Two-stage online detection circuit of thermocouple sensor

Abstract

The invention belongs to the technical field of sensor on-line detection, and provides a two-stage on-line detection circuit of a thermocouple sensor, which comprises a first-stage insertion detection circuit for detecting the on-off state of a mechanical switch contact in a connector, and outputting a first detection signal according to the on-off state to judge whether the thermocouple sensor is physically inserted into the connector or not. And the second-stage function detection circuit is used for detecting whether the signal line of the thermocouple sensor is normally connected or not and comprises a biasing circuit and an analog-to-digital converter, and the output signal of the thermocouple sensor is output to the differential input end of the analog-to-digital converter after being superposed with the bias voltage output by the biasing circuit. The first-stage insertion detection circuit and the second-stage function detection circuit work cooperatively to carry out two-stage online detection on the thermocouple sensor. According to the invention, two-stage detection is carried out on the thermocouple sensor, so that the reliability of on-line state monitoring of the thermocouple sensor is improved.

Description

Technical Field

[0001] This invention belongs to the field of online sensor detection technology, and relates to a two-stage online detection circuit for a thermocouple sensor. Background Technology

[0002] In critical fields such as aerospace, industrial automation, and energy, temperature is a core parameter reflecting the operating status of a system. Thermocouple sensors, due to their simple structure, wide temperature range, fast response, and resistance to harsh environments, are widely used for temperature monitoring in key components such as engine nozzles, lubrication lines, and exhaust systems. Their measurement accuracy and reliability are highly dependent on the physical installation of the sensor and the integrity of its electrical path.

[0003] However, in practical applications, thermocouples often experience poor contact or signal breakage due to improper installation, vibration, high-temperature aging, or mechanical damage. Typical failure modes include: (1) the sensor is not fully inserted or the connector is not locked, resulting in a loose connection, signal interruption, or abnormality; (2) the thermocouple wire is broken or the connector is detached, resulting in a completely open circuit. All of the above faults manifest as no signal or zero output, which can easily be misjudged as "low temperature" or "normal measurement," posing a serious safety hazard.

[0004] Existing detection methods mostly rely on whether the ADC sampling value is zero or exceeds the limit to determine faults. This logic is simplistic and makes it difficult to distinguish between different states such as "true low temperature," "not installed," and "installed but disconnected," which can easily lead to false alarms or missed alarms. Although some technologies use open-circuit detection or reference terminal compensation, they mainly focus on improving measurement accuracy and lack the ability to systematically diagnose the sensor connection status online.

[0005] Furthermore, with the development of Industry 4.0 and intelligent measurement and control systems, sensors need to possess self-diagnostic capabilities to achieve a shift from "passive acquisition" to "active sensing." Current technologies generally suffer from problems such as detection lag, lack of diagnostic layers, and inability to determine the physical installation and electrical connectivity status step by step, making it difficult to meet the requirements of high-reliability systems for real-time, accurate, and hierarchical fault identification.

[0006] Therefore, there is an urgent need for a detection solution that can reliably distinguish the sensor installation status and the continuity of the circuit online in order to improve system safety and maintenance efficiency. Summary of the Invention

[0007] To address the technical problem of the inability to reliably and accurately monitor the connection and functional status of sensors in real time in existing technologies, this invention discloses a two-stage online detection circuit for thermocouple sensors, comprising a first-stage insertion detection circuit and a second-stage functional detection circuit.

[0008] The first-stage insertion detection circuit detects the on / off state of the internal mechanical switch contacts of the connector and outputs a first detection signal based on the on / off state to determine whether the thermocouple sensor is physically inserted into the connector. The mechanical switch contacts are on when the thermocouple sensor is not inserted and are off when it is inserted into place.

[0009] The second-level functional detection circuit detects whether the signal line of the thermocouple sensor is properly connected. It includes a bias circuit and an analog-to-digital converter. The output signal of the thermocouple sensor is superimposed with the bias voltage output by the bias circuit and then output to the differential input terminal of the analog-to-digital converter.

[0010] The thermocouple sensor is subjected to two-stage online detection by working together with the first-stage insertion detection circuit and the second-stage functional detection circuit.

[0011] Furthermore, the first-stage insertion detection circuit includes a pull-down bias resistor, a positive bias resistor, and a positive voltage divider resistor. One end of the pull-down bias resistor is grounded, and the other end is connected to the third pin of the connector; the positive bias resistor and the positive voltage divider resistor are connected in series, with one end connected to the power supply VCC and the other end grounded; the midpoint of the series connection between the positive bias resistor and the positive voltage divider resistor is connected to the second pin of the connector.

[0012] Furthermore, the first detection signal is a logic level signal, which is output to the digital input port of the microcontroller.

[0013] Furthermore, the bias circuit includes a negative bias resistor, a positive bias resistor, and a positive voltage divider resistor. The negative bias resistor is connected to the negative terminal of the differential signal of the analog-to-digital converter, pulling down the voltage at the negative terminal of the differential signal to 0V; the midpoint of the series connection between the positive bias resistor and the positive voltage divider resistor is connected to the positive terminal of the differential signal of the analog-to-digital converter, providing a bias voltage of VCC / 2 to the positive terminal of the differential signal.

[0014] Furthermore, the positive bias resistor and the positive voltage divider resistor have a resistance of 2KΩ, and the negative bias resistor has a resistance of 10MΩ.

[0015] Furthermore, the positive output terminal of the thermocouple sensor is connected to the second-stage functional detection circuit through the first pin of the connector, and a current-limiting resistor is provided on the connection path between the first pin and the negative terminal of the differential signal.

[0016] Furthermore, a filter capacitor is provided between the current-limiting resistor and the negative terminal of the differential signal, with one end of the filter capacitor grounded and the other end connected to the negative terminal of the differential signal.

[0017] Furthermore, when the thermocouple sensor is working normally, the tiny voltage generated by temperature changes is superimposed on the bias voltage and input to the analog-to-digital converter, which converts it into a digital value within the measurement range and then outputs it. When the thermocouple sensor detaches or breaks in wire, the analog-to-digital converter outputs the maximum value.

[0018] Furthermore, the analog-to-digital converter is a 16-bit resolution analog-to-digital converter with an integrated programmable gain amplifier, model ADS1120.

[0019] Furthermore, the analog-to-digital converter outputs digital converted data through an SPI interface, which includes a chip select signal interface, a clock signal interface, a data input signal interface, a data output signal interface, and a data ready signal interface. The SPI interface is connected to the microcontroller.

[0020] Compared with the prior art, the two-stage online detection circuit and method for thermocouple sensors provided by the present invention have the following outstanding technical effects: 1. Achieved reliable dual testing of physical connection and electrical function: This invention innovatively employs a two-level diagnostic mechanism combining "first-level insertion detection" and "second-level functional detection." The first level accurately determines whether the sensor is physically installed by detecting the state of the mechanical switch contacts inside the connector; the second level analyzes the output characteristics of the analog-to-digital converter to monitor the electrical continuity of the signal line in real time. Working together, these two levels can effectively distinguish between various states such as "not installed," "installed but disconnected," and "normally online," solving the technical problem that traditional single-point detection cannot accurately identify "false connections" or "hidden disconnections," significantly improving the reliability and accuracy of system fault diagnosis.

[0021] 2. The detection principle is simple and reliable, requiring no additional dedicated chip: The first-stage insertion detection cleverly utilizes the inherent mechanical switching characteristics of the three-pin connector. A clear digital level signal can be generated using only a simple resistor network (R1, R3, R4), eliminating the need for additional microswitches or dedicated sensors. This results in a simple, low-cost, and durable structure. The second-stage functional detection reuses the system's existing analog-to-digital converter (such as the ADS1120) for fault diagnosis, eliminating the need for a separate open-circuit detection circuit. This fully utilizes existing hardware resources, achieving the design goals of high integration and low cost.

[0022] 3. The fault criteria are clear, and automated diagnosis is easily achieved: The second-level functional detection utilizes the characteristic that the input voltage difference reaches saturation after a thermocouple disconnection, causing the analog-to-digital converter (ADC) to output a full-scale value (e.g., 32767) as a fault criterion. This criterion is a clear, discrete numerical threshold. The microcontroller only needs to determine whether the ADC reading is equal to the maximum value to make a judgment. The algorithm is simple, has a fast response, and an extremely low false positive rate, making it very easy to program and implement in embedded systems, which is beneficial for the intelligent and automated operation and maintenance of the system.

[0023] 4. High compatibility and wide applicability: The detection method of this invention does not depend on the specific type of thermocouple (such as type K, type E, etc.) or the measurement temperature range. As long as the gain and reference voltage of the analog-to-digital converter are properly configured so that its output is in the non-saturation range (such as [0-30000]) during normal operation, it can be applied to various types of thermocouple sensors. At the same time, the circuit design is highly versatile and can be widely used in industrial automation, energy and power, rail transportation and other fields where real-time monitoring of thermocouple status is required.

[0024] 5. Improved system security and maintainability: Through real-time, online two-level detection, the system can issue an alarm immediately upon sensor detachment or disconnection, preventing the collection of erroneous temperature data due to sensor failure. This avoids incorrect decisions by the control system and ensures the safety of equipment and personnel. Simultaneously, clear fault location information (whether it is not installed or installed but faulty) greatly facilitates on-site maintenance personnel in quickly diagnosing problems, reducing downtime, and improving system maintainability and operational efficiency.

[0025] In summary, this invention, through its innovative two-level detection architecture and simple, reliable circuit design, achieves comprehensive and accurate diagnosis of the thermocouple sensor status, making significant progress in terms of detection reliability, cost-effectiveness, ease of use, and safety. Attached Figure Description

[0026] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1 This is a schematic diagram of a two-stage online detection circuit for a thermocouple sensor. Figure 2 The judgment logic for two-stage online detection of thermocouple sensors; Figure 3 A flowchart of a two-stage online detection method for thermocouple sensors; The components include: 1. Thermocouple sensor; 2. Connector; 3. Pull-down bias resistor; 4. Negative bias resistor; 5. Positive bias resistor; 6. Positive voltage divider resistor; 7. Analog-to-digital converter; 8. Microcontroller; 9. Current limiting resistor; 10. Filter capacitor; 11. Chip select signal interface; 12. Clock signal interface; 13. Data input signal interface; 14. Data output signal interface; and 15. Data ready signal interface. Detailed Implementation

[0028] The embodiments of this application will now be described in detail with reference to the accompanying drawings.

[0029] The following specific examples illustrate the implementation of this application. Those skilled in the art can easily understand other advantages and effects of this application from the content disclosed in this specification. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. This application can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of this application. It should be noted that, in the absence of conflict, the following embodiments and features of the embodiments can be combined with each other. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0030] This invention discloses a two-stage online detection circuit for a thermocouple sensor. The thermocouple sensor 1 is installed by inserting it into a connector 2. The connector 2 can be a three-core aviation connector, with its three ends connected to the positive signal, negative signal, and internal insertion circuit detection circuit of the thermocouple sensor 1, respectively. This circuit can detect the connector's locking status in real time and perform online detection functions such as sensor detachment and wire breakage. Specifically, the two-stage online detection circuit includes a first-stage insertion detection circuit and a second-stage function detection circuit.

[0031] The first-stage insertion detection circuit detects the on / off state of the mechanical switch contacts inside the connector 2, and outputs a first detection signal based on the on / off state to determine whether the thermocouple sensor 1 is physically inserted into the connector 2. The mechanical switch contacts are on when the thermocouple sensor 1 is not inserted, and are off when it is inserted into place.

[0032] See Figure 1 As shown, the second-level functional detection circuit detects whether the signal line of the thermocouple sensor 1 is normally connected. It includes a bias circuit and an analog-to-digital converter 7. The output signal of the thermocouple sensor 1 is superimposed with the bias voltage output by the bias circuit and then output to the differential input terminal of the analog-to-digital converter 7.

[0033] The present invention performs two-stage online detection of the thermocouple sensor 1 by having the first-stage insertion detection circuit and the second-stage functional detection circuit work together.

[0034] In one embodiment, see Figure 1 As shown, the first-stage insertion detection circuit includes a pull-down bias resistor 3, a positive bias resistor 5, and a positive voltage divider resistor 6. One end of the pull-down bias resistor 3 is grounded, and the other end is connected to the third pin of the connector 2; the positive bias resistor 5 and the positive voltage divider resistor 6 are connected in series, with one end connected to the power supply VCC and the other end grounded; the midpoint of the series connection between the positive bias resistor 5 and the positive voltage divider resistor 6 is connected to the second pin of the connector 2.

[0035] In one embodiment, the first detection signal is a logic level signal, which is output to the digital input port of the microcontroller 8.

[0036] In one embodiment, see Figure 1 As shown, the bias circuit includes a negative bias resistor 4, a positive bias resistor 5, and a positive voltage divider resistor 6. The negative bias resistor 4 is connected to the negative terminal of the differential signal of the analog-to-digital converter 7, pulling down the voltage of the negative terminal of the differential signal to 0V; the midpoint of the series connection between the positive bias resistor 5 and the positive voltage divider resistor 6 is connected to the positive terminal of the differential signal of the analog-to-digital converter 7, providing a bias voltage of VCC / 2 to the positive terminal of the differential signal.

[0037] In one embodiment, the positive bias resistor 5 and the positive voltage divider resistor 6 have a resistance of 2KΩ, and the negative bias resistor 4 has a resistance of 10MΩ.

[0038] In one embodiment, see Figure 1 As shown, the positive output terminal of the thermocouple sensor 1 is connected to the second-stage functional detection circuit through the first pin of the connector 2, and a current-limiting resistor 9 is provided on the connection path between the first pin and the negative terminal of the differential signal.

[0039] In one embodiment, see Figure 1 As shown, a filter capacitor 10 is provided between the current-limiting resistor 9 and the negative terminal of the differential signal. One end of the filter capacitor 10 is grounded, and the other end is connected to the negative terminal of the differential signal. In implementation, the filter capacitor 10 can be an LM3853-2.5.

[0040] In one embodiment, when the thermocouple sensor 1 is operating normally, the minute voltage generated during temperature changes is superimposed on the bias voltage and input to the analog-to-digital converter 7, which converts it into a digital value within the measurement range and then outputs it. When the thermocouple sensor 1 detaches or breaks in wire, the analog-to-digital converter 7 outputs the maximum value.

[0041] In one embodiment, the analog-to-digital converter 7 is a 16-bit resolution analog-to-digital converter with an integrated programmable gain amplifier, model ADS1120, whose gain can be programmed to be selected from 1, 2, 4, 8, 16, 32, 64, and 128 times, and the sampling rate can be set to a maximum of 2KSPS to achieve high-precision and high-speed conversion.

[0042] The full-scale output value of the analog-to-digital converter 7 can be set to 32767. By configuring the programmable gain of the analog-to-digital converter 7, the output digital conversion value of the thermocouple sensor 1 during normal operation can be within the range of [0-30000]. When the read digital conversion value is equal to 32767, it is determined that the thermocouple sensor 1 has detached or broken wire.

[0043] In one embodiment, see Figure 1 As shown, the analog-to-digital converter 7 outputs digital conversion data through an SPI interface. The SPI interface includes a chip select signal interface 11, a clock signal interface 12, a data input signal interface 13, a data output signal interface 14, and a data ready signal interface 15. The SPI interface is connected to the microcontroller 8.

[0044] Furthermore, this invention also provides a two-stage online detection method for thermocouple sensors. Through dual detection of physical connection status and electrical function status, it achieves reliable and real-time diagnosis of the sensor's installation and operating status. Specifically, see [link to relevant documentation]. Figure 3 As shown, the method includes the following steps: S1: By detecting the on / off state of the mechanical switch contacts inside the connector 2, a first detection signal is generated to determine whether the thermocouple sensor 1 is physically inserted into the connector 2. The mechanical switch contacts are on when the thermocouple sensor 1 is not inserted and off when it is inserted. S2: The output signal of the thermocouple sensor 1 is superimposed with the bias voltage output by the bias circuit, and then input to the analog-to-digital converter 7 for analog-to-digital conversion; S3: Read the digital conversion value output by the analog-to-digital converter 7. If the digital conversion value is the full-scale output value, it is determined that the thermocouple sensor 1 has detached or broken wire. S4: Combining the judgment results of steps S1 and S3, perform two-level online detection on the state of the thermocouple sensor 1.

[0045] Now combined with the appendix Figures 1 to 3 The specific implementation methods described above are explained in detail below: First, the first-level insertion detection is performed through step S1: the first detection signal is generated by the pull-down bias resistor 3, the positive terminal bias resistor 5 and the positive terminal voltage divider resistor 6.

[0046] When thermocouple sensor 1 is not inserted into connector 2, the mechanical switch contacts inside connector 2 are in a conductive state, shorting the second and third pins of the connector. At this time, the power supply VCC is divided by the positive bias resistor 5 and the positive voltage divider resistor 6, and the voltage at the midpoint of their series connection is transmitted to the third pin through the conductive mechanical switch contacts, causing the first detection signal to be at a high level, which is determined to be in the "not inserted" state.

[0047] When thermocouple sensor 1 is inserted into connector 2 and installed in place, its mechanical structure pushes the connecting piece inside connector 2, causing the mechanical switch contact between the second and third pins to open. At this time, the first detection signal is connected to signal ground (GND) through the pull-down bias resistor 3 and is pulled down to a low level, indicating that it is in the "inserted" state.

[0048] The back-end microcontroller 8 reads the logic level of the first detection signal through its general-purpose digital input port, thereby realizing the first-level detection of the physical insertion state of the thermocouple sensor 1.

[0049] Secondly, a second-level functional test is performed through steps S2 and S3: see [link / reference] Figure 1 As shown, when thermocouple sensor 1 is connected normally, the signal of the tiny voltage it generates under temperature change is output through the first and third pins of connector 2.

[0050] This tiny voltage, after passing through an RC filter network consisting of current-limiting resistor 9 and filter capacitor 10, is input to the differential input terminal of the analog-to-digital converter 7 (model ADS1120) with integrated programmable gain amplifier. Specifically, the positive terminal of the thermocouple (pin 1) is pulled down to 0V through the negative bias resistor 4, and the negative terminal of the thermocouple (pin 3) receives a bias voltage of VCC / 2 through the midpoint of the voltage divider between the positive bias resistor 5 and the positive voltage divider resistor 6.

[0051] The amplification factor of the programmable gain amplifier (PGA) inside the analog-to-digital converter 7 can be configured via software within the range of 1 to 128 times to adapt to different temperature measurement ranges and signal amplitudes. This analog-to-digital converter 7 has a 16-bit resolution and a digital output range of -32768 to +32767. By properly configuring the gain and reference voltage, the output digital value of the thermocouple sensor 1 can be located within the range of [0-30000] during normal operating temperature, achieving accurate temperature measurement.

[0052] When thermocouple sensor 1 detaches or its signal line breaks, its output signal path is interrupted. At this time, the differential input terminal of analog-to-digital converter 7 is only affected by the bias circuit: the positive input is VCC / 2, and the negative input is 0V, forming a differential voltage of VCC / 2 between them. After being amplified by the PGA, this voltage is very likely to exceed the reference voltage of the analog-to-digital converter, causing output saturation and producing the maximum positive digital output value of 32767.

[0053] The microcontroller 8 reads the output data of the analog-to-digital converter 7 through the SPI interface. If the conversion result is detected to be the full-scale value 32767, it can be determined that the thermocouple sensor 1 has a "detachment or breakage" fault, and the second-level function detection is realized.

[0054] Finally, step S4 is used to comprehensively judge the results of the first-level insertion detection and the second-level functional detection: the judgment logic of the two-level online detection of thermocouple sensor 1 is as follows: Figure 2 As shown, it is completed collaboratively by two parts: connection signal detection (first-level insertion detection) and analog signal conversion detection (second-level function detection).

[0055] The first-stage insertion detection circuit outputs logic high and low level signals, which are read by the microcontroller 8 to obtain the physical connection status of the sensor; the second-stage function detection circuit outputs digital conversion values, which are read by the microcontroller 8 to determine the electrical connection status of the sensor based on the value range.

[0056] Specifically, the judgment logic for the two-level online detection of the state of thermocouple sensor 1 is as follows: If step S1 determines that the thermocouple sensor 1 is "not inserted", then the status of thermocouple sensor 1 is "not installed". If step S1 determines that the thermocouple sensor is "inserted" and step S3 determines that the output is "not full scale" (i.e., the output value is within the normal measurement range), then the thermocouple sensor 1 is in the "normal online" state. If step S1 determines "inserted" but step S3 determines "full-scale output" (i.e., output value is 32767), then the thermocouple sensor 1 status is "installed but faulty".

[0057] The two-level judgment logic described above can effectively distinguish between various fault modes such as "not installed" and "installed but disconnected", which significantly improves the accuracy and intelligence of system fault diagnosis.

[0058] Compared with the prior art, the two-stage online detection circuit and method for thermocouple sensors provided by the present invention have the following outstanding technical effects: 1. Achieved reliable dual testing of physical connection and electrical function: This invention innovatively employs a two-level diagnostic mechanism combining "first-level insertion detection" and "second-level functional detection." The first level accurately determines whether the sensor is physically installed by detecting the state of the mechanical switch contacts inside the connector; the second level analyzes the output characteristics of the analog-to-digital converter to monitor the electrical continuity of the signal line in real time. Working together, these two levels can effectively distinguish between various states such as "not installed," "installed but disconnected," and "normally online," solving the technical problem that traditional single-point detection cannot accurately identify "false connections" or "hidden disconnections," significantly improving the reliability and accuracy of system fault diagnosis.

[0059] 2. The detection principle is simple and reliable, requiring no additional dedicated chip: The first-stage insertion detection cleverly utilizes the inherent mechanical switching characteristics of the three-pin connector. A clear digital level signal can be generated using only a simple resistor network (R1, R3, R4), eliminating the need for additional microswitches or dedicated sensors. This results in a simple, low-cost, and durable structure. The second-stage functional detection reuses the system's existing analog-to-digital converter (such as the ADS1120) for fault diagnosis, eliminating the need for a separate open-circuit detection circuit. This fully utilizes existing hardware resources, achieving the design goals of high integration and low cost.

[0060] 3. The fault criteria are clear, and automated diagnosis is easily achieved: The second-level functional detection utilizes the characteristic that the input voltage difference reaches saturation after a thermocouple disconnection, causing the analog-to-digital converter (ADC) to output a full-scale value (e.g., 32767) as a fault criterion. This criterion is a clear, discrete numerical threshold. The microcontroller only needs to determine whether the ADC reading is equal to the maximum value to make a judgment. The algorithm is simple, has a fast response, and an extremely low false positive rate, making it very easy to program and implement in embedded systems, which is beneficial for the intelligent and automated operation and maintenance of the system.

[0061] 4. High compatibility and wide applicability: The detection method of this invention does not depend on the specific type of thermocouple (such as type K, type E, etc.) or the measurement temperature range. As long as the gain and reference voltage of the analog-to-digital converter are properly configured so that its output is in the non-saturation range (such as [0-30000]) during normal operation, it can be applied to various types of thermocouple sensors. At the same time, the circuit design is highly versatile and can be widely used in industrial automation, energy and power, rail transportation and other fields where real-time monitoring of thermocouple status is required.

[0062] 5. Improved system security and maintainability: Through real-time, online two-level detection, the system can issue an alarm immediately upon sensor detachment or disconnection, preventing the collection of erroneous temperature data due to sensor failure. This avoids incorrect decisions by the control system and ensures the safety of equipment and personnel. Simultaneously, clear fault location information (whether it is not installed or installed but faulty) greatly facilitates on-site maintenance personnel in quickly diagnosing problems, reducing downtime, and improving system maintainability and operational efficiency.

[0063] In summary, this invention, through its innovative two-level detection architecture and simple, reliable circuit design, achieves comprehensive and accurate diagnosis of the thermocouple sensor status, making significant progress in terms of detection reliability, cost-effectiveness, ease of use, and safety.

[0064] Obviously, those skilled in the art should understand that the modules or steps of the above-described embodiments of the present invention can be implemented using general-purpose computing devices. They can be centralized on a single computing device or distributed across a network of multiple computing devices. Optionally, they can be implemented using computer-executable program code, thereby storing them in a storage device for execution by a computing device. In some cases, the steps shown or described can be performed in a different order than those presented here, or they can be fabricated as separate integrated circuit modules, or multiple modules or steps can be fabricated as a single integrated circuit module. Thus, the embodiments of the present invention are not limited to any particular hardware and software combination.

[0065] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, various modifications and variations can be made to the embodiments of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A two-stage online detection circuit for a thermocouple sensor, characterized in that, include: The first-stage insertion detection circuit detects the on / off state of the mechanical switch contacts inside the connector (2), and outputs a first detection signal based on the on / off state to determine whether the thermocouple sensor (1) is physically inserted into the connector (2). The mechanical switch contacts are on when the thermocouple sensor (1) is not inserted, and off when inserted into place. The second-level functional detection circuit detects whether the signal line of the thermocouple sensor (1) is normally connected. It includes a bias circuit and an analog-to-digital converter (7). The output signal of the thermocouple sensor (1) is superimposed with the bias voltage output by the bias circuit and then output to the differential input terminal of the analog-to-digital converter (7). The first-stage insertion detection circuit and the second-stage function detection circuit work together to perform two-stage online detection on the thermocouple sensor (1).

2. The two-stage online detection circuit for the thermocouple sensor according to claim 1, characterized in that, The first-stage insertion detection circuit includes a pull-down bias resistor (3), a positive bias resistor (5), and a positive voltage divider resistor (6). One end of the pull-down bias resistor (3) is grounded, and the other end is connected to the third pin of the connector (2); the positive bias resistor (5) and the positive voltage divider resistor (6) are connected in series, with one end connected to the power supply VCC and the other end grounded; the midpoint of the series connection between the positive bias resistor (5) and the positive voltage divider resistor (6) is connected to the second pin of the connector (2).

3. The two-stage online detection circuit for the thermocouple sensor according to claim 1 or 2, characterized in that, The first detection signal is a logic level signal, and the logic level signal is output to the digital input port of the microcontroller (8).

4. The two-stage online detection circuit for the thermocouple sensor according to claim 1 or 2, characterized in that, The bias circuit includes a negative bias resistor (4), a positive bias resistor (5), and a positive voltage divider resistor (6). The negative bias resistor (4) is connected to the negative differential signal terminal of the analog-to-digital converter (7) to pull down the voltage of the negative differential signal terminal to 0V; the midpoint of the series connection between the positive bias resistor (5) and the positive voltage divider resistor (6) is connected to the positive differential signal terminal of the analog-to-digital converter (7) to provide a bias voltage of VCC / 2 to the positive differential signal terminal.

5. The two-stage online detection circuit for the thermocouple sensor according to claim 4, characterized in that, The positive bias resistor (5) and the positive voltage divider resistor (6) have a resistance of 2KΩ, and the negative bias resistor (4) has a resistance of 10MΩ.

6. The two-stage online detection circuit for the thermocouple sensor according to claim 1, characterized in that, The positive output terminal of the thermocouple sensor (1) is connected to the second-level functional detection circuit through the first pin of the connector (2), and a current-limiting resistor (9) is provided on the connection path between the first pin and the negative terminal of the differential signal.

7. The two-stage online detection circuit for the thermocouple sensor according to claim 6, characterized in that, A filter capacitor (10) is provided between the current limiting resistor (9) and the negative terminal of the differential signal. One end of the filter capacitor (10) is grounded and the other end is connected to the negative terminal of the differential signal.

8. The two-stage online detection circuit for the thermocouple sensor according to claim 1, characterized in that, When the thermocouple sensor (1) is working normally, the tiny voltage generated when the temperature changes is superimposed on the bias voltage and input to the analog-to-digital converter (7), which converts it into a digital value within the measurement range and then outputs it. When the thermocouple sensor (1) falls off or breaks, the analog-to-digital converter (7) outputs the maximum value.

9. The two-stage online detection circuit for the thermocouple sensor according to claim 1, characterized in that, The analog-to-digital converter (7) is a 16-bit resolution analog-to-digital converter with an integrated programmable gain amplifier, model ADS1120.

10. The two-stage online detection circuit for the thermocouple sensor according to claim 1 or 9, characterized in that, The analog-to-digital converter (7) outputs digital conversion data through the SPI interface, which includes a chip select signal interface (11), a clock signal interface (12), a data input signal interface (13), a data output signal interface (14), and a data ready signal interface (15). The SPI interface is connected to the microcontroller (8).

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