Mine wellhead preheating intelligent control system and control method

Abstract

The application discloses a mine shaft head preheating intelligent control system and a control method thereof. The system comprises an operation box main body, a programmable logic controller, a temperature acquisition module, a man-machine interaction module, an output control module, an audible and visual alarm module and a safety interlocking output module. At least three temperature sensors are arranged at different positions of the mine shaft head to collect multiple-point temperature, and the minimum value of the measurement values of the multiple sensors is taken as the current shaft head temperature. In combination with digital filtering and calibration technology, the single-point temperature measurement problem of easy missed detection is solved. Three-stage temperature threshold progressive judgment logic is adopted to realize accurate closed-loop control of the temperature and avoid frequent start and stop of the equipment. The hardware-level safety interlocking is realized by directly connecting the independent safety relay and the safety circuit of the hoist in series, and the sensor fault safety protection mechanism is provided, so that reliable protection can be realized even if the system fails or the sensor fails. The application essentially improves the safety of mine production, reduces the operation cost and is convenient for centralized management and fault tracing.

Description

Technical Field

[0001] This application relates to the field of mine safety equipment technology, and in particular to an intelligent control system and control method for mine wellhead preheating. Background Technology

[0002] In mining operations, temperature control at the mine entrance is crucial for preventing equipment freezing, ensuring personnel safety, and maintaining normal production. Especially in cold northern regions during winter, excessively low mine entrance temperatures can lead to serious problems such as icing, equipment jamming, and hydraulic system failure, directly threatening safe mine production.

[0003] Currently, most mines still rely on traditional manual methods for preheating control of the wellhead temperature, mainly depending on operators' on-site observation or experience to manually start and stop heaters and fans. Although some mines have attempted to use simple automatic control devices, they generally suffer from the following core defects: First, single-point temperature detection cannot fully cover the low-temperature area at the wellhead, easily leading to undetected localized icing; second, the control logic is simple, using only a single threshold to start and stop equipment, resulting in large temperature fluctuations and frequent equipment start-ups and shutdowns; third, safety interlocks largely rely on software logic, lacking hardware-level safety guarantees, and cannot effectively trigger protection actions in the event of system failure.

[0004] This traditional control method suffers from problems such as low control accuracy, poor stability, slow response, high energy consumption, and lack of centralized monitoring and data recording, making it difficult to meet the requirements of modern mine safety production. Therefore, there is an urgent need for a mine wellhead preheating intelligent control system that can achieve high precision, high reliability, and hardware-level safety interlocks to solve the aforementioned problems in existing technologies. Summary of the Invention

[0005] The technical problem to be solved by this application is to overcome the shortcomings of existing mine wellhead temperature control, such as reliance on manual operation, easy omissions in single-point temperature measurement, poor reliability of safety interlocks, and high energy consumption, and to provide an intelligent control system and control method for mine wellhead preheating.

[0006] To solve the above-mentioned technical problems, the technical solution adopted in this application is: a mine shaft preheating intelligent control system, including an operation box body, a programmable logic controller (PLC), a temperature acquisition module, a human-machine interaction module, and an output control module. The temperature acquisition module includes at least three temperature sensors installed at different locations at the mine shaft entrance, used to collect real-time temperature data of the shaft entrance area from multiple points and transmit it to the PLC. The PLC has a built-in digital filtering program and a temperature calibration program, used to preprocess the collected temperature data and take the minimum value of the multiple temperature sensor measurements as the current shaft entrance temperature. The controller is configured to compare the current wellhead temperature with preset three-level temperature thresholds sequentially, generate corresponding control commands based on the comparison results, and control the start / stop status of the heater and fan through the output control module. The system also includes an audible and visual alarm module and a safety interlock output module electrically connected to the programmable logic controller. The safety interlock output module uses an independent safety relay, and its output terminal is connected in series with the safety circuit of the mine hoist control system. When the current wellhead temperature is lower than the preset alarm lower limit temperature threshold, the programmable logic controller sends a prohibition signal to the hoist control system through the safety interlock output module, forcing the hoist to stop operating.

[0007] Furthermore, the programmable logic controller is configured to generate control instructions according to the following logic: when the current wellhead temperature is greater than or equal to a preset stop temperature threshold, a stop control instruction is generated to shut down the heater and fan through the output control module; otherwise, when the current wellhead temperature is less than a preset start temperature threshold, a start control instruction is generated to start the heater and fan through the output control module; when the current wellhead temperature is less than or equal to a preset alarm lower limit temperature threshold, an alarm control signal and a safety interlock signal are generated.

[0008] Furthermore, the temperature sensor is a platinum resistance temperature sensor, and a multi-wire connection method is used.

[0009] Furthermore, the programmable logic controller is also configured to: set a preset delay shutdown time when shutting down the heater and the fan; and start multiple heaters sequentially using a preset sequential start time interval.

[0010] Furthermore, the preset delay shutdown time is a preset first time, and the preset sequential start time interval is a preset second time.

[0011] Furthermore, the human-machine interaction module is an industrial touch screen with three levels of user permissions. Its operation interface includes a main monitoring page, a parameter setting page, a historical data page, an alarm record page, and a manual control page.

[0012] Furthermore, the output control module includes a digital output unit and multiple independent contactors or solid-state relays. Each contactor or solid-state relay controls the power circuit of a heater or a fan. The programmable logic controller monitors the equipment operating status in real time by collecting auxiliary contact signals from the contactors and solid-state relays. If no change in the state of the corresponding auxiliary contact is detected within a preset time after the output control command is issued, the system determines that the equipment is faulty and triggers an alarm.

[0013] Furthermore, the programmable logic controller is also configured to automatically trigger a safety interlock, force the hoist to stop running, and issue audible and visual alarms and sensor fault alarm signals when any temperature sensor signal is detected to be outside the normal range.

[0014] This application also provides an intelligent control method for mine wellhead preheating, comprising the following steps: collecting ambient temperature data of the wellhead area from multiple points using at least three temperature sensors installed at different locations at the mine wellhead; transmitting the collected temperature data to a programmable logic controller (PLC), preprocessing the data using a built-in digital filtering program and temperature calibration program, and taking the minimum value measured by multiple temperature sensors as the current wellhead temperature; comparing the current wellhead temperature with preset three-level temperature thresholds sequentially; automatically generating control commands based on the comparison results to control the start / stop status of the heater and fan; and when the current wellhead temperature is lower than the preset alarm lower limit temperature threshold, sending a prohibition signal to the hoist control system via an independent safety relay to force the hoist to stop operating.

[0015] Furthermore, the three-level temperature threshold comparison and judgment steps are as follows: the first level judges whether the current wellhead temperature is greater than or equal to the stop temperature threshold; if so, the heater and fan are turned off. Otherwise, the second level judges whether the current wellhead temperature is less than the start temperature threshold; if so, the heater and fan are started. Regardless of the results of the first two levels, the third level judges whether the current wellhead temperature is less than or equal to the alarm lower limit temperature threshold; if so, the safety interlock is triggered. When the temperature sensor signal is detected to be outside the normal range, it is determined to be a sensor malfunction and safety protection is triggered.

[0016] Compared with existing technologies, this application has the following beneficial effects: First, significantly improved control accuracy and reliability. By collecting temperature data at multiple points and using the minimum value as the control basis, the coldest area at the wellhead is prioritized for detection and control, completely eliminating blind spots caused by local icing. Combined with digital filtering and calibration technology, the problem of missed detection of local icing in single-point temperature measurement is solved. A three-level temperature threshold progressive judgment logic is adopted to form a closed-loop control with hysteresis, achieving stable temperature regulation, avoiding frequent equipment start-ups and shutdowns, and greatly improving system stability. Second, fundamentally improved safety. Multi-point minimum value detection ensures no blind spots in the physical environment, independent hardware interlocking ensures safety even when the control system fails, and sensor fault protection mechanism ensures safety even when the detection system fails. These three safety mechanisms together construct a complete safety protection system. The hardware-level interlocking method, which directly connects an independent safety relay to the hoist safety circuit, rather than software logic interlocking, ensures that even if the PLC or control system fails, the hoist power supply can still be reliably cut off when the temperature is too low, fundamentally eliminating hoisting accidents caused by wellhead icing. Third, safety assurance under failure modes. When the temperature sensor signal is detected to be outside the normal range, a safety interlock is automatically triggered, solving the major safety hazard of traditional systems that continue to operate even when temperature monitoring is lost due to sensor disconnection or short circuit. Fourth, significant energy-saving effect. Through precise temperature closed-loop control, combined with heater delayed shutdown and sequential start-up strategies, ineffective equipment operation and grid impact are avoided, effectively reducing operating energy consumption. Fifth, comprehensive improvement in management efficiency. An integrated human-machine interface supports parameter setting, status monitoring, data recording and export, and has comprehensive fault detection and alarm functions, realizing centralized system management and rapid fault handling, facilitating operation analysis and fault tracing. Attached Figure Description

[0017] Figure 1 This is a block diagram of the overall structure of the intelligent control system for mine wellhead preheating provided in the embodiments of this application.

[0018] Figure 2 A schematic flowchart of the intelligent control method for mine wellhead preheating provided in the embodiments of this application.

[0019] Figure 3 The system control logic flowchart provided in the embodiments of this application. Detailed Implementation

[0020] The present application will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only for explaining the present application and are not intended to limit the present application.

[0021] As shown in Figure 1, the intelligent control system for mine wellhead preheating provided in this application embodiment is an integrated industrial control device specifically designed for the harsh environment of mine wellheads. The system adopts a modular structure design and mainly includes an operation box body, a programmable logic controller, a temperature acquisition module, a human-machine interaction module, an output control module, an audible and visual alarm module, and a safety interlock output module. All core control components are integrated inside the operation box body, which facilitates on-site installation and maintenance.

[0022] The temperature acquisition module includes at least three temperature sensors and an analog input unit. In this embodiment, three temperature sensors are installed at the mine entrance, specifically at the air intake, beside the hoist track, and at the entrance of the mine control room. This forms a multi-point temperature monitoring network covering the core low-temperature area of ​​the mine entrance, providing a comprehensive and accurate reflection of the temperature distribution in the area. The temperature sensors are armored explosion-proof PT100 platinum resistance temperature sensors, suitable for the harsh environment of dusty, humid, and vibrating mines. A three-wire connection effectively eliminates measurement errors caused by wire resistance, achieving a measurement accuracy of ±0.1℃ and a response time of less than 1 second, enabling rapid capture of changes in ambient temperature. The analog input unit is integrated within the programmable logic controller (PLC), employing a 12-bit high-precision AD converter to convert the 4-20mA analog signal output from the temperature sensors into a digital signal. The PLC then converts the digital signal into the actual temperature value through its internal program.

[0023] The programmable logic controller (PLC), as the core control unit of the system, has built-in digital filtering and temperature calibration programs. The digital filtering program uses a moving average filtering algorithm to perform weighted averaging on 10 continuously collected temperature data points. The specific formula is: Filtered temperature value = (0.5 × Current value + 0.3 × Previous value + 0.2 × Previous two values), effectively eliminating measurement errors caused by electromagnetic interference and temperature fluctuations. The temperature calibration program supports inputting calibration coefficients through a human-machine interface module to compensate for measurement errors from the temperature sensors. The calibration formula is: Calibrated temperature = Measured temperature × Calibration coefficient + Offset. After preprocessing the measured values ​​from the three temperature sensors, the PLC takes the minimum of the three temperature values ​​as the current wellhead temperature. This ensures that the system can promptly detect the temperature of the coldest area at the wellhead, preventing undetected localized icing. When the signal from any temperature sensor exceeds the normal range of 4-20mA, the system determines it as a sensor fault, immediately triggers an alarm, and defaults to the current wellhead temperature being below the alarm threshold, initiating safety interlock protection.

[0024] The programmable logic controller (PLC) is configured to compare the current wellhead temperature with preset three-level temperature thresholds sequentially and generate control commands according to preset logic. In this embodiment, typical thresholds are set as follows: a stop temperature threshold of 8°C, a start temperature threshold of 3°C, and an alarm lower limit temperature threshold of 0°C. Specifically, the first level of judgment is performed: comparing the current wellhead temperature with the stop temperature threshold. If the current wellhead temperature is greater than or equal to the stop temperature threshold, it indicates that the wellhead temperature has reached the required level, and a stop control command is generated. Otherwise, the second level of judgment is performed: comparing the current wellhead temperature with the start temperature threshold. If the current wellhead temperature is less than the start temperature threshold, it indicates that the wellhead temperature is too low and heating is required, and a start control command is generated. Regardless of the results of the first two levels of judgment, the third level of judgment is performed: comparing the current wellhead temperature with the alarm lower limit temperature threshold. If the current wellhead temperature is less than or equal to the alarm lower limit temperature threshold, it indicates that the wellhead temperature is below the safe temperature, posing a risk of icing, and an alarm control signal and a safety interlock signal are immediately generated.

[0025] To further optimize system performance, the programmable logic controller (PLC) is also equipped with protection logic against frequent start-stop cycles and power grid impacts. In this embodiment, the first preset time for shutting down the heaters and fans is a 5-minute delay. This means that after the temperature reaches the stop threshold, the system will continue running for 5 minutes before shutting down, utilizing residual heat to maintain the wellhead temperature and preventing frequent start-stop cycles. When starting multiple heaters, this embodiment uses a 10-second interval for sequential start-up, activating each heater in turn to avoid simultaneous startup of multiple high-power devices causing power grid voltage fluctuations that could affect the normal operation of other mine equipment.

[0026] The output control module includes a digital output unit and multiple independent contactors or solid-state relays. The digital output unit is electrically connected to the programmable logic controller (PLC). Each contactor or solid-state relay controls the power circuit of one heater or one fan. In this embodiment, the system controls four heaters and two fans. Each heater is controlled by an AC contactor, and each fan is controlled by a solid-state relay. The PLC's digital output points drive the coils of the AC contactors and solid-state relays through intermediate relays, thereby controlling the on / off of the main circuit power supply for the heaters and fans. Simultaneously, the PLC also collects auxiliary contact signals from the contactors and solid-state relays through digital input points to monitor the actual operating status of the equipment in real time. When the PLC issues a device start command, if no corresponding auxiliary contact closure signal is detected within 3 seconds, it is determined to be a device malfunction, and a corresponding alarm signal is immediately issued.

[0027] The human-machine interface module uses an industrial touchscreen that communicates with the programmable logic controller (PLC) via an Ethernet interface. The touchscreen employs resistive touch technology, supports operation while wearing gloves, and is suitable for the mining environment. The touchscreen has three user access levels: operator, engineer, and administrator. Different levels of users have different operating permissions to prevent unauthorized personnel from modifying critical system parameters. The touchscreen's interface includes a main monitoring page, parameter setting page, historical data page, alarm log page, and manual control page. The main monitoring page displays real-time measurements from three temperature sensors, the operating status of the heaters and fans, the system operating mode, and the current time and date. The parameter setting page allows authorized users to set parameters such as start-up temperature threshold, stop temperature threshold, alarm lower limit temperature threshold, system cycle time, and temperature calibration coefficient. The historical data page displays the temperature change trend over the past 7 days in curve form, supports querying historical data by time, and allows data export to a USB drive. The alarm log page records the occurrence time, alarm type, and clearing time of all alarm events, storing up to 1000 alarm records. The manual control page allows users to individually control the start and stop of each heater and fan in manual mode, facilitating equipment debugging and maintenance.

[0028] The audible and visual alarm module includes a red LED alarm indicator and a high-decibel buzzer, mounted on the top of the control box. When the system detects a temperature below the alarm lower limit, equipment malfunction, or power abnormality, the programmable logic controller drives the audible and visual alarm module to issue an alarm. The alarm mode involves the alarm indicator flashing and the buzzer emitting intermittent beeps. Users can stop the buzzer from sounding using a mute button on the touchscreen, but the alarm indicator will continue to flash until the alarm conditions are cleared, ensuring that on-site personnel can promptly detect abnormalities.

[0029] The safety interlock output module uses an independent, high-reliability safety relay connected to the digital output point of the programmable logic controller (PLC). The safety relay's output contact capacity is AC250V / 10A, employing normally closed contact output to ensure automatic triggering of the safety interlock in the event of system power failure or PLC malfunction, conforming to fail-safe design principles. The output terminal of the safety interlock output module is connected in series with the safety circuit of the mine hoist control system. Electrical compatibility testing must be performed before system integration to confirm voltage and current level matching, avoiding damage to the existing hoist control system. When the system detects that the wellhead temperature is below the alarm lower limit temperature threshold, the PLC immediately drives the safety relay to disconnect the safety circuit of the hoist control system, forcing the hoist to stop operation and preventing hoist jamming or a fall accident due to wellhead icing. After the safety interlock is triggered, authorized personnel must manually reset it by entering a password on the touchscreen to deactivate the interlock and restore hoist operation, preventing accidents caused by misoperation.

[0030] The control method flow of this application is described in detail below with reference to Figures 2 and 3: After the system is powered on, initialization operations are first performed, including programmable logic controller (PLC) self-test, sensor detection, output loop detection, and parameter loading. After initialization, the system automatically enters the automatic control mode and begins to operate according to the preset control logic. Three temperature sensors collect the ambient temperature at their respective installation locations in real time, convert the temperature signals into 4-20mA analog signals, and transmit them to the analog input unit of the PLC. The PLC's analog input unit converts the analog signals into digital signals, and then preprocesses the measured values ​​of the three temperature sensors through a digital filtering program and a temperature calibration program, taking the minimum value of the three temperature values ​​as the current wellhead temperature.

[0031] The programmable logic controller sends the processed information, such as the current wellhead temperature, the operating status of the heater and blower, and the system operating mode, to the touch screen, which displays this information in real time.

[0032] The programmable logic controller (PLC) then compares the current wellhead temperature with three preset temperature thresholds. First, it performs a first-level check: if the current wellhead temperature is greater than or equal to the stop temperature threshold, a stop control command is generated, and all heaters and fans are sequentially shut down via the output control module, executing a preset delayed shutdown logic. Otherwise, it performs a second-level check: if the current wellhead temperature is less than the start temperature threshold, a start control command is generated, and all heaters and fans are sequentially started via the output control module, executing a preset time interval sequential start logic. Regardless of the results of the first two levels, a third-level check is performed: if the current wellhead temperature is less than or equal to the alarm lower limit temperature threshold, an alarm control signal and a safety interlock signal are immediately generated, driving the audible and visual alarm module to issue an audible and visual alarm prompt, and simultaneously driving the safety relay to disconnect the safety circuit of the hoist control system, forcing the hoist to stop operating. If the current wellhead temperature is greater than the alarm lower limit temperature threshold, the system maintains its current operating state without triggering an alarm or interlock. When a temperature sensor signal is detected to be outside the normal range, a sensor fault is determined, and safety protection is triggered. After waiting for one cycle, the system returns to the temperature acquisition stage and begins the next cycle. The entire control logic operates in this cycle, forming a closed-loop control system of "sensing-judgment-execution-feedback".

[0033] The system supports switching between manual and automatic control modes, which users can switch between via a mode switch button on the touchscreen. In manual mode, the system's automatic control logic is disabled, and users can individually control the start and stop of each heater and fan through the manual control page. Manual control mode is primarily used for equipment installation and commissioning, routine maintenance, and troubleshooting. It is important to note that the safety interlock function remains active in manual mode. When the temperature falls below the alarm lower limit or a sensor malfunctions, the system will still trigger alarms and safety interlocks to ensure production safety under all circumstances.

[0034] The system possesses comprehensive fault detection and alarm functions, capable of monitoring the operating status of temperature sensors, heaters, fans, and power supplies in real time. When a fault is detected, it immediately issues a corresponding alarm signal and displays the fault type and handling suggestions on the touchscreen. For example, when the programmable logic controller (PLC) detects that the temperature sensor signal is outside the normal range, it issues a temperature sensor fault alarm; when the PLC issues a heater start command but fails to detect the auxiliary contact closure signal of the contactor within a specified time, it issues a heater fault alarm. The system automatically records all operating data, including historical temperature curves, equipment start / stop records, and alarm records, facilitating subsequent operational analysis and fault tracing.

[0035] In the embodiments of this application, it is recommended that the heater be an explosion-proof electric heating air curtain or an infrared radiation heater, the fan be a low-temperature resistant industrial-grade product, and all electrical equipment should comply with mining explosion-proof safety standards. During system installation, a sufficient safe distance should be maintained from moving parts such as the hoist wire rope and rails.

[0036] The above description is merely a preferred embodiment of this application and is not intended to limit the scope of protection of this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. A mine shaft preheating intelligent control system, comprising an operation box body, a programmable logic controller, a temperature acquisition module, a human-machine interaction module, and an output control module, characterized in that: The temperature acquisition module includes at least three temperature sensors installed at different locations at the mine shaft entrance, used to collect real-time temperature data of the shaft entrance area from multiple points and transmit it to the programmable logic controller (PLC). The PLC has a built-in digital filtering program and temperature calibration program to preprocess the collected temperature data and take the minimum value of the multiple temperature sensor measurements as the current shaft entrance temperature. The PLC is configured to compare the current shaft entrance temperature with preset three-level temperature thresholds sequentially, generate corresponding control commands based on the comparison results, and control the start / stop status of the heater and fan through the output control module. The system also includes an audible and visual alarm module and a safety interlock output module electrically connected to the PLC. The safety interlock output module uses an independent safety relay, and its output terminal is connected in series with the safety circuit of the mine hoist control system. When the current shaft entrance temperature is lower than the preset alarm lower limit temperature threshold, the PLC sends a prohibition signal to the hoist control system through the safety interlock output module, forcing the hoist to stop operating.

2. The intelligent control system for mine wellhead preheating according to claim 1, characterized in that, The programmable logic controller is configured to generate control commands according to the following logic: when the current wellhead temperature is greater than or equal to a preset stop temperature threshold, a stop control command is generated to shut down the heater and fan through the output control module; otherwise, when the current wellhead temperature is less than a preset start temperature threshold, a start control command is generated to start the heater and fan through the output control module; when the current wellhead temperature is less than or equal to a preset alarm lower limit temperature threshold, an alarm control signal and a safety interlock signal are generated.

3. The intelligent control system for mine wellhead preheating according to claim 1, characterized in that, The temperature sensor is a platinum resistance temperature sensor, and it uses a multi-wire connection method.

4. The intelligent control system for mine wellhead preheating according to claim 1, characterized in that, The programmable logic controller is also configured to: set a preset delay shutdown time when shutting down the heater and the fan; and start multiple heaters sequentially using a preset sequential start time interval when starting multiple heaters.

5. The intelligent control system for mine wellhead preheating according to claim 4, characterized in that, The preset delay shutdown time is a preset first time, and the preset sequential start time interval is a preset second time.

6. The intelligent control system for mine wellhead preheating according to claim 1, characterized in that, The human-machine interaction module is an industrial touch screen with three levels of user permissions. Its operation interface includes a main monitoring page, a parameter setting page, a historical data page, an alarm record page, and a manual control page.

7. The intelligent control system for mine wellhead preheating according to claim 1, characterized in that, The output control module includes a digital output unit and multiple independent contactors or solid-state relays. Each contactor or solid-state relay controls the power circuit of a heater or a fan. The programmable logic controller monitors the equipment operating status in real time by collecting auxiliary contact signals from the contactors and solid-state relays. If no change in the status of the corresponding auxiliary contact is detected within a preset time after the output control command is issued, the system determines that the equipment is faulty and triggers an alarm.

8. The intelligent control system for mine wellhead preheating according to claim 1, characterized in that, The programmable logic controller is also configured to automatically trigger a safety interlock, force the hoist to stop running, and issue audible and visual alarms and sensor fault alarm signals when any temperature sensor signal is detected to be outside the normal range.

9. A method for intelligent control of mine wellhead preheating, characterized in that, The process includes the following steps: Collecting ambient temperature data from the mine entrance area using at least three temperature sensors installed at different locations; transmitting the collected temperature data to a programmable logic controller (PLC), preprocessing the data using a built-in digital filtering and temperature calibration program, and taking the minimum value measured by multiple temperature sensors as the current mine entrance temperature; comparing the current mine entrance temperature with preset three-level temperature thresholds; automatically generating control commands based on the comparison results to control the start / stop status of the heater and fan; and sending a prohibition signal to the hoist control system via an independent safety relay when the current mine entrance temperature falls below a preset alarm lower limit temperature threshold, forcing the hoist to stop.

10. The intelligent control method for mine wellhead preheating according to claim 9, characterized in that, The three-level temperature threshold comparison and judgment steps are as follows: The first level judges whether the current wellhead temperature is greater than or equal to the stop temperature threshold. If so, the heater and fan are turned off. Otherwise, the second level judges whether the current wellhead temperature is less than the start temperature threshold. If so, the heater and fan are started. Regardless of the results of the first two levels, the third level judges whether the current wellhead temperature is less than or equal to the alarm lower limit temperature threshold. If so, the safety interlock is triggered. When the temperature sensor signal is detected to be outside the normal range, it is determined to be a sensor malfunction and the safety protection is triggered.

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