Temperature measurement circuit and system with broken line detection function

Abstract

The invention relates to a temperature measurement circuit and system with a broken line detection function, and belongs to the technical field of temperature measurement. The temperature measurement branch circuits comprise a first acquisition branch circuit, a second acquisition branch circuit, a third acquisition branch circuit and a fourth acquisition branch circuit, the first acquisition branch circuit and the second acquisition branch circuit are connected with the first wiring terminal, and the third acquisition branch circuit and the fourth acquisition branch circuit are connected with the second wiring terminal. The second acquisition branch and the third acquisition branch are respectively connected with a current injection branch so as to be respectively connected with the first wiring terminal and the second wiring terminal, the second acquisition branch is also connected with a voltage injection branch, and the current injection branch and the voltage injection branch are respectively provided with a corresponding control switch; and each control switch is controlled by the control module. And the control module controls the corresponding control switch to realize temperature measurement and broken line detection according to the type access mode of the accessed temperature measurement sensor, so that not only is the universality strong, but also the comprehensiveness of the broken line detection is ensured.

Description

Technical Field

[0001] The invention relates to a temperature measuring circuit and a system with a disconnection detection function, belonging to the technical field of temperature measurement. Background Art

[0002] Commonly used temperature detectors include thermal resistor sensors and thermocouple sensors. The working principles of these two sensors are different; their main features are high measurement accuracy, good linearity, stable performance, and a wide range of operating temperatures. Among them, thermal resistors are mostly made of pure metal materials, with platinum and copper being the most widely used. Platinum thermal resistors have the highest resistance measurement accuracy. They are not only widely used in industrial temperature measurement, but also made into standard reference instruments. Thermal resistor temperature measurement is based on the characteristic that the resistance value of a metal conductor increases with the increase of temperature to measure temperature.

[0003] Since the temperature measurement principles of thermal resistor sensors and thermocouple sensors are different, the temperature measurement circuits based on these two sensors are also different. The current temperature measurement circuit is either based on thermal resistor sensors or based on thermocouple sensors, and the thermal resistor sensors also include 2-wire, 3-wire and 4-wire access methods. The access methods are diverse, and the corresponding temperature measurement circuits also need to change; and the current temperature measurement circuit includes a terminal and a temperature measurement branch for connecting to both ends of the temperature measurement sensor, but the temperature measurement branch is difficult to meet the above requirements at the same time, and the versatility is relatively poor. In addition, when one of the wires of the temperature measurement sensor and other circuits are broken, the corresponding collected value will have an error, which will lead to the calculation of the wrong temperature. Therefore, it is necessary to perform a disconnection detection on the temperature measurement circuit, and the current detection method can only perform a single-line disconnection detection, that is, it can only perform a temperature measurement disconnection detection circuit of a thermal resistor or a thermocouple, which cannot meet the demand for comprehensive disconnection detection of the temperature measurement circuit. Summary of the invention

[0004] The purpose of the present invention is to provide a temperature measurement circuit and system with a disconnection detection function to solve the problem that the current temperature measurement circuit is not universal and cannot perform comprehensive disconnection detection.

[0005] In order to solve the above technical problems, the present invention provides a temperature measuring circuit with a disconnection detection function. The temperature measuring circuit includes a wiring terminal and a temperature measuring branch for connecting to two ends of a temperature measuring sensor. The wiring terminal includes a first wiring terminal and a second wiring terminal. The temperature measuring branch includes a first acquisition branch and a second acquisition branch connected to the first wiring terminal, and a third acquisition branch and a fourth acquisition branch connected to the second wiring terminal. Each acquisition branch is used to access the analog input end of an AD chip through a corresponding control switch. The second acquisition branch and the third acquisition branch are respectively connected to current injection branches to respectively access the first wiring terminal and the second wiring terminal. The second acquisition branch is also connected to a voltage injection branch. Corresponding control switches are provided on the current injection branch and the voltage injection branch. Each control switch is controlled by a control module, and the control module realizes temperature measurement and disconnection detection of the temperature measuring sensor by controlling each control switch.

[0006] Furthermore, a reference resistor is also provided on the fourth acquisition branch.

[0007] Furthermore, the constant current sources respectively connected to the current injection branches of the first wiring terminal and the second wiring terminal are the same constant current source.

[0008] Furthermore, when the temperature measuring sensor connected to the first terminal and the second terminal is a thermistor sensor, and three-wire access is adopted, the control module controls the control switches on the current injection branch, the second acquisition branch, the third acquisition branch and the fourth acquisition branch, and performs wire break detection by comparing the current relationship between the fourth acquisition branch and the second acquisition branch and the third acquisition branch.

[0009] Furthermore, when the temperature measuring sensor connected to the first terminal and the second terminal is a thermocouple sensor, the control module is used to control the closure of the voltage injection branch and the control switches on the second acquisition branch and the third acquisition branch, and perform wire break detection based on the relationship between the reference voltage, the injection voltage and the voltage across the thermocouple sensor.

[0010] The present invention also provides a temperature measurement system with a disconnection detection function, comprising a temperature measurement circuit and a temperature measurement sensor, the temperature measurement circuit comprising a wiring terminal and a temperature measurement branch, the wiring terminal comprising a first wiring terminal and a second wiring terminal, the temperature measurement branch comprising a first acquisition branch and a second acquisition branch connected to the first wiring terminal, and a third acquisition branch and a fourth acquisition branch connected to the second wiring terminal, each acquisition branch is used to access the analog input end of the AD chip through a corresponding control switch, the second acquisition branch and the third acquisition branch are respectively connected to current injection branches to respectively access the first wiring terminal and the second wiring terminal, the second acquisition branch is also connected to a voltage injection branch, and corresponding control switches are provided on the current injection branch and the voltage injection branch; each control switch is controlled by a control module, and the control module realizes temperature measurement and disconnection detection of the temperature measurement sensor by controlling each control switch.

[0011] Furthermore, a reference resistor is also provided on the fourth acquisition branch.

[0012] Furthermore, the constant current sources respectively connected to the current injection branches of the first wiring terminal and the second wiring terminal are the same constant current source.

[0013] Furthermore, when the temperature measuring sensor is a thermistor sensor and is connected using three wires, the control module controls the control switches on the current injection branch, the second acquisition branch, the third acquisition branch and the fourth acquisition branch, and performs line break detection by comparing the current relationship between the fourth acquisition branch and the second acquisition branch and the third acquisition branch.

[0014] Furthermore, when the temperature measuring sensor is a thermocouple sensor, the control module is used to control the closure of the control switches on the voltage injection branch and the second acquisition branch and the third acquisition branch, and perform wire break detection based on the relationship between the reference voltage, the injection voltage and the voltage across the thermocouple sensor.

[0015] The beneficial effects of the present invention are as follows: as an improved invention, the temperature measurement branch provided by the present invention includes a first acquisition branch and a second acquisition branch connected to the first wiring terminal, and a third acquisition branch and a fourth acquisition branch connected to the second wiring terminal, each acquisition branch is used to access the analog input terminal of the AD chip through a corresponding control switch, and the second acquisition branch and the third acquisition branch are respectively connected to current injection branches to respectively access the first wiring terminal and the second wiring terminal, and the second acquisition branch is also connected to a voltage injection branch, and the current injection branch and the voltage injection branch are both provided with corresponding control switches; each control switch is controlled by a control module. The control module controls the corresponding control switch according to the type of the temperature sensor connected to achieve temperature measurement, and has strong versatility; at the same time, the control module can also complete various disconnection detections by controlling each control switch, thereby ensuring the comprehensiveness of disconnection detection. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a schematic diagram of a temperature measurement circuit with a disconnection detection function of the present invention. DETAILED DESCRIPTION

[0017] The specific implementation of the present invention will be further described below in conjunction with the accompanying drawings.

[0018] The temperature measurement branch provided in the present invention includes a first acquisition branch and a second acquisition branch connected to the first wiring terminal, and a third acquisition branch and a fourth acquisition branch connected to the second wiring terminal. Each acquisition branch is used to access the analog input end of the AD chip through a corresponding control switch. The second acquisition branch and the third acquisition branch are respectively connected to current injection branches to respectively access the first wiring terminal and the second wiring terminal. The second acquisition branch is also connected to a voltage injection branch. Corresponding control switches are provided on the current injection branch and the voltage injection branch; each control switch is controlled by a control module. The control module controls the corresponding control switch according to the type of temperature sensor connected. When the thermal resistor sensor is connected, the upper switch of the current injection branch is closed, and the control switch on each acquisition branch is controlled to be closed according to the wiring method, so as to achieve temperature measurement, and at the same time, the disconnection detection is performed by controlling the on and off of the current injection branch and the current on the fourth branch; when the thermocouple sensor is connected, the control switch on the voltage injection branch is closed, and the control switches on the second acquisition branch and the third acquisition branch are closed, so as to achieve thermocouple temperature measurement. When disconnection detection is required, it is only necessary to know the relationship between the voltage on the second acquisition branch and the third acquisition branch and the reference voltage and the injection voltage. It can be seen that the present application can realize the access of two types of sensors, and also supports different wiring methods, which can not only realize the temperature measurement of various sensors, but also realize disconnection detection.

[0019] Embodiment of a temperature measurement system with a disconnection detection function

[0020] The temperature measurement system in this embodiment includes a temperature measurement sensor and a temperature measurement circuit, wherein the temperature measurement circuit provides a connection terminal and a temperature measurement branch for connecting the temperature measurement sensor. In order to adapt to the access of two types of temperature measurement sensors and different wiring methods of thermistor sensors, the temperature measurement branch of the connection terminal provided by the present invention can meet different access requirements.

[0021] The specific temperature measurement circuit is as follows: Figure 1As shown, the wiring terminals include a first wiring terminal and a second wiring terminal. The temperature measurement branch includes a first acquisition branch and a second acquisition branch connected to the first wiring terminal, and a third acquisition branch and a fourth acquisition branch connected to the second wiring terminal. In this embodiment, the first acquisition branch is a line connected between the first wiring terminal and the first analog quantity acquisition terminal at the analog switch. The line is provided with a control switch S1 and a lead resistor R1. The lead resistor R1 is arranged close to the first analog quantity acquisition terminal. The area between the first analog quantity acquisition terminal and the lead resistor R1 is called point A. The first analog quantity acquisition terminal is used to access the analog quantity input terminal of the AD chip through the control switch S4. The second acquisition branch is a line connected between the first wiring terminal and the second analog quantity acquisition terminal at the analog switch. The line is provided with a lead resistor R2. The area between the second analog quantity acquisition terminal and the lead resistor R2 is called point B. The second analog quantity acquisition terminal is used to access the analog quantity input terminal of the AD chip through the control switch S5; the third acquisition branch is a line connected between the second wiring terminal and the third analog quantity acquisition terminal at the analog switch, and a lead resistor R3 is provided on the line. The area between the third analog quantity acquisition terminal and the lead resistor R3 is called point C. The third analog quantity acquisition terminal is used to access the analog quantity input terminal of the AD chip through the control switch S6; the fourth acquisition branch is a line connected between the second wiring terminal and the fourth analog quantity acquisition terminal at the analog switch. A lead resistor R4 and a reference resistor Rref are provided on the line. The lead resistor R4 is close to the second wiring terminal. The area between the reference resistor Rref and the lead resistor R4 is called point D. The fourth analog quantity acquisition terminal is used to access the analog quantity input terminal of the AD chip through the control switch S9.

[0022] The current injection branch includes a first current injection branch and a second current injection branch, wherein the first current injection branch is provided with a first constant current source (constant current source IS1) and a control switch S2 in series, and the first current injection branch is connected to point B of the second acquisition branch, and the second current injection branch is provided with a second constant current source (constant current source IS2) and a control switch S7 in series, and the second current injection branch is connected to point C of the third acquisition branch; in this way, the constant current sources IS1 and IS2 can respectively inject current into the first wiring terminal and the second wiring terminal under the control of the control switches S2 and S7, respectively.

[0023] In addition, a reference voltage Vbias input terminal is provided at the analog switch, and the reference voltage Vbias input terminal is used to access the reference voltage terminal of the AD chip through the control switch S8. Constant current sources IS1 and IS2 are also connected to the current source input terminal of the analog switch, and the current source input terminal is connected to the current source terminal of the AD chip through the switch S3.

[0024] The control switches S1, S2, S3, S4, S5, S6, S7, S8 and S9 are all controlled by the control module, and the control module controls each control switch according to the type and access mode of the temperature sensor. The following describes them respectively according to the type of the temperature sensor.

[0025] When the temperature sensor uses a thermal resistor sensor RTD, the first terminal and the second terminal are connected to the two ends of the thermal resistor sensor RTD respectively, and the measurement branch can be connected in a 2-, 3-, or 4-wire manner. When the 3-wire connection method is used, the control module closes the control switches S2, S3, S5, S6, S7, and S9. Since switches S5, S6, and S9 are all closed, B, C, and D can be connected to the AD chip through analog switches S5, S6, and S9; by closing switches S2 and S3, current sources Is1 and Is2 can be connected to the two ends of the thermal resistor sensor RTD respectively, and the AD chip obtains the voltage of the thermal resistor sensor RTD1 according to the three connected analog quantity acquisition terminals. The measurement circuit can measure the temperature range from -200℃ to +850℃, in which the thermal resistor sensor RTD1 is made of PT100 material, and its resistance is proportional to the change in temperature. The temperature measurement circuit adopts a ratio measurement method. The AD chip converts the voltage U on both sides of the measured RTD into the measured temperature by comparing it with the reference voltage from the same excitation source.

[0026] In order to further improve the measurement accuracy, the first constant current source (constant current source IS1) and the second constant current source (constant current source IS2) used in the present invention are the same constant current source. In this way, during the measurement process, the two currents from the same current source Is1 and Is2 have the same value, ensuring the close matching of the two current values. The two currents are fused on the branch where point D is located. The branch is connected to the fourth analog quantity acquisition terminal at the analog switch through a low drift reference resistor Rref. The voltage value generated by the reference resistor can offset the errors caused by the drift or noise of the temperature or excitation source in the circuit. These errors are common to the sensor signal and the reference, and therefore, the temperature measurement accuracy is further improved.

[0027] When it is necessary to detect the disconnection of the thermal resistor sensor, it can also be detected according to its wiring method. The following is an example of the circuit for the three-wire disconnection detection of the thermal resistor sensor. The three-wire detection method of the thermal resistor sensor is: when the currents Is1 and Is2 are added to the B and C lines, the monitoring function is enabled, and it can be detected that the current at D should be Is1+Is2, and it can be judged whether the line at D is broken; when the current Is1 is added to B, the monitoring function is enabled, and it can be detected that the current at D should be Is1, and it can be judged whether the line at B is broken; when the current Is2 is added to C, the monitoring function is enabled, and it can be judged whether the line at C is broken. Through this process, it can be seen that the disconnection detection of the thermal resistor sensor connected with a three-wire system can be realized.

[0028] As other implementation methods, it is also possible to implement disconnection detection for thermal resistor sensors connected using a 2-wire system or a 4-wire system. When a 2-wire system is used: close S2, S3, S5 and S6, and measure the temperature through RTD resistors in routes B and C; if disconnection detection is to be performed, add current Is1 to route B, enable the monitoring function, and detect the current Is1 at C, so as to determine whether the route C is disconnected. When a 4-wire system is used: similar to the 2-wire system, short-circuit A and B, C and D, measure the temperature through RTD resistors, close S1, S3, S4, S5, S6, S9, and the current does not flow through routes B and C during this process, and the voltage of the ADC input is equal to the voltage of the RTD; if disconnection detection is to be performed, add current Is1 to route A, enable the monitoring function, and detect whether the current at D is Is1, so as to determine whether the route D is disconnected.

[0029] When the temperature measuring sensor adopts a thermocouple sensor TC, the first terminal and the second terminal are respectively connected to the two ends of the thermocouple sensor, and switches S2, S3, S5, S6, S8, and S10 are closed at the same time to inject current Is1. Switch S10 is closed and the thermocouple sensor works. Closing switches S5 and S6 can collect the voltage across the thermocouple sensor, and closing switch S8 can obtain the corresponding reference voltage Vbias. The AD chip compares the collected voltage across the thermocouple sensor with the reference voltage Vbias and converts it into the measured temperature. In addition, the reference voltage Vibas can enable the thermocouple to collect positive and negative voltages, with the upper half of the waveform being positive and the lower half being negative.

[0030] Thermocouple sensor disconnection detection method:

[0031] The first terminal and the second terminal are connected to thermocouples respectively, and switches S2, S3, S5, S6 and S8 are closed. When the thermocouple is connected, Is1 outputs a current that flows through the thermocouple to generate a voltage V1, which is smaller than the input voltage of AD. When the thermocouple is open circuit, the voltage at B and C is clamped at V2 through the voltage regulator. When the voltage collected by the AD chip is V2, it is judged as a broken wire.

[0032] Embodiment of temperature measurement circuit with disconnection detection function

[0033] The temperature measurement circuit of this embodiment includes a connection terminal and a temperature measurement branch for connecting to both ends of the temperature measurement sensor, the connection terminal includes a first connection terminal and a second connection terminal, the temperature measurement branch includes a first acquisition branch and a second acquisition branch connected to the first connection terminal, and a third acquisition branch and a fourth acquisition branch connected to the second connection terminal, each acquisition branch is used to access the analog input end of the AD chip through a corresponding control switch, the second acquisition branch and the third acquisition branch are respectively connected to a current injection branch to respectively access the first connection terminal and the second connection terminal, the second acquisition branch is also connected to a voltage injection branch, and the current injection branch and the voltage injection branch are both provided with corresponding control switches; each control switch is controlled by a control module, and the control module realizes temperature measurement and disconnection detection of the temperature measurement sensor by controlling each control switch. The specific connection relationship and working principle have been described in detail in the embodiment of the temperature measurement system with disconnection detection function, and will not be repeated here.

Claims

1. A temperature measuring circuit with a disconnection detection function, the temperature measuring circuit comprising a connection terminal for connecting to both ends of a temperature measuring sensor and a temperature measuring branch, characterized in that: The wiring terminals include a first wiring terminal and a second wiring terminal, and the temperature measurement branch includes a first acquisition branch and a second acquisition branch connected to the first wiring terminal, and a third acquisition branch and a fourth acquisition branch connected to the second wiring terminal. Each acquisition branch is used to access the analog input end of the AD chip through a corresponding control switch. The second acquisition branch and the third acquisition branch are respectively connected to current injection branches to respectively access the first wiring terminal and the second wiring terminal. The second acquisition branch is also connected to a voltage injection branch. Corresponding control switches are provided on the current injection branch and the voltage injection branch; each control switch is controlled by a control module, and the control module realizes temperature measurement and disconnection detection of the temperature measurement sensor by controlling each control switch.

2. The temperature measuring circuit with disconnection detection function according to claim 1, characterized in that: The fourth acquisition branch is also provided with a reference resistor.

3. The temperature measuring circuit with disconnection detection function according to claim 1, characterized in that: The constant current sources respectively connected to the current injection branches of the first wiring terminal and the second wiring terminal are the same constant current source.

4. The temperature measuring circuit with disconnection detection function according to any one of claims 1 to 3, characterized in that: When the temperature measuring sensor connected to the first terminal and the second terminal is a thermistor sensor and three-wire access is adopted, the control module controls the control switches on the current injection branch, the second acquisition branch, the third acquisition branch and the fourth acquisition branch, and performs line break detection by comparing the current relationship between the fourth acquisition branch and the second acquisition branch and the third acquisition branch.

5. The temperature measuring circuit with disconnection detection function according to any one of claims 1 to 3, characterized in that: When the temperature measuring sensor connected to the first terminal and the second terminal is a thermocouple sensor, the control module is used to control the closing of the control switches on the voltage injection branch and the second acquisition branch and the third acquisition branch, and perform wire break detection based on the relationship between the reference voltage, the injection voltage and the voltage across the thermocouple sensor.

6. A temperature measurement system with a disconnection detection function, comprising a temperature measurement circuit and a temperature measurement sensor, wherein the temperature measurement circuit comprises a connection terminal and a temperature measurement branch, characterized in that: The wiring terminals include a first wiring terminal and a second wiring terminal, and the temperature measurement branch includes a first acquisition branch and a second acquisition branch connected to the first wiring terminal, and a third acquisition branch and a fourth acquisition branch connected to the second wiring terminal. Each acquisition branch is used to access the analog input end of the AD chip through a corresponding control switch. The second acquisition branch and the third acquisition branch are respectively connected to current injection branches to respectively access the first wiring terminal and the second wiring terminal. The second acquisition branch is also connected to a voltage injection branch. The current injection branch and the voltage injection branch are both provided with corresponding control switches; each control switch is controlled by a control module, and the control module realizes temperature measurement and disconnection detection of the temperature measurement sensor by controlling each control switch.

7. The temperature measurement system with disconnection detection function according to claim 6, characterized in that: The fourth acquisition branch is also provided with a reference resistor.

8. The temperature measurement system with disconnection detection function according to claim 6, characterized in that: The constant current sources respectively connected to the current injection branches of the first wiring terminal and the second wiring terminal are the same constant current source.

9. The temperature measurement system with disconnection detection function according to any one of claims 6 to 8, characterized in that: When the temperature measuring sensor is a thermistor sensor and is connected using three wires, the control module controls the control switches on the current injection branch, the second acquisition branch, the third acquisition branch and the fourth acquisition branch, and performs wire break detection by comparing the current relationship between the fourth acquisition branch and the second acquisition branch and the third acquisition branch.

10. The temperature measurement system with disconnection detection function according to any one of claims 6 to 8, characterized in that: When the temperature measuring sensor is a thermocouple sensor, the control module is used to control the voltage injection branch and the control switches on the second acquisition branch and the third acquisition branch to close, and perform line break detection based on the relationship between the reference voltage, the injection voltage and the voltage across the thermocouple sensor.

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