Box-type muffle furnace

Abstract

The utility model relates to a box type muffle furnace, which belongs to the technical field of muffle furnace heating, and comprises an explosion-proof box body, a furnace body assembly is arranged in the explosion-proof box body, the furnace body assembly comprises a fire-resistant inner furnace body and a heating device, the heating device is arranged on the fire-resistant inner furnace body, and a temperature sensor is arranged in the fire-resistant inner furnace body; a control assembly and a power supply circuit for supplying power to the whole muffle furnace are arranged on the explosion-proof box body, and the control assembly comprises a single chip microcomputer, a touch screen, a control circuit, a voltage monitoring current circuit and a current monitoring circuit. According to the utility model, the working condition of the muffle furnace is monitored and fed back in real time through the temperature sensor, the voltage monitoring circuit and the current monitoring circuit, the 380V power supply voltage obtained through input is efficiently converted into the voltage meeting the requirement of a heating device through the single chip microcomputer and the power supply circuit, and continuous adjustment is realized; power consumption is effectively reduced, the utilization rate of electric energy is improved, meanwhile, a transformer is omitted, and the overall weight of the muffle furnace is greatly reduced.

Description

Technical Field

[0001] The utility model belongs to the technical field of muffle furnace heating, and in particular relates to a box-type muffle furnace. Background Art

[0002] Muffle furnace is a commonly used high-temperature resistance furnace, which is used in industrial and mining enterprises and scientific research institutions to conduct various high-temperature tests, such as sintering, dissolution and analysis of metals and ceramics, and ash detection in coal quality analysis. Muffle furnaces are classified into many categories according to their heating devices, operating temperatures and controllers, such as electric wire muffle furnaces, silicon carbon rod muffle furnaces, silicon molybdenum rod muffle furnaces, etc. The temperature controller of the muffle furnace is an instrument used to control the internal temperature of the muffle furnace. Commonly used ones include PID adjustment controllers and program controllers.

[0003] An integrated high-temperature muffle furnace (CN206247833U) is disclosed, which includes a muffle furnace box and a control system; the control system is arranged at the bottom of the muffle furnace box, and the control system includes multiple indicator lights, a display screen, multiple control buttons, a buzzer, a transformer, a control transformer, a solid-state relay, a controller body and an alarm switch; the controller body is arranged in the control system, and the multiple indicator lights, the display screen, the multiple control buttons and the buzzer are respectively embedded on the outer end surface of the muffle furnace box, located at the front bottom of the muffle furnace box, and the multiple indicator lights, the display screen, the multiple control buttons and the buzzer are respectively electrically connected to the controller body; the transformer is arranged in the controller body, and the controller body is provided with thirteen connection The control transformer is connected to the first port, the second port and the third port of the controller body, and the solid-state relay is connected to the sixth port and the seventh port of the controller body; the alarm switch is connected to the tenth port and the eleventh port of the controller body, and the twelfth port and the thirteenth port of the controller body are externally connected to a 220V AC power supply; it has the characteristics of fast heating and cooling rate and energy saving; however, this type of muffle furnace also has the following problems: the transformer is large in size, which increases the overall weight of the muffle furnace, making it inconvenient to carry, and its energy consumption is high, while the power conversion efficiency is low; in addition, the insufficient voltage adjustment stability often directly restricts the precise control of the temperature in the furnace, and it lacks monitoring of voltage and current, which is the deficiency of the prior art. Summary of the invention

[0004] The purpose of the utility model is to provide a box-type muffle furnace to solve the problems existing in the prior art, in view of the fact that the control of the muffle furnace requires the participation of a transformer, and the provision of the transformer will increase the overall weight of the muffle furnace, making it difficult to carry the muffle furnace. In addition, the existing muffle furnace lacks the defect of monitoring the working voltage and current of the muffle furnace.

[0005] In order to achieve the above purpose, the utility model provides the following technical solutions:

[0006] A box-type muffle furnace comprises an explosion-proof box, a furnace body assembly is arranged inside the explosion-proof box, the furnace body assembly comprises a refractory inner furnace body and a heating device, the heating device is arranged on the refractory inner furnace body, and a temperature sensor is arranged inside the refractory inner furnace body;

[0007] The explosion-proof box is provided with a control component and a power supply circuit for supplying power to the entire muffle furnace. The control component includes a single-chip microcomputer, a touch screen, a control circuit, a voltage monitoring current circuit and a current monitoring circuit. The temperature sensor is connected to the first input terminal of the single-chip microcomputer, the touch screen is connected to the single-chip microcomputer for communication, the first output terminal of the single-chip microcomputer is connected to the first end of the control circuit, the second end of the control circuit is connected to the heating device, and the heating device is controlled to heat the refractory inner furnace body. The third end of the control circuit is connected to the first end of the voltage monitoring circuit and the first end of the current monitoring circuit, the second end of the voltage monitoring circuit is connected to the second input terminal of the single-chip microcomputer, and the second end of the current monitoring circuit is connected to the third input terminal of the single-chip microcomputer.

[0008] Further improvements of the technical solution include: the power supply circuit includes a power supply interface P1, an adjustable resistor R1, a rectifier bridge D1, a capacitor C1 and a capacitor C2, the first end of the power supply interface P1 is connected to an external 380V power supply, the second end of the power supply interface P1 is connected to the second output end of the single-chip microcomputer, the first end of the adjustable resistor R1 and the first end of the rectifier bridge D1, the third end of the power supply interface P1 is connected to the third output end of the single-chip microcomputer, the second end of the adjustable resistor R1 and the second end of the rectifier bridge D1, the third end of the rectifier bridge D1 is grounded, the fourth end of the rectifier bridge D1 is connected to the first end of the capacitor C1 and the first end of the capacitor C2, the second end of the capacitor C1 and the second end of the capacitor C2 are both grounded, and the fourth end of the rectifier bridge D1 outputs 311V DC.

[0009] A further improvement of the technical solution is that the control circuit includes a resistor R2, a resistor R3, a field effect transistor Q1, an isolation chip U1, a resistor R4, a resistor R5, a bidirectional transient suppression diode TVS1, a resistor R6, a capacitor C3, a field effect transistor Q2 and a heating device interface P2;

[0010] The first end of the resistor R2 is connected to the PWM output end of the single-chip microcomputer, the second end of the resistor R2 is connected to the first end of the resistor R3 and the gate of the field effect tube Q1, the second end of the resistor R3 and the source of the field effect tube Q1 are both grounded, the drain of the field effect tube Q1 is connected to the first pin of the isolation chip U1, the second pin of the isolation chip U1 is connected to the 5V power supply through the resistor R4, the third pin of the isolation chip U1 is connected to the first end of the bidirectional suppression diode TVS1, the first end of the resistor R6, the first end of the capacitor C3 and the gate of the field effect tube Q2 through the resistor R5, the fourth pin of the isolation chip U1 is connected to the external negative 9V power supply, the second end of the bidirectional suppression diode TVS1, the second end of the resistor R6 and the second end of the capacitor C3 are all grounded, the emitter of the field effect tube Q2 is connected to the voltage monitoring circuit and the current monitoring circuit, the collector of the field effect tube Q2 is connected to the first end of the heating device interface P2, and the second end of the heating device interface P2 is connected to the 311V direct current.

[0011] Further improvements of the technical solution include that the current monitoring circuit includes a current sensor U2, a capacitor C4, a resistor R7 and a resistor R8, the first pin and the second pin of the current sensor U2 are both connected to the emitter of the field effect tube Q2, the third pin and the fourth pin of the current sensor U2 are both grounded, the fifth pin of the current sensor U2 is connected to the first end of the capacitor C4 and the 5V power supply, the second end of the capacitor C4 is grounded, the sixth pin of the current sensor U2 is connected to the first end of the resistor R8 and the third input terminal of the microcontroller through the resistor R7, and the second end of the resistor R8 is grounded.

[0012] A further improvement of the technical solution is that the voltage monitoring circuit includes a resistor R9, a voltage transformer L1 and a resistor R10, the first end of the resistor R9 is connected to the emitter of the field effect tube Q2, the second end of the resistor R9 is connected to the same-name end of the primary winding of the voltage transformer L1, the other end of the primary winding of the voltage transformer L1 is grounded, the same-name end of the secondary winding of the voltage transformer L1 is connected to the first end of the resistor R10 and the second input end of the single-chip microcomputer, and the other end of the secondary winding of the voltage transformer L1 and the second end of the resistor R10 are both grounded.

[0013] A further improvement of the technical solution also includes a furnace body bracket, which is horizontally arranged in the explosion-proof box, with both ends of the furnace body bracket fixedly installed on the inner wall of the explosion-proof box, and the furnace body assembly is installed on the furnace body bracket.

[0014] Further improvements of the technical solution include: the furnace body assembly also includes a furnace shell, a heat-insulating fixing rod, a refractory furnace cover, a sealing ring and heat-insulating asbestos, the furnace shell is fixedly mounted on the furnace body bracket, the refractory inner furnace body is mounted in the furnace shell through the heat-insulating fixing rod, the space between the refractory inner furnace body and the furnace shell is filled with heat-insulating asbestos, a U-shaped furnace body is arranged on the refractory inner furnace body, the refractory furnace cover is matched with the refractory furnace body, and a sealing ring is also arranged between the refractory furnace cover and the refractory furnace body.

[0015] A further improvement of the technical solution is that three heat-insulating fixing rods are arranged in the furnace shell, and the three heat-insulating fixing rods are respectively arranged on the left and right rear sides of the refractory inner furnace body for supporting and fixing the refractory inner furnace body.

[0016] A further improvement of the technical solution is that a box door is provided on the explosion-proof box body, the box door is movably connected to the explosion-proof box body, and the refractory furnace cover is installed on the box door.

[0017] A further improvement of the technical solution is that a heat dissipation hole is arranged on the top of the explosion-proof box, and a pulley support foot is arranged on the bottom of the explosion-proof box.

[0018] The beneficial effect of the utility model is that the utility model monitors and feeds back the working condition of the muffle furnace in real time through the set temperature sensor, voltage monitoring circuit and current monitoring circuit, and efficiently converts the input 380V power supply voltage into a voltage suitable for the requirements of heating devices such as silicon molybdenum rods through the single-chip microcomputer and the power supply circuit, and realizes continuous adjustment, which effectively reduces power consumption and improves the utilization rate of electric energy, and also eliminates the transformer component, greatly reducing the overall weight of the muffle furnace.

[0019] In addition, the utility model has a reliable design principle, a simple structure and a very broad application prospect.

[0020] It can be seen that compared with the prior art, the present invention has outstanding substantive features and significant progress, and the beneficial effects of its implementation are also obvious. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a three-dimensional schematic diagram of the box-type muffle furnace.

[0022] Figure 2 It is a cross-sectional schematic diagram of the box-type muffle furnace.

[0023] Figure 3 It is a structural schematic diagram of the furnace body assembly.

[0024] Figure 4 This is the schematic diagram of the power supply circuit.

[0025] Figure 5 This is the schematic diagram of the control circuit.

[0026] Figure 6 This is the schematic diagram of the current monitoring circuit.

[0027] Figure 7 This is the schematic diagram of the voltage monitoring circuit.

[0028] 110 is an explosion-proof box, 111 is a box door, 112 is a heat dissipation hole, 113 is a pulley support foot, 121 is a refractory inner furnace body, 122 is a heating device, 123 is a furnace shell, 124 is a heat-insulating fixing rod, 125 is a refractory furnace cover, 126 is a sealing ring, 130 is a temperature sensor, 140 is a control component, 141 is a single-chip microcomputer, 142 is a touch screen, and 150 is a furnace body bracket. DETAILED DESCRIPTION

[0029] In order to enable those skilled in the art to better understand the technical solutions in the present invention, the following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0030] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used herein in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0031] The key terms appearing in the present invention are explained below.

[0032] PWM is the abbreviation of Pulse Width Modulation in English. It means pulse width modulation in Chinese. Pulse width modulation is a very effective technology to control analog circuits using the digital output of microprocessors. It is widely used in many fields from measurement, communication to power control and conversion. Pulse width modulation is an analog control method that modulates the bias of the transistor base or MOS tube gate according to the change of the corresponding load to achieve the change of the conduction time of the transistor or MOS tube, thereby achieving the change of the output of the switching regulated power supply. This method can keep the output voltage of the power supply constant when the working conditions change. It is a very effective technology to control analog circuits using the digital signal of the microprocessor.

[0033] like Figure 1 , Figure 2 and Figure 3As shown, the utility model provides a box-type muffle furnace, including an explosion-proof box, a furnace body assembly is arranged inside the explosion-proof box, the furnace body assembly includes a refractory inner furnace body and a heating device, the heating device is arranged on the refractory inner furnace body, and a temperature sensor is arranged inside the refractory inner furnace body; a control assembly and a power supply circuit for powering the entire muffle furnace are arranged on the explosion-proof box, the control assembly includes a single-chip microcomputer, a touch screen, a control circuit, a voltage monitoring current circuit and a current monitoring circuit, the temperature sensor is connected to the first input end of the single-chip microcomputer, the touch screen is connected to the single-chip microcomputer for communication, the first output end of the single-chip microcomputer is connected to the first end of the control circuit, the second end of the control circuit is connected to the heating device, the heating device is controlled to heat the refractory inner furnace body, the third end of the control circuit is connected to the first end of the voltage monitoring circuit and the first end of the current monitoring circuit, the second end of the voltage monitoring circuit is connected to the second input end of the single-chip microcomputer, and the second end of the current monitoring circuit is connected to the third input end of the single-chip microcomputer. The single-chip microcomputer automatically adjusts the power supply voltage and frequency according to the temperature sensor reading to ensure that the temperature in the furnace is stable within a preset range and achieve accurate temperature control. Among them, the heating device can use a silicon molybdenum rod.

[0034] In addition, the box-type muffle furnace also includes a furnace body bracket, which is transversely arranged in the explosion-proof box, with both ends of the furnace body bracket fixedly mounted on the inner wall of the explosion-proof box, and the furnace body assembly is mounted on the furnace body bracket.

[0035] In addition, the furnace body assembly also includes a furnace shell, an insulating fixing rod, a refractory furnace cover, a sealing ring and insulating asbestos. The furnace shell is fixedly installed on the furnace body bracket, the refractory inner furnace body is installed in the furnace shell through the insulating fixing rod, the refractory inner furnace body and the furnace shell are filled with insulating asbestos, a U-shaped furnace body is arranged on the refractory inner furnace body, the refractory furnace cover is matched with the refractory furnace body, a furnace chamber is formed between the refractory furnace cover and the refractory furnace body, a sealing ring is also arranged between the refractory furnace cover and the refractory furnace body, and the box door and the refractory inner furnace body adopt a sealing design to reduce heat loss; the sealing ring adopts a ceramic sealing ring, which can enhance the sealing effect inside the furnace chamber and reduce heat loss.

[0036] Specifically, three heat-insulating fixing rods are arranged in the furnace shell, and the three heat-insulating fixing rods are respectively arranged on the left, right and rear sides of the refractory inner furnace body for supporting and fixing the refractory inner furnace body.

[0037] The heat-insulating asbestos is filled in the heat-insulating cavity to ensure the effective retention of heat inside the furnace and reduce energy consumption.

[0038] The explosion-proof box is provided with a door, which is movably connected to the explosion-proof box, and the refractory furnace cover is installed on the door. The touch screen is set on the explosion-proof box below the door, and the touch screen integrates functions such as temperature setting, control mode switching, and operation status display. The use of an explosion-proof box improves the safety performance of the equipment and effectively prevents the risk of explosion caused by abnormal pressure inside the furnace.

[0039] In order to facilitate the internal and external heat exchange of the box-type muffle furnace and maintain the normal working temperature of the muffle furnace, heat dissipation holes are also arranged on the top of the explosion-proof box body; in order to facilitate the transportation of the box-type muffle furnace, pulley support feet are also arranged on the bottom of the explosion-proof box body.

[0040] like Figure 4 As shown, the power supply circuit includes a power supply interface P1, an adjustable resistor R1, a rectifier bridge D1, a capacitor C1 and a capacitor C2. The first end of the power supply interface P1 is connected to an external 380V power supply, the second end of the power supply interface P1 is connected to the second output end of the single-chip microcomputer, the first end of the adjustable resistor R1 and the first end of the rectifier bridge D1, the third end of the power supply interface P1 is connected to the third output end of the single-chip microcomputer, the second end of the adjustable resistor R1 and the second end of the rectifier bridge D1, the third end of the rectifier bridge D1 is grounded, the fourth end of the rectifier bridge D1 is connected to the first end of the capacitor C1 and the first end of the capacitor C2, the second end of the capacitor C1 and the second end of the capacitor C2 are both grounded, and the fourth end of the rectifier bridge D1 outputs 311V DC. The rectifier bridge D1 adopts a rectifier bridge of model GBJ5010.

[0041] like Figure 5 As shown, the control circuit includes a resistor R2, a resistor R3, a field effect transistor Q1, an isolation chip U1, a resistor R4, a resistor R5, a bidirectional transient suppression diode TVS1, a resistor R6, a capacitor C3, a field effect transistor Q2 and a heating device interface P2; the first end of the resistor R2 is connected to the PWM output end of the single-chip microcomputer, the second end of the resistor R2 is connected to the first end of the resistor R3 and the gate of the field effect transistor Q1, the second end of the resistor R3 and the source of the field effect transistor Q1 are both grounded, the drain of the field effect transistor Q1 is connected to the first pin of the isolation chip U1, the second pin of the isolation chip U1 is connected to the 5V power supply through the resistor R4, and the third pin of the isolation chip U1 is connected to the 5V power supply through the resistor R4. R5 is connected to the first end of the bidirectional suppression diode TVS1, the first end of the resistor R6, the first end of the capacitor C3 and the gate of the field effect tube Q2. The fourth pin of the isolation chip U1 is connected to the external negative 9V power supply. The second end of the bidirectional suppression diode TVS1, the second end of the resistor R6 and the second end of the capacitor C3 are all grounded. The emitter of the field effect tube Q2 is connected to the voltage monitoring circuit and the current monitoring circuit. The collector of the field effect tube Q2 is connected to the first end of the heating device interface P2. The second end of the heating device interface P2 is connected to 311V DC. If an additional heating device is added, another heating device interface P3 can be connected in parallel at both ends of the heating device interface P2. Among them, the isolation chip U1 adopts an optocoupler isolation chip with model CA-IS3211VBJ.

[0042] like Figure 6As shown, the current monitoring circuit includes a current sensor U2, a capacitor C4, a resistor R7 and a resistor R8. The first pin and the second pin of the current sensor U2 are both connected to the emitter of the field effect tube Q2, the third pin and the fourth pin of the current sensor U2 are both grounded, the fifth pin of the current sensor U2 is connected to the first end of the capacitor C4 and the 5V power supply, the second end of the capacitor C4 is grounded, the sixth pin of the current sensor U2 is connected to the first end of the resistor R8 and the third input end of the single-chip computer through the resistor R7, and the second end of the resistor R8 is grounded.

[0043] like Figure 7 As shown, the voltage monitoring circuit includes a resistor R9, a voltage transformer L1 and a resistor R10, a first end of the resistor R9 is connected to the emitter of the field effect tube Q2, a second end of the resistor R9 is connected to the same-name end of the primary winding of the voltage transformer L1, the other end of the primary winding of the voltage transformer L1 is grounded, the same-name end of the secondary winding of the voltage transformer L1 is connected to the first end of the resistor R10 and the second input end of the single-chip microcomputer, and the other end of the secondary winding of the voltage transformer L1 and the second end of the resistor R10 are both grounded.

[0044] The utility model monitors and feeds back the working condition of the muffle furnace in real time through the temperature sensor, voltage monitoring circuit and current monitoring circuit, and efficiently converts the input 380V power supply voltage into a voltage suitable for the requirements of heating devices such as silicon molybdenum rods through the single-chip microcomputer and the power supply circuit, and realizes continuous adjustment, effectively reducing power consumption and improving power utilization, while also eliminating the transformer component, greatly reducing the overall weight of the muffle furnace.

[0045] The above disclosure is only the preferred implementation mode of the utility model, but the utility model is not limited thereto. Any non-creative changes that can be thought of by technicians in this field, as well as several improvements and modifications made without departing from the principle of the utility model, should fall within the scope of protection of the utility model.

Claims

1. A box-type muffle furnace, characterized in that: It includes an explosion-proof box, a furnace assembly is arranged inside the explosion-proof box, the furnace assembly includes a refractory inner furnace body and a heating device, the heating device is arranged on the refractory inner furnace body, and a temperature sensor is arranged inside the refractory inner furnace body; The explosion-proof box is provided with a control component and a power supply circuit for supplying power to the entire muffle furnace. The control component includes a single-chip microcomputer, a touch screen, a control circuit, a voltage monitoring current circuit and a current monitoring circuit. The temperature sensor is connected to the first input terminal of the single-chip microcomputer, the touch screen is connected to the single-chip microcomputer for communication, the first output terminal of the single-chip microcomputer is connected to the first end of the control circuit, the second end of the control circuit is connected to the heating device, and the heating device is controlled to heat the refractory inner furnace body. The third end of the control circuit is connected to the first end of the voltage monitoring circuit and the first end of the current monitoring circuit, the second end of the voltage monitoring circuit is connected to the second input terminal of the single-chip microcomputer, and the second end of the current monitoring circuit is connected to the third input terminal of the single-chip microcomputer.

2. The box-type muffle furnace according to claim 1, characterized in that: The power supply circuit includes a power supply interface P1, an adjustable resistor R1, a rectifier bridge D1, a capacitor C1 and a capacitor C2. The first end of the power supply interface P1 is connected to an external 380V power supply. The second end of the power supply interface P1 is connected to the second output end of the single-chip microcomputer, the first end of the adjustable resistor R1 and the first end of the rectifier bridge D1. The third end of the power supply interface P1 is connected to the third output end of the single-chip microcomputer, the second end of the adjustable resistor R1 and the second end of the rectifier bridge D1. The third end of the rectifier bridge D1 is grounded. The fourth end of the rectifier bridge D1 is connected to the first end of the capacitor C1 and the first end of the capacitor C2. The second end of the capacitor C1 and the second end of the capacitor C2 are both grounded. The fourth end of the rectifier bridge D1 outputs 311V DC power.

3. The box-type muffle furnace according to claim 2, characterized in that: The control circuit includes a resistor R2, a resistor R3, a field effect transistor Q1, an isolation chip U1, a resistor R4, a resistor R5, a bidirectional transient suppression diode TVS1, a resistor R6, a capacitor C3, a field effect transistor Q2 and a heating device interface P2; The first end of the resistor R2 is connected to the PWM output end of the single-chip microcomputer, the second end of the resistor R2 is connected to the first end of the resistor R3 and the gate of the field effect tube Q1, the second end of the resistor R3 and the source of the field effect tube Q1 are both grounded, the drain of the field effect tube Q1 is connected to the first pin of the isolation chip U1, the second pin of the isolation chip U1 is connected to the 5V power supply through the resistor R4, the third pin of the isolation chip U1 is connected to the first end of the bidirectional suppression diode TVS1, the first end of the resistor R6, the first end of the capacitor C3 and the gate of the field effect tube Q2 through the resistor R5, the fourth pin of the isolation chip U1 is connected to the external negative 9V power supply, the second end of the bidirectional suppression diode TVS1, the second end of the resistor R6 and the second end of the capacitor C3 are all grounded, the emitter of the field effect tube Q2 is connected to the voltage monitoring circuit and the current monitoring circuit, the collector of the field effect tube Q2 is connected to the first end of the heating device interface P2, and the second end of the heating device interface P2 is connected to the 311V direct current.

4. The box-type muffle furnace according to claim 3, characterized in that: The current monitoring circuit includes a current sensor U2, a capacitor C4, a resistor R7 and a resistor R8. The first pin and the second pin of the current sensor U2 are both connected to the emitter of the field effect tube Q2, the third pin and the fourth pin of the current sensor U2 are both grounded, the fifth pin of the current sensor U2 is connected to the first end of the capacitor C4 and the 5V power supply, the second end of the capacitor C4 is grounded, the sixth pin of the current sensor U2 is connected to the first end of the resistor R8 and the third input end of the microcontroller through the resistor R7, and the second end of the resistor R8 is grounded.

5. The box-type muffle furnace according to claim 3, characterized in that: The voltage monitoring circuit includes a resistor R9, a voltage transformer L1 and a resistor R10. The first end of the resistor R9 is connected to the emitter of the field effect tube Q2, the second end of the resistor R9 is connected to the same-name end of the primary winding of the voltage transformer L1, the other end of the primary winding of the voltage transformer L1 is grounded, the same-name end of the secondary winding of the voltage transformer L1 is connected to the first end of the resistor R10 and the second input end of the single-chip microcomputer, and the other end of the secondary winding of the voltage transformer L1 and the second end of the resistor R10 are both grounded.

6. The box-type muffle furnace according to claim 1, characterized in that: It also includes a furnace body bracket, which is transversely arranged in the explosion-proof box, with both ends of the furnace body bracket fixedly installed on the inner wall of the explosion-proof box, and the furnace body assembly is installed on the furnace body bracket.

7. The box-type muffle furnace according to claim 6, characterized in that: The furnace body assembly also includes a furnace shell, a heat-insulating fixing rod, a refractory furnace cover, a sealing ring and heat-insulating asbestos. The furnace shell is fixedly mounted on the furnace body bracket, the refractory inner furnace body is mounted in the furnace shell through the heat-insulating fixing rod, the space between the refractory inner furnace body and the furnace shell is filled with heat-insulating asbestos, a U-shaped furnace body is arranged on the refractory inner furnace body, the refractory furnace cover is matched with the refractory furnace body, and a sealing ring is also arranged between the refractory furnace cover and the refractory furnace body.

8. The box-type muffle furnace according to claim 7, characterized in that: Three heat-insulating fixing rods are arranged in the furnace shell. The three heat-insulating fixing rods are respectively arranged on the left, right and rear sides of the refractory inner furnace body for supporting and fixing the refractory inner furnace body.

9. The box-type muffle furnace according to claim 7, characterized in that: The explosion-proof box body is provided with a box door, the box door is movably connected to the explosion-proof box body, and the refractory furnace cover is installed on the box door.

10. The box-type muffle furnace according to claim 1, characterized in that: The top of the explosion-proof box is provided with heat dissipation holes, and the bottom of the explosion-proof box is also provided with pulley support feet.

Images