JP4369452B2 - Concentration sensor and concentration detection device. - Google Patents

Description

  The present invention uses a piezoelectric piece, for example, a quartz piece, in which an adsorption layer for adsorbing a sensing object is formed on its surface, and its natural frequency changes due to the adsorption of the sensing object. The present invention relates to a technical field of an apparatus for detecting the concentration of a sensing object by detecting the above.

  As a technique for sensing a very small amount of substance, a concentration detection device using a crystal resonator is known. In this concentration detection device, an adsorption layer for adsorbing a sensing object is formed on the surface of a quartz oscillator to constitute a quartz sensor (concentration sensor). When the sensing object adheres to the adsorption layer, its natural frequency is increased. A measurement unit that measures the concentration of a sensing object by utilizing the change in accordance with the amount of adhesion, and more specifically, a measurement unit that connects an oscillation circuit to a crystal sensor and measures the oscillation frequency of the oscillation circuit The main part is configured. According to such a technique, there are advantages that the application range is wide, the apparatus is simple in configuration, and the sensitivity is high, so even a very small amount of substance can be measured.

  For example, in Patent Document 1, if a quartz sensor is used to analyze a plague marker substance contained in blood, urine, etc., it is an effective technique to replace an immune latex kit that requires an expensive and large automatic analyzer. Is described. As described above, when the quartz sensor is used as a biosensor, an adsorption layer made of an antibody that causes an antibody-antigen reaction with respect to the substance to be sensed is formed on the quartz vibrator.

By the way, when the quartz sensor is immersed in the liquid, the value of the equivalent series resistance of the quartz piece increases at a level of, for example, several hundreds Ω, and increases, for example, by about 150 Ω for pure water. For this reason, it is designed to give a large amount of energy to the crystal piece, but the interelectrode capacitance C0 of the crystal resonator consumes this energy, resulting in energy loss. For this reason, it is necessary to cancel the interelectrode capacitance C0 on the oscillation circuit side. However, even if a certain crystal sensor has the interelectrode capacitance C0 canceled by an inductor on the oscillation circuit side, a crystal sensor having a different interelectrode capacitance C0 is used. When replacing, it is necessary to adjust the inductance value of the inductor on the oscillation circuit side. This operation is complicated and time consuming, in which the user measures the interelectrode capacitance C0 with an LCR meter or the like for each type of quartz sensor, calculates the measured value based on the measured value, and replaces the inductor with a corresponding inductance value. Will be forced to work. Instead of exchanging the inductor, it may be possible to prepare an oscillation circuit corresponding to the type of crystal sensor to be used, but in this case, an expensive system is required.
Patent Document 2 describes that it is necessary to cancel the capacitance between the electrodes by connecting an inductance in parallel to the crystal resonator. However, the technical field is completely different and the problem of the present invention can be solved. Absent.

JP 2001-83154 A: Paragraphs 0002 and 0004 Japanese Utility Model Publication No. 61-85920: FIG.

  The present invention has been made under such circumstances, and a common oscillation circuit is used in a concentration sensor using a piezoelectric piece whose natural frequency changes due to adsorption of a sensing object and a concentration detection device using the same. However, it is to provide a technique capable of dealing with a plurality of types of density sensors.

The present invention is detachably connected to the instrument body to be placed outside the Rutotomoni sample solution comprising an oscillating circuit, at a concentration sensor for detecting the concentration of the sensing target,
A wiring board on which wiring is formed; and
A piezoelectric piece, an electrode provided on one side and the other side of the piezoelectric piece and connected to the wiring, and provided on the surface of the electrode on the one side, for adsorbing the sensing object in the sample liquid A piezoelectric vibrator including an adsorption layer, the natural frequency of which changes due to adsorption of the sensing object;
The piezoelectric piece is provided on the wiring substrate in parallel with the substrate, and the electrode on the other surface is provided so as to face a space partitioned from a region where the sample liquid is located;
Provided between the wirings on the wiring board so as to be connected in parallel to the piezoelectric vibrator, and suppresses the consumption of oscillation energy due to the interelectrode capacitance when the piezoelectric vibrator is placed in the sample liquid. An inductor for
Provided on the wiring board, electrically connected to the electrodes of the piezoelectric vibrator via the wiring, and connected to a terminal on the measuring instrument main body by inserting the wiring board into the measuring instrument main body. And a configured terminal portion .
Wherein forming a housing space for a fluid between the piezoelectric vibrator may be provided upper cover case having a fluid inlet communicating with the receiving space.
A concentration sensor comprising: an inductor connected in parallel to the piezoelectric vibrator and provided between a pair of conductive paths of the wiring board.

The inductance value of the inductor is the minimum of the inductance value that cancels the interelectrode capacitance of the piezoelectric vibrator at the resonance frequency of the piezoelectric vibrator and the inductance value that can oscillate when the piezoelectric vibrator is immersed in the fluid to be measured. It is preferable that an average value with respect to the value is set as a central value, and is set to a value of ± 20% with respect to the central value.
The wiring board is preferably provided with an opening, and the piezoelectric vibrator preferably has a structure in which a lower surface faces a recess formed on the opening.
The concentration sensor of the present invention is configured, for example, as a Langevin type crystal sensor using a crystal piece as a piezoelectric piece, and a crystal resonator is mounted on the substrate and the electrode of the crystal resonator is connected to the substrate via, for example, a conductive adhesive It is configured by connecting the printed wiring forming the upper conductive path and connecting the inductor between the printed wiring.

  The concentration detection apparatus of the present invention detects the concentration of the sensing object based on the above-described concentration sensor, a detachable terminal of the concentration sensor, an oscillation circuit for oscillating the piezoelectric piece, and an oscillation output from the oscillation circuit. And a measuring unit.

  According to the present invention, since the inductor is connected in parallel to the piezoelectric piece constituting the concentration sensor, the consumption of oscillation energy due to the capacitance between the electrodes is suppressed by determining the inductance value to be an appropriate value. The oscillation does not stop in various measured fluids (sample fluids) having different viscosities. And since the density sensor is provided with an inductor, it is not necessary to adjust the oscillation circuit side with respect to various density sensors, that is, it is possible to cope with various density sensors while being a common oscillation circuit. The troublesome and time-consuming work of adjusting the oscillation circuit side on the user side becomes unnecessary.

  Embodiments of the concentration detection apparatus according to the present invention will be described below. First, the overall structure of the concentration detection apparatus will be briefly described. As shown in FIG. 1, the concentration detection apparatus includes a plurality of, for example, eight concentration sensors (quartz sensors) 1 and a measuring instrument main body 100 to which these concentration sensors 1 are detachably attached. As shown in FIGS. 1 and 2, the density sensor 1 includes a wiring board, for example, a printed board 21, and an opening 23 a is formed in the printed board 21. A rubber sheet 22 is stacked on the surface side of the printed circuit board 21, and a concave portion 23 is provided in the rubber sheet 22. On the lower surface side of the rubber sheet 22, a portion corresponding to the recess 23 protrudes, and the protruding portion is fitted into the opening 23. A crystal resonator 24 that is a piezoelectric resonator is provided so as to close the recess 23. That is, one surface side (lower surface side) of the crystal unit 24 faces the opening 23 side, and the lower surface side of the crystal unit 24 is made into an airtight space by the concave portion 23, whereby a Langevin type concentration is obtained. A sensor is configured.

Further, an upper cover case 25 is mounted from above the rubber sheet 22. The upper lid case 25 is formed with an injection port 25a for injecting a sample solution, which is a fluid to be measured, and an observation port 25b for the sample solution. The sample solution is injected from the injection port 25a, and the upper surface side of the crystal resonator 24 The sample solution is filled in the space (the crystal piece is immersed in the sample solution).
The density sensor 1 has a structure in which a crystal resonator 24 is placed on the surface of the printed circuit board 21 so as to close the opening 23 a, and the peripheral portion of the crystal resonator 24 is pressed by the rubber sheet 22. It may be a structure.

  As shown in FIG. 3, the crystal resonator 24 is provided with electrodes 24a and 24b (for example, the back surface side electrode 24b is continuously formed on the peripheral portion on the front surface side) on both surfaces of a circular crystal piece 20, for example. The electrodes 24a and 24b are electrically connected to printed wirings 27a and 27b, which are a pair of conductive paths provided on the substrate 21, via a conductive adhesive 26, respectively. Further, an adsorption layer (not shown) for adsorbing the sensing object is formed on one surface of the crystal unit 24, for example, the surface of the electrode 24a.

Further, as shown in FIGS. 2 to 4, an inductor 3 made of, for example, an individual component is connected between the printed wirings 27 a and 27 b, and this inductor 3 is mounted on the wiring board 21 and is mounted by the upper lid case 25. Covered. The inductor 3 may be formed by a printed pattern.
A method for determining the inductance value of the inductor 3 will be described. The concentration sensor detects the concentration of the sensing substance in the fluid to be measured, for example, the solution to be measured, based on the amount of change in the oscillation frequency according to the mass of the sensing substance adhering to the special adsorption film. Do not stop oscillation in the fluid. However, according to experiments, when the crystal piece 20 is immersed in a liquid sample, the equivalent series resistance R1 of the crystal piece 20 increases dramatically, and the case where the crystal piece 20 is driven at 31 MHz is taken as an example. Is placed in a gas, it is 10Ω, but it is also 500Ω, which makes it very difficult to oscillate.

In order to overcome this problem, the present invention attempts to prevent oscillation by connecting the inductor 3 in parallel to the crystal piece 20 and controlling the phase of the crystal piece 20. However, if the inductance value of the inductor 3 is set to a value that cancels the interelectrode capacitance C0, the following problems occur.
FIG. 5 is a relationship diagram in which the relationship between the inductance value of the inductor 3 and the loop gain is obtained by calculation. Here, the equivalent series resistance R1 of the crystal piece 3 is set to three types of 6.8Ω, 100Ω and 500Ω. The reason why the three values are set in this way is to examine how the relationship between the inductance value and the oscillation loop gain changes using the equivalent series resistance R1 as a parameter, and the viscosity in the solution to be measured of the concentration sensor. This is because the equivalent series resistance R1 when the crystal piece 3 is immersed in the solution is estimated to be 500Ω, and the relationship under severe conditions is grasped. In this example, since the resonance frequency Fr of the crystal piece 20 is 31 MHz and the interelectrode capacitance C0 is 7.05 pF, the inductance value for canceling the interelectrode capacitance C0 at the series resonance point Fr of the crystal piece 20 is about 3, 8 μH. It becomes. This inductance value is represented by 1 / (C0 · ω ² ), where ω is the angular velocity of the resonance frequency Fr.

  However, when the equivalent series resistance R1 is 500Ω, the value of 3 and 8 μH is not an appropriate value because the oscillation loop gain approaches 1. Since this inductance value cannot be exceeded when setting the inductance value, this inductance value is referred to herein as Lmax (maximum value of the setting limit).

On the other hand, in any equivalent series resistance R1, if the inductance value is decreased, the influence of the interelectrode capacitance C0 cannot be canceled and oscillation does not occur, and its limit value is about 2.0 μH. Here, a method for obtaining the limit value of 2.0 μH will be described. The oscillation condition of the oscillation circuit is that the gain is 1 or more and the phase is an integral multiple of 360 degrees when the signal goes around the circuit that becomes the intended oscillation loop. The minimum inductance value that satisfies the latter phase condition is 2.0 μH.
As a specific example of how to obtain these conditions, one point of the intended oscillation loop is cut to form the contact A and the contact B. Then, a signal source of a small signal that allows the circuit to operate linearly is connected to the contact A and driven. At this time, the signal at the contact B is observed, the ratio of the signals at the contact A and the contact B is taken, and the gain and phase when the oscillation loop is completed are examined. Accordingly, when the inductance value of the inductor is changed, a minimum inductance value that does not satisfy the phase condition can be obtained. Then, when the gain is plotted using the inductance value of the inductor connected in parallel to the crystal resonator as a parameter, the result shown in FIG. 5 is obtained.

  The value of the inductance value of 2.0 μH is the inductance value Lmin evaluated as the minimum value of the inductance value that can oscillate when the crystal piece 20 is immersed in the fluid to be measured. As can be seen from FIG. 5, in the concentration sensor, it is not appropriate to set the inductance value to an inductance value Lmax that cancels the interelectrode capacitance C0, and the inductance when the crystal piece 20 is immersed in the liquid to be measured. From the relationship between the inductance value and the oscillation loop gain between the values Lmin and Lmax, it is appropriate to determine a value that provides a sufficient oscillation loop gain without being too close to the oscillation stop region. In this example, the range of 2.3 μH to 3.5 μH of ± 20% around the average value 2.9 μH of the inductance values Lmin and Lmax is handled as the optimum range of the inductance value of the inductor 3. Setting the inductance value in this way stabilizes the characteristics of the mass-produced product when mass-producing the concentration sensor.

  Here, as the equivalent series resistance R1 increases, the degree of decrease in the oscillation loop gain accompanying the increase in the inductance value of the inductor 3 increases, so that the fluid having the highest viscosity among the fluids to be measured in which the concentration sensor is used, for example, In the case of a concentration sensor for both gas and liquid, the inductance values Lmin and Lmax are obtained for the equivalent series resistance R1 when the viscosity is the highest among the liquids to be measured, and the relationship between the inductance value and the oscillation loop gain between them is obtained. Based on this, an appropriate value of the inductance value of the inductor 3 may be determined.

Next, the internal circuit of the measuring instrument main body 100 will be briefly described with reference to FIG. In FIG. 6, reference numeral 4 denotes an oscillation circuit for oscillating the crystal resonator 24 of the density sensor 1, and a measurement unit 6 is connected to the subsequent stage of the oscillation circuit 4 via a buffer amplifier 5. The oscillation circuit 4 is configured as a Colpitts type oscillation circuit, Tr is a transistor as an oscillation amplification element, 40 and 41 are capacitors forming a divided capacitance component, and Vc is a power source. For other parts, 42 to 44 are capacitors, and 45 to 48 are resistors. Reference numeral 49 denotes a terminal portion to which the concentration sensor 1 is detachably connected, and is provided on the measuring instrument main body 100 shown in FIG.
The measurement unit 6 includes, for example, a frequency counter that measures a signal related to the frequency of the oscillation output of the oscillation circuit 4 and a calculation unit that calculates a change in the count number.
In this example, eight density sensors 1 are attached to an eight-channel configuration, and eight channels of the circuit shown in FIG. 6 are prepared, and the output of each channel is switched and connected to the measuring unit 6. Yes.

  Next, the operation of this embodiment will be described. First, the concentration sensor 1 (see FIG. 1) is inserted into the measuring device main body 100, and for example, a solution containing no sensing object is filled in the concentration sensor 1 to obtain a blank value, and the crystal resonator 24 is oscillated. This solution may be pure water or other solution. The oscillation output in the oscillation circuit 3 is input to the measurement unit 6 via the buffer amplifier 5, and for example, the frequency of the oscillation output is measured. Next, in order to detect the sensing object, a solution to be measured, which is a specimen, is injected into the concentration sensor 1, and a change in the oscillation frequency due to insertion of the solution to be measured is obtained by the measuring unit 6, for example, a calibration curve prepared in advance. Based on the change, the concentration of the sensing object is detected.

According to the above-described embodiment, the inductor 3 is connected in parallel to the crystal piece 20, and the value evaluated as the minimum value of the inductance value that can be oscillated when the crystal piece 20 is immersed in the solution to be measured. Since Lmin and a value Lmax for canceling the interelectrode capacitance C0 are obtained, and the relationship between the inductance value and the oscillation loop gain is determined between them, the inductance value is determined to be an appropriate value. The consumption of oscillation energy due to the capacitance C0 can be suppressed, and oscillation does not stop even when used for various fluids with different viscosities. Since the inductor 3 is provided in the concentration sensor 1 that can be attached to and detached from the measuring instrument main body, appropriate measurement can be performed by using the concentration sensor 1 provided with the inductor 3 corresponding to the viscosity of the sample fluid. Therefore, since it is not necessary to adjust the oscillation circuit 4 side for various density sensors, that is, it is possible to cope with various density sensors even though the oscillation circuit 4 is common, the user adjusts the oscillation circuit 4 side. This eliminates the need for complicated and time-consuming work.
Furthermore, according to the above-described density sensor 1, the density sensor 1 can be replaced by attaching / detaching the printed circuit board 21 to / from the measuring instrument main body 100, so that the replacement work is easy. In addition, since the airtight space is formed on the lower surface side of the crystal resonator 24 using the opening 23a formed in the printed circuit board 21 to constitute the Langevin type density sensor, the structure for forming the airtight space is simple. is there.

  The concentration sensor of the present invention is not limited to the determination of the concentration of the sensing object, and includes a presence / absence sensor of the sensing object.

It is a perspective view which shows the external appearance of embodiment of the density | concentration detection apparatus containing the density | concentration sensor which concerns on this invention. It is a longitudinal cross-sectional view which shows the density | concentration sensor used for the said embodiment. It is explanatory drawing which shows the crystal oscillator used for the said embodiment, and surrounding wiring. It is a top view which shows the density | concentration sensor board | substrate and wiring which are used for the said embodiment. It is explanatory drawing which shows the data for determining the inductance value of the inductor provided in the density | concentration sensor used for the said embodiment. It is a block circuit diagram which shows the density | concentration detection apparatus of the said embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Concentration sensor 20 Crystal piece 24 Crystal oscillator 24a, 24b Electrode 27a, 27b Printed wiring which comprises a conductive path 3 Inductor 4 Oscillation circuit 49 Terminal part 5 Buffer amplifier 6 Measuring part 100 Measuring instrument main body

Claims (5)

Is detachably connected to the measuring instrument body to be placed outside the Rutotomoni sample solution comprising an oscillating circuit, at a concentration sensor for detecting the concentration of the sensing target,
A wiring board on which wiring is formed; and
A piezoelectric piece, an electrode provided on one side and the other side of the piezoelectric piece and connected to the wiring, and provided on the surface of the electrode on the one side, for adsorbing the sensing object in the sample liquid A piezoelectric vibrator including an adsorption layer, the natural frequency of which changes due to adsorption of the sensing object;
The piezoelectric piece is provided on the wiring substrate in parallel with the substrate, and the electrode on the other surface is provided so as to face a space partitioned from a region where the sample liquid is located;
Provided between the wirings on the wiring board so as to be connected in parallel to the piezoelectric vibrator, and suppresses the consumption of oscillation energy due to the interelectrode capacitance when the piezoelectric vibrator is placed in the sample liquid. An inductor for
Provided on the wiring board, electrically connected to the electrodes of the piezoelectric vibrator via the wiring, and connected to a terminal on the measuring instrument main body by inserting the wiring board into the measuring instrument main body. A density sensor comprising: a configured terminal portion . Wherein an accommodation space of the fluid is formed between the piezoelectric vibrator, the concentration sensor characterized by comprising an upper cover case having a liquid inlet communicating with the receiving space. The inductance value of the inductor is the minimum value of the inductance value that cancels the interelectrode capacitance of the piezoelectric vibrator at the resonance frequency of the piezoelectric vibrator and the inductance value that can be oscillated when the piezoelectric vibrator is immersed in the sample liquid. The density sensor according to claim 1 or 2, wherein the average value is set to a value of ± 20% with respect to the center value.   4. The wiring board according to claim 1, wherein an opening is provided in the wiring substrate, and the piezoelectric vibrator has a concave surface formed on the opening side facing a lower surface side. Concentration sensor. A concentration sensor according to any one of claims 1 to 4, a terminal portion to which the concentration sensor is detachably connected, and a measuring instrument body including an oscillation circuit for oscillating the piezoelectric vibrator, A concentration detection apparatus comprising:

Images