JP4504318B2 - Mirror surface dew point meter - Google Patents

Description

  In this invention, the mirror surface exposed to the gas to be measured is cooled using a thermoelectric cooling element such as a Peltier element, and a part of the water vapor contained in the gas to be measured is condensed on the mirror surface, so that there is no increase or decrease in the condensation. The present invention relates to a mirror-cooled dew point meter that detects the temperature of the mirror surface as a dew point.

  Conventionally, as a humidity measurement method, a dew point detection method is known in which a dew point is detected by measuring the temperature when the temperature of a gas to be measured is reduced and a part of water vapor contained in the gas to be measured is condensed. ing. For example, a mirror is cooled using a cryogen, a refrigerator, an electronic cooler, etc., a change in the intensity of reflected light on the mirror surface of the cooled mirror is detected, and the temperature of the mirror surface at this time is measured, thereby A mirror-cooled dew point meter that detects the dew point of moisture in a measurement gas is known.

  There are two types of mirror-cooled dew point meters depending on the type of reflected light used. One is a specularly reflected light detection method that uses specularly reflected light (see, for example, Patent Document 1), and the other is a scattered light detection method that uses scattered light (see, for example, Patent Document 2).

[Specular reflection detection method]
FIG. 11 shows a main part of a conventional mirror-cooled dew point meter that employs a regular reflection light detection method. The specular cooling dew point meter 101 includes a chamber 1 into which a gas to be measured is introduced and a thermoelectric cooling element (Peltier element) 2 provided inside the chamber 1. Bolts 4 are attached to the cooling surface 2-1 of the thermoelectric cooling element 2 via copper blocks 3, and radiating fins 5 are attached to the heating surface 2-2 of the thermoelectric cooling element 2. An upper surface 4-1 of the bolt 4 attached to the copper block 3 is a mirror surface. A winding type resistance temperature detector (temperature detection element) 6 is embedded in a side portion of the copper block 3 (see FIG. 13). Further, on the upper portion of the chamber 1, a light emitting element 7 that irradiates light obliquely to the upper surface (mirror surface) 4-1 of the bolt 4, and light emitted from the light emitting element 7 to the mirror surface 4-1. A light receiving element 8 for receiving the specularly reflected light is provided. A heat insulating material 9 is provided around the thermoelectric cooling element 2.

  In this mirror-cooled dew point meter 101, the mirror surface 4-1 in the chamber 1 is exposed to the gas to be measured flowing into the chamber 1. If there is no condensation on the mirror surface 4-1, almost all of the light emitted from the light emitting element 7 is regularly reflected and received by the light receiving element 8. Therefore, when there is no condensation on the mirror surface 4-1, the intensity of the reflected light received by the light receiving element 8 is high.

  When the current to the thermoelectric cooling element 2 is increased and the temperature of the cooling surface 2-1 of the thermoelectric cooling element 2 is lowered, water vapor contained in the gas to be measured condenses on the mirror surface 4-1, and the water molecules Part of the light emitted from the light emitting element 7 is absorbed or diffusely reflected. Thereby, the intensity of the reflected light (regular reflected light) received by the light receiving element 8 is reduced. By detecting the change in the specularly reflected light on the mirror surface 4-1, it is possible to know the change in the state on the mirror surface 4-1, that is, that moisture (water droplets) has adhered to the mirror surface 4-1.

  Furthermore, based on the amount of reflected light received by the light receiving element 8, the amount of reflected light received by the light receiving element 8 changes so as to be in an equilibrium state where there is no increase or decrease in condensation occurring on the mirror surface 4-1. The current to be supplied to the thermoelectric cooling element 2 so that the equilibrium state disappears, that is, the current in the positive direction with the surface 2-1 on the mirror 4 side as the low temperature side and the surface 2-2 on the radiation fin 5 side as the high temperature side. By controlling and measuring the temperature of the mirror surface 4-1 at this time with the temperature detection element 6, the dew point of the moisture in the gas to be measured can be known.

(Scattered light detection method)
FIG. 12 shows a main part of a conventional mirror-cooled dew point meter employing the scattered light detection method. This mirror-cooled dew point meter 102 has substantially the same configuration as the mirror-cooled dew point meter 101 employing the specular reflection light detection method, but the mounting position of the light receiving element 8 is different. In this mirror-cooled dew point meter 102, the light receiving element 8 is provided at a position for receiving scattered light, not at a position for receiving regular reflection light of light emitted from the light emitting element 7 to the mirror surface 4-1. Yes.

  In this mirror-cooled dew point meter 102, the mirror surface 4-1 is exposed to the gas to be measured that flows into the chamber 1. If there is no condensation on the mirror surface 4-1, almost all of the light emitted from the light emitting element 7 is regularly reflected, and the amount of light received by the light receiving element 8 is extremely small. Therefore, when no condensation occurs on the mirror surface 4-1, the intensity of the reflected light received by the light receiving element 8 is small.

  When the current to the thermoelectric cooling element 2 is increased and the temperature of the cooling surface 2-1 of the thermoelectric cooling element 2 is lowered, water vapor contained in the gas to be measured condenses on the mirror surface 4-1, and the water molecules Part of the light emitted from the light emitting element 7 is absorbed or diffusely reflected. Thereby, the intensity of the irregularly reflected light (scattered light) received by the light receiving element 8 increases. By detecting the change in the scattered light on the mirror surface 4-1, it is possible to know a change in the state on the mirror surface 4-1, that is, that moisture (water droplets) has adhered to the mirror surface 4-1.

  Furthermore, based on the amount of reflected light received by the light receiving element 8, the amount of reflected light received by the light receiving element 8 changes so as to be in an equilibrium state where there is no increase or decrease in condensation occurring on the mirror surface 4-1. The current to be supplied to the thermoelectric cooling element 2 so that the equilibrium state disappears, that is, the current in the positive direction with the surface 2-1 on the mirror 4 side as the low temperature side and the surface 2-2 on the radiation fin 5 side as the high temperature side. By controlling and measuring the temperature of the mirror surface 4-1 at this time with the temperature detection element 6, the dew point of the moisture in the gas to be measured can be known.

  In this mirror-cooled dew point meter, the mirror 4 is cooled by the thermoelectric cooling element 2 in any of the two types described above, but the dew point of the gas to be measured may suddenly increase during measurement. In this case, since the dew point cannot be measured if the mirror 4 is continuously cooled, the current to the thermoelectric cooling element 2 is interrupted, and the temperature of the mirror surface 4-1 naturally rises and waits for the dew point temperature to be reached. Thus, the measurement of the dew point temperature was resumed (for example, see Patent Document 3).

JP-A-61-75235 Japanese Examined Patent Publication No. 7-104304 JP-A-9-307030

  However, in the conventional specular cooling type dew point meter, when the dew point of the gas to be measured suddenly increases during the measurement, the current to the thermoelectric cooling element 2 is cut off, and the mirror surface by cutting off the current to the thermoelectric cooling element 2 is cut off. Since it was dependent on the natural rise in temperature of 4-1, a long waiting time had occurred until the dew point temperature could be measured.

  The present invention has been made to solve such a problem, and the object of the present invention is to quickly increase the mirror surface temperature when the dew point of the gas to be measured suddenly increases during measurement, and to increase the dew point temperature. The object of the present invention is to provide a mirror-cooled dew point meter that can greatly reduce the waiting time until the measurement.

(Scattered light detection method)
In order to achieve such an object, the first invention provides a thermoelectric cooling element that is supplied with a current in the positive direction and has one surface at a low temperature side and the other surface at a high temperature side, and this thermoelectric cooling. A mirror which is attached to one surface of the element and whose mirror surface is exposed to the gas to be measured, a light emitting means for irradiating the mirror surface with light, and a scattered light of light emitted from the light emitting means to the mirror surface are received. Based on the light receiving means, the temperature detecting means for detecting the temperature of the mirror surface, and the amount of received scattered light received by the light receiving means, the temperature is supplied to the thermoelectric cooling element so as to be in an equilibrium state in which the increase or decrease of the dew condensation occurring on the mirror surface is eliminated. A mirror-cooled dew point meter having a control means for controlling a current in the positive direction, based on a comparison between the amount of scattered light received by the light receiving means and a predetermined first threshold value. Coverage from equilibrium where there is no increase or decrease in condensation While detecting the rise of the dew point of the constant gas, based on a comparison between a second threshold value which the light receiving means it is predetermined and received light amount of scattered light received, the equilibrium from increase in the dew point of the gas to be measured Dew point rise detection means to detect the recovery of the dew point, and when the dew point rise is detected, the thermoelectric cooling element is forced to flow in the reverse direction opposite to the positive direction, while the dew point rises to the equilibrium state. And a means for returning the current supplied to the thermoelectric cooling element in the positive direction when the recovery is detected.

According to this invention, light is emitted from the light emitting means to the mirror surface of the mirror, the scattered light from the mirror surface of the irradiated light is received by the light receiving means, and the amount of scattered light received by the light receiving means is reduced. Based on this, the current in the positive direction supplied to the thermoelectric cooling element is controlled so that the dew condensation occurring on the mirror surface is in an equilibrium state. In this case, the temperature of the mirror surface when the dew condensation occurring on the mirror surface is in an equilibrium state is the dew point temperature, and this dew point temperature is detected by the temperature detecting means. During measurement of the dew-point temperature, the dew point of the gas to be measured increases, it becomes large amount of condensation occurring in the mirror. In the present invention, such an increase in the dew point is detected, and a current in the reverse direction is forced to flow through the thermoelectric cooling element. As a result, the thermoelectric cooling element has the surface (one surface) that has been on the low temperature side as the high temperature side, and the surface (the other surface) that has been on the high temperature side as the low temperature side, that is, the cooling surface The heating surface is switched, the mirror is actively heated, and the mirror surface temperature rises quickly. And if the recovery to the equilibrium state from the rise of the dew point of the gas to be measured is detected, the current supplied to the electric cooling element is returned to the positive direction.

An increase in the dew point of the gas to be measured is detected when, for example, the amount of scattered light received by the light receiving means exceeds a predetermined threshold, or an increase in the amount of scattered light received by the light receiving means. It is possible to detect when the amount of change in the direction exceeds a predetermined threshold.

[Specular reflection detection method]
Further, the second invention is provided with a thermoelectric cooling element that is supplied with a current in the positive direction and has one surface at a low temperature side and the other surface at a high temperature side, and is attached to one surface side of the thermoelectric cooling element. A mirror whose surface is exposed to the gas to be measured, a light emitting means for irradiating the mirror surface with light, a light receiving means for receiving the specularly reflected light emitted from the light emitting means to the mirror surface, and the temperature of the mirror surface Based on the received amount of specularly reflected light received by the light detecting means and the temperature detecting means for detecting the current, the current in the positive direction supplied to the thermoelectric cooling element is adjusted so that there is no increase / decrease in condensation on the mirror surface. In a specular cooling type dew point meter equipped with a control means for controlling, the increase or decrease of the dew condensation occurring on the mirror surface is based on a comparison between the amount of regular reflection light received by the light receiving means and a predetermined first threshold value. increase in the dew point of gas to be measured from the lost equilibrium While detecting, based on a comparison between a second threshold value which the light receiving means is predetermined and the light receiving amount of the specular reflection light received, the dew point for detecting the restoration of the equilibrium from increase in the dew point of the gas to be measured When rise detection means and dew point rise are detected, a current in the reverse direction opposite to the forward direction is forced to flow through the thermoelectric cooling element, while recovery from the dew point rise to equilibrium is detected. In this case, means for returning the current supplied to the thermoelectric cooling element in the positive direction is provided.

According to this invention, light is emitted from the light emitting means to the mirror surface of the mirror, and the regular reflection light from the mirror surface of the irradiated light is received by the light receiving means, and the regular reflection light received by the light receiving means is received. Based on the amount, the forward current supplied to the thermoelectric cooling element is controlled so that the dew condensation occurring on the mirror surface is in an equilibrium state. In this case, the temperature of the mirror surface when the dew condensation occurring on the mirror surface is in an equilibrium state is the dew point temperature, and this dew point temperature is detected by the temperature detecting means. During measurement of the dew-point temperature, the dew point of the gas to be measured increases, it becomes large amount of condensation occurring in the mirror. In the present invention, such an increase in the dew point is detected, and a current in the reverse direction is forced to flow through the thermoelectric cooling element. As a result, the thermoelectric cooling element has the surface (one surface) that has been on the low temperature side as the high temperature side, and the surface (the other surface) that has been on the high temperature side as the low temperature side, that is, the cooling surface The heating surface is switched, the mirror is actively heated, and the mirror surface temperature rises quickly. And if the recovery to the equilibrium state from the rise of the dew point of the gas to be measured is detected, the current supplied to the electric cooling element is returned to the positive direction.

An increase in the dew point of the gas to be measured is detected when, for example, the amount of specularly reflected light received by the light receiving means falls below a predetermined threshold, or the amount of specularly reflected light received by the light receiving means. It can be detected that the amount of change in the decreasing direction exceeds a predetermined threshold.

  According to the present invention, if the dew point of the gas to be measured suddenly increases during the measurement of the dew point temperature, a current in the reverse direction is forced to flow to the thermoelectric cooling element, and the surface that has been on the low temperature side until then is hot. Since the surface that has been set to the high temperature side is set to the low temperature side, the mirror is actively heated, the mirror surface temperature can be quickly increased, and the waiting time until the dew point temperature can be measured can be greatly shortened. It becomes like this.

Hereinafter, the present invention will be described in detail with reference to the drawings.
[Embodiment 1: Scattered light detection method]
FIG. 1 is a schematic configuration diagram showing an embodiment of a mirror-cooled dew point meter according to the present invention. The mirror-cooled dew point meter 201 has a sensor unit 201A and a control unit 201B.

  In the sensor unit 201 </ b> A, the mirror 10 is attached to the cooling surface 2-1 of the thermoelectric cooling element (Peltier element) 2. The mirror 10 is a silicon chip, for example, and the surface 10-1 is a mirror surface. Further, a thin film resistance temperature detector (temperature detection element) 11 made of, for example, platinum is formed on the joint surface between the mirror 10 and the cooling surface 2-1 of the thermoelectric cooling element 2. A cylindrical heat sink 18 is attached to the heating surface 2-2 of the thermoelectric cooling element 2, and a stainless steel tube 17 whose upper end is curved in a J shape is provided along the heat sink 18.

  As the tube 17, various tubes P accommodating optical fibers as shown in FIG. 2 can be used. In FIG. 2A, in the tube P, the light-emitting side optical fiber F1 and the light-receiving side optical fiber F2 are arranged side by side. In the tube P, the periphery of the light-emitting side optical fiber F1 and the light-receiving side optical fiber F2 is filled with a potting agent. In FIG. 2 (b), the light emitting side (or light receiving side) optical fiber F1 and the light receiving side (or light emitting side) optical fibers F21 to F24 are provided in the tube P in parallel. In FIG. 2C, the left half of the tube P is the light-emitting side optical fiber F1, and the right half is the light-receiving side optical fiber F2. In FIG. 2D, the light emission side optical fiber F <b> 1 and the light reception side optical fiber F <b> 2 are mixed in the tube P. In FIG. 2 (e), the central portion in the tube P is the light emitting side (or light receiving side) optical fiber F1, and the periphery of the optical fiber F1 is the light receiving side (or light emitting side) optical fiber F2.

  In the mirror-cooled dew point meter 201 shown in FIG. 1, the tube P of the type shown in FIG. 2 (a) is used as the tube 17, and an optical fiber 17-1 on the light emitting side and a light receiving side on the inside thereof. The optical fiber 17-2 is accommodated. The tip portions (light emitting portion and light receiving portion) of the light emitting side optical fiber 17-1 and the light receiving side optical fiber 17-2 which are curved in a J-shape are directed to the mirror surface 10-1 of the mirror 10, and this mirror surface 10 -1 with a predetermined inclination angle. As a result, the irradiation direction (optical axis) of the light from the optical fiber 17-1 and the light receiving direction (optical axis) of the light from the optical fiber 17-2 are made parallel, and the same inclination angle is set adjacently. The

  The control unit 201B includes a dew point temperature display unit 12, a dew condensation detection unit 13, a Peltier output control unit 14, a signal conversion unit 15, a received light amount sudden rise detection unit 16A, and a power supply unit 19. . The dew point temperature display unit 12 displays the temperature of the mirror 10 detected by the temperature detection element 11. The dew condensation detection unit 13 irradiates the mirror surface 10-1 of the mirror 10 with pulse light obliquely at a predetermined period from the tip of the optical fiber 17-1, and receives light reflected through the optical fiber 17-2. The difference between the upper limit value and the lower limit value of the pulsed light (scattered light) is obtained as the intensity of the reflected pulsed light, and a signal S1 corresponding to the intensity of the reflected pulsed light is sent to the Peltier output control unit 14 and the received light amount sudden rise detecting unit 16A. .

  Upon receiving the signal S1 corresponding to the intensity of the reflected pulsed light from the dew condensation detector 13, the received light quantity suddenly increasing detector 16A suddenly increases the intensity of the reflected pulsed light, that is, from the tip of the optical fiber 17-1 to the mirror surface 10-1. Is detected, and an instruction S4 is supplied to the Peltier output control unit 14 to flow a reverse current.

  The Peltier output control unit 14 receives the signal S1 from the dew condensation detection unit 13, compares the intensity of the reflected pulse light with a predetermined threshold th1, and the intensity of the reflected pulse light does not reach the threshold th1. Includes a control signal S2 for increasing the current to the thermoelectric cooling element 2 according to the value of the signal S1, and a signal to the current to the thermoelectric cooling element 2 when the intensity of the reflected pulse light exceeds the threshold th1. A control signal S2 to be decreased according to the value of S1 is output to the signal converter 15.

  In addition, when receiving the instruction S4 for flowing the reverse current from the light reception amount sudden rise detection unit 16A, the Peltier output control unit 14 interrupts the control according to the signal S1 corresponding to the intensity of the reflected pulse light from the dew condensation detection unit 13. Then, a signal S2 ′ for forcibly switching the current to the thermoelectric cooling element 2 from the current value in the forward direction to the reverse direction is sent to the signal conversion unit 15. The signal converter 15 supplies currents S3 and S3 'indicated by the control signals S2 and S2' from the Peltier output controller 14 to the thermoelectric cooling element 2 via the power supply unit 19.

[Measurement of dew point temperature]
In this mirror-cooled dew point meter 201, the sensor unit 201A is placed in the gas to be measured. Further, the dew condensation detector 13 irradiates the mirror surface 10-1 of the mirror 10 with pulsed light obliquely at a predetermined cycle from the tip of the optical fiber 17-1 (see FIG. 3A). If the mirror surface 10-1 is exposed to the gas to be measured and no condensation occurs on the mirror surface 10-1, almost all of the pulsed light irradiated from the tip of the optical fiber 17-1 is regularly reflected. The amount of reflected pulsed light (scattered light) from the mirror surface 10-1 received through the optical fiber 17-2 is extremely small. Accordingly, when no condensation occurs on the mirror surface 10-1, the intensity of the reflected pulse light received through the optical fiber 17-2 is small.

  In the dew condensation detection unit 13, the difference between the upper limit value and the lower limit value of the reflected pulse light received through the optical fiber 17-2 is obtained as the intensity of the reflected pulse light, and the signal S1 corresponding to the intensity of the reflected pulse light is obtained from the Peltier. It is sent to the output control unit 14 and the received light amount sudden rise detection unit 16A. In this case, since the intensity of the reflected pulse light is almost zero and has not reached the threshold th1, the Peltier output control unit 14 sends a control signal S2 for increasing the current to the thermoelectric cooling element 2 to the signal conversion unit 15. . Thereby, the electric current S3 supplied to the thermoelectric cooling element 2 increases, and the temperature of the cooling surface 2-1 of the thermoelectric cooling element 2 is lowered.

  When the temperature of the cooling surface 2-1 of the thermoelectric cooling element 2 is lowered, that is, the temperature of the mirror 10, the water vapor contained in the gas to be measured is condensed on the mirror surface 10-1 of the mirror 10, and the water molecules are optical fiber. Part of the pulsed light irradiated from the tip portion of 17-1 is absorbed or irregularly reflected. Thereby, the intensity | strength of the reflected pulsed light (scattered light) from the mirror surface 10-1 light-received via the optical fiber 17-2 increases.

  The dew condensation detection unit 13 obtains the difference between the upper limit value and the lower limit value of each pulse of the received reflected pulse light, and uses this difference as the intensity of the reflected pulse light. That is, as shown in FIG. 3B, a difference ΔL between the upper limit value Lmax and the lower limit value Lmin of one pulse of the reflected pulse light is obtained, and this ΔL is used as the intensity of the reflected pulse light. By the process in the dew condensation detection unit 13, the disturbance light ΔX included in the reflected pulse light is removed, and malfunction due to the disturbance light is prevented. A processing method for preventing malfunction by disturbance light using pulsed light in the dew condensation detection unit 13 is referred to as a pulse modulation method. With this process, the mirror cooled dew point meter 201 can eliminate the chamber from the sensor unit 201A.

  Here, when the intensity of the reflected pulse light received through the optical fiber 17-2 exceeds the threshold th1, the Peltier output control unit 14 generates a control signal S2 for reducing the current to the thermoelectric cooling element 2 as a signal conversion unit. Send to 15. Thereby, the fall of the temperature of the cooling surface 2-1 of the thermoelectric cooling element 2 is suppressed, and generation | occurrence | production of dew condensation is suppressed. Due to the suppression of the dew condensation, the intensity of the reflected pulse light received through the optical fiber 17-2 becomes small, and when it falls below the threshold th1, the control signal increases the current from the Peltier output control unit 14 to the thermoelectric cooling element 2. S2 is sent to the signal converter 15. By repeating this operation, the temperature of the cooling surface 2-1 of the thermoelectric cooling element 2 is adjusted so that the intensity of the reflected pulse light received through the optical fiber 17-2 is approximately equal to the threshold th1. The adjusted temperature, that is, the temperature at which the dew condensation that has occurred on the mirror surface 10-1 has reached an equilibrium state (dew point temperature) is displayed on the dew point temperature display unit 12 as the dew point temperature.

  In this mirror-cooled dew point meter 201, the attachment portions of the light-emitting side optical fiber 17-1 and the light-receiving side optical fiber 17-2 are gathered in one place, which contributes to the downsizing of the detection unit 201A. Further, since the light-emitting side optical fiber 17-1 and the light-receiving side optical fiber 17-2 are accommodated in the tube 17, the space between the light-emitting side optical fiber 17-1 and the light-receiving side optical fiber 17-2. There is no need for positioning at this point, and the workability during assembly is improved.

  Further, in this mirror-cooled dew point meter 201, the chamber is eliminated from the sensor unit 201A, and the suction pump, the suction tube, the exhaust tube, the flow meter, and the like can be omitted. Further downsizing of 201A is achieved, the assembling property is improved, and the cost is also reduced. Further, since it is not necessary to attach a suction pump, a suction tube, an exhaust tube, a flow meter, etc., installation in the measurement area (in the gas to be measured) is facilitated. The sensor unit 201A is not accompanied by a suction pump, a suction tube, an exhaust tube, a flow meter, or the like, and has two configurations of the sensor unit 201A and the control unit 201B.

[When the dew point of the measured gas suddenly increases during measurement]
If the dew point of the measured gas suddenly increases during the measurement of the dew point temperature described above, the amount of dew condensation that occurs on the mirror surface 10-1 suddenly increases. For this reason, the scattered light of the light irradiated to the mirror surface 10-1 from the front-end | tip part of the optical fiber 17-1 increases suddenly, and is scattered from the mirror surface 10-1 light-received via the optical fiber 17-2. The amount of light received increases rapidly. In the dew condensation detection unit 13, the difference between the upper limit value and the lower limit value of the reflected pulse light received via the optical fiber 17-2 is obtained as the intensity of the reflected pulse light, and the signal S1 corresponding to the intensity of the reflected pulse light is received. The amount is sent to the sudden rise detector 16A. The received light amount sudden rise detection unit 16A receives the signal S1 corresponding to the intensity of the reflected pulse light from the dew condensation detection unit 13, detects a sudden rise in the intensity of the reflected pulse light (a sudden rise in the dew point), and sends it to the Peltier output control unit 14 An instruction S4 for giving a reverse current is given. In the first embodiment, the received light amount sudden rise detection unit 16A corresponds to the dew point rise detection means in the present invention.

  FIG. 4 shows an example of the detection processing of the sudden increase in the intensity of the reflected pulsed light in the received light amount sudden rise detection unit 16A. The received light amount sudden rise detection unit 16A obtains the amount of scattered light received from the signal S1 corresponding to the intensity of the reflected pulse light from the dew condensation detection unit 13, and compares the amount of received scattered light with a predetermined threshold value α1. (Step 401).

  If the amount of scattered light received is greater than or equal to the threshold α1 (YES in step 401), the received light amount sudden rise detection unit 16A determines that the amount of scattered light received suddenly rises, and causes a reverse current to flow to the Peltier output control unit 14. Instruction S4 is output (step 402). The instruction S4 to flow the reverse current continues to be output to the Peltier output control unit 14 until the amount of scattered light received is equal to or less than a predetermined threshold value α2 (α2 <α1) (YES in step 403).

  In this example, the threshold value α1 is set as a sufficiently large value that the amount of scattered light received cannot be obtained by normal control based on the signal S2 from the Peltier output control unit 14. The threshold value α2 is set as a value close to the amount of scattered light received near the dew point temperature.

  FIG. 5 shows another example of the detection processing of the sudden increase in the intensity of the reflected pulsed light in the received light amount sudden rise detection unit 16A. The received light amount sudden rise detection unit 16A obtains the amount of scattered light received from the signal S1 corresponding to the intensity of the reflected pulse light from the dew condensation detection unit 13, and the amount of scattered light received and the amount of scattered light obtained a predetermined time before. The difference from the received light amount is obtained as the received light amount change amount (step 501). Then, it is checked whether the received light amount change amount is the received light amount change amount in the increasing direction or the received light amount change amount in the decreasing direction (step 502), and if it is the received light amount change amount in the increasing direction ( In step 502, a comparison is made with a predetermined threshold value β1 (step 503).

  When the amount of change in the amount of received light in the increasing direction is equal to or greater than the threshold value β1 (YES in step 503), the received light amount sudden increase detection unit 16A determines that the amount of received light of the scattered light is suddenly increased, and sends a reverse current to the Peltier output control unit 14 An instruction S4 is sent to the effect (step 504). The instruction S4 to flow the reverse current is output to the Peltier output control unit 14 until the amount of change in the amount of received light in the increasing direction is equal to or less than a predetermined threshold value β2 (β2 <β1) (YES in Step 505). Continue to be.

  In this example, the threshold value β1 is set as a sufficiently large value that the amount of change in the amount of received light in the increasing direction cannot be taken in the normal control based on the signal S2 from the Peltier output control unit 14. The threshold value β2 is set as a value close to zero.

  When the Peltier output control unit 14 receives the instruction S4 to flow the reverse current from the received light amount sudden rise detection unit 16A, the Peltier output control unit 14 interrupts the control according to the signal S1 corresponding to the intensity of the reflected pulsed light from the dew condensation detection unit 13, and A signal S2 ′ for forcibly switching the current to the cooling element 2 from the current value in the forward direction to the reverse direction is sent to the signal converter 15. The signal converter 15 supplies a current (reverse current) S3 'indicated by the control signal S2' from the Peltier output controller 14 to the thermoelectric cooling element 2 via the power supply unit 19.

  Thereby, as for the thermoelectric cooling element 2, the surface 2-1 used as the low temperature side until now is made into the high temperature side, and the surface 2-2 used as the high temperature side is made into the low temperature side, ie, a cooling surface and a heating surface Are switched, the mirror 10 is actively heated, and the mirror surface temperature rises quickly. And if the temperature of the mirror surface 10-1 becomes near dew point temperature, control signal S2 'from the Peltier output control part 14 will be switched to S2, and it will return to normal control. Thereby, compared with the case where the electric current to the conventional thermoelectric cooling element 2 is interrupted | blocked, the waiting time until dew point temperature measurement is reduced significantly.

  FIG. 6 shows a graph of the mirror surface temperature when the dew point of the measured gas suddenly increases during measurement. In the figure, characteristic I shows the change in the dew point temperature of the measured gas, characteristic II shows the change in the dew point temperature when the current to the thermoelectric cooling element is interrupted when the dew point of the measured gas suddenly rises (conventional), Characteristic III shows the change in dew point temperature (this application) when a reverse current is passed through the thermoelectric cooling element when the dew point of the gas to be measured rises rapidly. This graph also shows that the response is faster when a reverse current is passed when the dew point of the gas to be measured rises rapidly.

  In the mirror-cooled dew point meter 201 shown in FIG. 1, the tube 17 containing the light-emitting optical fiber 17-1 and the light-receiving optical fiber 17-2 is used in the sensor unit 201A. As shown in the sensor unit 201A ′, a light emitting diode 19 may be provided instead of the light-emitting side optical fiber 17-1, and a photocoupler 20 may be provided instead of the light-receiving side optical fiber 17-2.

[Embodiment 2: Regular reflection light detection method]
FIG. 8 is a schematic configuration diagram showing another embodiment of a mirror-cooled dew point meter according to the present invention. In this mirror-cooled dew point meter 202, the light-emitting side optical fiber 17-1 and the light-receiving side optical fiber 17-2 are provided symmetrically on the left and right sides of the mirror 10 rather than in the same direction. The tips of the light-emitting side optical fiber 17-1 and the light-receiving side optical fiber 17-2, which are curved in a J-shape, are directed to the mirror surface 10-1 of the mirror 10 and symmetrical with respect to the mirror surface 10-1. Is inclined at a predetermined inclination angle.

[Measurement of dew point temperature]
In this mirror-cooled dew point meter 202, the sensor unit 202A is placed in the gas to be measured. In addition, the dew condensation detection unit 13 irradiates the mirror surface 10-1 of the mirror 10 with pulsed light obliquely at a predetermined cycle from the tip of the optical fiber 17-1. If the mirror surface 10-1 is exposed to the gas to be measured and no condensation occurs on the mirror surface 10-1, almost all of the pulsed light irradiated from the tip of the optical fiber 17-1 is regularly reflected. Light is received through the optical fiber 17-2. Therefore, when no condensation occurs on the mirror surface 10-1, the intensity of the reflected pulse light (regular reflection light) received through the optical fiber 17-2 is high.

  In the dew condensation detector 13, the difference between the upper limit value and the lower limit value of the reflected pulse light received through the optical fiber 17-2 is obtained as the intensity of the reflected pulse light, and a signal S1 corresponding to the intensity of the reflected pulse light is obtained. It is sent to the Peltier output control unit 14 and the received light amount sudden drop detection unit 16B. In this case, since the intensity of the reflected pulse light is large and exceeds the threshold th2, the Peltier output control unit 14 sends a control signal S2 for increasing the current to the thermoelectric cooling element 2 to the signal conversion unit 15. Thereby, the electric current S3 supplied to the thermoelectric cooling element 2 increases, and the temperature of the cooling surface 2-1 of the thermoelectric cooling element 2 is lowered.

  When the temperature of the cooling surface 2-1 of the thermoelectric cooling element 2 is lowered, that is, the temperature of the mirror 10, the water vapor contained in the gas to be measured is condensed on the mirror surface 10-1 of the mirror 10, and the water molecules are optical fiber. Part of the pulsed light irradiated from the tip portion of 17-1 is absorbed or irregularly reflected. Thereby, the intensity | strength of the reflected pulsed light (regular reflected light) from the mirror surface 10-1 light-received via the optical fiber 17-2 reduces.

  Here, when the intensity of the reflected pulse light received through the optical fiber 17-2 is lower than the threshold th2, the Peltier output control unit 14 generates a control signal S2 for reducing the current to the thermoelectric cooling element 2 as a signal conversion unit. Send to 15. Thereby, the fall of the temperature of the cooling surface 2-1 of the thermoelectric cooling element 2 is suppressed, and generation | occurrence | production of dew condensation is suppressed. By controlling the dew condensation, the intensity of the reflected pulse light received through the optical fiber 17-2 increases. When the intensity exceeds the threshold th2, the control signal increases the current from the Peltier output control unit 14 to the thermoelectric cooling element 2. S2 is sent to the signal converter 15. By repeating this operation, the temperature of the cooling surface 2-1 of the thermoelectric cooling element 2 is adjusted so that the intensity of the reflected pulse light received through the optical fiber 17-2 is substantially equal to the threshold value th2. The adjusted temperature, that is, the temperature at which the dew condensation that has occurred on the mirror surface 10-1 has reached an equilibrium state (dew point temperature) is displayed on the dew point temperature display unit 12 as the dew point temperature.

[When the dew point of the measured gas suddenly increases during measurement]
If the dew point of the measured gas suddenly increases during the measurement of the dew point temperature described above, the amount of dew condensation that occurs on the mirror surface 10-1 suddenly increases. For this reason, the regular reflection light of the light irradiated from the front-end | tip part of the optical fiber 17-1 with respect to the mirror surface 10-1 decreases suddenly, and from the mirror surface 10-1 received via the optical fiber 17-2. The amount of specular reflection light suddenly drops. In the dew condensation detection unit 13, the difference between the upper limit value and the lower limit value of the reflected pulse light received via the optical fiber 17-2 is obtained as the intensity of the reflected pulse light, and the signal S1 corresponding to the intensity of the reflected pulse light is received. The amount is sent to the sudden drop detection unit 16B. The received light amount sudden drop detection unit 16B receives the signal S1 corresponding to the intensity of the reflected pulse light from the dew condensation detection unit 13, detects a sudden drop in the intensity of the reflected pulse light (a sudden rise in the dew point), and sends it to the Peltier output control unit 14 An instruction S4 for giving a reverse current is given. In the second embodiment, the received light amount sudden drop detection unit 16B corresponds to the dew point rise detection means in the present invention.

  FIG. 9 shows an example of processing for detecting a sudden drop in the intensity of the reflected pulsed light in the received light amount sudden drop detector 16B. The light reception amount sudden drop detection unit 16B obtains the amount of regular reflection light from the signal S1 corresponding to the intensity of the reflected pulse light from the dew condensation detection unit 13, and receives the amount of regular reflection light and a predetermined threshold value γ1. Are compared (step 601).

  When the received light amount of the specularly reflected light is equal to or less than the threshold value γ1 (YES in Step 601), the received light amount sudden drop detecting unit 16B determines that the received light amount of the regular reflected light is suddenly lowered and sends a reverse current to the Peltier output control unit 14. An instruction S4 to flow is output (step 602). The instruction S4 to flow the reverse current continues to be output to the Peltier output control unit 14 until the received light amount of the specularly reflected light is equal to or greater than a predetermined threshold value γ2 (γ2> γ1) (YES in Step 603). .

  In this example, the threshold value γ1 is set as a sufficiently small value that the amount of received regular reflected light cannot be taken in normal control based on the signal S2 from the Peltier output control unit 14. Further, the threshold value γ2 is set as a value close to the amount of regular reflection light received near the dew point temperature.

  FIG. 10 shows another example of the detection processing of the sudden drop of the intensity of the reflected pulsed light in the received light amount sudden drop detector 16B. The received light amount sudden drop detection unit 16B obtains the amount of specular reflection light from the signal S1 corresponding to the intensity of the reflected pulse light from the dew condensation detection unit 13, and receives the amount of specular reflection light and the positive amount obtained a predetermined time ago. The difference from the received light amount of the reflected light is obtained as the received light amount change amount (step 701). Then, it is checked whether the amount of received light amount change is the amount of received light amount change in the increasing direction or the amount of received light amount change in the decreasing direction (step 702). (YES in step 702), a comparison is made with a predetermined threshold value δ1 (step 703).

  If the amount of received light amount change in the decreasing direction is greater than or equal to the threshold δ1 (YES in step 703), the received light amount sudden drop detection unit 16B determines that the amount of received light of the specularly reflected light is abruptly lowered, and sends a reverse current to the Peltier output control unit 14 An instruction S4 is sent to the effect (step 704). The instruction S4 to flow the reverse current is output to the Peltier output control unit 14 until the amount of change in the amount of received light in the decreasing direction is equal to or less than a predetermined threshold value δ2 (δ2 <δ1) (YES in step 705). Continue to be.

  In this example, the threshold value δ1 is set as a sufficiently large value that the amount of change in the amount of received light in the decreasing direction cannot be taken in the normal control based on the signal S2 from the Peltier output control unit 14. The threshold value δ2 is set as a value close to zero.

  When the Peltier output control unit 14 receives an instruction S4 to flow a reverse current from the received light amount sudden drop detection unit 16B, the Peltier output control unit 14 interrupts the control according to the signal S1 corresponding to the intensity of the reflected pulse light from the dew condensation detection unit 13, and A signal S2 ′ for forcibly switching the current to the cooling element 2 from the current value in the forward direction to the reverse direction is sent to the signal converter 15. The signal conversion unit 15 supplies a current (reverse current) S3 'indicated by the control signal S2' from the Peltier output control unit 14 to the thermoelectric cooling element 2 via the power supply unit 19.

  Thereby, as for the thermoelectric cooling element 2, the surface 2-1 used as the low temperature side until now is made into the high temperature side, and the surface 2-2 used as the high temperature side is made into the low temperature side, ie, a cooling surface and a heating surface Are switched, the mirror 10 is positively heated, and the mirror surface temperature quickly drops. And if the temperature of the mirror surface 10-1 becomes near dew point temperature, control signal S2 'from the Peltier output control part 14 will be switched to S2, and it will return to normal control. Thereby, compared with the case where the electric current to the conventional thermoelectric cooling element 2 is interrupted | blocked, the waiting time until dew point temperature measurement is reduced significantly.

  Note that the current value of the current (reverse current) S3 ′ indicated by the control signal S2 ′ may be an arbitrary value set in advance, or the same value as S3 flowing immediately before the control signal S2 ′ is indicated ( However, the flow direction may be reversed) and may be determined arbitrarily.

It is a schematic block diagram which shows one Embodiment (Embodiment 1) of the mirror surface cooling-type dew point meter which concerns on this invention. It is a figure which illustrates the structure which provides the optical fiber by the side of light emission, and the optical fiber by the side of light reception in parallel in one tube. It is a figure which shows the pulsed light irradiated with respect to a detection surface back surface, and the reflected pulse light received from a detection surface back surface. It is a flowchart which shows an example of the detection process of the sudden rise of the intensity | strength of the reflected pulsed light in a received light amount sudden rise detection part. It is a flowchart which shows another example of the detection process of the sharp rise of the intensity | strength of reflected pulsed light in a received light amount sudden rise detection part. It is a graph which shows the change of mirror surface temperature when the dew point of to-be-measured gas becomes high rapidly during measurement. It is a figure which shows the modification of the sensor part of the mirror surface cooling-type dew point meter of Embodiment 1. FIG. It is a schematic block diagram which shows other embodiment (Embodiment 2) of the mirror surface cooling-type dew point meter which concerns on this invention. It is a flowchart which shows an example of the detection process of the sudden fall of the intensity | strength of the reflected pulsed light in a received light amount sudden fall detection part. It is a flowchart which shows another example of the detection process of the sudden fall of the intensity | strength of the reflected pulsed light in a received light amount sudden fall detection part. It is a figure which shows the principal part of the conventional mirror surface cooling-type dew point meter which employ | adopted the regular reflection light detection system. It is a figure which shows the principal part of the conventional mirror surface cooling-type dew point meter which employ | adopted the scattered light detection system. It is a perspective view which shows the attachment structure of the mirror and temperature detection element in the conventional mirror surface cooling dew point meter.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 2 ... Thermoelectric cooling element (Peltier element), 2-1 ... Cooling surface, 2-2 ... Heating surface, 10 ... Mirror, 10-1 ... Mirror surface, 11 ... Temperature detection element (thin film resistance thermometer), 12 ... Dew point Temperature display unit, 13 ... dew condensation detection unit, 14 ... Peltier output control unit, 15 ... signal conversion unit, 16A ... received light amount sudden rise detection unit, 16B ... received light amount sudden fall detection unit, 17 ... tube, 17-1 ... light emission side Optical fiber, 17-2 ... Optical fiber on the light receiving side, 18 ... Heat sink, 19 ... Power supply unit, 201, 202 ... Specular cooling dew point meter, 201A, 202A ... Sensor unit, 201B, 202B ... Control unit.

Claims (6)

A thermoelectric cooling element that is supplied with current in the positive direction and has one surface at a low temperature side and the other surface at a high temperature side;
A mirror that is attached to the one surface side of the thermoelectric cooling element and whose mirror surface is exposed to the gas to be measured;
A light emitting means for irradiating the mirror surface with light;
A light receiving means for receiving scattered light of the light emitted from the light emitting means to the mirror surface;
Temperature detecting means for detecting the temperature of the mirror surface;
Control means for controlling the current in the positive direction supplied to the thermoelectric cooling element so as to be in an equilibrium state where there is no increase or decrease in dew condensation generated on the mirror surface based on the amount of scattered light received by the light receiving means. In the mirror-cooled dew point meter
On the basis of the comparison of the first threshold light receiving means is predetermined and received light amount of scattered light received, the increase in the dew point of the gas to be measured from equilibrium decrease eliminates condensation generated in the mirror On the other hand, the recovery from the rise of the dew point of the measured gas to the equilibrium state is detected based on a comparison between the amount of scattered light received by the light receiving means and a predetermined second threshold value. Dew point rise detection means
When an increase in the dew point is detected, a current in the reverse direction opposite to the forward direction is forced to flow through the thermoelectric cooling element, while a recovery from the increase in the dew point is detected. And a means for returning the current supplied to the thermoelectric cooling element in the positive direction. In the mirror-cooled dew point meter according to claim 1,
The dew point rise detection means
The case where the amount of scattered light received by the light receiving means exceeds the first threshold is detected as an increase in the dew point, while the amount of scattered light received near the dew point is smaller than the first threshold. A mirror-cooled dew point meter, wherein a case where the value falls below the second threshold value set as a close value is detected as a recovery from an increase in the dew point to an equilibrium state. In the mirror-cooled dew point meter according to claim 1,
The dew point rise detection means
While the amount of change in the increasing direction of the amount of scattered light received by the light receiving means exceeds the first threshold is detected as an increase in the dew point, it is smaller than the first threshold and close to zero A specular cooling type dew point meter, wherein a case where the value falls below the second threshold value set as a value is detected as a recovery from an increase in the dew point to an equilibrium state. A thermoelectric cooling element that is supplied with current in the positive direction and has one surface at a low temperature side and the other surface at a high temperature side;
A mirror that is attached to the one surface side of the thermoelectric cooling element and whose mirror surface is exposed to the gas to be measured;
A light emitting means for irradiating the mirror surface with light;
A light receiving means for receiving specularly reflected light of the light emitted from the light emitting means to the mirror surface;
Temperature detecting means for detecting the temperature of the mirror surface;
Control means for controlling the current in the positive direction supplied to the thermoelectric cooling element so as to achieve an equilibrium state in which the increase or decrease of the dew condensation occurring on the mirror surface is eliminated based on the amount of received regular reflection light received by the light receiving means; In the mirror-cooled dew point meter with
Based on a comparison between the amount of specularly reflected light received by the light receiving means and a predetermined first threshold value, the dew point of the gas to be measured is raised from an equilibrium state where there is no increase or decrease in the dew condensation occurring on the mirror surface. Is detected, and the recovery from the rise of the dew point of the gas to be measured to the equilibrium state is performed based on a comparison between the amount of specularly reflected light received by the light receiving means and a predetermined second threshold value. Dew point rise detecting means for detecting
When an increase in the dew point is detected, a current in the reverse direction opposite to the forward direction is forced to flow through the thermoelectric cooling element, while a recovery from the increase in the dew point is detected. And a means for returning the current supplied to the thermoelectric cooling element in the positive direction. In the specular cooling type dew point meter according to claim 4,
The dew point rise detection means
When the amount of the regularly reflected light received by the light receiving means falls below the first threshold, it is detected as an increase in the dew point, while receiving the regularly reflected light near the dew point that is larger than the first threshold. A specular cooling type dew point meter, wherein a case where the value falls below the second threshold value set as a value close to the amount is detected as a recovery from an increase in the dew point to an equilibrium state. In the specular cooling type dew point meter according to claim 4,
The dew point rise detection means
A case where the amount of change in the decreasing direction of the amount of specularly reflected light received by the light receiving unit exceeds the first threshold is detected as an increase in the dew point, while being smaller than the first threshold and zero. A mirror-cooled dew point meter, wherein a case where the value falls below the second threshold value set as a close value is detected as a recovery from an increase in the dew point to an equilibrium state.

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