the measurement space of the test light and the reference light is adjusted.

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