A high-precision temperature measurement circuit and calibration method based on NTC

Abstract

A high-precision temperature measurement circuit and calibration method based on NTC, including an NTC temperature sensor, a voltage-dividing resistor, a MOS switching switch module, a filter, an AD converter and an MCU controller; the NTC temperature sensor is connected to the voltage-dividing resistor, the MOS switching switch module, a reference ground and the filter respectively, and the other end of the voltage-dividing resistor is connected to the AD converter; the input end of the filter is connected to the NTC temperature sensor and the reference ground, the output end of the filter is connected to the AD converter, and the AD converter is connected to the MCU controller; the MOS switching switch module is used to control whether the NTC temperature sensor is connected in parallel with the resistor to switch different temperature measurement ranges. The invention has low cost, wider temperature measurement range, higher accuracy, and meets the requirements of high-precision temperature measurement under the full temperature range.

Description

Technical Field

[0001] The invention relates to a temperature measurement circuit and a calibration method, in particular to a high-precision temperature measurement circuit and a calibration method based on NTC. Background Art

[0002] As is known, the internal part of the NTC temperature sensor is equivalent to a variable resistor, and its principle is: the resistance value decreases as the temperature rises. Since temperature measurement plays an extremely important role in cold chain transportation and life production, NTC temperature sensors are widely used in related fields of temperature measurement, and the accuracy of temperature measurement determines the accuracy of intelligent control and judgment.

[0003] like Figure 1 As shown, a known high-precision temperature acquisition circuit based on an NTC temperature sensor includes an NTC temperature sensor array, a voltage regulator, an AD converter, a controller, an external interface, a standard resistor array, a first switch array, and a second switch array, wherein the first switch array and the second switch array are respectively connected to one of the standard resistor arrays and one of the NTC temperature sensor arrays; the AD converter is used to acquire the voltage division signal between the connected standard resistor and the connected NTC temperature sensor, and perform analog-to-digital conversion; the controller is used to provide a switch selection signal and calculate the temperature value of the NTC temperature sensor; the external interface is used to provide the acquired data to an external device. The circuit can obtain good accuracy in a wide acquisition temperature range, and has low development cost and is easy to implement.

[0004] The above circuit uses different combinations of multi-channel standard resistors and multi-channel sensors to achieve full-range temperature measurement, but standard resistors have defects such as high cost and difficulty in batch purchase and production. In addition, the temperature measurement circuit is generally not calibrated, so the cumulative error of the measurement circuit is large. Summary of the invention

[0005] In order to overcome the above-mentioned deficiencies in the prior art, the present invention provides a high-precision temperature measurement circuit and calibration method based on NTC, which has low cost, wider temperature measurement range, higher accuracy, and can meet the requirements of high-precision temperature measurement in the full temperature range.

[0006] The technical solution adopted by the present invention to solve the technical problem is:

[0007] A high-precision temperature measurement circuit based on NTC comprises an NTC temperature sensor, a voltage-dividing resistor, a MOS switching switch module, a filter, an AD converter and an MCU controller; the NTC temperature sensor is respectively connected to the voltage-dividing resistor, the MOS switching switch module, a reference ground and the filter, and the other end of the voltage-dividing resistor is connected to the AD converter; the input end of the filter is connected to the NTC temperature sensor and the reference ground, the output end of the filter is connected to the AD converter, and the AD converter is connected to the MCU controller; the MOS switching switch module is used to control whether the NTC temperature sensor is connected in parallel with the resistor to switch different temperature measurement ranges.

[0008] A high-precision temperature calibration method based on NTC is used to calibrate two temperature measurement ranges of a high-precision temperature measurement circuit based on NTC, including the following steps:

[0009] 1) Every time the NTC temperature sensor changes by 1 degree, the corresponding resistance value forms an RT table, and the RT table is written into the program;

[0010] 2) Connect an external resistor box and adjust the resistance value of the resistor box to make it consistent with the resistance value of the NTC temperature sensor. The resistance value of the resistor box and the voltage value collected by the current AD converter form an RV table, and the RV table is written into the program;

[0011] 3) Adjust the resistance value of the resistance box so that the resistance value of the resistance box is consistent with the temperature at both ends of the measurement range of the NTC temperature sensor. At this time, the two sets of voltage values ​​collected by the AD converter are used to calculate two parameters k and b with the two sets of voltages corresponding to step 2) and save them in the MCU controller;

[0012] 4) The MCU controller collects the voltage value X through the AD converter, calculates the latest voltage value through the formula k*X+b, and obtains the resistance value R through the RV table in step 2), and then obtains the temperature value through the RT table in step 1. The current temperature value is the actual value of the NTC temperature sensor.

[0013] Compared with the prior art, the high-precision temperature measurement circuit and calibration method based on NTC of the present invention have the following significant advantages:

[0014] 1. In the circuit design, ordinary resistors and high-precision NTC temperature sensors are used, the overall cost is relatively low and the circuit complexity is low;

[0015] 2. By switching the measuring range, segmented measurement is introduced to achieve a very wide temperature range of measurement, and the measurement error is corrected through calibration to achieve high-precision measurement in the full temperature range; 3. The parameters of the circuit are corrected through the program to achieve low cost while ensuring high precision. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The present invention is further described below in conjunction with the accompanying drawings and embodiments.

[0017] Figure 1 It is a circuit diagram of the prior art.

[0018] Figure 2 A circuit diagram of an embodiment of the present invention.

[0019] Figure 3 It is a circuit diagram of an embodiment of the present invention in a measuring range state.

[0020] Figure 4 It is a circuit diagram of an embodiment of the present invention in another range state. DETAILED DESCRIPTION

[0021] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0022] Figures 2 to 4 FIG. 1 is a schematic diagram showing a structure of a preferred embodiment of the present invention. Figure 1 A high-precision temperature measurement circuit based on NTC, comprising an NTC temperature sensor, a voltage-dividing resistor, a MOS switching switch module, a filter, an AD converter and an MCU controller; the NTC temperature sensor is respectively connected to the voltage-dividing resistor, the MOS switching switch module, a reference ground and the filter, and the other end of the voltage-dividing resistor is connected to the AD converter; the filter is a four-port circuit, the input end of the filter is connected to the NTC temperature sensor and the reference ground, the output end of the filter is connected to the AD converter, and the AD converter is connected to the MCU controller; the MOS switching switch module is used to control whether the NTC temperature sensor is connected in parallel with the resistor to switch different temperature measurement ranges.

[0023] In this embodiment, the MOS switching switch module is composed of a resistor R3, a MOS tube and a resistor R6. The S source terminal of the MOS tube is connected to the NTC temperature sensor, the D drain terminal of the MOS tube is connected to the resistor R3, the G gate terminal of the MOS tube is respectively connected to one end of the resistor R6 and the MCU controller, and the other end of the resistor R6 is connected to the reference ground.

[0024] In this embodiment, the filter is composed of a common-mode inductor L1, a capacitor C6, a capacitor C7 and a capacitor C10. The common-mode inductor L1 is provided with 4 pins. The first pin of the common-mode inductor L1 is connected to the MOS switching module, the second pin of the common-mode inductor L1 is connected to one end of the capacitor C6, the third pin of the common-mode inductor L1 is connected to the NTC temperature sensor, the fourth pin of the common-mode inductor L1 is connected to one end of the capacitor C10, the other end of the capacitor C6 is connected to the reference ground, the other end of the capacitor C10 is connected to the reference ground, one end of the capacitor C7 is connected to the capacitor C6, and the other end of the capacitor C7 is connected to the capacitor C10.

[0025] The temperature measurement circuit of the present invention can achieve a temperature measurement range of -50 to 150 degrees, which is divided into two ranges for measurement through the MOS switching module. Figure 3 In this embodiment, the range of the temperature measurement circuit is -50 to 30 degrees. At this time, the MOS tube is turned on, and the resistor R3 and the NTC temperature sensor are in parallel. Figure 4 In this embodiment, the temperature measurement circuit has a range of 25 to 150 degrees, at which time the MOS tube is not conducting.

[0026] Since there are errors in the voltage divider resistors, resistor R3, and the output voltage of the AD converter on different circuit boards, it is necessary to correct the error through a calibration method. A high-precision temperature calibration method based on NTC adopted in an embodiment of the present invention includes the following steps:

[0027] 1) Every time the NTC temperature sensor changes by 1 degree, the corresponding resistance value forms an RT table, and the RT table is written into the program;

[0028] 2) Connect an external resistor box and adjust the resistance value of the resistor box to make it consistent with the resistance value of the NTC temperature sensor. The resistance value of the resistor box and the voltage value collected by the current AD converter form an RV table, and the RV table is written into the program;

[0029] 3) Adjust the resistance value of the resistance box so that the resistance value of the resistance box is consistent with the temperature at both ends of the measurement range of the NTC temperature sensor. At this time, the two sets of voltage values ​​collected by the AD converter are used to calculate two parameters k and b with the two sets of voltages corresponding to step 2) and save them in the MCU controller;

[0030] 4) The MCU controller collects the voltage value X through the AD converter, calculates the latest voltage value through the formula k*X+b, and obtains the resistance value R through the RV table in step 2), and then obtains the temperature value through the RT table in step 1. The current temperature value is the actual value of the NTC temperature sensor.

[0031] The above calibration method is applicable to the calibration of the error caused by a circuit of a certain range in a high-precision temperature measurement circuit based on NTC of the present invention, and the error caused by a circuit of another range can be calibrated using the same principle.

[0032] The resistance value and temperature value of the NTC temperature sensor of the present invention are in a one-to-one correspondence. The resistance value of the NTC temperature sensor is simulated by a resistance box. The measurement error of the calibrated measurement circuit in the full range is less than 0.1 degrees, achieving a truly high-precision level.

[0033] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Any simple modification and equivalent changes made to the above embodiments based on the technical essence of the present invention shall fall within the protection scope of the present invention.

Claims

1. A high-precision temperature calibration method based on NTC, which calibrates two temperature measurement ranges of a high-precision temperature measurement circuit based on NTC respectively. The NTC-based high-precision temperature measurement circuit comprises an NTC temperature sensor, a voltage-dividing resistor, a MOS switching switch module, a filter, an AD converter and an MCU controller; the NTC temperature sensor is respectively connected to the voltage-dividing resistor, the MOS switching switch module, a reference ground and the filter, and the other end of the voltage-dividing resistor is connected to the AD converter; the input end of the filter is connected to the NTC temperature sensor and the reference ground, the output end of the filter is connected to the AD converter, and the AD converter is connected to the MCU controller; the MOS switching switch module is used to control whether the NTC temperature sensor is connected in parallel with the resistor to switch different temperature measurement ranges; It is characterized in that The steps include: 1) Every time the NTC temperature sensor changes by 1 degree, the corresponding resistance value forms an RT table, and the RT table is written into the program; 2) Connect an external resistor box and adjust the resistance value of the resistor box to make it consistent with the resistance value of the NTC temperature sensor. The resistance value of the resistor box and the voltage value collected by the current AD converter form an RV table, and the RV table is written into the program; 3) Adjust the resistance value of the resistance box so that the resistance value of the resistance box is consistent with the temperature at both ends of the measurement range of the NTC temperature sensor. At this time, the two sets of voltage values ​​collected by the AD converter and the two sets of voltages corresponding to step 2) are used to calculate two parameters k and b, and save them in the MCU controller; 4) The MCU controller collects the voltage value X through the AD converter, calculates the latest voltage value through the formula k*X+b, and obtains the resistance value R through the RV table in step 2), and then obtains the temperature value through the RT table in step 1. The current temperature value is the actual value of the NTC temperature sensor.

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