Electric heater with self-test function

Abstract

This electric heater, with self-testing function, relates to the field of heater equipment technology. It includes an electric heater body and a battery. The upper end of the electric heater body has a housing and also includes a switching circuit, an open-circuit detection circuit, a low-resistance detection circuit, a leakage detection circuit, and a fixing mechanism. The leakage detection circuit has at least two paths. The battery, switching circuit, open-circuit detection circuit, low-resistance detection circuit, and leakage detection circuit are installed in the housing and electrically connected. The fixing mechanism includes a vacuum suction cup, a magnetic ring, a spring, and a spiral power cord. This new invention can automatically detect whether there is an open circuit or decreased resistance in the electric heater body, and can also detect whether there is leakage in the electric heater body or the heated equipment. In the event of such an event, different LEDs will illuminate to prompt the user to perform maintenance, ensuring that the heated equipment can operate normally and reducing the probability of electric shock accidents. In summary, this invention has good application prospects.

Description

Technical Field

[0001] This utility model relates to the field of heater equipment technology, and in particular to an electric heater with a self-testing function. Background Technology

[0002] An electric heater is a device that provides heat to related devices (such as providing heat to the interior of an electric oven for baking food, or providing heat to an electric steam generator to make water evaporate) through heating methods such as resistance wire. It is widely used in industrial and civil fields.

[0003] With the advancement of industrial technology, the functions of electric heaters have become increasingly sophisticated. For example, the authorized utility model patent in my country with patent number "202220240534.1" and patent title "Electric Heater" describes that "This application relates to an electric heater, which includes a support base and at least two heating elements arranged at intervals between each other. Each heating element includes a positive electrode, a negative electrode, and a heating part. Each positive electrode and each negative electrode are assembled on the support base, and the two opposite ends of each heating part are respectively connected to the positive electrode and the negative electrode within the same heating element. The electric heater provided in this application is an electric heater with both high heat transfer efficiency and small size." For example, the authorized patent in my country with patent number "201120267723.X", also titled "Electric Heater", describes itself as follows: "This utility model provides an electric heater, including a metal heating element and an electrode plate. The electric heater also includes a ceramic insulator connector. The ceramic insulator connector has an axially arranged through hole A and a through hole B perpendicular to the through hole A. The through hole A is divided into two sections by the through hole B, namely section A1 and section A2. The cross-sectional shapes of sections A1 and A2 are different. The electrode plate is disposed in section A2. The electrode plate and the metal heating element are connected at the intersection of through hole A and through hole B. The electric heater also has a glass shell. The electric heater of this utility model has good safety performance." As can be seen above, although the two comparative patents respectively achieve the advantages of high heat transfer efficiency, small size, and good safety performance, they still have the following technical problems due to their structural and functional limitations. First, it lacks a self-testing function for its critical component, the electric heating resistance wire. If the resistance wire becomes open-circuited or its resistance decreases (e.g., part of the resistance wire is electrically conductive in contact with the heater casing), it cannot promptly alert the user. Before or during operation, the user cannot understand the specific fault and thus cannot perform maintenance or replacement, which can adversely affect the normal operation of the heated equipment. Second, it lacks leakage detection and alerting functions for both itself and the heated equipment. When leakage occurs due to various reasons, either itself or the heated equipment may occur, and the user, unaware of this, may be at risk of electric shock upon contact with the heater or the heated equipment casing. Utility Model Content

[0004] To overcome the shortcomings of existing electric heaters based on resistance wire heating, which, due to structural limitations, lack self-detection functions for open circuits and reduced resistance of the resistance wire, as well as the ability to monitor leakage in the heater itself and the heated equipment, resulting in limited functionality and poor safety, this utility model provides an electric heater with self-detection function that, under the action of a relevant mechanism, automatically detects whether the resistance wire is open-circuited or has reduced resistance (including short circuits) after each shutdown, and detects whether there is leakage in the electric heater body and the heated equipment during operation. In the event of any such situation, it can promptly prompt the user for maintenance, thereby ensuring that the heated equipment can operate normally and reducing the probability of electric shock accidents.

[0005] The technical solution adopted by this utility model to solve its technical problem is:

[0006] An electric heater with self-testing function includes an electric heater body and a battery. A housing is fixedly installed on the upper end of the electric heater body. It also includes a switching circuit, an open-circuit detection circuit, a low-resistance detection circuit, a leakage current detection circuit, and a fixing mechanism. The leakage current detection circuit has at least two paths. The battery, switching circuit, open-circuit detection circuit, low-resistance detection circuit, and leakage current detection circuit are installed inside the housing. The fixing mechanism includes a vacuum suction cup, a magnet ring, a spring, and a spiral power cord. The upper end of the spring is fixedly installed inside the upper part of the vacuum suction cup, and the magnet ring is fixedly installed on the upper side of the lower part of the vacuum suction cup. The vacuum suction cup and magnet ring are adsorbed onto the outer end of the metal housing of the heated equipment. The upper end of the spring and the lower end of the spiral power cord are fixedly installed together. The signal output terminal of the switching circuit is electrically connected to the signal input terminals of the open-circuit detection circuit and the low-resistance detection circuit. The power output terminal of the switching circuit is electrically connected to the power input terminal of the electric heater body. The outer end of the heating tube of the electric heater body, the upper part of the spiral power cord, and the signal input terminals of the two leakage current detection circuits are electrically connected respectively.

[0007] Furthermore, the height of the spring is greater than the height of the vacuum suction cup, and the inner diameter of the inner ring of the magnet is greater than the outer diameter of the lower upper end of the vacuum suction cup.

[0008] Furthermore, the switching circuit includes an electrically connected relay, resistor, capacitor, transistor, and three-terminal voltage detector. The two power input terminals and two normally open contacts of the first relay are respectively connected to the two power input terminals of the second relay. The positive power input terminal and control power input terminal of the third relay are connected to the control power input terminal of the second relay. The normally open contact of the third relay is connected to one normally closed contact of the first relay. The normally closed contact of the second relay is connected to one end of the first resistor. The other end of the first resistor is connected to the positive terminal of the capacitor and the positive power input terminal of the three-terminal voltage detector. The power output terminal of the three-terminal voltage detector is connected to one end of the second resistor. The other end of the second resistor is connected to the base of the transistor. The collector of the transistor is connected to the negative power input terminal of the third relay. The negative terminal of the capacitor is connected to the negative power input terminal of the three-terminal voltage detector and the emitter of the transistor.

[0009] Furthermore, the open-circuit detection circuit includes an electrically connected relay, a resistor, and a light-emitting diode. One end of the resistor is connected to the normally closed contact of the relay, the other end of the resistor is connected to the positive terminal of the light-emitting diode, and the negative terminal of the light-emitting diode is connected to the negative power input terminal of the relay.

[0010] Furthermore, the low resistance detection circuit includes an electrically connected resistor, a transistor, and a light-emitting diode. One end of the first resistor and one end of the second resistor are connected to the base of the transistor. The collector of the transistor is connected to one end of the third resistor. The other end of the third resistor is connected to the negative terminal of the light-emitting diode. The other end of the second resistor is connected to the emitter of the transistor.

[0011] Furthermore, the leakage current detection circuit includes an electrically connected resistor, a silicon controlled rectifier (SCR), and a light-emitting diode (LED). One end of the first resistor is connected to one end of the second resistor and one end of the third resistor. The other end of the third resistor is connected to the control electrode of the SCR. The cathode of the SCR is connected to one end of the fourth resistor. The other end of the fourth resistor is connected to the positive electrode of the LED. The negative electrode of the LED is connected to the other end of the second resistor.

[0012] Compared with the prior art, the advantages of this utility model are as follows: The electric heater body based on the resistance wire heating method of this utility model can automatically detect whether there is an open circuit or a decrease in resistance (including short circuit) in the resistance wire of the electric heater body after each power failure under the action of the control circuit. Under the joint action of two leakage detection circuits, it can detect whether there is leakage in the electric heater body or the heated equipment (such as an electric steam generator) heated by the electric heater body. When the corresponding situation occurs, different light-emitting diodes can light up in time to prompt the user to carry out maintenance, thus ensuring that the heated equipment can be heated and operated normally as much as possible and reducing the probability of electric shock accidents. Attached Figure Description

[0013] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0014] Figure 1 This is a schematic diagram of the overall structure of this utility model.

[0015] Figure 2 This is a partial structural schematic diagram of the present invention.

[0016] Figure 3 This is the circuit diagram of this utility model. Detailed Implementation

[0017] Figure 1 , 2 As shown in Figure 3, the electric heater with self-testing function includes a heater body RT based on resistance wire, a battery G1, and a power supply module Y1. An engineering plastic heat insulation plate 2 is fixedly installed on the upper end of the flange 1 of the heater body RT. A housing 3 is fixedly installed on the upper end of the insulation plate 2. It also has a switching circuit 4, an open circuit detection circuit 5, a low resistance detection circuit 6, a leakage current detection circuit 7, and a fixing mechanism 8. The leakage current detection circuit 7 has at least two paths. The battery G1, the power supply module Y1, the switching circuit 4, the open circuit detection circuit 5, the low resistance detection circuit 6, and the leakage current detection circuit 7 are installed inside the housing 3. On the plate; the fixing mechanism 8 includes a rubber vacuum suction cup 81, a permanent annular magnet ring 82, and a spring 83. The upper end of the spring 83 is fixedly installed inside the upper end of the vacuum suction cup 81, and the annular magnet ring 82 is fixedly installed on the upper end of the lower suction cup surface ring of the vacuum suction cup 81. The fixing mechanism 8 is attached to the outer end of the metal shell of the heated equipment (not shown in the figure) by the vacuum suction cup 81 (for non-steel shells, such as aluminum or copper shells) or by the magnet ring 82 (for steel shells). The upper end of the spring 83 is welded to the lower end of a spiral power cord 84, and the upper part of the spiral power cord 84 is located outside the upper end of the vacuum suction cup 81.

[0018] Figure 1 , 2As shown in Figure 3, the height of spring 83 is greater than the height of vacuum suction cup 81 (ensuring that the lower end of spring 83 can contact the outer end of the outer shell of the heated equipment). The inner diameter of the inner ring of the annular magnet ring 82 is slightly larger than the outer diameter of the upper end of the lower suction cup surface ring of vacuum suction cup 81 (similar to the structure of a household kitchen vacuum suction cup). The switching circuit includes relays J1, J2, and J3 connected via circuit board wiring, resistors R1 and R2, capacitor C1, transistor T1, and three-terminal voltage detector Y2; the two power input terminals and two normally open contacts of the first relay J1 are connected to the two power input terminals of the second relay J2 respectively, the positive power input terminal and control power input terminal of the third relay J3 are connected to the control power input terminal of the second relay J2, and the normally open contact terminal of the third relay J3 is connected to one normally closed contact terminal of the first relay J1, the second... The normally closed contact of relay J2 is connected to one end of the first resistor R1. The other end of the first resistor R1 is connected to the positive terminal of capacitor C1 and pin 2 of the positive power input terminal of three-terminal voltage detector Y2. Pin 1 of the power output terminal of three-terminal voltage detector Y2 is connected to one end of the second resistor R2. The other end of the second resistor R2 is connected to the base of transistor T1. The collector of transistor T1 is connected to the negative power input terminal of the third relay J3. The negative terminal of capacitor C1 is connected to pin 3 of the negative power input terminal of three-terminal voltage detector Y2 and the emitter of transistor T1. The open-circuit detection circuit includes relay J4, resistor R3, and LED V1 connected via circuit board wiring. One end of resistor R3 is connected to the normally closed contact of relay J4, and the other end of resistor R3 is connected to the positive terminal of LED V1. The negative terminal of LED V1 is connected to the negative power input terminal of relay J4. The low-resistance detection circuit includes resistors R4, R5, and R6, transistor T2, and LED V2 connected via circuit board wiring. One end of the first resistor R4, one end of the second resistor R5, and the base of transistor T2 are connected. The collector of transistor T2 is connected to one end of the third resistor R6. The other end of the third resistor R6 is connected to the cathode of LED V2. The other end of the second resistor R5 is connected to the emitter of transistor T2. The first leakage current detection circuit includes resistors R7, R8, R9, and R10, a silicon controlled rectifier (SCR) VT, and LED V3 connected via circuit board wiring. One end of the first resistor R7, one end of the second resistor R8, and one end of the third resistor R9 are connected. The other end of the third resistor R9 is connected to the gate electrode of SCR VT. The cathode of SCR VT is connected to one end of the fourth resistor R10. The other end of the fourth resistor R10 is connected to the anode of LED V3. The cathode of LED V3 is connected to the other end of the second resistor R8.The second leakage current detection circuit includes resistors R11, R12, R13, R14 and a silicon controlled rectifier (SCR) VT1, and an LED V4 connected via circuit board wiring. One end of the first resistor R12 is connected to one end of the second resistor R11 and one end of the third resistor R13. The other end of the third resistor R13 is connected to the control electrode of the SCR VT1. The cathode of the SCR VT1 is connected to one end of the fourth resistor R14. The other end of the fourth resistor R14 is connected to the positive electrode of the LED V3. The negative electrode of the LED V3 is connected to the other end of the second resistor R11.

[0019] Figure 1 , 2 As shown in Figure 3, the power input terminals 1 and 2 of the power supply module Y1, the two power input terminals of relays J1 and J2 in the switching circuit, and the AC 220V power supply are connected by wires. The power output terminals 3 and 4 of the power supply module Y1, the power input terminals of the switching circuit, the power input terminal controlled by relay J3 and the emitter of transistor T1, the power input terminal controlled by relay J4 in the open circuit detection circuit and the negative terminal of LED V1, the power input terminal of the low resistance detection circuit, the positive terminal of LED V2 and the emitter of transistor T2, the power input terminal of battery G1, the power input terminal of leakage current detection circuit, the anode of SCR VT and the negative terminal of LED V3, and the anode of SCR VT1 and the negative terminal of LED V4 are connected by wires. The normally open contact of relay J3 and one normally closed contact of relay J1 are connected by wires, and the other normally closed contact of relay J1 and the positive power input terminal of relay J4 and the other end of resistor R4 are connected by wires. The two control power input terminals of relay J1 are connected to the power input terminal of the electric heater body RT via wires. The upper part of the left end M of the heating tube outside the resistance wire of the electric heater body (the wire connected to the heating tube enters the outer casing through the insulating plate and the opening on the side of the outer casing, and the opening is sealed with heat-resistant sealant), the upper part of the spiral power line M1, and the other end of the signal input terminals of the two sets of leakage current detection circuits, resistor R7 and resistor R12, are respectively connected via wires. Figure 3In the diagram, power supply module Y1 is a finished product of AC 220V to DC 12V power supply module; relays J1 and J2 are AC 220V relays; relays J3 and J4 are DC 12V relays; transistors T1 and T2 are model 9013 (NPN); three-terminal voltage detection module Y2 is model AN051A; LEDs V1, V2, V3, and V4 are red, yellow, green, and blue LEDs respectively (the light-emitting surfaces of the four LEDs are located outside the four openings on the front of the casing); thyristors VT and VT1... The model is MCR100-1 encapsulated unidirectional thyristor; the battery G1 is a 12V / 10Ah lithium battery; the capacitor C1 is a 4.7μF / 25V electrolytic capacitor; the resistance values ​​of resistors R1, R2, R3, R4, R5, R6, R7, R8, R9, R10, R12, R11, R13, and R14 are 1.3MΩ, 47KΩ, 1.8KΩ, 11.3KΩ, 1KΩ, 1.8KΩ, 100KΩ, 1KΩ, 1KΩ, 1.8KΩ, 100KΩ, 1KΩ, 1KΩ, and 1.8KΩ, respectively.

[0020] Figure 1 , 2As shown in Figure 3, the electric heater body RT of this novel resistance wire-based device is used to attach either a vacuum suction cup 81 (for non-steel shells, such as aluminum or copper shells) or a magnetic ring 82 (for steel shells, where the lower end of the vacuum suction cup is thin and does not affect magnetic attachment) to the outer end of the metal shell of the heated equipment (not shown in the figure) before use. During operation, after turning on the main power switch S, 220V AC power enters the power input terminal of the electric heater body RT through the two control power input terminals and two normally open contacts of relay J1 (220V AC power enters the power input terminals of relays J1 and J2, energizing relays J1 and J2 to close their control power input terminals and normally open contacts, and opening their control power input terminals and normally closed contacts). The electric heater body RT then generates heat, heating the heated equipment (such as an electric steam generator). After the 220V AC power enters the power input terminal of power module Y1, pins 3 and 4 of power module Y1 output a stable 12V DC power supply, which enters the power input terminals of the open circuit detection circuit, switching circuit, leakage detection circuit, and low resistance detection circuit (simultaneously, the 12V power supply enters the power input terminal of battery G1 to charge relay G1, so that the relevant circuits can still be powered and operate after the AC power is cut off). When the 220V AC power is cut off, relays J1 and J2 are de-energized and no longer engage, opening the control power input terminal and normally open contact terminal, and closing the control power input terminal and normally closed contact terminal (the 220V power supply no longer supplies power to the electric heater body RT through the two control power input terminals and two normally open contacts of relay J1). In this way, the positive terminal of the 12V power supply will enter the other end of resistor R1 through the control power input terminal and normally closed contact terminal of relay J2 to charge capacitor C1.During the initial charging period (e.g., less than 6 seconds), when capacitor C1 is not fully charged, the 12V power supply, after being stepped down and current-limited by resistor R1, enters the three-terminal voltage detector Y2. The voltage at pin 2 is lower than its internal 4.75V threshold voltage. Therefore, pin 1 of the three-terminal voltage detector Y2 has no output, relay J3 will not be energized, and the positive terminal of the 12V power supply will not enter the power input terminal of the electric heater body RT. After charging for a period of time (e.g., more than 6 seconds), when capacitor C1 is fully charged, the 12V power supply, after being stepped down and current-limited by resistor R1, enters the three-terminal voltage detector. If the voltage at pin 2 of Y2 is higher than its internal 4.75V threshold voltage, then pin 1 of the three-terminal voltage detector Y2 will output a high level. This high level is then stepped down and current-limited by resistor R2, entering the base of transistor T1. Transistor T1 conducts, and its collector outputs a low level, entering the negative power input terminal of relay J3. Relay J3 is energized and its control power input terminal and normally open contact close. Thus, the positive 12V power supply enters the first normally closed contact of relay J1 via the control power input terminal and normally open contact of relay J3, and then flows through the first control power input terminal of relay J1... The power input terminals of the heater body RT and the electric heater body RT are connected to another control power input terminal of relay J1, and then from the other normally closed contact terminal of relay J1, they are connected to the positive power input terminal of relay J4 and the other end of resistor R4. Through this process, each time the main power switch S is turned off, the 12V power supply is connected in series with the power input terminals of the electric heater body RT and the other end of relay J4 to the positive power input terminal of resistor R4. Subsequently, the system automatically detects whether the electric heater body RT is open-circuited or its resistance value decreases (including short-circuiting). A 6-second delay using capacitor C1 and a three-terminal voltage detector prevents damage caused by excessive voltage in the instant the control power input terminal and normally open contact terminal of relay J1 separate when it loses power. In extreme cases, the induced power generated by the contact arcing during separation could cause the LED V2 to be damaged due to excessive voltage. Since the control power input terminal and normally open contact terminal of relay J1 are completely separated after a 6-second delay, the LED V2 will not be damaged by overvoltage.

[0021] Figure 1 , 2As shown in Figure 3, in the open-circuit detection circuit, when the electric heater body RT is not open-circuited, the 12V power supply will enter the positive power input terminal of relay J4 through the control power input terminal and normally open contact terminal of relay J3, one normally closed contact terminal and one control power input terminal of relay J1, the power input start terminal and the power input end terminal of electric heater body RT, and the other control power input terminal and the other normally closed contact terminal of relay J1. Relay J4 is energized and its control power input terminal and normally closed contact terminal are open-circuited. Thus, LED V1 will not be energized and will not light up, indicating that the electric heater body RT... No open circuit occurred; when the electric heater body RT (5KW) is open-circuited, the 12V power supply no longer enters the positive power input terminal of relay J4 through the control power input terminal and normally open contact terminal of relay J3, the two normally closed contacts and two control power input terminals of relay J1, and the power input terminal of the electric heater body RT. Relay J4 is de-energized and no longer closes its control power input terminal and normally closed contact terminal. In this way, the 12V power supply will enter the positive power input terminal of LED V1 through resistor R3 with voltage reduction and current limiting. As a result, LED V1 will be energized and light up to indicate to the user that the electric heater body RT has been damaged by an open circuit. In the low resistance detection circuit, when the resistance of the electric heater body RT does not decrease (including short circuit), the 12V power supply, after passing through the control power input terminal and normally open contact terminal of relay J3, the two normally closed contacts and two control power input terminals of relay J1, and the power input terminal of the electric heater body RT, enters the other end of resistor R4. After being divided by resistors R4 and R5, the power supply enters the base of transistor T2 at a voltage below 0.7V. Therefore, transistor T2 will not conduct, and LED V2 will not be energized, indicating that the resistance of the electric heater body RT has not decreased or short-circuited. When the resistance of the heater body RT decreases (including short circuit), the 12V power supply enters the other end of resistor R4 through the power input terminal and normally open contact of relay J3, the two normally closed contacts and two control power input terminals of relay J1, and the power input terminal of the heater body RT. After the power supply is divided by resistors R4 and R5, it enters the base of transistor T2, which is higher than 0.7V. Then, transistor T2 will conduct, and the collector will output a low level, which enters the negative power input terminal of LED V2. LED V2 will be energized and light up, indicating that the resistance of the heater body RT has decreased or short circuited. When there is no leakage in the electric heater body RT, the thyristor VT will not conduct and the LED V3 will not light up, indicating that there is no leakage in the electric heater body RT. When there is leakage in the electric heater body RT, the leakage current will pass through the outer end of the heating tube M of the electric heater body, through the voltage divider of resistors R7 and R8, and the voltage reduction and current limiting of resistor R9 to trigger the control electrode of the thyristor VT. The thyristor VT will conduct, and the cathode output high level will pass through the voltage reduction and current limiting of resistor R10 to enter the positive power input terminal of LED V3. The LED V3 will be energized and light up, indicating that there is leakage in the electric heater body RT.When there is no leakage in the heated equipment, the thyristor VT1 will not conduct and the LED V4 will not light up, indicating that there is no leakage in the casing of the heated equipment. When there is leakage in the heated equipment, the leakage current will pass through the casing M1, spring 83, and through the voltage divider of resistors R12 and R11. Resistor R13 will reduce the voltage and limit the current, triggering the control electrode of the thyristor VT1. The thyristor VT1 will conduct, and the cathode will output a high level. After being reduced by resistor R14 and the current limited, it will enter the positive power input terminal of the LED V4. The LED V4 will be energized and light up, indicating that there is leakage in the casing of the heated equipment.

[0022] Figure 1 , 2 As shown above, the electric heater body based on the resistance wire heating method of this new type can automatically detect whether there is an open circuit or a decrease in resistance (including short circuit) in the resistance wire of the electric heating tube body after each power failure. During operation, it can detect whether there is leakage in the electric heater body or the heated equipment (such as an electric steam generator) heated by the electric heater body. In the event of such a situation, different light-emitting diodes will light up in time to prompt the user to perform maintenance, thereby ensuring that the heated equipment can be heated and operated normally and reducing the probability of electric shock accidents.

[0023] The foregoing has shown and described the basic principles, main features, and advantages of this utility model. It will be apparent to those skilled in the art that this utility model is limited to the details of the exemplary embodiments described above, and that it can be implemented in other specific forms without departing from the spirit or basic characteristics of this utility model. Therefore, the embodiments should be considered exemplary and non-limiting in all respects. The scope of this utility model is defined by the appended claims rather than the foregoing description, and thus all variations falling within the meaning and scope of equivalents of the claims are intended to be included within this utility model.

[0024] Furthermore, it should be understood that although this specification describes the embodiments, the embodiments do not necessarily contain only one independent technical solution. This way of describing the specification is only for clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in the embodiments can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. An electric heater with self-checking function, comprising an electric heater body, a storage battery, and an outer shell body fixedly installed at the upper end of the electric heater body, characterized in that, It also includes a switching circuit, an open-circuit detection circuit, a low-resistance detection circuit, a leakage current detection circuit, and a fixing mechanism. The leakage current detection circuit has at least two paths. The battery, switching circuit, open-circuit detection circuit, low-resistance detection circuit, and leakage current detection circuit are installed inside the outer casing. The fixing mechanism includes a vacuum suction cup, a magnetic ring, a spring, and a spiral power cord. The upper end of the spring is fixedly installed inside the upper part of the vacuum suction cup, and the magnetic ring is fixedly installed on the upper side of the lower part of the vacuum suction cup. The vacuum suction cup and the magnetic ring are adsorbed onto the outer end of the metal casing of the heated equipment. The upper end of the spring and the lower end of the spiral power cord are fixedly installed together. The signal output terminal of the switching circuit is electrically connected to the signal input terminals of the open-circuit detection circuit and the low-resistance detection circuit. The power output terminal of the switching circuit is electrically connected to the power input terminal of the electric heater body. The outer end of the heating tube of the electric heater body, the upper part of the spiral power cord, and the signal input terminals of the two sets of leakage current detection circuits are electrically connected respectively.

2. The electric heater with self-testing function according to claim 1, characterized in that, The height of the spring is greater than the height of the vacuum chuck, and the inner diameter of the inner ring of the magnet is greater than the outer diameter of the upper part of the lower part of the vacuum chuck.

3. The electric heater with self-testing function according to claim 1, characterized in that, The switching circuit includes electrically connected relays, resistors, capacitors, transistors, and a three-terminal voltage detector. The two power input terminals and two normally open contacts of the first relay are connected to the two power input terminals of the second relay. The positive power input terminal and control power input terminal of the third relay are connected to the control power input terminal of the second relay. The normally open contact of the third relay is connected to one normally closed contact of the first relay. The normally closed contact of the second relay is connected to one end of the first resistor. The other end of the first resistor is connected to the positive terminal of the capacitor and the positive power input terminal of the three-terminal voltage detector. The power output terminal of the three-terminal voltage detector is connected to one end of the second resistor. The other end of the second resistor is connected to the base of the transistor. The collector of the transistor is connected to the negative power input terminal of the third relay. The negative terminal of the capacitor is connected to the negative power input terminal of the three-terminal voltage detector and the emitter of the transistor.

4. The electric heater with self-testing function according to claim 1, characterized in that, The open-circuit detection circuit includes an electrically connected relay, a resistor, and a light-emitting diode. One end of the resistor is connected to the normally closed contact of the relay, the other end of the resistor is connected to the positive terminal of the light-emitting diode, and the negative terminal of the light-emitting diode is connected to the negative power input terminal of the relay.

5. The electric heater with self-testing function according to claim 1, characterized in that, The low resistance detection circuit includes an electrically connected resistor, a transistor, and a light-emitting diode. One end of the first resistor and one end of the second resistor are connected to the base of the transistor. The collector of the transistor is connected to one end of the third resistor. The other end of the third resistor is connected to the negative terminal of the light-emitting diode. The other end of the second resistor is connected to the emitter of the transistor.

6. The electric heater with self-testing function according to claim 1, characterized in that, The leakage current detection circuit includes an electrically connected resistor, a silicon controlled rectifier (SCR), and a light-emitting diode (LED). One end of the first resistor is connected to one end of the second resistor and one end of the third resistor. The other end of the third resistor is connected to the control electrode of the SCR. The cathode of the SCR is connected to one end of the fourth resistor. The other end of the fourth resistor is connected to the positive electrode of the LED. The negative electrode of the LED is connected to the other end of the second resistor.

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