Three-electrode in-situ test pool with in-situ heating function and working method of three-electrode in-situ test pool

Abstract

The invention belongs to the technical field of electrochemical cells, and discloses a three-electrode in-situ test cell with an in-situ heating function and a working method thereof.The three-electrode in-situ test cell comprises a working electrode block, a reference electrode block and an auxiliary electrode block which are sequentially connected, an electric heating element is arranged in the auxiliary electrode block, and a temperature detection element is arranged outside the auxiliary electrode block; the electric heating element and the temperature detection element are connected with a controllable power supply; the controllable power supply is used for controlling the electric heating element to heat through a detection signal of the temperature detection element, so that the auxiliary electrode block is maintained at a preset temperature; and the auxiliary electrode block is made of a conductive and heat-conducting metal material. The three-electrode in-situ test pool can be heated in situ, so that the original constant temperature can be removed, the equipment investment can be reduced, the space can be saved, the use of a long lead can be avoided, the test precision can be improved, and the experimental operation can be simplified.

Description

Technical Field

[0001] The invention belongs to the technical field of electrochemical cells, and in particular relates to a three-electrode in-situ test cell with an in-situ heating function and a working method thereof. Background Art

[0002] Supercapacitors are a new type of electrochemical energy storage device with long cycle life, high power performance and wide operating temperature range. Since its theoretical cycle number can reach millions of times, in order to quickly determine the working conditions of the positive and negative electrodes after long-term service, a high-temperature floating charge aging experiment based on a three-electrode test is one of the necessary test contents. However, the widely used three-electrode test cell does not have an in-situ heating function. It is necessary to put the entire test cell into a constant temperature box and lead out long wires to connect to the electrochemical workstation for testing, which results in more equipment required, a large footprint, and long wires, which directly reduce the test accuracy and reliability.

[0003] At present, the high temperature floating charge aging experiment of supercapacitor based on three-electrode test is realized by combining three-electrode Hohsen test cell with constant temperature test box. The overall structure of three-electrode Hohsen test cell can be referred to Figure 1 :The test cell adopts stainless steel as the main material, and the main body includes a working electrode block, a reference electrode block and an auxiliary electrode block. The working electrode block, the reference electrode block and the auxiliary electrode block 9 are connected and pressed and fixed by bolts to form a sealed test cell. After the test cell is assembled, it is placed in a thermostat as a whole. The side wall of the thermostat has a special hole for leading out the electrode wire and is equipped with pearl cotton for insulation. The electrode wire is finally connected to an electrochemical workstation to monitor the test data. The limitation of the prior art is that the three-electrode Hohsen cell does not have an in-situ heating function. It is necessary to put the test cell as a whole into a thermostat and lead out a long wire to connect to the electrochemical workstation for testing, resulting in a large number of required equipment, a large footprint, and a long wire, which directly reduces the test accuracy and reliability. Summary of the invention

[0004] In order to solve the problems existing in the prior art, the purpose of the present invention is to provide a three-electrode in-situ test cell with in-situ heating function and a working method thereof. The present invention can perform in-situ heating on the three-electrode in-situ test cell, thereby removing the original constant temperature and reducing equipment investment and saving space. At the same time, it can also avoid the use of long wires, thereby improving the test accuracy and simplifying the experimental operation.

[0005] To achieve the above purpose, the technical solution adopted by the present invention is as follows: A three-electrode in-situ test cell with an in-situ heating function comprises a working electrode block, a reference electrode block and an auxiliary electrode block which are connected in sequence, wherein an electric heating element is arranged in the auxiliary electrode block, and a temperature detection element is arranged outside the auxiliary electrode block, and both the electric heating element and the temperature detection element are connected to a controllable power supply; the controllable power supply is used to control the heating of the electric heating element through a detection signal of the temperature detection element, so that the auxiliary electrode block is maintained at a preset temperature; the auxiliary electrode block is made of a metal material which can conduct electricity and heat.

[0006] Preferably, the electric heating element is arranged at the periphery of the installation cavity of the auxiliary electrode block, and the auxiliary electrode block is provided with an accommodating cavity for accommodating the electric heating element.

[0007] Preferably, the auxiliary electrode block is provided with an electric heating element terminal, one end of which extends into the accommodating cavity and is connected to the electric heating element, and the auxiliary electrode block is insulated from the electric heating element terminal.

[0008] Preferably, the electric heating element comprises a heating wire and an insulating tube sleeved on the outside of the heating wire.

[0009] Preferably, the electric heating wire is a spiral electric heating wire, and the material of the insulating tube is alumina ceramic, silicon nitride ceramic, silicon boride ceramic or zirconium oxide ceramic.

[0010] Preferably, in the radial direction of the auxiliary electrode block, the distance from the accommodating cavity to the inner surface of the mounting cavity is equal to the distance from the accommodating cavity to the outer surface of the auxiliary electrode block.

[0011] Preferably, the temperature detection element is a chip temperature sensor, the detection portion of the chip temperature sensor is attached to the outer surface of the auxiliary electrode block, and the detection portion of the chip temperature sensor corresponds to the radial position of the electric heating element of the auxiliary electrode block.

[0012] Preferably, the auxiliary electrode block is made of stainless steel, aluminum, aluminum alloy, copper, copper alloy, gold or silver.

[0013] Preferably, the controllable power supply adopts a direct current power supply controlled by a single chip microcomputer.

[0014] The present invention also provides a working method of the three-electrode in-situ test cell with in-situ heating function as described above, comprising the following process: The controllable power supply is connected to an external power supply. The controllable power supply controls the output voltage or current to make the electric heating element work and heat up. The temperature detection element detects the temperature of the auxiliary electrode block in real time. The controllable power supply determines whether the temperature of the test pool reaches the preset value based on the temperature detected by the temperature detection element. If the temperature is lower than the preset value, the electric heating element is controlled to heat with a fixed power; if the temperature is higher than the preset value, the power supply is disconnected to suspend heating.

[0015] Compared with the prior art, the present invention has the following beneficial effects: The three-electrode in-situ test cell with in-situ heating function of the present invention is based on the existing three-electrode in-situ test cell, and an electric heating element is arranged in the auxiliary electrode block. At the same time, the material of the auxiliary electrode block needs to adopt a metal material that can conduct electricity and heat. First, the material of the auxiliary electrode block needs to be able to conduct electricity in order to meet its basic requirements as a three-electrode in-situ test cell. Secondly, the material of the auxiliary electrode block needs to be able to conduct heat. On the one hand, it is to enable the auxiliary electrode block itself to transfer the heat generated by the electric heating element to the installation chamber of the auxiliary electrode block when the electric heating element is heated. On the other hand, it is to enable the auxiliary electrode block to transfer the heat generated by the heat electric heating element to the outer surface of the auxiliary electrode block, which is convenient for the detection of the temperature detection element. The present invention can control the heating temperature of the electric heating element by using the detection information of the temperature detection element by setting a controllable power supply, thereby achieving the test cell reaching a preset temperature to meet the heating requirements. It can be seen from the above scheme that the three-electrode in-situ test cell of the present invention can realize in-situ heating. Compared with the prior art, on the one hand, the original constant temperature equipment is removed, which reduces equipment investment and saves space. On the other hand, compared with the existing scheme, the length of the wire used is much shorter. Therefore, the present invention also removes the long wire to improve the test accuracy. At the same time, the present invention uses electric heating, which has higher and faster heating efficiency and greatly simplifies the experimental operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0017] Figure 1 is an appearance diagram of a three-electrode in-situ test cell with in-situ heating function in an embodiment of the present invention; Figure 2 1 is an exploded view of a three-electrode in-situ test cell with in-situ heating function according to an embodiment of the present invention.

[0018] In the figure, 1-electrode cover, 2-small spring, 3-working electrode rod, 4-working electrode block body, 5-reference electrode block, 6-large spring, 7-working electrode stage, 8-reference electrode holder, 9-auxiliary electrode block, 9-1-installation chamber, 9-2-accommodation chamber, 10-nut, 11-first screw sleeve, 12-O-ring, 13-second screw sleeve, 14-reference electrode sleeve, 15-flat washer, 16-screw, 17-working electrode block, 18-electric heating element, 19-working electrode, 20-insulating film, 21-counter electrode. DETAILED DESCRIPTION

[0019] In order to make the objectives, technical solutions and advantages of the present invention more clear, the embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0020] See also Figure 1 and Figure 2 The three-electrode in-situ test cell of this embodiment has an in-situ heating function. The three-electrode in-situ test cell of this embodiment is similar in appearance and structure to the existing three-electrode Hohsen cell, including a working electrode block 17, a reference electrode block 5 and an auxiliary electrode block 9 connected in sequence, such as Figure 2 As shown, an electric heating element 18 is provided in the auxiliary electrode block 9, and a temperature detection element (not shown in the figure) is provided outside the auxiliary electrode block 9. Both the electric heating element 18 and the temperature detection element are connected to a controllable power supply (not shown in the figure); the controllable power supply is used to control the heating of the electric heating element 18 through the detection signal of the temperature detection element, so that the auxiliary electrode block 9 is maintained at a preset temperature; the material of the auxiliary electrode block 9 is a metal material that can conduct electricity and heat.

[0021] The working method of the three-electrode in-situ test cell with in-situ heating function in the above embodiment includes the following process: The controllable power supply is connected to an external power supply. The controllable power supply controls the output voltage or current to make the electric heating element 18 work and heat up. The temperature detection element detects the temperature of the auxiliary electrode block 9 in real time. The controllable power supply determines whether the temperature of the test pool reaches the preset value based on the temperature detected by the temperature detection element. If the temperature is lower than the preset value, the electric heating element 18 is controlled to heat with a fixed power; if the temperature is higher than the preset value, the power supply is disconnected to suspend heating.

[0022] As a preferred embodiment of the present invention, in this embodiment, the electric heating element 18 is arranged at the periphery of the mounting chamber 9-1 of the auxiliary electrode block 9, and the auxiliary electrode block 9 is provided with a receiving chamber 9-2 for receiving the electric heating element 18. The receiving chamber 9-2 is an annular chamber, and its cross-sectional shape matches the cross-sectional shape of the electric heating element 18, and can be circular, rectangular or triangular. Figure 2 As shown, the electric heating element 18 is arranged here mainly because the wall thickness of the auxiliary electrode block 9 is relatively thin at this point, so the heat conduction speed is relatively fast, and thus the heating speed is also fast.

[0023] As a preferred embodiment of the present invention, in this embodiment, an electric heating element terminal (not shown) is provided on the auxiliary electrode block 9, one end of which extends into the accommodating cavity 9-2 and is connected to the electric heating element 18, and the auxiliary electrode block 9 is insulated from the electric heating element terminal. The electric heating element 18 can be connected to a controllable power supply through the electric heating element terminal, so the structure is simple and the wiring is convenient.

[0024] As a preferred embodiment of the present invention, in this embodiment, the electric heating element 18 includes a heating wire and an insulating tube sleeved outside the heating wire. The insulating tube can prevent the heating wire from contacting the auxiliary electrode block 9 to prevent leakage.

[0025] As a preferred implementation scheme of the present invention, in this embodiment, the above-mentioned electric heating wire adopts a spiral electric heating wire, which has high heating efficiency. When heating is controlled by power, the speed of temperature change is well controllable; the material of the insulating tube adopts alumina ceramic, silicon nitride ceramic, silicon boride ceramic or zirconium oxide ceramic. The insulating tube made of these ceramic materials can, on the one hand, play a good insulating role between the electric heating wire and the auxiliary electrode block 9, and at the same time has good thermal conductivity to meet the heating requirements, and these ceramic materials have high strength, which can improve the service life and safety of the present invention.

[0026] As a preferred embodiment of the present invention, in this embodiment, in the radial direction of the auxiliary electrode block 9, the distance from the accommodating cavity 9-2 to the inner surface of the installation chamber 9-1 is equal to the distance from the accommodating cavity 9-2 to the outer surface of the auxiliary electrode block 9, so that the heat transfer distance of the electric heating element 18 inward and outward is the same, so that the temperature detected by the temperature detection element is closer to the temperature inside the installation chamber 9-1, which helps to improve the accuracy of the experimental results.

[0027] As a preferred embodiment of the present invention, in this embodiment, the temperature detection element adopts a patch temperature sensor, the detection part of the patch temperature sensor is attached to the outer surface of the auxiliary electrode block 9, and the detection part of the patch temperature sensor corresponds to the radial position of the electric heating element 18 of the auxiliary electrode block 9. The temperature detection element has a simple structure and accurate and reliable detection results, which helps to improve the accuracy of the experimental results.

[0028] As a preferred embodiment of the present invention, in this embodiment, the auxiliary electrode block 9 is made of stainless steel, aluminum, aluminum alloy, copper, copper alloy, gold or silver. These materials can ensure that the auxiliary electrode block 9 has good electrical and thermal conductivity.

[0029] As a preferred implementation scheme of the present invention, in this embodiment, the controllable power supply adopts a DC power supply controlled by a single-chip microcomputer, which has good temperature control effect and relatively low cost.

[0030] In the above scheme of the present invention, the main structure of the three-electrode in-situ test cell with in-situ heating function of the present invention is similar to the existing three-electrode Hohsen cell theme structure. On the basis of the original Hohsen cell design, an electric heating element 18 is installed in the lower cover (i.e., the auxiliary electrode block 9), and the electric heating element 18 electrode is installed in the original cell body shell. The in-situ heating and temperature control can be realized by connecting the external power supply of the external controller. Since the reference electrode, the counter electrode and the working electrode are all in the groove of the lower cover (i.e., the installation chamber 9-1) when the original Hohsen cell is correctly installed, it is only necessary to install the electric heating element 18 in the lower cover. Therefore, the present invention installs a ring-shaped electric heating element 18 in the lower cover of the original Hohsen cell, and adds a corresponding terminal at the shell, and connects a DC power supply controlled by a single-chip microcomputer to adjust the power of the heating wire by adjusting the voltage. Since the thermal conductivity of the auxiliary electrode block 9 material is high, it can be determined by detecting the shell temperature whether the test cell temperature reaches the preset value. If the temperature is lower than the preset value, it is heated with a fixed power; if the temperature is higher than the preset value, the power is disconnected and the heating is suspended.

[0031] Example The three-electrode in-situ test cell with in-situ heating function in this embodiment includes a working electrode block 17, a reference electrode block 5 and an auxiliary electrode block 9 connected in sequence. The auxiliary electrode block 9 is made of stainless steel, such as Figure 2 As shown, the electric heating element 18 is arranged at the periphery of the mounting chamber 9-1 of the auxiliary electrode block 9, and a housing chamber 9-2 for housing the electric heating element 18 is arranged at the periphery of the mounting chamber 9-1 in the auxiliary electrode block 9, and the housing chamber 9-2 is an annular chamber, and the electric heating element 18 includes a spiral electric heating wire and an alumina ceramic tube sleeved on the outside of the spiral electric heating wire, and the outer envelope surface of the spiral electric heating wire and the inner wall of the alumina ceramic tube are clearance-matched, and the cross-sectional shape of the housing chamber 9-2 is circular, and the outer diameter of the alumina ceramic tube is the same as the inner diameter of the housing chamber 9-2, and the auxiliary electrode block 9 is provided with an electric heating element terminal, and one end of the electric heating element terminal extends into the housing chamber 9-2 and is connected to the electric heating wire, and the auxiliary electrode block 9 is insulated from the electric heating element terminal. In the radial direction of the auxiliary electrode block 9, the distance from the housing chamber 9-2 to the inner surface of the mounting chamber 9-1 is equal to the distance from the housing chamber 9-2 to the outer surface of the auxiliary electrode block 9. A patch temperature sensor is provided outside the auxiliary electrode block 9, and the detection part of the patch temperature sensor is attached to the outer surface of the auxiliary electrode block 9. The detection part of the patch temperature sensor corresponds to the radial position of the electric heating element 18 of the auxiliary electrode block 9. The electric heating element terminal and the patch temperature sensor are both externally connected to a DC power supply controlled by a single-chip microcomputer; the DC power supply controlled by the single-chip microcomputer can control the heating of the spiral electric heating wire through the detection signal of the patch temperature sensor, so that the auxiliary electrode block 9 is maintained at a preset temperature.

[0032] The working method of the three-electrode in-situ test cell with in-situ heating function in this embodiment is as follows: Connecting a DC power supply controlled by the single chip microcomputer to an external power supply, controlling the output voltage or current by the DC power supply controlled by the single chip microcomputer, thereby controlling the heating power of the spiral electric heating wire, and the spiral electric heating wire is heated under the control of the DC power supply controlled by the single chip microcomputer, thereby heating the auxiliary electrode block 9; The chip temperature sensor detects the temperature of the auxiliary electrode block 9 in real time on the outer surface of the auxiliary electrode block 9, and the DC power supply controlled by the single chip microcomputer receives the temperature information detected by the chip temperature sensor in real time; The DC power supply controlled by the single chip compares the received temperature information uploaded by the SMD temperature sensor with the preset target heating temperature of the auxiliary electrode block 9 to determine whether to continue heating; When the temperature information uploaded by the patch temperature sensor is lower than the target heating temperature of the auxiliary electrode block 9, the DC power supply controlled by the single chip microcomputer controls the spiral electric heating wire to continue heating; When the temperature information uploaded by the patch temperature sensor is not lower than the target heating temperature of the auxiliary electrode block 9, the DC power supply controlled by the single chip microcomputer cuts off the power of the spiral electric heating wire, and the spiral electric heating wire stops heating; When the auxiliary electrode block 9 is heated, the above process is repeated continuously so that the auxiliary electrode block 9 is maintained within the target temperature range.

[0033] Since the spiral electric heating wire of the present invention is arranged inside the auxiliary electrode block 9, although the auxiliary electrode block 9 is made of stainless steel with good thermal conductivity, there are certain air gaps in the annular cavity of the spiral electric heating wire, between the spiral electric heating wire and the alumina ceramic tube, and between the alumina ceramic tube and the accommodating cavity 9-2. The existence of the air gap makes the thermal resistance of the spiral electric heating wire when the heat is conducted outward larger than that of pure stainless steel. The patch temperature sensor is arranged on the outer surface of the auxiliary electrode block 9 and has a certain hysteresis in temperature detection. Therefore, when heating the auxiliary electrode block 9, a DC power supply controlled by a single-chip microcomputer is required to control the spiral electric heating wire. The heating power of the spiral electric heating wire should not be too large, otherwise due to the above-mentioned hysteresis, the actual temperature of the spiral electric heating wire is higher than the target heating temperature of the auxiliary electrode block 9, and the temperature detected by the patch temperature sensor has not reached the target heating temperature of the auxiliary electrode block 9. At this time, the DC power supply controlled by the single-chip microcomputer will also control the spiral electric heating wire to continue heating, which will cause the actual temperature of the auxiliary electrode block 9 to be higher than the target temperature. Excessive temperature may damage other components in the test pool. Therefore, it is necessary to consider the above-mentioned hysteresis and control the appropriate heating power so that the heat generated by the spiral electric heating wire has enough time to be conducted to the outer surface of the auxiliary electrode block 9. The above-mentioned power can be obtained through experiments, and the present invention does not make specific limitations. At the same time, the heating power should not be too small, otherwise the heating efficiency will be relatively slow.

[0034] like Figure 2 As shown, in the three-electrode in-situ test cell with in-situ heating function, the working electrode block 17 is an integrated structure assembled from an electrode cover 1, a small spring 2, a working electrode rod 3 and a working electrode block body 4; the working electrode 19, an insulating film 20, a counter electrode 21, a reference electrode sleeve 14, a reference electrode holder 8, a working electrode stand 7 and a large spring 6 are arranged in the installation chamber 9-1 of the auxiliary electrode block 9, an O-ring 12 and a flat washer 15 are arranged between the reference electrode block 5 and the working electrode block body 4 and between the reference electrode block 5 and the auxiliary electrode block 9, the working electrode block body 4, the reference electrode block 5 and the auxiliary electrode block 9 are detachably fixedly connected by a plurality of screws 16 and matching nuts 10, wherein the screw 16 passes through the outer edges of the working electrode block body 4, the reference electrode block 5 and the auxiliary electrode block 9, a first screw sleeve 11 for the screw 16 to pass through is arranged on the working electrode block body 4, and a second screw sleeve 13 for the screw 16 to pass through is arranged on the reference electrode block 5. The working electrode block body 4 , the reference electrode block 5 and the auxiliary electrode block 9 are all connected with terminals or plugs for wiring.

[0035] The three-electrode test cell with in-situ heating function shown in the present invention has the characteristics of compact structure, simple operation, high test accuracy, etc. First, the original constant temperature can be removed to reduce equipment investment and save space; second, long wires can be removed to improve test accuracy; third, experimental operations can be simplified.

[0036] The original test scheme requires the purchase of a thermostat, which occupies a large space and is relatively expensive. The incubator can be omitted by adopting the scheme of the present invention. The original test scheme requires a longer wire to lead the test electrode wiring from the incubator, which has a significant adverse effect on the test of parameters such as resistance. The original test scheme requires the installation of the test pool first, then the incubator is set, and finally the wire is pulled out to start the test, which is very cumbersome.

[0037] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed in the present application should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

Claims

1. A three-electrode in-situ test cell with in-situ heating function, characterized in that: The invention comprises a working electrode block (17), a reference electrode block (5) and an auxiliary electrode block (9) which are connected in sequence. The auxiliary electrode block (9) is provided with an electric heating element (18). The outside of the auxiliary electrode block (9) is provided with a temperature detection element. Both the electric heating element (18) and the temperature detection element are connected to a controllable power supply. The controllable power supply is used to control the heating of the electric heating element (18) through a detection signal of the temperature detection element, so that the auxiliary electrode block (9) is maintained at a preset temperature. The auxiliary electrode block (9) is made of a metal material that is electrically and thermally conductive.

2. A three-electrode in-situ test cell with in-situ heating function according to claim 1, characterized in that: The electric heating element (18) is arranged at the periphery of the installation chamber (9-1) of the auxiliary electrode block (9), and a receiving chamber (9-2) for receiving the electric heating element (18) is provided in the auxiliary electrode block (9).

3. A three-electrode in-situ test cell with in-situ heating function according to claim 2, characterized in that: An electric heating element terminal is provided on the auxiliary electrode block (9), one end of the electric heating element terminal extends into the accommodating cavity (9-2) and is connected to the electric heating element (18), and the auxiliary electrode block (9) and the electric heating element terminal are insulated.

4. The three-electrode in-situ test cell with in-situ heating function according to claim 1, characterized in that: The electric heating element (18) comprises a heating wire and an insulating tube sleeved on the outside of the heating wire.

5. A three-electrode in-situ test cell with in-situ heating function according to claim 4, characterized in that: The electric heating wire is a spiral electric heating wire, and the material of the insulating tube is alumina ceramics, silicon nitride ceramics, silicon boride ceramics or zirconium oxide ceramics.

6. The three-electrode in-situ test cell with in-situ heating function according to claim 3, characterized in that: In the radial direction of the auxiliary electrode block (9), the distance from the accommodating cavity (9-2) to the inner surface of the mounting chamber (9-1) is equal to the distance from the accommodating cavity (9-2) to the outer surface of the auxiliary electrode block (9).

7. The three-electrode in-situ test cell with in-situ heating function according to claim 1, characterized in that: The temperature detection element adopts a patch type temperature sensor, the detection part of the patch type temperature sensor is attached to the outer surface of the auxiliary electrode block (9), and the detection part of the patch type temperature sensor corresponds to the radial position of the electric heating element (18) of the auxiliary electrode block (9).

8. The three-electrode in-situ test cell with in-situ heating function according to claim 1, characterized in that: The auxiliary electrode block (9) is made of stainless steel, aluminum, aluminum alloy, copper, copper alloy, gold or silver.

9. The three-electrode in-situ test cell with in-situ heating function according to claim 1, characterized in that: The controllable power supply adopts a direct current power supply controlled by a single chip microcomputer.

10. A method for operating a three-electrode in-situ test cell with in-situ heating function according to any one of claims 1 to 9, characterized in that: The process includes the following: The controllable power supply is connected to an external power supply, and the controllable power supply controls the output voltage or current to make the electric heating element (18) work and heat up. The temperature detection element detects the temperature of the auxiliary electrode block (9) in real time. The controllable power supply determines whether the temperature of the test pool reaches a preset value based on the temperature detected by the temperature detection element. If the temperature is lower than the preset value, the electric heating element (18) is controlled to heat at a fixed power; if the temperature is higher than the preset value, the power supply is disconnected to suspend heating.

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