Sensing device

Abstract

To achieve stable temperature control of a piezoelectric vibrator in a sensing device that detects a substance to be detected, under relatively low temperature conditions. [Solution] The sensing device of the present invention comprises a piezoelectric vibrator, an oscillation circuit for causing the piezoelectric vibrator to oscillate, a Peltier element for changing the temperature of the piezoelectric vibrator, a case for housing the piezoelectric vibrator, the oscillation circuit, and the Peltier element, a temperature sensor provided attached to the case for detecting the ambient temperature, and a selection unit for selecting one of the following: a first state in which the polarity of the voltage applied to the Peltier element can be changed so that heating and cooling of the piezoelectric vibrator are possible, and a second state in which the polarity of the voltage applied to the Peltier element is fixed so that only heating of the piezoelectric vibrator is possible.

Description

Technical Field

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

Background Art

[0002] Quartz thermogravimetric analysis (QTGA) using a quartz crystal oscillator is known. Specifically, in this QTGA, by heating or cooling a quartz crystal oscillator, substances contained in the gas around the quartz crystal oscillator are caused to adhere to or desorb from the quartz crystal oscillator. Based on the change in the oscillation frequency of the quartz crystal oscillator that occurs thereby, analysis regarding the substance is performed, which is an analysis method using QCM (Quartz crystal microbalance).

[0003] As an apparatus for performing such QTGA, for example, a sensing sensor equipped with a quartz crystal oscillator and an oscillation circuit is configured to be placed in a desired measurement environment, and an example of such an apparatus is shown in Patent Document 1. The apparatus of this Patent Document 1 includes two types of sensing sensors. One of the sensing sensors includes a heater for heating a quartz crystal oscillator cooled by liquid nitrogen as a temperature adjustment mechanism, and the other one can switch heating and cooling of the quartz crystal oscillator using a Peltier element as a temperature adjustment mechanism.

[0004] Each sensing sensor transmits an ID signal to a main body part that applies a voltage to the temperature adjustment mechanism, and the main body part can identify the type of the sensing sensor and apply a voltage within a range corresponding to the temperature adjustment mechanism to the temperature adjustment mechanism. Therefore, it is possible to properly use the sensing sensors according to the purpose of measurement and the like. Further, each sensing sensor is equipped with a temperature sensor, and the voltage applied to the temperature adjustment mechanism is controlled based on the detection result of this temperature sensor.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

[0006] There is a need to deploy the above-mentioned sensing sensors in various environments and perform measurements. These environments include those where transportation is restricted, such as outer space. Therefore, in order to miniaturize the device, it is sometimes desirable to configure the sensing device using only one of the two types of sensing sensors described above. Furthermore, QTGA is being considered for use in environments with various temperatures, and for this purpose, it is desirable to use a sensing sensor equipped with a Peltier element that can both heat and cool the quartz oscillator. Given this background, there are cases where it is necessary to configure the sensing device using the sensing sensor equipped with a Peltier element, one of the two types of sensing sensors shown in Patent Document 1.

[0007] However, if a sensing sensor equipped with a Peltier element is placed in a relatively low-temperature environment, and the Peltier element cools the quartz oscillator so that the temperature detected by the temperature sensor reaches the target temperature, the Peltier element may overheat, causing the temperature detected by the temperature sensor to rise. As a result, a voltage may be applied to further cool the Peltier element, potentially making it impossible to control the temperature of the Peltier element. Patent Document 1 does not show a method to solve this problem.

[0008] The present invention has been made in view of the above circumstances, and its purpose is to provide a technology that enables stable temperature control of a piezoelectric vibrator in a relatively low temperature environment in a sensing device that senses a substance to be sensed. [Means for solving the problem]

[0009] The present invention is a sensing device that senses a substance to be sensed contained in the gas surrounding a piezoelectric vibrator based on a change in the oscillation frequency of the piezoelectric vibrator, The piezoelectric vibrator and, An oscillation circuit for causing the piezoelectric vibrator to oscillate, A Peltier element for changing the temperature of the piezoelectric vibrator, A case housing the piezoelectric vibrator, the oscillation circuit, and the Peltier element, A temperature sensor for detecting ambient temperature is provided in conjunction with the aforementioned case, A selection unit that selects one of the following: a first state in which the polarity of the voltage applied to the Peltier element can be changed so that heating and cooling of the piezoelectric vibrator are possible, and a second state in which the polarity of the voltage applied to the Peltier element is fixed so that only heating of the piezoelectric vibrator is possible. It is equipped with. [Effects of the Invention]

[0010] According to the sensing device of the present invention, stable temperature control of a piezoelectric vibrator can be performed in a sensing device that detects a substance to be detected, even in a relatively low temperature environment. [Brief explanation of the drawing]

[0011] [Figure 1] This is a longitudinal cross-sectional side view of a sensing device according to one embodiment of the present invention. [Figure 2] This is a block diagram of the aforementioned sensing device. [Figure 3] This is a circuit diagram of the control voltage supply section in the control unit of the aforementioned sensing device. [Figure 4] This chart shows the flow of how the voltage applied to the Peltier element by the aforementioned sensing device is determined. [Modes for carrying out the invention]

[0012] A sensing device 1, which is one embodiment of the present invention, will be described with reference to the longitudinal cross-sectional side view of Figure 1. The sensing device 1 is a device for performing QTGA and consists of a sensing sensor 10 including a quartz crystal oscillator 5 and oscillation circuits 61 and 62, a connecting 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. The sensing device 1 is configured to allow components (substances to be sensed) contained in the gas of the surrounding environment (the environment in which the sensing sensor 10 is placed) to adhere to and detach from the quartz crystal oscillator 5 by temperature control of the quartz crystal oscillator 5, and to measure the frequency change of the quartz crystal oscillator 5.

[0013] The sensing sensor 10 is composed of a base 2, a Peltier element unit 3, and a transducer holder 4, arranged in that order, with adjacent components connected to each other. In describing the configuration of the sensing sensor 10 below, it will be assumed that the base 2 and transducer holder 4 are positioned downwards and upwards, respectively. However, the arrangement of the sensing sensor 10 is not limited to this description; the orientation of the sensing sensor 10 during use is arbitrary. The crystal oscillator 5 is supported from below by the transducer holder 4.

[0014] Base 2 is constructed as a circular block in plan view, with its central portion protruding upward to form a circular base 21, on which the Peltier element unit 3 is mounted. The lower surface of Base 2 also protrudes, forming a rectangular connector 22. When the connector 22 is inserted into the recess 24 of the connecting member 23, the terminals formed on the connector 22 are electrically connected to the control unit 7 via a conductive path (not shown) formed in the connecting member 23. The connecting member 23 is cooled by a cooling mechanism (not shown), which cools Base 2 by contacting it from below when the connector 22 is inserted into the recess 24.

[0015] The above-described Peltier element unit 3 heats and cools a crystal oscillator 5, which is a piezoelectric oscillator, via a vibrator holder 4, and is composed of Peltier elements 31 and 32 laminated on each other. The Peltier element 31 is arranged on the lower side and the Peltier element 32 is arranged on the upper side, respectively.

[0016] Regarding the first Peltier element 31 and the second Peltier element 32, when cooling the crystal oscillator 5, both the upper surfaces are heat absorption surfaces and the lower surfaces are heat radiation surfaces, and when heating the crystal oscillator 5, both the upper surfaces are heat radiation surfaces and the lower surfaces are heat absorption surfaces. In this way, when cooling the crystal oscillator 5, the first Peltier element 31 cools the heat radiation surface of the second Peltier element 32, so the Peltier element unit 3 can cool the crystal oscillator 5 to a relatively low temperature. Regarding the heat generated from the heat radiation surface of the first Peltier element 31 during the cooling, it is exhausted to the connection member 23 via the base 2. By this Peltier element unit 3, the temperature of the crystal oscillator 5 is changed within a range of, for example, -80°C to +125°C.

[0017] A sealed space 25 is formed in the central part of the base 2 in plan view, and a substrate 26 is provided in the sealed space 25. Note that a heat insulating member (not shown) is interposed between the substrate 26 and the wall surface forming the sealed space 25 so that the substrate 26 is not affected by the heat radiation of the above-described Peltier element unit 3. An integrated circuit chip (IC chip) 27 is provided on the substrate 26. The first oscillation circuit 61 and the second oscillation circuit 62, which will be described later, are formed in the integrated circuit chip 27.

[0018] The vibrator holder 4 is configured as a substrate in a horizontal posture having a recess 41 that opens upward. The opening edge of the recess 41 supports the peripheral edge of the crystal oscillator 5 from the lower surface side and holds the crystal oscillator 5 in a horizontal posture so that the lower surfaces of the first oscillation region 51 and the second oscillation region 52 of the crystal oscillator 5, which will be described later, face the recess 41.

[0019] Next, the structure of the crystal oscillator 5 will be described. The crystal oscillator 5 includes, for example, a circular crystal piece 50 which is a piezoelectric piece of AT cut. On one side (upper side) and the other side (lower side) of this crystal piece 50, a pair of first excitation electrodes (detection electrodes) 51 and 53 and a pair of second excitation electrodes (reference electrodes) 52 and 54 are arranged spaced apart from each other. In the crystal piece 50, the region sandwiched between the first excitation electrodes 51 and 53 constitutes a first vibration region 55, and the region sandwiched between the second excitation electrodes 52 and 54 constitutes a second vibration region 56. The first vibration region 55 and the second vibration region 56 can vibrate individually.

[0020] Also, in order to detect the temperature of the crystal oscillator 5, a temperature sensor 58 which is a platinum resistor is provided on the crystal piece 50, and its resistance value changes according to the temperature of the crystal oscillator 5. The control unit 7 described later can acquire this change in resistance value as a change in voltage and detect the temperature. The excitation electrodes 51 to 54 and the temperature sensor 58 are connected to the terminals of the substrate 26 via a conductive pattern provided on the oscillator holder 4 and a rod-shaped conductive member 28 extending vertically between the oscillator holder 4 and the substrate 26.

[0021] Note that the terminals of the connector 22 of the base 2 described above are electrically connected to the respective terminals of the Peltier element unit 3 and the substrate 26 via a conductive path provided in the base 2. As described above, when the connector 22 is inserted into the recess 24 of the connecting member 23 and the terminals of the connector 22 are connected to the control unit 7, the integrated circuit chip 27, the temperature sensor 58, the excitation electrodes 51 to 54 constituting the crystal oscillator 5, and the Peltier element unit 3 on the substrate 26 are electrically connected to the control unit 7.

[0022] The sensing sensor 10 is also equipped with a cover 11. The cover 11 comprises a main part 12 that is circular in plan view and covers the top of the crystal oscillator 5 and the oscillator holder 4, and a cylindrical part 13 that extends downward from the periphery of the main part 12 and surrounds the sides of the oscillator holder 4 and the Peltier element unit 3, with the lower end of the cylindrical part 13 in contact with the outside of the stand 21 on the base 2. The main part 12 has a circular through hole 14 formed in a position that overlaps with the first excitation electrode 51 in plan view, and the periphery of the through hole 14 extends downward to form a cylindrical shield 15 that is close to the first excitation electrode 51. With the cover 11 formed in this way, the substance to be sensed contained in the gas surrounding the sensing sensor 10 adheres exclusively to the excitation electrode 51 among the excitation electrodes 51 to 54. The cover 11 and the base 2 form a case 16 that houses the crystal oscillator 5 and the oscillation circuit.

[0023] As described above, the control unit 7 in the sensing device 1 acquires the oscillation frequency of the first vibration region 55 where the substance to be detected contained in the gas adheres, and the oscillation frequency of the second vibration region 56 where the substance to be detected does not adhere. By calculating the difference between the oscillation frequencies output from the first vibration region 55 and the second vibration region 56, the influence of temperature changes around the sensing sensor 10 can be canceled out, and the state of adhesion of the substance to be detected to the first vibration region 55 can be detected with high accuracy. Therefore, the first vibration region 55 is a vibration region for detecting the substance to be detected, and the second vibration region 56 is a vibration region for reference. In the following explanation, the oscillation frequency of the first vibration region 55 will be denoted as F1, and the oscillation frequency of the second vibration region 56 as F2.

[0024] As described above, the integrated circuit chip 27 is provided with a first oscillator circuit 61 and a second oscillator circuit 62. The first excitation electrodes 51 and 53 are connected to the first oscillator circuit 61, and the second excitation electrodes 52 and 54 are connected to the second oscillator circuit 62. Therefore, the first vibration region 55 and the second vibration region 56 are oscillated by the first oscillator circuit 61 and the second oscillator circuit 62, respectively.

[0025] Next, the control unit 7 will be described with reference to the block diagram in Figure 2. The control unit 7 includes switches 70 and 71, a frequency detection unit 72, a temperature conversion unit 73, a variable regulator 74, a constant voltage regulator 75, a temperature adjustment unit 76, a control voltage supply unit 77, an operation switching unit 78, and a memory unit 79. By operating switch 71, the first oscillation circuit 61 is connected to the frequency detection unit 72 and the second oscillation circuit 62 is connected to the frequency detection unit 72 are switched in a time-division manner, and the oscillation frequencies of the first vibration region 55 and the second vibration region 56 are detected by the frequency detection unit 72.

[0026] Furthermore, the temperature conversion unit 73 is connected to the temperature sensor 58 and applies a voltage (referred to as the temperature detection voltage) to the temperature adjustment unit 76, which is in the range of, for example, 0V to 10V, corresponding to the change in the resistance value of the temperature sensor 58. The temperature corresponding to this temperature detection voltage is taken as the temperature detected by the temperature sensor 58. The temperature adjustment unit 76 then applies a voltage (referred to as the temperature adjustment voltage) to the control voltage supply unit 77. This temperature adjustment voltage changes according to the difference between the temperature detection voltage input to the temperature adjustment unit 76 and the voltage corresponding to the target temperature of the crystal oscillator 5.

[0027] Continuing the explanation of the control unit 7, we will provide supplementary information about the Peltier elements 31 and 32 that constitute the Peltier element unit 3. For illustrative purposes, only one of the Peltier elements 31 and 32 is shown in Figure 2. The terminals of Peltier elements 31 and 32 are designated as the positive terminal A1 and the negative terminal A2, respectively. A positive voltage is applied to Peltier elements 31 and 32 when the voltage applied to the positive terminal (first terminal) A1 is greater than the voltage applied to the negative terminal (second terminal) A2. In this case, current flows from the positive terminal A1 to the negative terminal A2, causing the upper surfaces of Peltier elements 31 and 32 to become heat dissipation surfaces and heat the crystal oscillator 5. A negative voltage is applied to Peltier elements 31 and 32 when the voltage applied to the positive terminal A1 is less than the voltage applied to the negative terminal A2. In this case, current flows from the negative terminal A2 to the positive terminal A1, causing the upper surfaces of Peltier elements 31 and 32 to become heat absorption surfaces and cool the crystal oscillator 5.

[0028] The Peltier elements 31 and 32 are connected in parallel to, for example, a variable regulator 74 and a constant voltage regulator 75, with the variable regulator 74 connected to each positive terminal A1. The constant voltage regulator 75 is connected to each negative terminal A2 via a switch 70 and is also grounded. A voltage of, for example, 24V is applied to the variable regulator 74 and the constant voltage regulator 75. The constant voltage regulator 75 is configured to output a voltage of 9V. Therefore, by turning the switch 70 on and off, the voltage applied to the negative terminal A2 can be switched between 0V and 9V.

[0029] Next, the control voltage supply unit 77 will be explained with reference to the circuit diagram in Figure 3. The control voltage supply unit 77, which is connected to the variable regulator 74, is configured as a non-inverting amplifier circuit using an operational amplifier 85, and is configured to provide feedback from the output side of the operational amplifier 85 to the - input side via resistor R1. The output side of the operational amplifier 85 is connected to an adjustment terminal for adjusting the output voltage of the variable regulator 74, and a temperature adjustment voltage is input to the + input side of the operational amplifier from the temperature adjustment unit 76. Resistors R2 and R3 are provided in parallel with each other on the - input side of the operational amplifier 85, and the on / off connection of resistor R2 is switched by switch 86.

[0030] Turning off switch 86 increases the combined resistance Rs of resistors R2 and R3 compared to when switch 86 is on, and the amplification factor of the amplification circuit decreases. In other words, switching switch 86 on or off changes the range of voltage that can be applied to the output voltage adjustment terminal of the variable regulator 74 (referred to as the control voltage). Specifically, when switch 86 is on, the control voltage changes so that the output voltage from the variable regulator 74 is between 0 and 18V, and when switch 86 is off, the control voltage changes so that the output voltage from the variable regulator 74 is between 0 and 9V. The larger the temperature difference obtained by subtracting the temperature detected by the temperature sensor 58 from the target temperature of the crystal oscillator 5, the larger the output voltage of the variable regulator 74 will be within the above range.

[0031] Returning to Figure 2, let's explain the memory unit 79. The memory unit 79 is configured, for example, with an EEPROM, and stores data for the temperature range used in the execution of the flow described later. This temperature range is the temperature range in which the Peltier element unit 3 can cool the crystal oscillator 5, and more specifically, it is the temperature range in which temperature control of the Peltier element unit 3 does not become impossible due to the heat generated by the Peltier element unit 3, as described in the section on problems the invention aims to solve. Therefore, from a different perspective, if the temperature detected by the temperature sensor 58 is lower than this temperature range, and the cooling operation of the crystal oscillator 5 by the Peltier element unit 3 is performed, a state in which temperature control of the Peltier element unit 3 becomes impossible may occur. The temperature range stored in this memory unit 79 is the coolable temperature range. Specifically, this coolable temperature range is, for example, -220°C or higher.

[0032] Next, the operation switching unit 78 will be described. The operation switching unit 78 is programmed to perform the flow described later. The operation switching unit 78 switches the on and off of switches 70 and 86 based on the temperature detected by the temperature sensor 58 and the cooling temperature range of the memory unit 79. Although not shown in the figures, the control unit 7 is provided with a display unit and an operation unit. The display unit is composed of, for example, a liquid crystal screen and displays the measured oscillation frequencies F1 and F2. The operation unit is composed of buttons and switches, and the user performs various operations, including turning the device's power on and off, from this operation unit.

[0033] The control performed by the sensing device 1 is outlined below. In this sensing device 1, the voltage applied to the Peltier elements 31 and 32 changes according to the temperature detected by the temperature sensor 58, thereby controlling the temperature of the crystal oscillator 5. In performing this temperature control of the crystal oscillator 5, the voltage applied to the positive terminal A1 and the negative terminal A2 is controlled so as not to cause a situation in which the temperature control of the Peltier element unit 3 described above becomes impossible. This control of the applied voltage is performed by switching between a first state in which either a positive or negative voltage can be applied to the Peltier elements 31 and 32, and a second state in which only a positive voltage can be applied to the Peltier elements 31 and 32, depending on the comparison result between the temperature detected by the temperature sensor 58 and the coolable temperature range. In other words, the first state is a state in which the polarity of the voltage applied to the Peltier elements 31 and 32 can be switched, while the second state is a state in which the polarity of this voltage is fixed and it is not possible to switch the polarity.

[0034] More specifically, in the first state, switches 70 and 86 are turned on, so that the voltage applied to the positive terminal A1 is a value corresponding to the temperature detected by the temperature sensor 58 within the range of 0V to 18V, and the voltage applied to the negative terminal A2 is 9V. In the second state, switches 70 and 86 are turned off, so that the voltage applied to the positive terminal A1 is a value corresponding to the temperature detected by the temperature sensor 58 within the range of 0V to 9V, and the voltage applied to the negative terminal A2 is 0V.

[0035] Therefore, in the first state, the voltage applied to the negative terminal A2 is greater than the lower limit and less than the upper limit of the voltage range that can be applied to the positive terminal A1. Then, in the second state, the voltage applied to the negative terminal A2 is equal to the lower limit of the voltage range that can be applied to the positive terminal A1. With the applied voltage set in this way, in the first state, the voltage applied to the positive terminal A1 is less than the voltage applied to the negative terminal A2, which cools the crystal oscillator 5, and the voltage applied to the positive terminal A1 is greater than the voltage applied to the negative terminal A2, which heats the crystal oscillator 5. However, in the second state, the voltage applied to the positive terminal A1 is greater than or equal to the voltage applied to the negative terminal A2, so only heating is possible for the crystal oscillator 5.

[0036] The control unit 7 is configured as a selection unit that selects between the first and second states described above. The variable regulator 74, constant voltage regulator 75, operation switching unit 78, and switches 70 and 86 are configured as voltage changing units that change the voltage applied to the positive terminal A1 (first voltage) and the voltage applied to the negative terminal A2 (second voltage), respectively. The variable regulator 74 corresponds to the first voltage application unit, while the constant voltage regulator 75 and switch 70 correspond to the second voltage application unit.

[0037] Next, the operation of the sensing device 1 will be explained using the flowchart in Figure 4. When the user of the film deposition apparatus 1 turns on the power of the sensing device 1, it is determined whether the detected temperature acquired by the temperature sensor 58 falls within the coolable temperature range stored in the memory unit 79 (step S1).

[0038] If it is determined in step S1 that the temperature is within the coolable temperature range, switches 70 and 86 are turned on, and the first state described above is reached. As a result, a voltage of 9V is applied to the negative terminal A2 of the Peltier elements 31 and 32, and a voltage corresponding to the difference between the target temperature of the crystal oscillator 5 and the temperature detected by the temperature sensor 58 within the range of 0V to 18V is applied to the positive terminal A1 of the Peltier elements 31 and 32 (step S2). As a result, a positive or negative voltage is applied to the Peltier elements 31 and 32 according to the potential difference between the positive terminal A1 and the negative terminal A2, causing the crystal oscillator 5 to be heated or cooled, or a voltage of 9V is applied to the positive terminal A1 and the negative terminal A2, so no current flows between these terminals and the crystal oscillator 5 is heated or cooled (step S3).

[0039] If it is determined in step S1 that the temperature is not within the coolable temperature range, switches 70 and 86 are turned off, resulting in the second state described above. As a result, the voltage applied to the negative terminal A2 of the Peltier elements 31 and 32 becomes 0V, and a voltage corresponding to the difference between the target temperature of the crystal oscillator 5 and the temperature detected by the temperature sensor 58 within the range of 0V to 9V is applied to the positive terminal A1 of the Peltier elements 31 and 32 (step S4). As a result, either a positive voltage is applied to the Peltier elements 31 and 32, causing the crystal oscillator 5 to heat up, or no voltage is applied to the positive terminal A1 and the negative terminal A2 (the applied voltage becomes 0V), so no current flows between these terminals and neither heating nor cooling occurs (step S5).

[0040] The flow of steps S1 to S5 is performed as needed, and while power is supplied to the sensing device 1, the temperature of the crystal oscillator 5 is controlled to reach the target temperature. The target temperature of the crystal oscillator 5 is set in advance, but it may be set to remain constant during frequency measurement or to change over time.

[0041] While the temperature of the quartz oscillator 5 is controlled in this manner, the control unit 7 acquires the oscillation frequencies F1 and F2, which are displayed on the display unit. The temperature control of the quartz oscillator 5 causes components contained in the gas in the environment where the sensing sensor 10 is placed to adhere to and detach from the first excitation electrode 51, causing the oscillation frequency F1 to change. The user performs various analyses, such as identifying the above components and detecting the amount of adhesion, based on the time-dependent changes in oscillation frequencies F1-F2. Then, the user operates the sensing device 1 to stop acquiring the oscillation frequencies F1 and F2 at a desired timing and turns off the power to the sensing device 1.

[0042] With the sensing device 1 described above, even when the sensing sensor 10 is placed in a relatively low temperature environment, it is possible to prevent the temperature control of the Peltier elements 31 and 32 from becoming impossible, and the quartz oscillator 5 can oscillate stably. Furthermore, the sensing device 1 does not have a configuration that includes multiple types of sensing sensors, as in the sensing device of Patent Document 1, and has the advantage of being able to be miniaturized by reducing the number of components that make up the film deposition apparatus 1.

[0043] Incidentally, assuming that the temperature detected by the temperature sensor 58 is the temperature of the environment in which the sensing sensor 10, including the Peltier elements 31 and 32, is placed, the determination in step S1 of the above flow is made, and as described above, the cooling operation of the Peltier elements 31 and 32 is restricted according to the determination result. However, there may be a discrepancy between this detected temperature and the temperature of the environment in which it is placed.

[0044] To explain in more detail, suppose the temperature of the environment in which the sensing sensor 10 is placed is, for example, B1°C, which is lower than the lower limit of the coolable temperature range mentioned above. Then, after placing the sensing sensor 10 in that environment and performing frequency measurement according to the flow described above, the power to the sensing device 1 is turned off. Suppose the power is turned on again immediately afterward. In this case, due to the residual heat of the crystal oscillator 5 when the power was turned on earlier, the detected temperature may be B2°C, which is relatively higher than B1°C. Therefore, if step S1 of the above flow is executed immediately after the power is turned on again, the judgment in step S1 should, in principle, determine that the detected temperature is not within the coolable temperature range, but it will instead be determined to be within the coolable temperature range.

[0045] As described above, if the above flow is executed immediately after the device is powered on, a state may occur where temperature control of the Peltier elements 31 and 32 becomes impossible. To prevent this, the sensing device 1 monitors the temperature detected by the temperature sensor 58 immediately after the power is turned on, and the timing for the first determination in step S1 is determined based on the change in this detected temperature per unit time. Accordingly, the first state and the second state are selected based on the change per unit time.

[0046] Specifically, for example, the difference between the newly acquired detected temperature and the detected temperature acquired a predetermined time before the newly acquired temperature is calculated as the change in detected temperature per unit time. This difference is then compared with a preset reference value, and if the difference is greater than or equal to the reference value, step S1 is not performed. On the other hand, if the difference is lower than the reference value, the acquired detected temperature is considered to be the ambient temperature of the sensing sensor 10, and step S1 is performed. The timing of performing step S1 is adjusted, for example, by the program of the operation switching unit 78.

[0047] By the way, the configuration is not limited to automatically selecting the first and second states based on the detected temperature, as in the examples described above. The first and second states may be selected by the user through the control unit 7's operation panel, and the sensing device 1 may be operated accordingly. For example, if the sensing sensor 10 is placed in a relatively cold environment and it is clear that the detected temperature will not fall within the cooling temperature range, the user can select the second state to operate the device.

[0048] Furthermore, the temperature sensor 58 may be provided on the oscillator holder 4, for example, instead of being provided on the crystal oscillator 5. In addition, a dedicated temperature sensor for making the determination in step S1 may be provided on the sensing sensor 10, separate from the temperature sensor 58 of the crystal oscillator 5. In other words, the determination in step S1 may be made based on the detection result of the temperature sensor dedicated to the determination, and the temperature control of the crystal oscillator 5 may be made based on the detection result of the temperature sensor 58. In this case, the temperature sensor dedicated to the determination only needs to be able to detect the temperature around the sensing sensor 10, so it may be provided on the surface of the case 16, which consists of the cover 11 and the base 2, for example.

[0049] Thus, the temperature sensor for making the determination in step S1 can be provided attached to the case 16 so as to be able to detect the temperature of the environment in which the sensing sensor 10 is placed, and is not limited to being provided on the crystal oscillator 5. Here, being attached to the case 16 means moving together with the case 16 when the case is moved, and therefore specifically refers to being provided inside the case, or being provided on the case 16 itself.

[0050] Furthermore, the Peltier element is not limited to being provided in multiple quantities; only one may be provided. Also, the crystal oscillator 5 is not limited to forming both the first vibration region 55 and the second vibration region 56; a configuration in which only the first vibration region 55 is formed is also possible. Additionally, the voltage applied to the negative terminal A2 is not limited to being changed by a combination of a constant voltage regulator 75 and a switch 70; it may be changed by providing a variable regulator, similar to the voltage applied to the positive terminal A1.

[0051] The embodiments disclosed herein should be considered in all respects as illustrative and not restrictive. The above embodiments may be omitted, replaced, modified and combined in various ways without departing from the scope and spirit of the appended claims. [Explanation of Symbols]

[0052] 1 Sensing device 13 Cover 2 bases 5 crystal oscillator 61 First Oscillator Circuit 62 Second Oscillator Circuit 7 Control Unit

Claims

1. In a sensing device that detects a substance to be detected contained in the gas surrounding a piezoelectric vibrator based on a change in the oscillation frequency of the piezoelectric vibrator, The piezoelectric vibrator and, An oscillation circuit for causing the piezoelectric vibrator to oscillate, A Peltier element for changing the temperature of the piezoelectric vibrator, A case housing the piezoelectric vibrator, the oscillation circuit, and the Peltier element, A temperature sensor for detecting ambient temperature is provided in conjunction with the aforementioned case, A selection unit that selects one of the following: a first state in which the polarity of the voltage applied to the Peltier element can be changed so that heating and cooling of the piezoelectric vibrator are possible, and a second state in which the polarity of the voltage applied to the Peltier element is fixed so that only heating of the piezoelectric vibrator is possible. A sensing device equipped with the following features.

2. The aforementioned selection unit is The sensing device according to claim 1, which selects one of the first state and the second state based on the detected temperature detected by the temperature sensor.

3. The aforementioned selection unit is A first voltage application unit and a second voltage application unit apply a first voltage and a second voltage, respectively, to the first and second terminals provided on the Peltier element. A voltage changing unit that changes the first voltage and the second voltage based on the detected temperature, The sensing device according to claim 2, including the following:

4. The temperature sensor is provided on the piezoelectric vibrator. The sensing device according to claim 3, wherein the selection of the first state and the second state is made at a timing based on the change in the detected temperature per unit time.

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