Patent Application
20100139389
The present invention relates to a flow sensor that is used in flow meters, to a sensor temperature controlling method, and to an abnormality recovering method.
The flow speed sensor having the housing structure disclosed in Japanese Unexamined Patent Application Publication S60-220864 (“JP '864”) has a sensor chip built into a package that is layered together with a flat base member. In the base member, a flat trench-shaped flow path is provided in the sensor chip mounting surface of the base member, where the inlet and outlet of the flow path are formed in the opposite end surfaces of the package. Additionally, the sensor chip electrodes are connected electrically, through wire bonding or solder bumps, or the like, to electrodes that are formed integrally with the base member.
The thermal flow meter disclosed in Japanese Unexamined Patent Application Publication 2002-168669 (“JP '669”) has a structure wherein a substrate whereon a sensor chip is mounted is tightly adhered to the inner wall of a pipe-shaped body. A trench is formed parallel to the mounting surface in the sensor chip or the substrate, and a sensor flow path is formed by a main flow path and the trench in the inside of the body.
Additionally, the flow sensor disclosed in Japanese Unexamined Patent Application Publication 2006-118929 (“JP '929”) has a flow path formed on a sensor surface of a sensor chip through the provision of a sensor chip in a square hole in a base, and through the provision of a cover through disposition of a wiring substrate that is provided with a slit, or through the disposition of two wiring substrates that are facing each other across a gap. Note that the sensor chip electrodes and electrode pads for connecting to external circuitry, of the wiring substrate, are connected together using solder or an electrically conductive adhesive agent, or the like.
Furthermore, a gas sensor having a ceramic heater structure is disclosed in Patent Reference 4. The gas sensor as set forth in Japanese Unexamined Patent Application Publication 2004-327255 (“JP '255”) and is provided with a ceramic heater structure is structured through the provision of a heater portion having a heat-producing unit pattern built into the inside of an insulating ceramic unit, inside a ceramic substrate.
In the conventional sensor, when there is no flow in the gas to be measured, and the gas is in the flow path, there is a problem in that condensation or moisture will adhere to the sensor chip surface, causing the output of the sensor to be unstable. The sensor as set forth in JP '255 heats the sensor detecting portion up to the temperature required for measurement in the sensor structure (at least 300° C.), but cannot perform temperature control in regards to adhered condensation or moisture.
The present invention is to solve the problem areas such as set forth above, and the object thereof is to provide a sensor, a temperature controlling method, and an aberration recovering method capable of preventing the adhesion of condensation or moisture to the sensor surface, and capable of increasing the sensor accuracy through controlling the ambient temperature so as to be uniform, even when there is no flow of the gas to be measured, and it is within the flow path.
The sensor as set forth in the present invention comprises a sensor chip for detecting a physical quantity of a gas to be measured, and a package, structured by stacking a plurality of substrates, and having a flow path within the package wherein the gas to be measured is exposed to the sensor surface within the sensor chip.
In a sensor according to the present invention, the package is structured from stacking together a first flat substrate wherein a hole portion for housing a sensor chip is formed; a second flat substrate wherein hole portions are formed to form the flow path within the package for guiding, to the sensor chip, the gas to be measured; and a third flat substrate wherein hole portions are formed, on the same end surface of the package, for an inlet and outlet of the gas to be measured.
In a sensor according to the present invention, the package is structured by stacking, on a fourth flat substrate, a fifth flat substrate wherein a hole portion is formed to become a flow path within the package, for guiding the gas to be measured to the sensor chip, and a sixth flat substrate, having a step in an opening portion so that the sensor chip is fitted to the step so that the sensor surface will be on the flow path side within the package, so that the back surface of the sensor chip will be coplanar with the package end surface, and so that the opening portion that is not covered by the sensor chip will form hole portions that will be the inlet and the outlet for the gas to be measured, connected to the flow path within the package.
In the temperature controlling method of the sensor according to the present invention, the sensor set forth above is provided with a step for detecting the ambient temperature of the sensor chip in the package, and a step for controlling the temperature within the package through controlling the magnitude of the electric current to a heater pattern in accordance with the ambient temperature of the sensor chip.
In the aberration recovering method for a sensor as set forth in the present invention, the sensor set forth above is provided with a step for determining that there is condensation on the surface of the sensor, based on an output value that is obtained from the sensor chip within the package, and, when it has been determined that there is condensation on the sensor chip, a step for heating, for a predetermined time interval to a temperature that is higher than the normal set temperature, the package by controlling the magnitude of the electric current to the heater pattern, and a step for ensuring that the condensation has been eliminated, based on an output value that is obtained from the sensor chip that has returned to the set temperature after a predetermined amount of time has elapsed.
Given the present invention, a heater pattern is provided on at least one of the substrates, and thus there is the effect of being able to set a desired temperature within the package.
Given the present invention, the ambient temperature of the sensor chip within the package is detected, and the temperature within the package is controlled by controlling the magnitude of the electric current to a heater pattern in accordance with the ambient temperature of the sensor chip, and thus there is the effect of being able to increase the sensor accuracy by controlling the surrounding of the sensor to a predetermined temperature.
Given the present invention, there is a step for determining that there is condensation on the surface of the sensor, based on an output value that is obtained from the sensor chip within the package, and, when it has been determined that there is condensation on the sensor chip, a step for heating, for a predetermined time interval to a temperature that is higher than the normal set temperature, the package by controlling the magnitude of the electric current to the heater pattern, and a step for ensuring that the condensation has been eliminated, based on an output value that is obtained from the sensor chip that has returned to the set temperature after a predetermined amount of time has elapsed, and thus there is the effect of being able to recover from a condensation anomaly, through a simple method, even if there is condensation on the surface of the sensor.
s A-7C are diagrams for explaining the sealed state in a conventional flow sensor.
In order to explain the present invention in greater detail, a most preferred form for carrying out the invention will be explained below according to the appended drawings.
Note that the substrates 2a through 2c that structure the package of the flow sensor 1 are flat substrates wherein there are no indented portions or raised portions formed for fitting together with the substrates that are above and below when stacking the substrates vertically, and should have a flat end surfaces to the degree wherein each of the substrates may be stacked together without modification. Additionally, when ceramic substrates are used, the flat end surfaces of the substrates in the present invention need not be absolutely flat end surfaces, but rather include also those wherein some degree of surface roughness occurs through sintering of green sheets.
Additionally, this flow sensor 1 may be mounted while maintaining the tight seal of the flow path through interposing seal rings 4, disposed at the inlet 3a and the outlet 3b of the flow path within the package, between the package surface (the substrate 2c surface) and the attachment surface on the side for the mounting.
Here the following effects (A) through (C) can be obtained through having the flat substrates that structure the package be the ceramic substrates 2a, 2b, and 2c:
It is possible to maintain the electrical insulation within the package even if, for some reason, the electrical connection in the sensor surface (the detection surface) of the sensor chip were to become detached. For example, wire bonding is used in the electrical connection to the sensor surface in a thermal flow sensor, where the wire bonds are exposed to the flow path within the package. Consequently, if the package were made out of a metal, such as stainless steel, and a wire bond were to become detached for some reason, then it would not be possible to maintain the electrical insulation because a short would occur within the package. In contrast, in the flow sensor 1 according to the first form of embodiment, the package is structured by layering ceramic substrates, which are electrically insulated. Because of this, even if a wire bond on the sensor surface were to become detached, the electrical insulation could still be maintained, preventing the occurrence of secondary failures due to the short. Note that the same effect could still be obtained even if the flat substrates were structured from resin.
The thermal compatibility with the sensor chip can be improved through the use of ceramic substrates as the flat substrates for structuring the package. For example, the sensor chip in a thermal flow sensor is structured from single crystal silicon. Because of this, if the package were a metal, such as stainless steel, the sensor chip would break, or there might be differences in the sensor characteristics, due to differences in coefficients of thermal expansion if a thermal load were applied. In contrast, in the flow sensor according to the first form of embodiment, a ceramic having a coefficient of thermal expansion near to that of the sensor chip is used in the flat substrates for the package, making it possible to suppress the occurrence of problems caused by differences in the coefficients of thermal expansion. Note that there is no limitation to being a ceramic substrate, but rather the same effect can be obtained even when structuring from a resin flat substrate, insofar as the coefficient of thermal expansion is near to that of ceramic.
Structuring the package from ceramic substrates can achieve an improvement in the mass production efficiency. For example, if the package were made from a metal such as stainless steel, then it would be necessary to produce each component of the package through cutting, machining, etching, etc. of the metal. In contrast, in the present invention, manufacturing can be performed through stacking and sintering, as a batch, a plurality of ceramic green sheets, and then, after the sensor chips have been inserted, dividing into the individual packages. Because of this, it is possible to make a substantial improvement in mass production efficiency when compared to the case of fabricating packages out of a metal such as stainless steel. Furthermore, batch fabrication manufacturing is enabled, making an improvement in mass production efficiency possible, even in the case wherein resin substrates are used for the flat substrates that structure the package.
When a metal with a melting point that is higher than that of solder or an electrically conductive adhesive is used as the electrically conductive bonding material 20, then when connecting the package to another substrate or when mounting electrical components onto the package end surface, one can anticipate the effect of suppressing any reduction in useful life of the connecting portions within the package that would be caused by the application of temperatures near to the melting point or glass transition point of the solder or electrically conductive adhesive within the package. Note that the electrically conductive bonding material 20 according to the present invention is not limited to the high melting point material set forth above, but rather solder, or the like, that has been used conventionally may also be used.
As illustrated in
For example, as illustrated in
Additionally, in the conventional sensor 100B illustrated in
On the other hand, with the flow sensor 1 according to an embodiment, not only is it possible to mount through sealing the surface of the flow path inlet 3a and outlet 3b, but also it is possible to form the required electrical circuits on the sensor structure using the other package surfaces. For example, it is possible to mount all of the electrical components of the electrical circuits, which have conventionally been mounted on a substrate, or the like, that has been electrically connected through a lead from the base substrate or the header, such as connectors 7a for connecting electrical signals to the outside or other electrical elements 8, or the like, instead onto the package surface (substrate 2a surface) that is opposite from the surface that is provided with the inlet 3a and the outlet 3b for the flow path, as illustrated in
Concentrating the electrical circuits on one end surface of the package in this way enables a substantial miniaturization in the size of the sensor. Furthermore, because the base substrate and the header are unnecessary, it is possible to reduce the number of components, which is beneficial also in reducing cost.
Note that while in
As is clear from
Additionally, as is illustrated in
The sealed state of the flow sensor in the embodiment will be explained next. First, for comparison, the sealed state will be explained using, as an example, the conventional flow sensor disclosed in JP '699.
As illustrated in
In contrast, in the flow sensor 1, the end surface wherein the inlet and outlet of the flow path of the package are formed at is a flat surface, and thus no position that can cause leaking is formed even when sealing the inlet and outlet of the flow paths within the package using seal rings 4. In this way, in the flow sensor 1 according to an embodiment, not only can the seal be performed easily, but it is possible to stabilize the characteristics of sensor pressure and flow because it is possible to reduce the seal leakage.
Additionally, the flow sensor 1 according to the embodiment may be structured as set forth below.
The package of the flow sensor illustrated in
The same effects as in the structure illustrated in
Furthermore, even in this structure, the inlet 3a and the outlet 3b of the flow path within the package are formed on the same flat end surface, in the same manner as with the structure illustrated in
Additionally, when a sensor chip having about the same width as the flow path is used as the sensor chip 5, the package may be structured as set forth below.
Additionally, the flow path within the package is both sealed and positioned/secured through filling in the seal material 14, having thixotrapy, between the side wall of the sensor chip 5 and the inner wall of the trench wherein the flow path side is blocked by the positioning portion 6A, as illustrated in
Furthermore, because the inlet 3a and the outlet 3b of the flow path within the package are formed on the same flat end surface in this structure as well, not only is it possible to form a reliable seal that will not cause leaks, but also the inlet 3a and the outlet 3b can each be sealed individually using seal rings 4, as illustrated in
(2) Improved Flow Path within the Package
Given this, in the flow sensor 1 in the first form of embodiment, a bent flow path is formed in parallel with the substrate 2b surface, as the flow path 6A within the package, having the inlet 3a and the outlet 3b on the same end surface of the package, as illustrated in, for example,
Given this structure, when a gas to be measured flows around the angle portion 15A in the flow path 6A in the package, the portion of that dust that is included in the gas that does not make the turn at the angle portion 15 collides with the inner wall of the flow path 6A to accumulate in the vicinity of the angle portion 15. Note that by having the angle of the angle portion 15 be a right angle or an acute angle that is less than that, in the flow path 6A of the package, makes it possible to increase the effects of the inertial dust removal.
Additionally, instead of simply a bend for the flow path that is parallel to the substrate 2b surface, instead, as illustrated in
When structured as in
Note that in a conventional flow sensor there are cases wherein a mesh or a filter is provided upstream of the inlet of the flow path within the package to remove the dust; however, in the flow sensor 1 according to the embodiment, it is possible to obtain the dust removing effect, through having the flow path within the package be structured as described above, without the provision of a mesh or a filter.
As is illustrated in
A trench 6d for carrying the gas to be measured to the sensor surface of the sensor chip 5 and hole portions 6c that serve as the flow paths for carrying the gas to be measured to and from the dust collecting impactor are formed in the substrate 2b, which serves as the flow path layer. This substrate 2 is layered onto the substrate 2a, as illustrated in
These substrates 2c-1 and 2c-2 being layered sequentially on the substrate 2b and then each of these substrates being bonded together through, for example, sintering structures a package that has a flow path that is bent perpendicularly to the substrate surface (in the vertical direction), as illustrated in
In a structure as set forth above wherein the flow path within the package is bent perpendicularly from the substrate surface, the punching shape for forming the flow path within the package is no more complicated than in the structure wherein the flow path is bent in a direction that is parallel to the substrate surface, as set forth above, and thus it is easy to produce accurate dimensions, and the manufacturing is easy. Additionally, when compared to the case wherein the bend is in a direction that is parallel to the substrate surface, the dimension of the package in the horizontal direction can be made smaller. Note that while the case wherein the bend is in a direction that is parallel to the substrate surface and the case wherein the bend is in a direction that is perpendicular to the substrate surface were explained as separate structures for the flow path within the package, instead there can be a bend in a direction that is parallel to the substrate surface and a bend in the direction that is perpendicular to the substrate surface. Furthermore, the structure that serves as the dust collecting impactor may also be provided in the direction that is perpendicular to the substrate surface.
Moreover, in the mounting structure illustrated in
As a result, the seal ring 4 that is illustrated in the cross-sectional diagram along the section 14C-14C in
The covering by the resin 19 in this way can be through monolithic molding wherein melted resin 19 is caused to flow around the package in the mold, and then to harden. Note that in the conventional plastic molding that uses nylon, ABS, or the like, there is the potential for electronic components to undergo pressure damage with the injection pressures between several hundred kgf to 1 ton per square centimeter. On the other hand, when thermoplastic hot melt adhesive is used, the molding can be performed at a relatively low injection pressure of between several and 50 kgf per square centimeter. Here monolithic molding is performed using the thermoplastic hot melt adhesive as the resin 19. Note that a material other than a hot melt adhesive may be used, insofar as it is a material that enables low pressure molding so as to not damage the sensor package. Furthermore, a bushing-shape raised portion 19a is formed from the resin 19, as illustrated in
As illustrated in
As illustrated in
In this way, the flow sensor 1A can be attached for an installation wherein the gas to be measured can be introduced and returned through the tubes 3A1 and 3B1, and there is no need for tightening using fastening screws. Additionally, even in a case wherein there is no space for installing the flow sensor 1A in a pipe, or the like, for the gas to be measured, it is still possible to route the tubes 3A1 and 3B1 to be attached in a location wherein there is adequate space. In this way, the flow sensor 1A enables the handling of measurement operations in more complex places, with a greater degree of freedom in the installation.
The flow sensor 1 can be mounted suitably in, for example, the flow meter disclosed in International Publication Number WO 2005/121718 (See FIG. 1) (“WO '718”). In the flow meter disclosed in WO '718, even though conventionally a flow sensor has been used such as illustrated in JP '929, the sensor has been attached using an adhesive to the circuit board within the flow meter, without being able to use automated equipment, such as a mounter, when performing the mounting. Additionally, in the conventional sensor as illustrated in JP '929, the sensor chip has been mounted onto the substrate using die bonding or wire bonding, and larger sensor sizes have been the cause for increased sizes in the flow meters.
Given this, by mounting the flow sensor 1 according to the embodiment, instead of the conventional flow sensor, in a flow meter, it is possible to simplify the structure of the flow meter and possible to achieve a miniaturization of the flow meter. In other words, the flow sensor 1 is structured as a package chip, bonded to the substrate as set forth above, enabling mounting using automated equipment, such as a chip mounter, in the same manner as for other electrical components that are mounted onto circuit boards in the flow meter. Furthermore, the flow sensor 1 can be attached even in a narrow installation space, wherein wire bonding cannot be used for the electrical contacts. Doing so makes it possible to reduce the space that is required for the installation of the flow sensor 1, enabling miniaturization of the flow meter itself.
In the flow sensor 1, after the package is structured by layering the substrates 2a through 2c, as, for example, illustrated in
Additionally, when, as illustrated in
Given this, in the first form of embodiment, a hole portion having a step 21, as illustrated in
Additionally, when a material having thixotropy is used as the resin seal material 14, then when the sensor chip 5 is fitted into the square hole 5A (which, in this case, may be a normal square hole without a step), the seal material 14 fills into the gap between the side wall of the sensor chip 5 and the inner wall of the square hole 5A. Doing so makes it possible both to seal the sensor chip 5 and to cause the cross-sectional area of the flow path to be uniform. In this case, the injection conditions, such as the dispenser injection pressure and injection time, and the like, for performing an appropriate injection, wherein the amount of fill of the seal material 14 does not drip into the flow path, are determined in advance, and injection volume control is performed based thereon.
Note that a case of applying a sensor installation structure illustrated in
There are cases where in variability occurs in the dimensions in the height direction of the sensor chip 5 due to variability in the compression tolerance (melt tolerance) of the electrically conductive bonding material or variability in the force with which the sensor chip 5 is pressed against the substrate 2b when electrically connecting the electrodes of the substrate 2b to the electrodes of the sensor chip 5 that is mounted face-down in the square hole 5a. When there is this type of variability in the height direction of the sensor chip 5, then there will be variability in the sensor characteristics due to non-uniformity in the flow path and in the cross-sectional area of the flow path that is regulated by the sensor surface that is exposed thereto.
Given this, in the flow sensor 1 according to the first form of embodiment, a spacer portion for maintaining the sensor chip 5 at a uniform position in the height direction (a uniform position in the depth direction of the square hole 5a) is provided on the substrate 2b.
The spacer portion 22 has a uniform height dimension at (a uniform dimension in the depth direction of the square hole 5a), as illustrated in
Furthermore, because the spacer portion 22 has a uniform height dimension, there will be no variability in the height direction of the sensor chip 5 that is mounted in the square hole 5a, so that the cross-sectional area of the flow path will be maintained uniformly. This makes it possible to produce uniform sensor characteristics. Note that insofar as the sensor is one wherein a sensor chip is mounted in a mounting hole portion of a package, the structure illustrated in
The spacer portion 22a has a uniform height dimension (a uniform dimension along the direction of depth of the square hole 5a), as illustrated in
Even if the sensor chip 5 is pushed into the square hole 5a illustrated in
Because the spacer portion 22a also has a uniform height dimension, there will be no variability in the position, in the height direction, of the sensor chip 5 that is pressed into the square hole 5a, so the cross-sectional area of the flow path will be formed uniformly. Doing so makes it possible to obtain uniform sensor characteristics. Furthermore, the spacer portion 22a that is formed in the shape of an embankment of the trench 6 has the function of a breakwater to prevent the insulating resin material that protects the connection portions, from the electrically conductive bonding material, from spreading into the flow path.
Note that while in the explanation above a case was shown wherein the sensor installation structure illustrated in
In a thermal sensor, if the flow of the gas to be measured is stopped so that the gas becomes stationary in the flow path within the package, then condensation or moisture may adhere to the sensor surface, which can disrupt the relationship with the temperature of the gas to be measured at the surface of the sensor, damaging the accuracy of the sensor in terms of the gas flow, causing the output of the sensor to be incorrect. Given this, in the flow sensor 1 according to the embodiment, heater patterns are formed in order to heat the substrate that form the package, and the temperature is controlled based on the ambient temperature that is detected by a temperature detecting portion on the sensor chip 1.
The substrate 2b-1A is a ceramic substrate provided with a trench 6 to serve as the flow path within the package, where a heater pattern 23 is formed in a zigzag pattern on both sides, in the lengthwise direction, of this trench 6. Furthermore, the substrate 2b-2a is a ceramic substrate without the heater pattern 23, where a trench 6 that serves as the flow path within the package is provided in the center thereof.
These substrates 2a-1A, 2a-2A, 2b-1A, and 2b-2A are stacked sequentially, and a ceramic substrate, not shown, provided with an inflow opening 3a and an outflow opening 3b for the flow path within the package, corresponding to the substrate 2c-2 in
Additionally, the sensor chip 5 that is illustrated in
When the sensor portion 26 is used in a gas flow speed meter, the heater 23a is driven so as to have a temperature that is uniformly higher than the ambient temperature that is measured by the ambient temperature sensor 25, where the temperature sensors 24a and 24b are driven with a constant current or constant voltage. When the speed of flow of the gas to be measured is zero, then the temperatures of the temperature sensors 24a and 24b will be identical, so there will be no difference in the resistance values of the temperature sensors 24a and 24b.
When the gas to be measured is flowing, then the temperature sensor 24a that is positioned upstream is cooled by the heat being carried away by the flow of gas towards the direction of the heater 23a. On the other hand, the temperature sensor 24b that is positioned downstream is heated by the flow of gas from the direction of the heater 23a. As a result, there will be a difference between the resistance values of the temperature sensor 24a on the upstream side and the temperature sensor 24b on the downstream side, where the difference in the resistance values is detected as a difference in a voltage values, making it possible to calculate the velocity of flow b of the gas to be measured. This flow velocity b can be multiplied by the cross-sectional area S of the flow path to calculate the flow quantity Q of the gas to be measured.
Additionally, in the case wherein the sensor portion 26 is used in a gas thermal conductivity measurement, the heater 23a is driven so as to be at a temperature that is uniformly higher than the ambient temperature measured by the ambient temperature sensor 25, and the heater power Ph that is consumed by the heater 23a is calculated from the voltage and current in the heater at this time. The heater power Ph will vary depending on the thermal conductivity of the gas to which the sensor portion 26 is exposed, thus making it possible to calculate the thermal conductivity from the heater power Ph. Note that in the thermal conductivity measurement of the gas, there will be tolerance error when the flow speed is not zero; however, it is possible to check whether or not the flow speed is in a zero state by confirming that there is no difference in resistance values between the temperature sensors 24a and 24b on both sides of the heater 23a.
In
The heater pattern power controlling portion 29 controls the amount of current to the heater pattern 23. The calculation processing portion 30 controls the heater pattern power controlling portion 29 based on the ambient temperature that is inputted from the temperature sensor inputting portion 28. Note that the temperature controlling device 27 can be achieved through the use of, for example, a normal temperature adjusting device under the control of a microcontroller. Additionally, all or part of the temperature controlling device 27 may be structured within the flow sensor 1.
Additionally, the flow sensor controlling device 31 is provided with a heater driving portion 32 and a temperature sensor inputting portion 33. The heater driving portion 32 not only controls the driving of the heater 23a of the sensor portion 26, but also has a function for monitoring the electric current value for the electric current that flows in the heater 23a. A temperature sensor inputting portion 33 measures the gas flow volume from the output of the temperature sensors 24a and 24b of the sensor portion 26. Note that the flow sensor controlling device 31 can be achieved through the use of a controlling device, or the like, under the control of a microcontroller. Furthermore, all or part of the flow sensor controlling device 31 may be structured within the flow sensor 1. The operation will be explained next and the temperature controlled by the temperature controlling device 27 will be explained first.
The temperature sensor inputting portion 28 of the temperature controlling device 27 inputs the temperature within the flow path (the temperature within the substrate) of the flow sensor 1 that is detected by the temperature sensor 24c, through the connector 7b for connecting to the outside. When the temperature within the flow path (the temperature within the substrate) is inputted from the temperature sensor inputting portion 28, the calculation processing portion 30 compares to a predetermined use temperature that is stored in an internal memory, and, based on the comparison results, controls the heater pattern power controlling portion 29 so that the temperature within the substrate will go to the aforementioned use temperature.
The heater pattern power controlling portion 29 controls the electric current to the heater pattern 23 of the flow sensor 1 in accordance with a control signal from the calculation processing portion 30. This maintains the temperature within the substrate of the flow sensor 1 at the predetermined use temperature. This use temperature is set to a value that is higher than the temperature of the gas to be measured, in consideration of the occurrence of condensation on objects wherein the surface temperature is colder than the gas that is adjacent thereto.
This type of control not only prevents condensation on the surfaces of the sensor chip 5, but also maintains a uniform ambient temperature, thereby reducing the effect of variability in the ambient temperature, thereby enabling improved sensor accuracy. Additionally, in terms of the temperature controlling method by the calculation processing portion 30, the use temperature may be controlled constantly based on the temperature that is inputted from the temperature sensor inputting portion 28, or the temperature may be controlled selectively in response to the temperature of the gas or the flow path, and the heating may be driven either continuously or discontinuously. Moreover, because dust is less likely to adhere to warm places, the temperature control may prevent the adhesion of dust to the inner wall of the flow path by constantly heating the flow sensor 1.
The process for recovering from a condensation state, through the flow sensor controlling device 31, will be explained next.
The heater driving portion 32 of the flow sensor controlling device 31 determines that condensation has occurred in the sensor portion 26 of the sensor chip 5 when an increase in the value of the electric current flowing in the heater 23a of the sensor portion 26 exceeds a predetermined threshold value. This causes the process for recovering from the condensation state to commence. Note that, to make the determination that there is condensation, the methods for identifying condensation may use other well-known technologies for identifying condensation in addition to monitoring the value of the electric current in the heater 23a as described above, such as using a method for identifying condensation from the change in inductance between exposed interlaced electrodes.
When the occurrence of condensation has been identified, then the heater driving portion 32 provides notification to this effect to the calculation processing portion 30 of the temperature controlling device 27. The calculation processing portion 30, when notification that condensation has occurred has been received, switches the operation of the heater pattern power controlling portion 29 to a heater pattern high-temperature sequence. In the high-temperature sequence process, the heater pattern power controlling portion 29 performs control of the electric current to the heater pattern 23 to perform heating over a predetermined time interval to a temperature that is higher than that of the normal heating status for causing the temperature within the package of the flow sensor 1 to be uniform.
When the aforementioned specific time interval has elapsed, then the calculation processing portion 30 controls the heater pattern power controlling portion 29 to return, to the normal value, the magnitude of the electric current to the heater pattern 23, to cause the temperature to go to the normal set temperature. At this time, the calculation processing portion 30 measures the time that elapses after performing the process to return the temperature within the package to the normal set temperature, and if a predetermined amount of time expires, then provides notification to that effect to the flow sensor controlling device 31.
The heater driving portion 32 of the flow sensor controlling device 31, upon receipt of this notification, monitors the value of the electric current that flows in the heater 23a of the sensor portion 26 to determine whether or not the threshold value described above is exceeded. If, at this time, the value of the electric current flowing in the heater 23a is less than the threshold value, then a determination is made that there has been a recovery from the condensation, but if still greater than the threshold value, then the recovery process described above is repeated. This type of control is able to drive off adhered moisture through heating when there is condensation on the surface of the sensor, to attempt to restore the sensor characteristics.
Given the embodiment, as set forth above, a flow path is provided within the package for introducing the gas to be measured to the sensor chip 5, having an inlet 3a and an outlet 3b for the gas to be measured on the same flat end surface of the package, and thus only one end surface of the package needs to be sealed at the time of mounting, and the sealing can be done easily because the surface is flat. Additionally, because the other surfaces of the package can be used, there is flexibility in the installation structure, making it possible to achieve miniaturization.
Furthermore, given the embodiment, spacer portions 22 and 22a are provided, for defining the position of the sensor chip 5 in the direction of depth of the square hole 5a, on the substrate 2b surface within the package, facing the sensor surface of the sensor chip 5 that is mounted within the square hole 5a of the package, and thus the variability of the sensor chip 5 in the direction of height is controlled, making it possible to obtain uniform sensor characteristics.
Furthermore, while, given the embodiment, the mounted sensor chip 5 protrudes from a step surface, a square hole 5A, having a depth dimension so that the sensor chip 5 will not protrude to the outside surface of the package, may be provided to facilitate the operations to rework the mounting position of the sensor chip 5, and to prevent incursion of the resin seal material 14 onto the substrate 2a surface. Furthermore, the use of a thixatropic material as the resin seal material 14 makes it possible to achieve both the sealing of the sensor chip 5 and a uniform flow path cross-sectional area through filling the seal material 14 into the gap between the side surface of the sensor chip 5 and the inner wall of the square hole 5A when the sensor chip 5 is fitted into the square hole 5A. Additionally, given the embodiment, a heater pattern 23 is provided on at least one of the substrates that structure the package, and the magnitude of the electric current to the heater pattern 23 is controlled in accordance with the ambient temperature of the sensor chip 5 within the package, to control the temperature within the package, and thus even if the flow of the gas to be measured were to stop to cause the gas within the flow path to be stationary, it is still possible to prevent condensation and adhesion of moisture to the surface of the sensor, and even if there were condensation on the sensor, it is possible to drive off the adhered moisture to attempt to restore the sensor characteristics, and also possible to improve the sensor accuracy through controlling the ambient temperature so as to be uniform.
Note that while in the first form of embodiment an example was illustrated wherein ceramic substrates were used as the substrates for structuring the package, resin the substrates may be used instead, insofar as the material is one wherein the sensor package can be structured through bonding together a plurality of substrates. Furthermore, while in the first form of embodiment, set forth above, the structure illustrated in
The flow sensor according to the present invention not only is able to connect to a pipe of a gas to be measured while maintaining a tight seal, but also has flexibility in the installation structure and enables miniaturization, and thus is applicable to flow meters that are used with narrow installation spaces and used under difficult operating conditions.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2007-049468 | Feb 2007 | JP | national |
This is a U.S. national phase application under 35 U.S.C. §371 of International Patent Application No. PCT/JP2008/000234, filed Feb. 15, 2008 and claims the benefit of Japanese Application No. 2007-049468, filed Feb. 28, 2007. The International Application was published on Sep. 4, 2008 as International Publication No. WO/2008/105144 under PCT Article 21(2) the contents of these applications are incorporated herein in their entirety.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2008/000234 | 2/15/2008 | WO | 00 | 8/27/2009 |
