JP2010156590A - Concentration sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To precisely detect concentration in a concentration sensor composed to detect concentration of chemical substances in a solution to be inspected by utilizing surface acoustic waves. <P>SOLUTION: The concentration sensor is composed as a self-excitation type concentration sensor including a short channel 34A and an open channel 34B. In this case, electronic components 90 for composing oscillation circuits of the respective channel sections 34A, 34B are disposed under environmental temperature nearly equal to that of the respective channel sections 34A, 34B abutting to the solution to be inspected. More specifically, a lower frame 74 of a casing 70 where a storage space 80 of the solution to be inspected is formed is composed of members having small thermal resistance. Then, the rear of a support substrate 92 where the electronic components 92 have been packaged on the front is brought into face contact with a lower surface of a floor-like section 74g of the lower frame 74, thus heat of the solution to be inspected is transferred to the electronic components 90 via the floor-like section 74g and the support substrate 92, thereby enabling to nearly accurately grasp factors of environmental temperature when calculating the concentration of chemical substances. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a concentration sensor configured to detect a chemical substance concentration in a test solution using surface acoustic waves, and in particular, a concentration having a short channel and an open channel as the sensor body. It relates to sensors.

  2. Description of the Related Art Conventionally, a sensor using surface acoustic waves is known as a concentration sensor for detecting a chemical substance concentration (for example, methanol concentration) in a test solution.

  This concentration sensor has a channel body in which a pair of cross-finger electrodes are arranged on a piezoelectric substrate at a predetermined interval as described in, for example, “Patent Document 1” as the sensor body. It has become.

  In this concentration sensor, one cross finger electrode is excited to generate a surface acoustic wave on the piezoelectric substrate, and the surface acoustic wave propagated to the other cross finger electrode is thereby received by the cross finger electrode. It has a configuration. At this time, since the propagation speed of the surface acoustic wave changes depending on the chemical substance concentration, it is possible to detect the concentration based on the frequency of the surface acoustic wave received by the other interdigitated electrode.

  Many of the conventional concentration sensors perform so-called excitation of one cross finger electrode by applying a predetermined high-frequency signal voltage to the cross finger electrode as described in "Patent Document 1". It is configured as a separately excited type density sensor.

  At that time, in “Patent Document 2”, in such a separately excited type concentration sensor, the region on the piezoelectric substrate between the two crossed finger electrodes is used as the ground electrode finger of the two crossed finger electrodes as the channel portion of the sensor body. A configuration comprising a short channel covered by a short-circuited conductive layer and an open channel in which a region on the piezoelectric substrate between the two interdigitated electrodes is exposed, and both channel portions are arranged in parallel The configuration is described.

  In the concentration sensor described in “Patent Document 2”, the concentration detection is performed based on the difference between the propagation speed of the surface acoustic wave in the short channel and the propagation speed of the surface acoustic wave in the open channel. It has become.

JP 2005-315646 A Japanese Patent Laid-Open No. 9-80035

  Each of the above conventional density sensors is configured as a separately excited type density sensor. However, a so-called self-excited type sensor in which a self-oscillation is generated by connecting a circuit for oscillation to a channel portion to form a closed-loop circuit. It can also be configured as a density sensor.

  At that time, the oscillation circuit of the self-excited concentration sensor is configured to include a high-frequency amplifier and an automatic gain control circuit for adjusting the gain, and the oscillation circuit is provided for each of the short channel and the open channel. When connected to form a closed loop circuit, the oscillation frequency signal output from the high frequency amplifier of the short channel oscillation circuit, the gain adjustment voltage signal output from the automatic gain control circuit, and the open channel The chemical substance concentration in the test solution can be calculated based on the oscillation frequency signal output from the high frequency amplifier of the oscillation circuit on the side and the gain adjustment voltage signal output from the automatic gain control circuit. . By adopting such a configuration, it is possible to perform density detection with higher accuracy than a separately excited density sensor.

  However, when such a self-excited concentration sensor concentration is adopted, each oscillation frequency signal and each gain adjustment voltage signal are easily affected by disturbance, and an error is likely to occur in the output value. There is also a problem.

  That is, the output value of each oscillation frequency signal depends on the environmental temperature. Therefore, when calculating the chemical substance concentration, it is necessary to accurately grasp the cause of the environmental temperature. However, in the concentration sensor, the environmental temperature differs between each channel portion that comes into contact with the test solution and each oscillation circuit that is located away from the storage space in which the test solution is stored. For this reason, when calculating the chemical substance concentration, there is a problem that the factor of the environmental temperature cannot be accurately grasped, and therefore the accuracy of concentration detection is also lowered.

  The present invention has been made in view of such circumstances, and in a concentration sensor configured to detect the concentration of a chemical substance in a test solution using surface acoustic waves, the concentration detection is performed with high accuracy. An object of the present invention is to provide a density sensor that can be used.

  In the present invention, a self-excited concentration sensor having a short channel and an open channel is adopted, and the arrangement of electronic components constituting the oscillation circuit is devised to achieve the above object. is there.

That is, the concentration sensor according to the present invention is
A housing in which a storage space for storing a test solution is formed;
On the piezoelectric substrate, a first channel part in which a pair of cross finger electrodes are arranged at a predetermined interval, and a pair of cross finger electrodes are arranged in parallel with the first channel part at a predetermined interval. A sensor body attached to the housing in a state where the first and second channel portions are exposed to the housing space, and a second channel portion is formed.
A first oscillation circuit and a second oscillation circuit that are connected to each channel portion of the sensor body and constitute a closed-loop circuit that causes self-excited oscillation with the channel portion;
The first channel portion is configured as a short channel in which a region on the piezoelectric substrate between the two crossed finger electrodes of the channel portion is covered with a conductive layer short-circuited to the ground electrode fingers of the two crossed finger electrodes. And the second channel portion is configured as an open channel exposing a region on the piezoelectric substrate between both crossed finger electrodes of the channel portion,
Each oscillation circuit includes a high-frequency amplifier and an automatic gain control circuit that adjusts the gain of the high-frequency amplifier.
Among the pair of cross finger electrodes in each channel part, one cross finger electrode is excited to generate a surface acoustic wave on the piezoelectric substrate, and the surface acoustic wave propagated to the other cross finger electrode is In the concentration sensor configured to receive vibration with the interdigitated electrode,
The electronic components constituting the first and second oscillation circuits are arranged at substantially the same environmental temperature as the first and second channel portions.

  The type of “chemical substance concentration in the test solution” that is a target for concentration detection by the concentration sensor according to the present invention is not particularly limited, and for example, methanol concentration, formic acid concentration, or the like can be employed.

  As long as the “electronic component” is disposed at substantially the same environmental temperature as the first and second channel portions, the specific mode of the arrangement is not particularly limited.

  As shown in the above configuration, the concentration sensor according to the present invention is configured as a self-excited concentration sensor including a first channel portion that constitutes a short channel and a second channel portion that constitutes an open channel. The oscillation frequency signal output from the high frequency amplifier of the oscillation circuit on the short channel side and the gain adjustment voltage signal output from the automatic gain control circuit, and the oscillation frequency signal output from the high frequency amplifier of the oscillation circuit on the open channel side Based on the gain adjustment voltage signal output from the automatic gain control circuit, it is possible to calculate the chemical substance concentration in the test solution, thereby making it possible to accurately detect the concentration.

  In this case, in the present invention, the electronic components constituting the first and second oscillation circuits are arranged at substantially the same environmental temperature as the first and second channel portions that are in contact with the test solution. Therefore, when calculating the chemical substance concentration, it is possible to grasp the cause of the environmental temperature substantially accurately, and thereby the concentration can be detected with high accuracy.

  As described above, according to the present invention, it is possible to accurately detect the concentration in the concentration sensor configured to detect the chemical substance concentration in the test solution using the surface acoustic wave.

  In the above configuration, the specific aspect of the arrangement of the electronic components is not particularly limited as described above. However, the electronic component may be arranged in the following manner.

  For example, it is assumed that at least a part of the peripheral wall portion surrounding the accommodation space in the housing is made of a member having low thermal resistance, and the electronic component is mounted on the surface of the support substrate, and this support It is possible to adopt a configuration in which the substrate is arranged so that the back surface thereof is in surface contact with the outer surface of the portion made of a member having a low thermal resistance in the peripheral wall portion of the housing.

  When such a configuration is adopted, the heat of the test solution accommodated in the accommodation space is transferred by heat conduction to the electronic component through the portion formed of a member having a small thermal resistance in the peripheral wall portion and the support substrate. Since the heat is transmitted, the temperature of each oscillation circuit configured as an electronic component can be made substantially the same as the temperature of each channel portion by this conduction heat.

  In this case, the “member with low thermal resistance” means a member made of a material having a thermal conductivity of 1 W / m · K or more, and if it is a member satisfying this condition, its type Is not particularly limited, and for example, a metal member or a member made of a high thermal conductive resin in which a metal, ceramics, inorganic filler, or the like is mixed with a resin material can be employed.

  In the above configuration, as another specific aspect of the arrangement of the electronic components, the electronic components may be arranged inside the accommodation space in a state of being covered with a film.

  When such a configuration is adopted, the electronic component also comes into contact with the test solution via the coating film, as with each channel portion. The degree of coincidence between the temperature of the circuit and the temperature of each channel portion can be further increased. Further, by adopting such a configuration, the housing can be configured in a compact manner.

  At that time, the “coating” covering the electronic component has the desired insulation, heat resistance and thermal conductivity, and prevents the electronic component from interfering with its function due to direct contact with the test solution. The specific configuration such as the type and the film thickness is not particularly limited as long as it can transmit the ambient heat to the electronic component.

  In this case, the specific arrangement of the electronic components inside the accommodation space is not particularly limited. However, if the electronic components are mounted on the piezoelectric substrate, the sensor body is attached to the housing. Thus, the electronic component is automatically arranged in the accommodation space, so that the configuration and assembly work of the concentration sensor can be simplified.

  In the above configuration, if the entire casing is configured with a member having low thermal resistance, and the casing is covered with a heat insulating material, each oscillation circuit configured as an electronic component The degree of coincidence between the temperature and the temperature of each channel portion can be further increased.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a block diagram showing a concentration sensor 10 according to an embodiment of the present invention.

  As shown in the figure, the concentration sensor 10 according to this embodiment includes a sensor unit 20 and a control unit 50 connected to the sensor unit 20. At that time, the sensor unit 20 includes a sensor main body 30 and first and second oscillation circuits 40A and 40B.

  The concentration sensor 10 detects the concentration of a chemical substance (for example, methanol) contained in the test solution in a state where the sensor body 30 is disposed in the test solution.

  The sensor body 30 has a first channel portion 34A in which a pair of crossed finger electrodes 34A1 and 34A2 are arranged at a predetermined interval on a piezoelectric substrate 32, and a pair in parallel with the first channel portion 34A. The cross channel electrodes 34B1 and 34B2 are arranged at the same interval as the second interval 34B.

  In the first channel portion 34A, one electrode finger in one of the cross finger electrodes 34A1 constitutes an input electrode finger 34Ai, and one electrode finger in the other cross finger electrode 34A2 is an output electrode. The finger 34Ao is configured.

  On the other hand, in the second channel portion 34B, one electrode finger in one cross finger electrode 34B1 constitutes an input electrode finger 34Bi, and one electrode finger in the other cross finger electrode 34B2 is output. The electrode finger 34Bo is configured.

  The other electrode finger of each cross finger electrode 34A1, 34A2 of the first channel portion 34A and the other electrode finger of each cross finger electrode 34B1, 34B2 of the second channel portion 34B are common ground electrode fingers. 34g is comprised.

  Each of the channel portions 34A and 34B is configured to generate a transverse wave type surface acoustic wave on the piezoelectric substrate 32 by exciting one of the interdigitated electrodes 34A1 and 34B1. The surface acoustic wave propagated on the substrate 32 to the other cross finger electrodes 34A2 and 34B2 is received by the cross finger electrodes 34A2 and 34B2.

  The first and second channel portions 34A and 34B have a line-symmetric configuration with each other and are disposed adjacent to each other, but the following configurations are different between the two.

  That is, the first channel portion 34A is configured as a short channel in which the region on the piezoelectric substrate 32 between the cross finger electrodes 34A1 and 34A2 is covered with the conductive layer 34A3 short-circuited to the ground electrode finger 34g. On the other hand, the second channel portion 34B is configured as an open channel in which a region on the piezoelectric substrate 32 between the interdigitated electrodes 34B1 and 34B2 is exposed.

  Hereinafter, the first channel portion 34A is referred to as “short channel 34A”, and the second channel portion 34B is referred to as “open channel 34B”.

  In the first and second oscillation circuits 40A and 40B, the first oscillation circuit 40A is connected to the short channel 34A, and the second oscillation circuit 40B is connected to the short channel 34B. The oscillation circuit 40A constitutes a closed loop circuit 22A that causes self-excited oscillation with the short channel 34A, and the oscillation circuit 40B causes self-excited oscillation with the open channel 34B. A closed loop circuit 22B is configured.

  The short channel side oscillation circuit 40A includes a high frequency amplifier 42A, an automatic gain control circuit 44A, and a low pass filter 46A.

  The high frequency amplifier 42A is configured to amplify the oscillation frequency signal output from the output electrode finger 34Ao of the short channel 34A and return it to the input electrode finger 34Ai of the short channel 34A.

  The automatic gain control circuit 44A adjusts the gain of the high frequency amplifier 42A by keeping the voltage amplitude of the output signal from the high frequency amplifier 42A (that is, the input signal to the short channel 34A) constant.

  The low-pass filter 46A is provided between the output electrode finger 34Ao of the short channel 34A and the high-frequency amplifier 42A in order to prevent oscillation in a frequency region higher than the frequency (for example, 50 MHz) to be oscillated in the closed loop circuit 22A. Has been placed.

  The open channel side oscillation circuit 40B has the same configuration as the short channel side oscillation circuit 40A. That is, the oscillation circuit 40B includes a high frequency amplifier 42B, an automatic gain control circuit 44B, and a low pass filter 46B.

  The sensor unit 20 includes a signal of the oscillation frequency fs output from the high frequency amplifier 42A in the oscillation circuit 40A on the short channel side and a signal of the gain adjustment voltage (AGC voltage) Vs output from the automatic gain control circuit 44A. The signal of the oscillation frequency fo output from the high frequency amplifier 42B in the oscillation circuit 40B on the open channel side and the signal of the gain adjustment voltage Vo output from the automatic gain control circuit 44B are input to the control unit 50. Yes.

  The control unit 50 includes a CPU 52, a frequency counter 54 and an A / D converter 56 connected to the CPU 52.

  The frequency counter 54 is supplied with the signal of the oscillation frequency fs output from the closed loop circuit 22A on the short channel side and the signal of the oscillation frequency fo output from the closed loop circuit 22B on the open channel side. . The frequency counter 54 measures the oscillation frequencies fs and fo.

  The A / D converter 56 receives the signal of the gain adjustment voltage Vs output from the closed loop circuit 22A on the short channel side and the signal of the gain adjustment voltage Vo output from the closed loop circuit 22B on the open channel side. It is like that. The A / D converter 56 A / D converts the signals of these gain adjustment voltages Vs and Vo.

  The CPU 52 determines the chemistry in the test solution based on the output values fs and fo of each oscillation frequency signal measured by the frequency counter 54 and the output values Vs and Vo of each gain adjustment voltage signal subjected to A / D conversion. The substance concentration is calculated.

  The calculation of the chemical substance concentration by the CPU 52 is performed as follows.

  That is, the oscillation frequency fs has a value corresponding to the velocity of the surface acoustic wave propagating on the piezoelectric substrate 32 of the short channel 34A, and the oscillation frequency fo is the surface acoustic wave propagating on the piezoelectric substrate 32 of the open channel 34B. It becomes a value according to the speed.

  On the other hand, when the chemical substance concentration in the test solution changes, the dielectric constant of the test solution also changes accordingly. When the dielectric constant changes, the propagation speed of the surface acoustic wave also changes. At this time, the degree of change in the propagation speed of the surface acoustic wave with respect to the change in the dielectric constant differs between the short channel 34A and the open channel 34B depending on the presence or absence of the conductive layer 34A3.

  The difference in the propagation speed of the surface acoustic wave appears as a difference between the oscillation frequency fs output from the closed loop circuit 22A on the short channel side and the oscillation frequency fo output from the closed loop circuit 22B on the open channel side. The gain adjustment voltages Vs and Vo are values corresponding to the degree of energy attenuation when the surface acoustic wave propagates.

  Therefore, the chemical substance concentration in the test solution is calculated by performing an operation based on a predetermined algorithm using the four output values of the oscillation frequencies fs and fo and the gain adjustment voltages Vs and Vo. ing.

  On / off switches 62A and 62B are arranged between the high frequency amplifiers 42A and 42B of the oscillation circuits 40A and 40B in the sensor unit 20 and the power supply 60, respectively. The on / off switches 62A and 62B are opened and closed by a control signal from the CPU 52.

  FIG. 2 is a plan view showing the sensor body 30 as a single product.

  As shown in the figure, the piezoelectric substrate 32 is a substrate made of lithium tantalate and has a hexagonal outer shape in which the shape of the left and right side edges is set in a mountain shape in plan view. The short channel 34 </ b> A and the open channel 34 </ b> B are formed in a portion near one side end (a portion near the right end in the figure) on the upper surface of the piezoelectric substrate 32.

  Five external connection terminals 36Ai, 36Ao, 36Bi, 36Bo, 36g are formed at substantially equal intervals in the vicinity of the other end (the vicinity of the left end in the figure) on the upper surface of the piezoelectric substrate 32.

  The external connection terminal 36Ai is formed as a terminal portion of a strip-like conductive layer 38Ai extending leftward from the input electrode finger 34Ai of the short channel 34A, and is connected to the output end of the high-frequency amplifier 42A.

  The external connection terminal 36Ao is formed as a terminal portion of a strip-like conductive layer 38Ao extending leftward from the output electrode finger 34Ao of the short channel 34A, and is connected to the input end of the low-pass filter 46A.

  The external connection terminal 36Bi is formed as a terminal portion of a strip-like conductive layer 38Bi extending leftward from the input electrode finger 34Bi of the open channel 34B, and is connected to the output end of the high-frequency amplifier 42B.

  The external connection terminal 36Bo is formed as a terminal portion of a strip-like conductive layer 38Bo extending leftward from the output electrode finger 34Bo of the open channel 34B, and is connected to the input end of the low-pass filter 46B.

  The external connection terminal 36g is formed as a terminal portion of a strip-like conductive layer 38g extending leftward from the ground electrode finger 34g common to the short channel 34A and the open channel 34B, and is grounded to the ground potential.

  FIG. 3 is a plan sectional view showing the sensor unit 20, and is a sectional view taken along line III-III in FIG. 4 is a cross-sectional view taken along line IV-IV in FIG.

  As shown in these drawings, the sensor unit 20 has a structure in which a sensor main body 30 is attached to a housing 70.

  The housing 70 includes an upper frame 72, a lower frame 74 on which the upper frame 72 is placed and fixed, a base plate 76 disposed so as to contact the lower surface of the lower frame 74, and so as to cover them from above. The cover member 78 is caulked and fixed to the base plate 76 in the disposed state.

  At that time, the upper frame 72, the lower frame 74, and the base plate 76 are made of a member made of a high thermal conductive resin having a low thermal resistance, and the cover member 78 is made of a metal member.

  The lower frame 74 has a configuration in which a rectangular hole 74a is formed on the upper surface of a thick plate member having a substantially rectangular outer shape in plan view.

  The upper frame 72 is formed in a plate-like member having substantially the same outer shape as the lower frame 74 in plan view, and has a rectangular opening that penetrates the upper frame 72 in the vertical direction with the same cross-sectional shape as the rectangular hole 74a of the lower frame 74. 72a is formed.

  Then, the upper frame 72 placed and fixed on the lower frame 74 is covered with the cover member 78, so that an accommodation space 80 for accommodating the test solution is formed inside the rectangular hole 74a and the rectangular opening 72a. It is supposed to be formed.

  On the left end surface of the lower frame 74 (that is, the side surface on the other end side), a U-shaped bottomed cutout portion 74b is formed in plan view. A cutout portion 72b having the same cross-sectional shape as the bottomed cutout portion 74b in plan view is formed on the left end surface of the upper frame 72.

  The sensor main body 30 has the short channel 34A and the open channel 34B exposed to the accommodation space 80, and the five external connection terminals 36Ai, 36Ao, 36Bi, 36Bo, 36g are exposed to the external space of the housing 70. The case 70 is cantilevered.

  This cantilever support is performed by sandwiching the sensor body 30 between the upper frame 72 and the lower frame 74. At this time, the clamping is performed at a position closer to the left edge than the center position in the left-right direction of the sensor body 30.

  On the upper surface of the belt-like protrusion 74c between the rectangular hole 74a and the bottomed cutout 74b in the lower frame 74, a step-down recess 74d for mounting the sensor body 30 is formed. The step-down concave portion 74d is a portion that is one step lower than the other portions on the upper surface of the belt-like protrusion 74c, and is formed slightly deeper than the thickness of the sensor main body 30. Is also slightly wider.

  The sensor main body 30 is placed on the step-down recess 74d via a seal member 82. In the step-down recess 74d, seal grooves 74e for disposing the seal member 82 are formed on the bottom surface portion and the side wall portions on both sides thereof. The seal groove 74e is formed in a circular arc shape so as to pass through a substantially central position in the left-right direction of the belt-like protrusion 74c. Thus, when the sensor body 30 is placed in the step-down recess 74d in which the seal member 82 is disposed in the seal groove 74e, the seal member 82 overflows somewhat from the seal groove 74e to both sides thereof.

  The mounting and fixing of the upper frame 72 with respect to the lower frame 74 is performed via a seal member 84. At that time, a seal groove 72c is formed on the lower surface of the upper frame 72 so as to surround the rectangular opening 72a at a substantially equal distance. The seal groove 72c is formed in an arc shape in cross section so as to pass through a substantially central position in the left-right direction of the beam-like portion 72d located between the rectangular opening 72a and the notch 72b in the upper frame 72. . Thus, when the upper frame 72 in which the seal member 84 is disposed in the seal groove 72c is placed on the lower frame 74, the seal member 84 overflows somewhat from the seal groove 72c to both sides thereof.

  The cover member 78 is mounted and fixed on the upper frame 72 via a seal member 86. At that time, a seal groove 72e is formed on the upper surface of the upper frame 72 so as to surround the rectangular opening 72a at a substantially equal distance. The seal groove 72e is formed in a circular arc shape so as to pass through a position substantially directly above the seal groove 72c. Thus, when the cover member 78 is placed on the upper frame 72 in which the seal member 86 is disposed in the seal groove 72e, the seal member 86 overflows somewhat from the seal groove 74e to both sides thereof.

  As each of the sealing members 82, 84, 86, a material having elasticity even after sealing is used. Specifically, for example, it is possible to use a one-component thermosetting olefin-based sealant “ThreeBond 1152B, ThreeBond 1153B” (both trade names) manufactured by ThreeBond Co., Ltd.

  A box-shaped cavity 74 f is formed on the lower surface of the lower frame 74. The hollow portion 74f is formed with an opening area slightly larger than the rectangular hole 74a below the rectangular hole 74a, and communicates with the space of the bottomed cutout portion 74b at the upper portion of the left end surface thereof. The floor portion 74g between the bottom surface of the rectangular hole 74a and the ceiling surface of the hollow portion 74f in the lower frame 74 is formed to be relatively thin.

  A support substrate 92 is disposed in the cavity 74 f of the lower frame 74. At this time, the electronic components 90 constituting the oscillation circuits 40A and 40B are mounted on the lower surface of the support substrate 92. The support substrate 92 is in a state in which the upper surface thereof is in surface contact with the substantially entire area of the ceiling surface of the cavity portion 74f, and the left end portion thereof is protruded into the space of the bottomed cutout portion 74b. Is arranged in. The mounting position of the electronic component 90 with respect to the support substrate 92 is set so that the electronic component 90 is positioned directly below the center of the rectangular hole 74a.

  On the lower surface of the support substrate 92, five strip-shaped conductive layers 94 extend from the mounting position of the electronic component 90 leftward to the vicinity of the left edge thereof. Further, five pad-like conductive layers 96 are formed in the vicinity of the left edge on the upper surface of the support substrate 92. Each of these conductive layers 96 is electrically connected to each conductive layer 94 via a through hole or the like (not shown). The conductive layers 96 are electrically connected to the external connection terminals 36Ai, 36Ao, 36Bi, 36Bo, and 36g of the sensor body 30 through bonding wires 98, respectively.

  The base plate 76 is a plate-like member having substantially the same outer shape as that of the lower frame 74 in a plan view, and a substantially rectangular stepped recess 76a is formed in a substantially central position of each side on the lower surface of the base plate 76 in a plan view. Has been.

  The abutment of the base plate 76 with respect to the lower frame 74 is performed by bringing the upper surface of the base plate 76 into surface contact with the lower surface of the lower frame 74.

  The cover member 78 has a box-shaped outer shape with an open bottom wall, and a tab-shaped protrusion 78a is formed at the lower end edge of each side wall portion. The cover member 78 is formed on the base plate 76 by bending the four protrusions 78a inward with the upper frame 72, the lower frame 74, and the base plate 76 accommodated in the cover member 78. The base plate 76 is caulked and fixed by being engaged with four raised recesses 76a. As a result, the liquid tightness of the accommodation space 80 is sufficiently secured.

  An inflow hole 78 b and a discharge hole 78 c for the test solution are formed on the upper surface wall of the cover member 78. The inflow hole 78b and the discharge hole 78c are respectively formed in a chimney shape so as to be positioned at both ends of the accommodation space 80.

  Next, the effect of this embodiment is demonstrated.

  Since the concentration sensor 10 according to the present embodiment is configured as a self-excited concentration sensor having a short channel 34A and an open channel 34B, an oscillation frequency signal output from the high frequency amplifier 42A of the oscillation circuit 40A on the short channel side. And the gain adjustment voltage signal output from the automatic gain control circuit 44A, the oscillation frequency signal output from the high frequency amplifier 42B of the oscillation circuit 40B on the open channel side, and the gain adjustment voltage output from the automatic gain control circuit 44B. Based on the signal, it is possible to calculate the concentration of the chemical substance in the test solution, which makes it possible to accurately detect the concentration.

  At this time, in the present embodiment, the lower frame 74 of the housing 70 is made of a member made of a high thermal conductive resin having a low thermal resistance, and the support substrate 92 on which the electronic component 90 is mounted on the lower surface is Since the upper surface thereof is arranged so as to be in surface contact with the lower surface of the floor-like portion 74g of the lower frame 74, the following operational effects can be obtained.

  That is, the heat of the test solution accommodated in the accommodating space 80 is transmitted by heat conduction to the electronic component 90 through the floor-like portion 74g of the lower frame 74 and the support substrate 92. Accordingly, the short channel side oscillation circuit 40A and the open channel side oscillation circuit 40B configured as the electronic component 90 are arranged at substantially the same environmental temperature as the short channel 34A and the open channel 34B in contact with the test solution. Will be. For this reason, when calculating the chemical substance concentration, it is possible to grasp the cause of the environmental temperature substantially accurately, and thereby the concentration can be detected with high accuracy.

  As described above, according to the present embodiment, the concentration sensor 10 configured to detect the chemical substance concentration in the test solution using the surface acoustic wave can accurately detect the concentration.

  In addition, in the present embodiment, the support substrate 92 is in surface contact with the entire area of the floor portion 74g of the lower frame 74, and the electronic component 90 is located directly below the center of the floor portion 74g. In addition, heat transfer from the test solution to the electronic component 90 can be performed efficiently.

  In the above-described embodiment, the upper frame 72, the lower frame 74, and the base plate 76 that constitute the housing 70 have been described as being configured by members having low thermal resistance. Only the portion 74g may be formed of a member having a low thermal resistance. In such a case, heat transfer from the test solution to the electronic component 90 is performed efficiently, and the heat of the test solution is made difficult to escape from the storage space 80 to the outside. Can do.

  Next, a first modification of the above embodiment will be described.

  FIG. 5 is a view similar to FIG. 4 showing the sensor unit 120 according to this modification.

  As shown in the figure, the sensor unit 120 has a configuration in which a casing 70 in the sensor unit 20 according to the embodiment is covered with a heat insulating material 100. The heat insulating material 100 has a structure in which an upper heat insulating material 102 and a lower heat insulating material 104 are integrated by bonding or the like, and the housing 70 is provided with inflow holes 78b and discharge holes 78c of the cover member 78. Except for the entire circumference.

  By adopting the configuration of the present modification, the entire portion corresponding to the sensor unit 20 of the above embodiment can be confined in the space inside the heat insulating material 100, and therefore the entire portion is disposed at substantially the same environmental temperature. be able to. For this reason, it is possible to further increase the degree of coincidence between the temperatures of the oscillation circuits 40A and 40B configured as the electronic component 90 and the temperatures of the channel portions 34A and 34B.

  Next, a second modification of the above embodiment will be described.

  FIG. 6 is a view similar to FIG. 4 showing the sensor unit 220 according to this modification.

  As shown in the figure, the sensor unit 220 has the same basic configuration as the sensor unit 20 according to the above embodiment, but the arrangement of the electronic components 90 is different from that in the above embodiment. Accordingly, the configurations of the sensor main body 230 and the housing 270 are also partially different from those in the above embodiment.

  In other words, in this modification, the electronic component 90 is arranged inside the accommodation space 80 in a state of being covered with the coating 202. Specifically, the electronic component 90 is mounted in a portion near one side end (a portion near the right end in the figure) of the lower surface of the piezoelectric substrate 32 of the sensor body 230 and covered with the coating film 202 in this state. It has been broken.

  On the lower surface of the piezoelectric substrate 32 in the sensor main body 230, five strip-shaped conductive layers 294 extend from the mounting position of the electronic component 90 to the left side and near the left edge thereof. The conductive layers 294 are electrically connected to the external connection terminals 36Ai, 36Ao, 36Bi, 36Bo, and 36g of the sensor main body 230 through through holes or the like (not shown).

  As described above, since the electronic component 90 is arranged inside the accommodation space 80, the configuration of the housing 270 is also different from that in the above embodiment.

  That is, the lower frame 274 of the present modification is not formed with a cavity 74f like the lower frame 74 of the above embodiment on the lower surface, and the support substrate 92 of the above embodiment is not provided. For this reason, the cover member 278 of this modification is considerably lower than the cover member 78 of the above embodiment.

  By adopting the configuration of this modified example, the electronic component 90 also comes into contact with the test solution in the storage space 80 through the coating film 202 as in the case of the channel portions 34A and 34B. The degree of coincidence between the temperatures of the oscillation circuits 40A and 40B configured as the electronic component 90 and the temperatures of the channel portions 34A and 34B can be further increased. Moreover, the housing | casing 270 can be comprised compactly by employ | adopting such a structure.

  Further, if the electronic component 90 is mounted on the piezoelectric substrate 32 as in this modification, the electronic component 90 is automatically placed in the accommodation space 80 by attaching the sensor body 230 to the housing 270. Therefore, the configuration and assembly work of the sensor unit 220 can be simplified.

  Also in this modification, the housing 270 of the sensor unit 220 can be configured to be covered with the same heat insulating material as the heat insulating material 100 of the first modification.

  In addition, the numerical value shown as a specification in the said embodiment and each modification is only an example, and of course, you may set these to a different value suitably.

The block diagram which shows the density | concentration sensor which concerns on one Embodiment of this invention. Plan view showing the sensor body of the concentration sensor as a single item FIG. 4 is a plan sectional view showing the sensor unit of the concentration sensor, taken along the line III-III in FIG. IV-IV sectional view of FIG. The figure similar to FIG. 4 which shows the sensor unit which concerns on the 1st modification of the said embodiment. The figure similar to FIG. 4 which shows the sensor unit which concerns on the 2nd modification of the said embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Concentration sensor 20, 120, 220 Sensor unit 22A Short channel side closed loop circuit 22B Open channel side closed loop circuit 30, 230 Sensor body 32 Piezoelectric substrate 34A Short channel (first channel part)
34Ai, 34Bi Input electrode finger 34Ao, 34Bo Output electrode finger 34A1, 34A2, 34B1, 34B2 Cross finger electrode 34A3 Conductive layer 34B Open channel (second channel portion)
34g Ground electrode finger 36Ai, 36Ao, 36Bi, 36Bo, 36g External connection terminal 38Ai, 38Ao, 38Bi, 38Bo, 38g Conductive layer 40A Short channel side oscillation circuit (first oscillation circuit)
40B Open channel oscillation circuit (second oscillation circuit)
42A, 42B High frequency amplifier 44A, 44B Automatic gain control circuit 46A, 46B Low pass filter 50 Control unit 52 CPU
54 Frequency counter 56 A / D converter 60 Power supply 62A, 62B On / off switch 70, 270 Housing 72 Upper frame 72a Rectangular opening 72b Notch 72c, 72e, 74e Seal groove 72d Beam-like part 74, 274 Lower frame 74a Rectangular Hole 74b Bottom notch 74c Band-shaped projection 74d Step-down recess 74f Cavity 74g Floor-like portion 76 Base plate 76a Step-up recess 78, 278 Cover member 78a Projection 78b Inflow hole 78c Discharge hole 80 Housing space 82, 84, 86 Seal member 90 Electronic component 92 Support substrate 94, 96, 294 Conductive layer 98 Bonding wire 100 Heat insulating material 202 Coating

Claims (5)

A housing in which a storage space for storing a test solution is formed;
On the piezoelectric substrate, a first channel part in which a pair of cross finger electrodes are arranged at a predetermined interval, and a pair of cross finger electrodes are arranged in parallel with the first channel part at a predetermined interval. A sensor body attached to the housing in a state where the first and second channel portions are exposed to the housing space, and a second channel portion is formed.
A first oscillation circuit and a second oscillation circuit that are connected to each channel portion of the sensor body and constitute a closed-loop circuit that causes self-excited oscillation with the channel portion;
The first channel portion is configured as a short channel in which a region on the piezoelectric substrate between the two crossed finger electrodes of the channel portion is covered with a conductive layer short-circuited to the ground electrode fingers of the two crossed finger electrodes. And the second channel portion is configured as an open channel exposing a region on the piezoelectric substrate between both crossed finger electrodes of the channel portion,
Each oscillation circuit includes a high-frequency amplifier and an automatic gain control circuit that adjusts the gain of the high-frequency amplifier.
Among the pair of cross finger electrodes in each channel part, one cross finger electrode is excited to generate a surface acoustic wave on the piezoelectric substrate, and the surface acoustic wave propagated to the other cross finger electrode is In the concentration sensor configured to receive vibration with the interdigitated electrode,
A concentration sensor, wherein electronic components constituting the first and second oscillation circuits are arranged at substantially the same environmental temperature as the first and second channel portions. At least a part of the peripheral wall portion surrounding the accommodation space in the housing is configured by a member having a low thermal resistance,
The electronic component is mounted on the surface of the support substrate,
The support substrate is arranged so that the back surface of the support substrate is brought into surface contact with an outer surface of a portion made of a member having low thermal resistance in the peripheral wall portion of the housing. 1. The concentration sensor according to 1.   The concentration sensor according to claim 1, wherein the electronic component is disposed in the housing space in a state of being covered with a film.   The concentration sensor according to claim 3, wherein the electronic component is mounted on the piezoelectric substrate. The entire casing is composed of a member having low thermal resistance,
The concentration sensor according to claim 1, wherein the casing is covered with a heat insulating material.

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