Sensing device

Abstract

To enhance the convenience of a sensing device which senses a material to be sensed contained in ambient gas around a piezoelectric vibrator on the basis of a change of an oscillatory frequency of the piezoelectric vibrator.SOLUTION: A sensing device which senses a material to be sensed contained in ambient gas around a piezoelectric vibrator on the basis of a change of an oscillation frequency of the piezoelectric vibrator, includes the piezoelectric vibrator to which the material to be sensed attaches, a first oscillation circuit which makes the piezoelectric vibrator vibrate in a first vibration order, a second oscillation circuit which makes the piezoelectric vibrator vibrate in a second vibration order larger than the first vibration order, a frequency measurement part which measures oscillation frequencies output from each of the first oscillation circuit and the second oscillation circuit, a temperature change part which changes the temperature of the piezoelectric vibrator, and a temperature control part which increases the temperature of the piezoelectric vibrator by the temperature change part on the basis of a frequency signal output from the second oscillation circuit.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a sensing device using a piezoelectric vibrator. [Background technology]

[0002] Quartz Thermogravimetric Analysis (QTGA) using a quartz crystal oscillator is well known. Specifically, QTGA involves heating or cooling a quartz crystal oscillator to cause substances contained in the gas surrounding the quartz crystal oscillator to adhere to or desorb from the quartz crystal oscillator. This analysis uses a QCM (quartz crystal microbalance) to analyze the substances based on the resulting change in the oscillation frequency of the quartz crystal oscillator.

[0003] Such a device for performing QTGA is configured to sense the state of adhesion of substances in the gas to the quartz crystal oscillator by including a quartz crystal oscillator, an oscillation circuit, a means for changing the temperature of the quartz crystal oscillator, and a means for monitoring the oscillation frequency of the quartz crystal oscillator. For example, Patent Document 1 shows such a device. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 6714235 DISCLOSURE OF THE INVENTION [Problem to be solved by the invention]

[0005] When performing QTGA, it may be necessary to place a module containing a quartz crystal oscillator for the above-mentioned sensing device in an analysis environment for a relatively long time, allowing substances contained in the gas to adhere to the quartz crystal oscillator while monitoring the oscillation frequency. In this case, there is a concern that the amount of adhered substances may become excessive, causing the quartz crystal oscillator to stop oscillating, making it impossible to perform QTGA. As will be described in detail in the embodiments of the present invention, when performing QTGA, it is desirable to obtain oscillation frequencies at higher vibrational orders in addition to lower vibrational orders. However, oscillations at these higher vibrational orders are more likely to stop.

[0006] For these reasons, it may be necessary to prepare multiple quartz crystal oscillator sensors and perform analysis using a new sensor instead of the one previously used before the quartz crystal oscillator stops oscillating, or to heat the quartz crystal oscillator at a preset timing after the start of measurement to desorb the substance and then reattach it. However, increasing the number of sensors used as described above increases the effort and cost of the analysis. Furthermore, because the quartz crystal oscillator's oscillation stops depending on various factors, such as the temperature and vacuum level in the analysis environment and the type of substance attached, it is difficult to accurately determine when the oscillation will actually stop. Therefore, when heating the quartz crystal oscillator as described above, the heating timing is set relatively far ahead of the expected timing of oscillation stop. As a result, it is not possible to continuously observe the state of substance adhesion to the quartz crystal oscillator for a sufficient period of time, which may result in insufficient analysis accuracy.

[0007] The device in Patent Document 1 describes that, in identifying the desorption temperature and desorption rate of gas from a quartz crystal oscillator, it utilizes the fundamental wave and the triple wave of the oscillation frequency of a detection quartz crystal oscillator configured to allow the adhesion of substances contained in the gas, and a reference quartz crystal oscillator to which the substances cannot adhere. However, Patent Document 1 does not disclose a method for solving the above problem.

[0008] The present invention has been made in consideration of the above circumstances, and its purpose is to provide a technology that can improve the convenience of a sensing device that senses a substance to be sensed contained in a gas surrounding a piezoelectric vibrator based on changes in the oscillation frequency of the piezoelectric vibrator. [Means for solving the problem]

[0009] The sensing device of the present invention senses a substance to be sensed contained in a gas surrounding a piezoelectric vibrator based on a change in the oscillation frequency of the piezoelectric vibrator, the piezoelectric vibrator to which the substance to be sensed adheres; a first oscillation circuit that causes the piezoelectric vibrator to oscillate at a first vibration order; a second oscillation circuit that causes the piezoelectric vibrator to oscillate at a second vibration order greater than the first vibration order; a frequency measurement unit that measures the oscillation frequencies output from the first oscillation circuit and the second oscillation circuit; a temperature change unit that changes the temperature of the piezoelectric vibrator; a temperature control unit that raises the temperature of the piezoelectric vibrator using the temperature change unit based on a frequency signal output from the second oscillation circuit; Equipped with. [Effects of the Invention]

[0010] According to the sensing device of the present invention, the temperature of the piezoelectric vibrator is raised to prevent the frequency signal from the first oscillation circuit, which oscillates the piezoelectric vibrator at a low vibration order, from becoming unobtainable, and the timing of this temperature rise can be prevented from being significantly advanced from the timing at which the frequency signal from the first oscillation circuit becomes unobtainable. Therefore, the transition of the frequency signal from the first oscillation circuit until the temperature rise can be observed over a long period of time, the sensing target substance can be sensed with high sensitivity using the frequency signal from the second oscillation circuit, and work can be prevented from being stopped due to the frequency signals from both the first and second oscillation circuits becoming unobtainable. Due to these advantages, the sensing device of the present invention is highly convenient. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a longitudinal sectional side view of a sensing device according to an embodiment of the present invention; [Figure 2] FIG. 2 is a block diagram of the sensing device. [Figure 3] FIG. 2 is a block diagram showing the connection between a crystal oscillator and an oscillation circuit in the sensing device. [Figure 4] FIG. 10 is a graph illustrating an example of operation of the sensing device. DETAILED DESCRIPTION OF THE INVENTION

[0012] A sensing device 1 according to one embodiment of the present invention will be described with reference to the vertical cross-sectional side view of Fig. 1. The sensing device 1 is a device for performing QTGA, and is composed of a sensing sensor 10 including a quartz crystal resonator 5 and an oscillation circuit, a connection member 23 to which the sensing sensor 10 is attached and detached, and a control unit 7 that detects the oscillation frequency and supplies power to each part of the sensing sensor 10.

[0013] The detection sensor 10 is configured by arranging a base 2, a Peltier element unit 3, and a vibrator holder 4 in this order, and adjacent members among these components are connected to each other. In the following description of the configuration of the detection sensor 10, the description will be given assuming that the base 2 and the vibrator holder 4 are positioned on the lower and upper sides, respectively. However, the arrangement of the detection sensor 10 is not limited to the orientation described here, and the orientation of the detection sensor 10 during use is arbitrary. The above-mentioned quartz crystal vibrator 5 is supported from below by the vibrator holder 4.

[0014] The base 2 is configured as a circular block in a plan view, with its central portion protruding upward to form a circular platform 21, on which the Peltier element unit 3 is mounted. The underside of the base 2 also protrudes, forming a square connector 22. When the connector 22 is inserted into a recess 24 of the connection member 23, a terminal formed on the connector 22 is electrically connected to the control unit 7 via a conductive path (not shown) formed in the connection member 23. The connection member 23 is cooled by a cooling mechanism (not shown), and when the connector 22 is inserted into the recess 24, it comes into contact with the base 2 from below and cools the base 2.

[0015] The Peltier element unit 3 described above is a temperature change unit that heats and cools the crystal unit 5, which is a piezoelectric vibrator, via the vibrator holder 4, and is composed of a first Peltier element 31 and a second Peltier element 32 stacked on top of each other. The first Peltier element 31 is disposed on the bottom, and the second Peltier element 32 is disposed on the top. When cooling the crystal unit 5, the top surface of the first Peltier element 31 and the second Peltier element 32 act as heat absorption surfaces and heat dissipation surfaces, respectively. When heating the crystal unit 5, the top surface of the first Peltier element 31 and the second Peltier element 32 act as heat dissipation surfaces and heat absorption surfaces, respectively. In this way, when cooling the crystal unit 5, the first Peltier element 31 cools the heat dissipation surface of the second Peltier element 32, so the Peltier element unit 3 can cool the crystal unit 5 to a relatively low temperature. Heat generated from the heat dissipation surface of the first Peltier element 31 during cooling is dissipated to the connecting member 23 via the base 2. The Peltier element unit 3 changes the temperature of the crystal oscillator 5 within a range of, for example, -80°C to +125°C.

[0016] An enclosed space 25 is formed in the center of the base 2 in a plan view, and a circuit board 26 is provided in the enclosed space 25. Note that a heat insulating member (not shown) is interposed between the circuit board 26 and the wall surface that forms the enclosed space 25 so that the circuit board 26 is not affected by the heat dissipation from the Peltier element unit 3. An integrated circuit chip (IC chip) 27 is provided on the circuit board 26. The integrated circuit chip 27 includes a first oscillation circuit 61, a second oscillation circuit 62, and switches 63 to 65, which will be described later.

[0017] The resonator holder 4 is configured as a horizontally oriented substrate having a recess 41 that opens upward. The opening edge of the recess 41 supports the peripheral edge of the quartz crystal resonator 5 from the underside so that the undersides of a first vibrating region 51 and a second vibrating region 52 of the quartz crystal resonator 5 (described later) face the recess 41, and holds the quartz crystal resonator 5 in a horizontal position.

[0018] Next, the configuration of the quartz crystal unit 5 will be described with reference to FIG. 2. FIG. 2 shows the top surface of the quartz crystal unit 5 and is also a block diagram showing the configuration of the integrated circuit chip 27. The quartz crystal unit 5 includes a circular quartz crystal blank 50, which is, for example, an AT-cut piezoelectric piece. A pair of first excitation electrodes (detection electrodes) 51, 53 and a pair of second excitation electrodes (reference electrodes) 52, 54, each made of, for example, gold (Au), are arranged spaced apart on one side (top side) and the other side (bottom side) of the quartz crystal blank 50. In the quartz crystal blank 50, the region sandwiched between the first excitation electrodes 51, 53 forms a first vibrating region 55, and the region sandwiched between the second excitation electrodes 52, 54 forms a second vibrating region 56. These first vibrating region 55 and second vibrating region 56 can vibrate independently.

[0019] The excitation electrodes 51-54 are circular, and part of the edge of the circle is extended toward the periphery of the quartz crystal unit 5 to form an extension electrode 57. In addition, a platinum (Pt) resistor, for example, is provided on the quartz crystal blank 50 as a temperature sensor 58, and both ends of the resistor are connected to a conductive pattern 59 made of Au formed on the quartz crystal blank 50. The control unit 7 supplies current to the temperature sensor 58 and detects its resistance value, and the control unit 7 detects the temperature of the quartz crystal unit 5 based on the detected resistance value. The extension electrode 57 and the conductive pattern 59 are connected to terminals of the circuit board 26 via a conductive pattern provided on the resonator holder 4 and a rod-shaped conductive member 28 extending vertically between the resonator holder 4 and the circuit board 26.

[0020] The terminals of the connector 22 of the base are electrically connected to the respective terminals of the Peltier element unit 3 and the circuit board 26 via conductive paths provided in the base 2. As described above, the connector 22 is inserted into the recess 24 of the connection member 23, and the terminals of the connector 22 are connected to the control unit 7, whereby the integrated circuit chip 27 on the circuit board 26, the temperature sensor 58, the excitation electrodes 51 to 54 that constitute the crystal resonator 5, and the Peltier element unit 3 are electrically connected to the control unit 7. Figure 3 is a block diagram showing the state in which such connections have been made.

[0021] The detection sensor 10 also includes a cover 11. The cover 11 includes a main portion 12 that is circular in plan view and covers the crystal oscillator 5 and the oscillator holder 4 from above, and a tubular portion 13 that extends downward from the periphery of the main portion 12 and surrounds the sides of the oscillator holder 4 and the Peltier element unit 3, with the lower end of the tubular portion 13 contacting the outside of the platform 21 on the base 2. A circular through-hole 14 is formed in the main portion 12 at a position that overlaps the first excitation electrode 51 in plan view, and the periphery of the through-hole 14 extends downward to form a tubular shield 15 that is close to the first excitation electrode 51. By forming the cover 11 in this manner, the substance to be sensed that is contained in the gas surrounding the detection sensor 10 adheres exclusively to the excitation electrode 51 of the excitation electrodes 51 to 54 (the first vibration region 55 as a vibration region, and the first vibration region 55 of the second vibration region 56).

[0022] In the sensing device 1, the control unit 7 acquires the oscillation frequency of the first vibration area 55 to which the sensed substance contained in the gas adheres, as described above, and the oscillation frequency of the second vibration area 56 to which the sensed substance does not adhere. By calculating the difference between the oscillation frequencies output from the first vibration area 55 and the second vibration area 56, it is possible to cancel the influence of temperature changes around the sensing sensor 10 and to detect with high accuracy the adhesion state of the sensed substance to the first vibration area 55. Therefore, the first vibration area 55 is a vibration area for detecting the sensed substance, and the second vibration area is a vibration area for reference.

[0023] To explain the acquisition of the oscillation frequency in more detail, the sensing device 1 switches between oscillation at the fundamental wave and oscillation at the third harmonic (third overtone of the fundamental wave) in a time-division manner for each of the first vibration region 55 and the second vibration region 56. Therefore, the device is configured to be able to acquire the oscillation frequency of the fundamental wave in the first vibration region 55 and the oscillation frequency of the fundamental wave in the second vibration region 56 and calculate the difference therebetween, and also to acquire the oscillation frequency of the third harmonic in the first vibration region 56 and the oscillation frequency of the third harmonic in the third vibration region 56 and calculate the difference therebetween.

[0024] The first oscillation circuit 61 included in the integrated circuit chip 27 causes the first vibrating area 55 and the second vibrating area 56 to oscillate at a fundamental wave, and the second oscillation circuit 62 causes the first vibrating area 55 and the second vibrating area 56 to oscillate at a third harmonic wave. Specifically, for example, at room temperature, the first oscillation circuit 61 oscillates the first vibrating area 55 and the second vibrating area 56 at 10 MHz and the second oscillation circuit 62 oscillates the first vibrating area 55 and the second vibrating area 56 at 30 MHz, respectively.

[0025] The reason for oscillating at the fundamental wave with a vibration order of 1 and the triple wave with a vibration order of 3 is as follows: The higher the vibration order, the greater the amount of change in frequency relative to the amount of sensed substance adhering to the excitation electrode, thereby increasing the detection sensitivity of the sensed substance. However, the higher the vibration order, the lower the negative resistance of the oscillation circuit, thereby reducing the oscillation margin. This means that the amount of sensed substance that can adhere to the excitation electrode before oscillation stops is reduced, and therefore the range of frequencies that can be measured is narrower.

[0026] In other words, whether it is advantageous to use the fundamental wave or the third harmonic wave to perform QTGA depends on the amount of gas in the environment in which the sensing sensor 10 is placed. To give a specific example, suppose that in order to observe the release status of gas (outgassing) from a component (such as a part or adhesive) constituting a system used in space, such as an artificial satellite, the component and the sensing sensor 10 are placed in an arbitrary environment and frequency measurements are performed. If a small amount of outgas is released from the component, it is advantageous to use an oscillation frequency at the third harmonic wave to observe the release status of the outgas, as this allows for a highly accurate understanding of the release status. On the other hand, if the amount of outgassing is relatively large, it is advantageous to observe the release status using an oscillation frequency at the fundamental wave, which is less likely to cause the oscillation output to stop even if a large amount of material adheres to the excitation electrode.

[0027] Therefore, the sensing device 1 is configured to acquire the oscillation frequencies of the fundamental wave and the third harmonic wave as described above. The sensing device 1 utilizes the property that, as the deposition of substances contained in the gas on the first excitation electrode 51 progresses, the oscillation of the third harmonic wave in the first vibration region 55 stops before the oscillation of the fundamental wave, and heats and raises the temperature of the quartz crystal oscillator 5 based on the timing of the stop of the oscillation of the third harmonic wave. This prevents the oscillation of the fundamental wave from stopping. More specifically, the control unit 7 constituting the sensing device 1 detects whether or not a frequency signal of the third harmonic wave in the first vibration region 55 is output to the control unit 7. That is, it is detected whether or not the oscillation of the third harmonic wave in the first vibration region 55 has stopped. When the control unit 7 detects that the output of the third harmonic frequency signal has stopped, the control unit 7 uses the Peltier element unit 3 to heat the quartz oscillator 5, causing the sensed substance adhering to the first excitation electrode 51 to detach, thereby preventing the fundamental wave of the first vibration region 55 from halting oscillation and enabling the acquisition of the oscillation frequency at the fundamental wave to continue.

[0028] Returning to Fig. 2, the elements provided on the integrated circuit chip 27 will be described. A switch 63 is provided downstream of the first excitation electrodes 51, 53 and the second excitation electrodes 52, 54, and a switch 64 is provided downstream of the switch 63. Note that the first excitation electrode 53 and the second excitation electrode 54 on the underside are not shown in Fig. 2. A first oscillation circuit 61 and a second oscillation circuit 62 are provided downstream of the switch 64, a switch 65 is provided downstream of the first oscillation circuit 61 and the second oscillation circuit 62, and a control unit 7 is provided downstream of the switch 65.

[0029] The switches 63 and 64 sequentially switch in a time-division manner among a state in which the first excitation electrodes 51 and 53 are connected to the first oscillation circuit 61 and the first vibration area 55 oscillates with the fundamental wave, a state in which the first excitation electrodes 51 and 53 are connected to the second oscillation circuit 62 and the first vibration area 55 oscillates with the third harmonic wave, a state in which the second excitation electrodes 52 and 54 are connected to the first oscillation circuit 61 and the second vibration area 56 oscillates with the fundamental wave, and a state in which the second excitation electrodes 52 and 54 are connected to the second oscillation circuit 62 and the second vibration area 56 oscillates with the third harmonic wave. The switch 65 operates in synchronization with the operation of the switches 63 and 64, and alternately switches between the connection of the first oscillation circuit 61 to the control unit 7 and the connection of the second oscillation circuit 62 to the control unit 7 in a time-division manner.

[0030] By the operation of the switches 63 to 65, the first vibrating area 55 and the second vibrating area 56 oscillate in a time-division manner, and the fundamental frequency signal from the first vibrating area 55, the third harmonic frequency signal from the first vibrating area 55, the fundamental frequency signal from the second vibrating area 56, and the third harmonic frequency signal from the second vibrating area 56 are repeatedly output in time-division order to the control unit 7. Hereinafter, with regard to the frequency of the signal output from the first oscillation circuit 61, the fundamental frequency in the first vibrating area 55 will be referred to as the fundamental detection frequency F1, and the fundamental frequency in the second vibrating area 56 will be referred to as the fundamental reference frequency F1'. With regard to the frequency of the signal output from the second oscillation circuit 62, the third harmonic frequency in the first vibrating area 55 will be referred to as the third harmonic detection frequency F3, and the third harmonic frequency in the second vibrating area 56 will be referred to as the third harmonic reference frequency F3'.

[0031] Next, the control unit 7 constituting the temperature control section will be described with reference to FIG. 3. The control unit 7 includes a power supply section 71, a frequency measurement section 72, a screen display section 73, a temperature detection section 74, and a temperature control program 75. The power supply section 71 supplies power to each section of the device, such as the integrated circuit chip 27, the Peltier element unit 3, and the temperature sensor 58; however, for convenience, FIG. 3 shows the power supply section 71 supplying power only to the integrated circuit chip 27 and the Peltier element unit 3. The frequency measurement section 72 receives the frequency signal output from the integrated circuit chip 27 and measures the fundamental wave detection frequency F1, the fundamental wave reference frequency F1', the third harmonic detection frequency F3, and the third harmonic reference frequency F3'. The screen display section 73 displays the fundamental wave detection frequency F1, the fundamental wave reference frequency F1', the third harmonic detection frequency F3, and the third harmonic reference frequency F3' measured by the frequency measurement section 72.

[0032] As described above, the temperature detection unit 74 detects the temperature of the crystal unit 5 from the resistance value of the temperature sensor 58. The temperature control program 75 monitors the third harmonic detection frequency F3 and controls the power supplied from the power supply unit 71 to the Peltier element unit 3, thereby controlling the temperature of the crystal unit 5. This temperature control program 75 controls the temperature of the crystal unit 5 when it becomes impossible to obtain the third harmonic detection frequency F3. The value detected by the temperature detection unit 74 is used to control the temperature of the crystal unit 5 in this manner. An example of temperature control of the crystal unit executed by this temperature control program 75 will be shown in the operation example of the device described below.

[0033] Next, an example of operation of the sensing device 1 will be described with reference to Fig. 4. Fig. 4 is a chart showing the changes in the fundamental wave detection frequency F1, fundamental wave reference frequency F1', third harmonic wave detection frequency F3, and third harmonic wave reference frequency F3' obtained during measurement, in correspondence with the changes in the temperature of the crystal resonator 5 obtained by the temperature sensor 58 during measurement.

[0034] In this measurement, the detection sensor 10 and the member to be measured are placed in a measurement environment that has been evacuated, and the outgassing status from the member to be measured is observed. The measurement environment is provided with, for example, a shutter that can be opened and closed, and it is possible to switch between a state in which the member to be measured and the detection sensor 10 are isolated by closing the shutter, and a state in which the member to be measured and the detection sensor 10 are not isolated by opening the shutter.

[0035] At time t0 in the chart, the control unit 7 begins acquiring the fundamental wave detection frequency F1, fundamental wave reference frequency F1', third harmonic detection frequency F3, and third harmonic reference frequency F3'. At the following time t1, the Peltier element unit 3 begins cooling the crystal oscillator 5, lowering the temperature of the crystal oscillator 5. The change in temperature changes the oscillation characteristics of the crystal oscillator 5, causing each of the frequencies F1, F1', F3, and F3' to change.

[0036] As cooling by the Peltier element unit 3 continues, the temperature of the crystal oscillator 5 further drops, and when the crystal oscillator 5 is cooled to a preset temperature (time t2), it is maintained at that temperature. The shutter of the measurement space opens, and the outgas emitted from the component to be measured and supplied to the periphery of the crystal oscillator 5 is cooled, causing the substance to be sensed contained in the gas to adhere to the first excitation electrode 51. This adhesion causes the fundamental wave detection frequency F1 and the third harmonic wave detection frequency F3 to decrease (time t3). Note that the third harmonic wave detection frequency F3 decreases by a larger amount per unit time than the fundamental wave detection frequency F1.

[0037] As the adhesion of the substance to be sensed contained in the gas progresses, the fundamental wave detection frequency F1 and the third harmonic wave detection frequency F3 decrease, but when the adhesion becomes excessive, the oscillation due to the third harmonic wave in the first vibration region 55 stops, and it becomes impossible to obtain the third harmonic wave detection frequency F3 (time t4). Note that, as mentioned above, since the oscillation due to the higher harmonic wave stops before the oscillation due to the lower harmonic wave, the acquisition of the fundamental wave detection frequency F1 continues even when the oscillation due to the third harmonic wave stops.

[0038] Since the third harmonic detection frequency F3 is no longer acquired, the Peltier element unit 3 stops cooling the crystal oscillator 5 and starts heating the crystal oscillator 5 (time t4). As the temperature of the crystal oscillator 5 rises, the sensing substance adhering to the first excitation electrode 51 is desorbed and removed into the measurement space, and the fundamental detection frequency F1 increases. As the desorption of the sensing substance progresses in this manner, the first vibration region 55 becomes capable of oscillating at the third harmonic again, and the third harmonic detection frequency F3 is again acquired (time t5). As the desorption of the sensing substance continues, the third harmonic detection frequency F3 also increases, similar to the fundamental detection frequency F1. When the desorption of the sensing substance is complete, the fundamental detection frequency F1 and the third harmonic detection frequency F3 become constant or remain approximately constant (time t6). Then, when the temperature of the crystal oscillator 5 reaches a preset temperature, the temperature increase of the crystal oscillator 5 stops (time t7). The temperature control of the crystal oscillator 5 from time t4 to time t7 is executed by the temperature control program 75 described above.

[0039] For example, after time t4 when the temperature of the crystal oscillator 5 is raised, the shutter of the measurement space may be closed to isolate the sensing sensor 10 from the object to be measured, and the operation from time t0 onward may be repeated to acquire the frequencies F1, F1', F3, and F3' anew and use them for analysis along with the frequencies acquired up to that point. Alternatively, only the frequencies F1, F1', F3, and F3' acquired up to time t4 may be used for analysis. Note that, as described above, in order to cancel the effect on frequency due to changes in the ambient temperature of the crystal oscillator 5, F1-F1' and F3-F3' at each time may be calculated, and the time series data of F1-F1' and F3-F3' may be used. The control unit 7 may be configured to calculate and display the time series data of F1-F1' and F3-F3'.

[0040] As described above, the sensing device 1 heats and raises the temperature of the crystal resonator 5 based on whether or not the third harmonic wave detection frequency F3 has been acquired (i.e., whether or not the first vibration region 56 oscillates at the third harmonic wave), thereby preventing the output of the fundamental wave detection frequency F1 from being stopped and preventing the timing of this heating from being too early relative to the timing of the output of the fundamental wave detection frequency F1 being stopped.This makes the device highly convenient.

[0041] 4, the Peltier element unit 3 starts heating the crystal unit 5 at the same time that it becomes impossible to acquire the third harmonic wave detection frequency F3, but the timing of heating the crystal unit 5 is not limited to the same time that it becomes impossible to acquire the third harmonic wave detection frequency F3. For example, heating may start after a preset time has elapsed since it becomes impossible to acquire the third harmonic wave detection frequency F3.

[0042] Furthermore, the decrease in the third harmonic detection frequency F3 per unit time is greater than the decrease in the fundamental detection frequency F1 per unit time. Therefore, heating of the crystal unit 5 may be initiated when the third harmonic detection frequency F3 decreases after starting measurement and reaches a preset frequency (reference frequency). Alternatively, heating of the crystal unit 5 may be initiated when the third harmonic detection frequency F3 decreases by a predetermined amount. Therefore, controlling the timing of heating of the crystal unit 5 based on the third harmonic detection frequency F3 is not limited to triggering the occurrence of the inability to acquire the third harmonic detection frequency F3 (stopping of third harmonic oscillation), as in the examples described above. However, heating the crystal unit 5 while the third harmonic oscillation is occurring may result in heating being initiated relatively much earlier than the timing at which the fundamental detection frequency F1 cannot be acquired. Therefore, from the perspective of lengthening the period during which the fundamental detection frequency F1 is acquired before heating the crystal unit 5, it is preferable to trigger heating of the crystal unit 5 when the third harmonic detection frequency F3 cannot be acquired, as described above.

[0043] Although the above example illustrates the acquisition of the frequencies of the fundamental wave and the third harmonic wave, the acquired frequencies are not limited to the fundamental wave and the third harmonic wave. For example, the device may acquire the fundamental wave and the fifth harmonic wave (fifth harmonic wave as the vibration order), or the third harmonic wave and the fifth harmonic wave. As described above, when the sensing substance accumulates on the excitation electrode of the quartz crystal oscillator, the oscillation of the higher harmonic wave stops before the oscillation of the lower harmonic wave. Therefore, when the fundamental wave and the fifth harmonic wave are used, the cessation of the oscillation of the fifth harmonic wave, which has a higher vibration order, is triggered to heat the quartz crystal oscillator 5. Similarly, when the third harmonic wave and the fifth harmonic wave are used, the cessation of the oscillation of the fifth harmonic wave, which has a higher vibration order, is triggered to heat the quartz crystal oscillator 5. However, as described above, the higher the vibration order, the smaller the amount of sensing substance that can be attached while vibrating the first vibration region 55. Therefore, it is preferable to use the fundamental wave and the third harmonic wave from the viewpoint of observing the state of the sensing substance around the sensing sensor by performing frequency measurement over a relatively long period of time.

[0044] However, the sensing device is not limited to a configuration including the Peltier element unit 3. As a specific example, instead of the Peltier element unit 3, a rod-shaped support member extending upward is provided on the base 2, and this support member supports the oscillator holder 4, and the oscillator holder 4 is provided with a heater whose temperature can be changed. Then, the connection member 23 into which the connector 22 of the base 2 is inserted can be cooled to a relatively low, constant temperature by, for example, liquid nitrogen, and the crystal oscillator 5 can also be cooled to a relatively low temperature by heat transfer via the base 2, the support member, and the oscillator holder 4. When the device is configured in this way, the heater of the oscillator holder 4 is the temperature changer, and changing the temperature of the heater changes the temperature of the crystal oscillator 5.

[0045] Furthermore, in the above-described sensing device 1, the crystal oscillator that vibrates at the fundamental wave and the crystal oscillator that vibrates at the third harmonic wave are the same. That is, the crystal oscillator 5 is configured to be shared by the first oscillation circuit 61 and the second oscillation circuit 62, but a crystal oscillator may be provided for each oscillation circuit. When raising the temperature of the crystal oscillator 5, the power supplied to the Peltier element unit 3 may be reduced to reduce the cooling performance of the Peltier element unit 3. That is, raising the temperature is not limited to heating the crystal oscillator 5.

[0046] The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive, and various omissions, substitutions, modifications, and combinations may be made to the above-described embodiments without departing from the scope and spirit of the appended claims. [Explanation of symbols]

[0047] 3 Peltier element unit 5 crystal oscillator 61 First oscillator circuit 62 Second oscillator circuit 72 Frequency measurement section 75 Temperature Control Program

Claims

1. 1. A sensing device that senses a substance to be sensed contained in a gas surrounding a piezoelectric vibrator based on a change in the oscillation frequency of the piezoelectric vibrator, the piezoelectric vibrator to which the substance to be sensed adheres; a first oscillation circuit that causes the piezoelectric vibrator to oscillate at a first vibration order; a second oscillation circuit that causes the piezoelectric vibrator to oscillate at a second vibration order greater than the first vibration order; a frequency measurement unit that measures the oscillation frequencies output from the first oscillation circuit and the second oscillation circuit; a temperature change unit that changes the temperature of the piezoelectric vibrator; a temperature control unit that raises the temperature of the piezoelectric vibrator using the temperature change unit based on a frequency signal output from the second oscillation circuit; A sensing device comprising:

2. The sensing device according to claim 1 , wherein the temperature control unit increases the temperature of the piezoelectric vibrator using the temperature change unit when the second oscillation circuit stops outputting the frequency signal.

3. 3. The sensing device according to claim 2, wherein the first oscillation circuit oscillates the piezoelectric vibrator with a fundamental wave, and the second oscillation circuit oscillates the piezoelectric vibrator with a third harmonic wave.

4. the piezoelectric vibrator is shared by the first oscillation circuit and the second oscillation circuit, 4. The sensing device according to claim 3, which is oscillated in a time-division manner.

5. the piezoelectric vibrator includes a first vibration region and a second vibration region; a cover is provided that covers the second vibration region to prevent the substance from adhering to the second vibration region; 5. The sensing device according to claim 4, wherein the first vibration region and the second vibration region oscillate in a time-division manner.

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