JP6093722B2 - Capacitive pressure sensor - Google Patents

Description

  The present invention relates to a capacitance type pressure sensor that detects a change in a diaphragm (diaphragm) that is bent under the pressure of a fluid to be measured as a change in capacitance.

  2. Description of the Related Art Conventionally, a capacitance type pressure sensor that detects a change in a diaphragm that is bent under the pressure of a fluid to be measured as a change in capacitance has been widely known. For example, a capacitive pressure sensor is used to measure a vacuum pressure during a thin film formation process in a semiconductor manufacturing apparatus or the like, and a capacitive pressure sensor for measuring the vacuum pressure is used. This is called a diaphragm gauge.

  This diaphragm vacuum gauge is a sensor that detects a change in the capacitance of a housing that has an introduction portion of a fluid to be measured and that is deflected by the pressure of the fluid to be measured guided through the introduction portion of the housing as a change in capacitance. It has a chip and a sensor case that covers the main body of the housing that houses the sensor chip.

  In this diaphragm vacuum gauge, basically, the same material as the thin film to be processed and its by-products are deposited on the diaphragm. Hereinafter, this deposited substance is called a contaminant. When this pollutant accumulates on the diaphragm, the stress caused by them causes the diaphragm to bend, resulting in a shift (zero drift) in the output signal of the sensor. Further, since the diaphragm is apparently thick due to the accumulated contaminants, the diaphragm is difficult to bend, and the change width (span) of the output signal due to the pressure application is also smaller than the change width of the original output signal.

  Therefore, in the diaphragm vacuum gauge, there is a baffle between the introduction portion and the diaphragm that prevents the deposition of contaminants contained in the measured fluid on the diaphragm by making the plate surface perpendicular to the direction of passage of the measured fluid. Is provided. Further, by heating with a heater, the temperature in the sensor case is kept at a high temperature at which no contaminants are deposited (see, for example, Patent Document 1).

  In Patent Document 1, a heater is provided in the sensor case. For example, as shown in Patent Documents 2 and 3, a heater is wound around the outer peripheral wall of the sensor case, or a slot-shaped heater is tightened from the outside. A method such as mounting is also conceivable.

  Such a diaphragm vacuum gauge is used not only in semiconductor manufacturing apparatuses but also in freeze-drying apparatuses. In the freeze-drying apparatus, heat is applied to the frozen (preliminarily frozen) product under vacuum, and the water is directly evaporated from the frozen state and removed as water vapor.

  Even when a diaphragm vacuum gauge is used in such a freeze-drying apparatus, the output to the heater is controlled so that the temperature in the sensor case becomes a predetermined temperature. In particular, liquid (water) is guided to the inside of the housing through the introduction portion to perform cleaning. This cleaning by introducing the liquid (water) is called CIP.

JP 2007-155500 A Japanese Patent Laid-Open No. 5-281073 JP 2007-002986 A JP 2002-1111011 A

  However, in the freeze-drying device, the fluid (gas) to be measured is guided through the gap of the baffle in the normal environment during the process, but in the CIP (special environment during non-process), the liquid (water) enters through the gap of the baffle. , Reach the diaphragm. Unlike the manufacturing process, CIP has an extremely large amount of liquid (water) as compared to normal pressure measurement. For this reason, the cooling history of the sensor unit is affected, the residual stress in the pressure receiving unit is affected, and problems such as zero shift occur.

  Although it is possible to reduce the adverse effects of the cooling history by adjusting the position of the baffle, CIP is not a precise process, so the shift can be suppressed as expected due to variations in the washing water temperature and washing time. Things that can't be done can happen.

  The present invention has been made to solve such problems, and the object of the present invention is to simply estimate the adverse effects of the cooling history due to cleaning and to determine whether or not it is suitable for pressure measurement. It is an object of the present invention to provide a capacitance type pressure sensor capable of knowing at an early stage.

  In order to achieve such an object, the present invention relates to a change in the capacitance of a housing having an introduction portion for a fluid to be measured and a diaphragm that is bent by receiving the pressure of the fluid to be measured guided through the introduction portion. A sensor chip that covers the body of the housing that houses the sensor chip, a heater that heats the inside of the sensor case, a temperature sensor that measures the temperature inside the sensor case, and the temperature inside the sensor case And a heater control unit that controls the output to the heater so as to reach a predetermined temperature, and the electrostatic capacity type in which the liquid is guided to the inside of the housing through the introduction unit during the control of the output to the heater In the pressure sensor, based on at least one of the transition of the temperature in the sensor case measured by the temperature sensor and the transition of the output from the heater controller to the heater Characterized in that it comprises determining state determination unit that determines whether a state suitable for measurement of pressure (claim 1).

  For example, in the present invention, the temperature in the sensor case measured by the temperature sensor is the measured temperature Tpv, the predetermined temperature is the set temperature Tsp, and the output to the heater is set so that the measured temperature Tpv is equal to the set temperature Tsp ( In the case of closed-loop control of the heater output), it is determined whether or not it is in a state suitable for pressure measurement based on the heater output when the measured temperature Tpv and the set temperature Tsp are equally controlled ( Claim 2).

  In the case of closed loop control, for example, when the remaining amount of cleaning water is large, the heater output may be higher than the normal value and may not return to the original value (or return may be slow). In this case, by comparing the heater output when the measured temperature Tpv and the set temperature Tsp are controlled to be equal (when reaching a high temperature) with the normal value (standard value), whether or not the adverse effect of the cooling history due to cleaning is large. Can be determined.

  In the present invention, the temperature in the sensor case measured by the temperature sensor is set as the measured temperature Tpv, the predetermined temperature is set as the set temperature Tsp, and the output to the heater is set so that the measured temperature Tpv becomes equal to the set temperature Tsp ( When the closed loop control of the heater output) is performed, it is determined whether or not the state is suitable for pressure measurement based on at least one of the measured temperature Tpv during cleaning and the heater output (claim 3).

  In the case of closed loop control, for example, when the temperature of the wash water is lower than normal or the amount of water is higher than normal, the measured temperature Tpv during cleaning is lower than the normal value, or the heater output is normal. It may be higher than the hour value. In this case, by comparing the measured temperature Tpv during cleaning with a normal value and by comparing the heater output during cleaning with a normal value, it is determined whether or not the adverse effect of the cooling history due to cleaning is large. Is possible.

  Further, in the present invention, when the predetermined temperature is set as the target temperature Ttp and the output to the heater (heater output) is subjected to open loop control so that the temperature in the sensor case becomes the target temperature Ttp, the temperature sensor measures. The temperature in the sensor case is acquired as the measured temperature Tpv, and it is determined whether or not it is in a state suitable for pressure measurement based on at least one of the measured temperature Tpv during cleaning and the measured temperature Tpv at the completion of cleaning. (Claim 4).

  In the case of open loop control, for example, when the temperature of the wash water is lower than normal or the amount of water is higher than normal, the measured temperature Tpv during cleaning is lower than the normal value. When the remaining amount of cleaning water is large, the measured temperature Tpv at the completion of cleaning may be lower than the normal value and may not return (or return slowly). In this case, by comparing the measured temperature Tpv during cleaning with a normal value, or by comparing the measured temperature Tpv when cleaning is completed with a normal value (target temperature Tsp), the adverse effect of the cooling history due to cleaning is reduced. It is possible to determine whether or not is large.

  According to the present invention, based on at least one of the transition of the temperature in the sensor case measured by the temperature sensor and the transition of the output from the heater control unit to the heater, it is determined whether or not the state is suitable for the pressure measurement. Since the measurement temperature Tpv and the set temperature Tsp are controlled to be equal to each other, it is determined whether or not the pressure is suitable for the measurement of the pressure based on the heater output. Based on at least one of the temperature Tpv and the heater output, it is determined whether or not it is in a state suitable for pressure measurement, or based on at least one of the measured temperature Tpv during cleaning and the measured temperature Tpv at the completion of cleaning. Whether it is suitable for pressure measurement, such as by determining whether it is suitable for pressure measurement, or simply estimating the adverse effects of cooling history due to cleaning, and whether it is suitable for pressure measurement Whether it is possible to know at an early stage. As a result, it is possible to detect a state where the probability of occurrence of a malfunction of the capacitive pressure sensor is not low, and to improve the health of the capacitive pressure sensor itself.

It is a longitudinal cross-sectional view which shows the principal part of one Embodiment of the capacitive pressure sensor which concerns on this invention. It is a top view of the baffle used for this diaphragm vacuum gauge. It is a figure which shows the principal part of the 1st example of the heating control circuit in this diaphragm vacuum gauge. It is a time chart for demonstrating operation | movement of the 1st example of a heating control circuit. It is a figure which shows the principal part of the 2nd example of the heating control circuit in this diaphragm vacuum gauge. It is a time chart for demonstrating operation | movement of the 2nd example of a heating control circuit. It is a figure which shows the principal part of the 3rd example of the heating control circuit in this diaphragm vacuum gauge. It is a time chart for demonstrating operation | movement of the 3rd example of a heating control circuit. It is a time chart when there is much remaining amount of washing water at the time of open loop control.

  Hereinafter, the present invention will be described in detail with reference to the drawings. FIG. 1 is a longitudinal sectional view showing a main part of an embodiment of a capacitive pressure sensor according to the present invention.

  This capacitive pressure sensor (diaphragm vacuum gauge) 1 includes a housing 10, a pedestal plate 20 accommodated in the housing 10, and a sensor chip 30 that is also accommodated in the housing 10 and joined to the pedestal plate 20. And an electrode lead portion 40 that is directly attached to the housing 10 and electrically connects the inside and outside of the housing 10.

  The pedestal plate 20 includes a first pedestal plate 21 and a second pedestal plate 22. The pedestal plate 20 is spaced from the housing 10 and is supported by the housing 10 only through the support diaphragm 50. .

  The housing 10 includes a lower housing 11, an upper housing 12, and a cover 13. The lower housing 11, the upper housing 12, and the cover 13 are made of Inconel, which is a corrosion-resistant metal, and are joined by welding.

  The lower edging 11 has a shape in which cylindrical bodies having different diameters are connected, the large diameter portion 11a has a joint portion with the support diaphragm 50, and the small diameter portion 11b forms an introduction portion 10A into which a fluid to be measured flows. Yes.

  The upper housing 12 has a substantially cylindrical shape, and forms an independent vacuum reference vacuum chamber 10 </ b> B in the housing 10 via the cover 13, the support diaphragm 50, the pedestal plate 20, and the sensor chip 30. The reference vacuum chamber 10B is provided with a gas adsorbing material called a getter (not shown) to maintain the degree of vacuum.

  Further, the cover 13 is made of a circular plate, and an electrode lead insertion hole 13a is formed at a predetermined position of the cover 13, and the electrode lead portion 40 is embedded through a hermetic seal 60, and the sealing performance of this portion is ensured. Has been.

  On the other hand, the support diaphragm 50 is made of an Inconel thin plate having an outer shape matched to the shape of the housing 10, and is sandwiched between the first pedestal plate 21 and the second pedestal plate 22 and its outer peripheral portion ( The peripheral edge) is sandwiched between the lower housing 11 and the upper housing 12 and joined by welding or the like.

  The thickness of the support diaphragm 50 is, for example, several tens of microns in the case of the present embodiment, and is sufficiently thinner than the pedestal plates 21 and 22. Further, a large-diameter hole 50 a that forms a slit-like space (cavity) 20 </ b> A is formed between the first pedestal plate 21 and the second pedestal plate 22 in the central portion of the support diaphragm 50.

  The first pedestal plate 21 and the second pedestal plate 22 are made of sapphire, which is a single crystal of aluminum oxide, and the first pedestal plate 21 is spaced from the inner surface of the housing 10 on the upper surface of the support diaphragm 50. The second pedestal plate 22 is bonded to the lower surface of the support diaphragm 50 while being separated from the inner surface of the housing 10.

  The first pedestal plate 21 is formed with an introduction hole 21a for a fluid to be measured that communicates with a slit-shaped space (cavity) 20A at the center thereof. The second pedestal plate 22 has a slit-like shape. A plurality of (four in this example) lead-out holes 22a are formed in the sensor chip 30 and communicated with the space (cavity) 20A.

  Each pedestal plate 21, 22 is sufficiently thick as described above with respect to the thickness of the support diaphragm 50, and has a structure in which the support diaphragm 50 is sandwiched between both pedestal plates 21, 22. ing. This prevents this portion from warping due to thermal stress generated by the difference in thermal expansion coefficient between the support diaphragm 50 and the base plate 20.

  A sensor chip 30 having a rectangular shape in a top view made of sapphire, which is a single crystal of aluminum oxide, is bonded to the second pedestal plate 22 via an aluminum oxide-based bonding material. The sensor chip 30 joining method is described in detail in Patent Document 4 and will not be described here.

  The sensor chip 30 has a size of 1 cm square or less in a top view, a spacer 31 made of a rectangular thin plate, a sensor diaphragm 32 that is bonded to the spacer 31 and generates a strain in response to application of pressure, and a sensor diaphragm. The sensor pedestal 33 is formed so as to form a vacuum capacity chamber (reference chamber) 30A. The vacuum capacity chamber 30 </ b> A and the reference vacuum chamber 10 </ b> B maintain the same degree of vacuum through a communication hole (not shown) drilled at an appropriate position of the sensor base 32.

  The spacer 31, the sensor diaphragm 32, and the sensor pedestal 33 are joined together by so-called direct joining to constitute an integrated sensor chip 30. The sensor diaphragm 32 which is a component of the sensor chip 30 corresponds to the diaphragm referred to in the present invention.

  Further, in the capacity chamber 30A of the sensor chip 30, a fixed electrode (not shown) made of a conductor such as gold or platinum is formed on the inner surface of the sensor pedestal 33, and the inner surface of the sensor diaphragm 32 facing the fixed electrode. A movable electrode (not shown) made of a conductor such as gold or platinum is formed on the (back surface). Further, contact pads 35 and 36 made of gold or platinum are formed on the upper surface of the sensor chip 30, and the fixed electrode and the movable electrode in the capacity chamber 30A are connected to the contact pads 35 and 36 by wiring (not shown).

  On the other hand, the electrode lead portion 40 includes an electrode lead pin 41 and a metal shield 42. The electrode lead pin 41 is embedded in the metal shield 42 with a hermetic seal 43 made of an insulating material such as glass, An airtight state is maintained between both end portions of the lead pin 41. One end of the electrode lead pin 41 is exposed to the outside of the housing 10 so that the output of the diaphragm vacuum gauge 1 is transmitted to an external signal processing unit through a wiring (not shown). A hermetic seal 60 is interposed between the shield 42 and the cover 13 as described above. Further, conductive contact springs 45 and 46 are connected to the other end of the electrode lead pin 41.

  Even if the support diaphragm 50 is slightly changed due to a sudden pressure increase caused by a sudden flow of the fluid to be measured from the introduction portion 10A, the contact springs 45 and 46 have a biasing force of the contact springs 45 and 46 of the sensor chip 30. It is soft enough not to affect the measurement accuracy.

  In this diaphragm vacuum gauge 1, between the sensor diaphragm 32 of the sensor chip 30 and the introduction part 10A, the plate surface is orthogonal to the measurement fluid passage direction F at the outlet of the measurement fluid from the introduction part 10A. Thus, a first baffle 70 made of Inconel is disposed.

  FIG. 2 shows a plan view of the baffle 70. The baffle 70 has tabs 70 a formed at predetermined angular intervals on the outer periphery thereof, and the fluid to be measured passes through the gap 70 b between the tabs 70 a and is sent to the sensor diaphragm 32.

  Further, a second baffle 71 is provided in the middle of the conduit of the introduction portion 10 </ b> A for the purpose of preventing liquid (water) from entering the housing 10.

  Further, in the diaphragm vacuum gauge 1, the housing 10 is provided inside the cylindrical sensor case 80 so that the introduction portion (pressure guiding tube) 10A of the fluid to be measured is drawn out (downward). The upper part of the sensor case 80 is closed with a lid 80a that forms a part of the sensor case 80, that is, the body of the housing 10 that houses the sensor chip 30 is covered with the sensor case 80, and this sensor Through the lead-out hole (not shown) provided in the lid 80a of the case 80, the wiring connected to the electrode lead pin 41 is guided to an external signal processing unit.

  Further, in this diaphragm vacuum gauge 1, a heater 90 is provided so as to surround the outer peripheral wall of the sensor case 80 and the portion where the second baffle 71 of the introducing portion 10A is located. The sensor case 80 including the heater 90 is covered with a heat insulating material 100.

  On the other hand, the diaphragm vacuum gauge 1 is provided with a heating control circuit 400 that controls the heating of the heater 90. The heating control circuit 400 uses a measured value (measured temperature) Tpv of the temperature in the sensor case 80 and a predetermined temperature (set temperature Tsp for feedback control, target temperature Ttp for open loop control). As an input, the output to the heater 90 for heating (heater output) is controlled.

  In this example, the temperature sensor 14 is provided outside the housing 10, and the sensor temperature detected by the temperature sensor 14 is sent to the heating control circuit 400 as the measured temperature Tpv in the sensor case 80. It is said that.

  In the heating control circuit 400, the set temperature Tsp (target temperature Ttp) is set to 125 ° C., for example. The heating control circuit 400 is realized by hardware including a processor and a storage device, and a program that realizes various functions in cooperation with the hardware.

  Further, the diaphragm vacuum gauge 1 is used in a freeze-drying apparatus, and a liquid (water) is introduced into the housing 10 through the introduction portion 10A periodically while controlling the heater output to the heater 90 for heating by the heating control circuit 400. Cleaning (CIP) is performed.

[First example of heating control circuit (Embodiment 1): Closed loop control, when the remaining amount of cleaning water is large]
The principal part of the 1st example of the heating control circuit 400 is shown in FIG. The heating control circuit 400 (400A) includes a closed loop temperature control unit 401A, a state determination unit 402A, and an alarm signal transmission unit 403A.

  The closed loop temperature control unit 401A performs closed loop control of the heater output Pout to the heater 90 so that the measured temperature Tpv from the temperature sensor 14 becomes equal to the set temperature Tsp. In this example, feedback control such as PID control is adopted as closed loop control.

  The state determination unit 402A receives the measured temperature Tpv from the temperature sensor 14, the heater output Pout from the closed loop temperature control unit 401A, and the set temperature Tsp, and the measured temperature Tpv and the set temperature Tsp are controlled to be equal. It is determined whether the diaphragm vacuum gauge 1 is in a state suitable for pressure measurement based on the heater output Pout.

  In the state determination unit 402A, the normal value (standard value) of the heater output Pout when the measured temperature Tpv and the set temperature Tsp are controlled to be equal is set as Pst, which is suitable for pressure measurement. A threshold value used for determining whether or not is α is set.

  The alarm signal transmission unit 403A receives the determination result as to whether or not the state is suitable for pressure measurement from the state determination unit 402A, and transmits the determination result to a higher-level device (not shown).

  Hereinafter, the operation of the heating control circuit 400A will be specifically described with reference to the time chart shown in FIG. In the time chart shown in FIG. 4, FIG. 4 (a) shows a change in the measured temperature Tpv, and FIG. 4 (b) shows a change in the heater output Pout.

  The closed loop temperature control unit 401A controls the heater output Pout to the heater 90 (closed loop control) so that the measured temperature Tpv from the temperature sensor 14 becomes equal to the set temperature Tsp. During the control of the heater output Pout to the heater 90, CIP (cleaning) is periodically performed.

  Since the measured temperature Tpv decreases during the CIP, the closed loop temperature control unit 401A increases the heater output Pout so as to return the decreased measured temperature Tpv to the set temperature Tsp.

  The example shown in FIG. 4 shows a case where the CIP is normally performed in the periods T1, T2, and T3, but the remaining amount of the cleaning water after the cleaning in the period T3 is large. In this case, even if the measured temperature Tpv is equal to the set temperature Tsp, the heater output Pout is higher than the normal value (normal value (standard value) Pst) and does not return to the original value (or the return is slow).

  The state determination unit 402A monitors the heater output Pout when the measured temperature Tpv and the set temperature Tsp are controlled to be equal, and the heater output Pout is measured when the measured temperature Tpv and the set temperature Tsp are controlled equally. When the threshold value α is higher than the normal value (standard value) Pst, it is determined that there is a possibility that the cleaning water may enter the inside of the sensor and cause a zero point shift, and it is determined that the state is not suitable for pressure measurement. The result is sent to the alarm signal transmission unit 403A. The alarm signal transmission unit 403A transmits the determination result from the state determination unit 402A to the host device.

  In this manner, in the heating control circuit 400A, the heater output Pout when the measured temperature Tpv and the set temperature Tsp are controlled to be equal (at the time of reaching high temperature) is processed with data (difference from the normal value (standard value) Pst). ) Can be easily estimated to determine the adverse effect of the cooling history due to CIP, so that it is possible to know at an early stage whether the pressure is suitable for measurement. As a result, it is possible to detect a state in which the probability of occurrence of the malfunction of the diaphragm vacuum gauge 1 is not low and improve the health of the diaphragm vacuum gauge 1 itself.

[Second Example of Heating Control Circuit (Embodiment 2): Closed Loop Control, When Washing Water Temperature is Lower than Normal or Water Volume is More Than Normal]
FIG. 5 shows a main part of a second example of the heating control circuit 400. The heating control circuit 400 (400B) of the second example includes a closed loop temperature control unit 401B, a state determination unit 402B, and an alarm signal transmission unit 403B.

  In the heating control circuit 400B, the functions of the closed loop temperature control unit 401B and the alarm signal transmitting unit 403B are the same as those of the closed loop temperature control unit 401A and the alarm signal transmitting unit 403A in the heating control circuit 400A of the first example. . In the heating control circuit 400B of the second example, only the function of the state determination unit 402B is different from the state determination unit 402A in the heating control circuit 400A of the first example.

  In this heating control circuit 400B, the normal value (standard value) of the heater output Pout when the measured temperature Tpv and the set temperature Tsp are controlled to be equal is set as Pst in the state determination unit 402B. The first threshold value used for determining whether or not the state is suitable for measurement is set as β, and the second threshold value is set as γ.

  Hereinafter, the operation of the heating control circuit 400B will be specifically described with reference to a time chart shown in FIG. In the time chart shown in FIG. 6, FIG. 6 (a) shows a change in the measured temperature Tpv, and FIG. 6 (b) shows a change in the heater output Pout.

  The closed loop temperature control unit 401B controls the heater output Pout to the heater 90 (closed loop control) so that the measured temperature Tpv from the temperature sensor 14 becomes equal to the set temperature Tsp. During the control of the heater output Pout to the heater 90, CIP (cleaning) is periodically performed.

  Since the measured temperature Tpv decreases during the CIP, the closed loop temperature control unit 401B increases the heater output Pout so as to return the decreased measured temperature Tpv to the set temperature Tsp.

  In the example shown in FIG. 6, CIP is normally performed in the periods T1 and T2, but CIP is not normally performed in the period T3, and the temperature of the washing water is lower than normal or the amount of water is normal. It shows the case of more than. In this case, in the CIP of the period T3, the measured temperature Tpv is lower than the normal value, and the heater output Pout is higher than the normal value.

  The state determination unit 402B monitors the measured temperature Tpv and heater output Pout during CIP, the measured temperature Tpv during CIP is lower than the set temperature Tsp by a threshold value β or more, and the heater output Pout during CIP is set to the measured temperature Tpv. When the temperature Tsp is equally controlled and the normal value (standard value) Pst is higher than the threshold value γ, it is determined that there is a possibility that the cleaning water may enter the inside of the sensor and cause a zero point shift. The determination result indicating that the state is not suitable for the measurement is sent to the alarm signal transmitting unit 403B. The alarm signal transmission unit 403B transmits the determination result from the state determination unit 402B to the host device.

  The threshold value β in the state determination unit 402B is determined as a value where Tsp−β is smaller than the normal value of the measured temperature Tpv during CIP. Thereby, the normal value of the measured temperature Tpv during CIP is substantially compared with the measured temperature Tpv during CIP. The threshold value γ in the state determination unit 402B is determined as a value at which Pst + γ is larger than the normal value of the heater output Pout during CIP. Thereby, the normal value of the heater output Pout during CIP is substantially compared with the heater output Pout during CIP.

  In this way, in the heating control circuit 400B, the measured temperature Tpv and the heater output Pout in the CIP are processed (detecting a difference from the normal value), thereby simplifying the adverse effects of the cooling history due to the CIP. It is possible to estimate at an early stage whether or not the state is suitable for pressure measurement. As a result, it is possible to detect a state in which the probability of occurrence of the malfunction of the diaphragm vacuum gauge 1 is not low and improve the health of the diaphragm vacuum gauge 1 itself.

  In this example, both the measured temperature Tpv and the heater output Pout in CIP are monitored, but either one may be monitored. That is, only the measured temperature Tpv in CIP is monitored, and when this measured temperature Tpv is lower than the set temperature Tsp by a threshold value β or more, a determination result indicating that the pressure is not suitable is measured to the alarm signal transmitting unit 403B. Only the heater output Pout in the CIP may be monitored, and if this heater output Pout is higher than the normal value (standard value) Pst by a threshold γ or more, it is determined that the state is not suitable for pressure measurement. The result may be sent to the alarm signal transmission unit 403B.

[Third example of heating control circuit (Embodiment 3): Open loop control, when the temperature of the washing water is lower than normal, or when the amount of water is higher than normal)
FIG. 7 shows a main part of a third example of the heating control circuit 400. The heating control circuit 400 (400C) of the third example includes an open loop temperature control unit 401C, a state determination unit 402C, and an alarm signal transmission unit 403C.

  In the heating control circuit 400C, the open loop temperature control unit 401C performs open loop control of the heater output Pout to the heater 90 so that the temperature in the sensor case 80 becomes the target temperature Ttp. As the open loop control in the heating control circuit 400C, feedforward control is adopted.

  The state determination unit 402C receives the measured temperature Tpv from the temperature sensor 14, the heater output Pout from the open loop temperature control unit 401C, and the target temperature Ttp as inputs, and sets the measured temperature Tpv during CIP and the measured temperature Tpv when CIP is completed. Based on this, it is determined whether the diaphragm vacuum gauge 1 is in a state suitable for pressure measurement.

  In the state determination unit 402C, the first threshold value used for determining whether or not the state is suitable for pressure measurement is set as σ, and the second threshold value is set as δ.

  The alarm signal transmission unit 403C receives the determination result from the state determination unit 402C as to whether or not the state is suitable for pressure measurement, and transmits the determination result to a higher-level device (not shown).

  Hereinafter, the operation of the heating control circuit 400C will be specifically described with reference to a time chart shown in FIG. In the time chart shown in FIG. 8, FIG. 8A shows a change in the measured temperature Tpv, and FIG. 8B shows a change in the heater output Pout.

  The open loop temperature control unit 401C controls the heater output Pout to the heater 90 (open loop control) so that the temperature in the sensor case 80 becomes the target temperature Ttp. CIP is periodically performed during control of the heater output Pout to the heater 90.

  Since the temperature in the sensor case 80 decreases during the CIP, the open loop temperature control unit 401C increases the heater output Pout so that the temperature in the sensor case 80 becomes the target temperature Ttp.

  In the example shown in FIG. 8, the CIP is normally performed in the periods T1 and T2, but the CIP is not normally performed in the period T3, and the temperature of the washing water is lower than normal or the amount of water is normal. It shows the case of more than. In this case, in the CIP in the period T3, the measured temperature Tpv is lower than the normal value. Further, even when CIP in the period T3 is completed, the measured temperature Tpv is lower than the normal value (target temperature Ttp) and does not return (or return is slow).

  The state determination unit 402C monitors the measured temperature Tpv during CIP and when CIP is completed, the measured temperature Tpv during CIP is lower than the target temperature Ttp by the threshold σ, and the measured temperature Tpv when CIP is completed is lower than the target temperature Ttp. If the threshold value δ is lower than the threshold value δ, it is determined that there is a possibility that the cleaning water may enter the inside of the sensor and cause a zero point shift, and a determination result indicating that the pressure is not suitable is measured to the alarm signal transmission unit 403C. send. The alarm signal transmission unit 403C transmits the determination result from the state determination unit 402C to the host device.

  The threshold σ in the state determination unit 402C is determined as a value where Ttp−σ is smaller than the normal value of the measured temperature Tpv during CIP. Thereby, the normal value of the measured temperature Tpv during CIP is substantially compared with the measured temperature Tpv during CIP.

  In this way, in this heating control circuit 400C, the measured temperature Tpv during CIP and the measured temperature Tpv at the completion of CIP are data-processed (detection of a difference from the normal value), thereby adversely affecting the cooling history due to CIP. It is possible to easily estimate whether or not it is in a state suitable for pressure measurement. As a result, it is possible to detect a state in which the probability of occurrence of the malfunction of the diaphragm vacuum gauge 1 is not low and improve the health of the diaphragm vacuum gauge 1 itself.

  In this example, both the measured temperature Tpv during CIP and the measured temperature Tpv at the completion of CIP are monitored, but either one may be monitored. That is, only the measured temperature Tpv in the CIP is monitored, and when this measured temperature Tpv is lower than the target temperature Ttp by the threshold σ, a determination result indicating that the pressure is not suitable is measured to the alarm signal transmitting unit 403C. Only the measured temperature Tpv at the completion of CIP may be monitored, and if this measured temperature Tpv is lower than the target temperature Ttp by a threshold value δ or more, an alarm is sent indicating that the pressure is not suitable for measurement. You may make it send to the equal signal transmission part 403C.

  Also, both the measured temperature Tpv during CIP and the measured temperature Tpv at the completion of CIP are monitored, and if either one falls below a threshold value determined for the target temperature Ttp, it is not in a state suitable for pressure measurement. The determination result may be sent to the alarm signal transmission unit 403C. By doing so, it is possible to determine when the remaining amount of cleaning water is large. For example, as shown in FIG. 9, when the CIP is normally performed in the periods T1, T2, and T3, but the remaining amount of cleaning water after the cleaning in the period T3 is large, the heater output is output when the CIP cleaning is completed. Even if Pout is returned to the normal value (standard value) Pst, the measured temperature Tpv does not reach the target temperature Ttp. In such a case, by comparing the measured temperature Tpv at the time of completion of CIP and the target temperature Ttp using the threshold value δ, it can be determined whether or not it is in a state suitable for pressure measurement.

[Extension of the embodiment]
The present invention has been described above with reference to the embodiment. However, the present invention is not limited to the above embodiment. Various changes that can be understood by those skilled in the art can be made to the configuration and details of the present invention within the scope of the technical idea of the present invention.

  DESCRIPTION OF SYMBOLS 1 ... Diaphragm gauge (capacitance type pressure sensor), 10 ... Housing, 10A ... Introduction part, 11 ... Lower housing, 12 ... Upper housing, 13 ... Cover, 14 ... Temperature sensor, 20 ... Base plate, 21 ... No. 1 pedestal plate, 22 ... second pedestal plate, 30 ... sensor chip, 31 ... sensor plate, 32 ... sensor diaphragm, 33 ... sensor pedestal, 50 ... support diaphragm, 70, 71 ... baffle, 80 ... sensor case, 90 ... Heating heater, 100 ... Insulating material, 400 (400A to 400C) ... Heating control circuit, 401A, 401B ... Closed loop temperature control unit, 401C ... Open loop temperature control unit, 402A to 402C ... State determination unit, 403A to 403C ... Alarm signal transmission unit.

Claims (4)

A housing having an introduction section for a fluid to be measured;
A sensor chip that detects a change in the diaphragm that is deflected by receiving the pressure of the fluid to be measured guided through the introduction unit, as a change in capacitance;
A sensor case that covers the body of the housing that houses the sensor chip;
A heater for heating the inside of the sensor case;
A temperature sensor for measuring the temperature in the sensor case;
A heater control unit that controls the output to the heater so that the temperature in the sensor case becomes a predetermined temperature;
In the capacitive pressure sensor in which cleaning is performed by introducing a liquid into the housing through the introduction portion during control of the output to the heater,
A state in which it is determined whether or not it is a state suitable for pressure measurement based on at least one of a transition in temperature in the sensor case measured by the temperature sensor and a transition in output from the heater control unit to the heater A capacitance type pressure sensor comprising a determination unit. The capacitive pressure sensor according to claim 1,
The heater control unit
The temperature in the sensor case measured by the temperature sensor is a measured temperature Tpv, the predetermined temperature is a set temperature Tsp, and the output to the heater is closed loop so that the measured temperature Tpv is equal to the set temperature Tsp. Control
The state determination unit
It is determined whether or not it is in a state suitable for pressure measurement based on an output to the heater from the heater control unit when the measured temperature Tpv and the set temperature Tsp are controlled to be equal. Capacitance type pressure sensor. The capacitive pressure sensor according to claim 1,
The heater control unit
The temperature in the sensor case measured by the temperature sensor is a measured temperature Tpv, the predetermined temperature is a set temperature Tsp, and the output to the heater is closed loop so that the measured temperature Tpv is equal to the set temperature Tsp. Control
The state determination unit
It is determined whether or not it is in a state suitable for pressure measurement based on at least one of the measured temperature Tpv during the cleaning and the output from the heater control unit to the heater. Pressure sensor. The capacitive pressure sensor according to claim 1,
The heater control unit
The predetermined temperature is set as the target temperature Ttp, and the output to the heater is subjected to open loop control so that the temperature in the sensor case becomes the target temperature Ttp,
The state determination unit
The temperature in the sensor case measured by the temperature sensor is acquired as a measured temperature Tpv, and is in a state suitable for pressure measurement based on at least one of the measured temperature Tpv during the cleaning and the measured temperature Tpv when the cleaning is completed. A capacitance type pressure sensor characterized by determining whether or not.

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