CN106404207B - Wide-range high-precision temperature measuring instrument based on platinum resistor and measuring method thereof - Google Patents
Wide-range high-precision temperature measuring instrument based on platinum resistor and measuring method thereof Download PDFInfo
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- CN106404207B CN106404207B CN201610978073.7A CN201610978073A CN106404207B CN 106404207 B CN106404207 B CN 106404207B CN 201610978073 A CN201610978073 A CN 201610978073A CN 106404207 B CN106404207 B CN 106404207B
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Abstract
The invention discloses a wide-range high-precision temperature measuring instrument based on a platinum resistor and a measuring method thereof, wherein the temperature measuring width is-200-800 ℃, and the wide-range high-precision temperature measuring instrument based on the platinum resistor comprises the following components: the temperature control circuit comprises a power supply circuit (1), a constant current source driving circuit (2), a temperature sensor (3), a signal processing circuit (4), an A/D conversion circuit (5), a single chip microcomputer (6), a display (7), a storage (8), a key module (9), a reset circuit (10), a crystal oscillator circuit (11), a temperature calibration module (12) and a data signal processing module (13). The invention meets the measurement requirement, and the temperature measurement precision of the calibrated high-precision temperature measuring instrument reaches five thousandths of a year in the temperature measurement interval of 0-100 ℃. The temperature measurement precision is high, the temperature measurement range is wide, the price is low, and the economic value and the social value are great.
Description
Technical Field
The invention relates to the technical field of structural design and application of temperature measuring instruments, and particularly provides a wide-range high-precision temperature measuring instrument based on a platinum resistor and a measuring method thereof.
Background
The temperature measurement provides a basis for people to know the temperature and the application temperature, and the temperature measurement device is widely applied to actual production and life, and the application range of the temperature measurement device is from daily life to scientific research. The high-precision temperature measurement technology is the key for improving the control of the ambient temperature, which makes the high-precision temperature measurement technology a non-negligible factor in the industrial development. Therefore, it is necessary to design a high-precision temperature measuring instrument with high precision and wide temperature measuring range, which will greatly promote the development of our society and bring great convenience to the production and life of people.
People urgently want to obtain a high-precision temperature measuring instrument with excellent technical effect.
Disclosure of Invention
The invention aims to provide a wide-range high-precision temperature measuring instrument based on a platinum resistor and a measuring method thereof.
The wide-range high-precision temperature measuring instrument based on the platinum resistor and the measuring method thereof comprise the following steps: the device comprises a power supply circuit 1, a constant current source driving circuit 2, a temperature sensor 3, a signal processing circuit 4, an A/D conversion circuit 5, a singlechip 6, a display 7, a storage 8, a key module 9, a reset circuit 10, a crystal oscillator circuit 11, a temperature calibration module 12 and a data signal processing module 13; wherein, the power supply circuit 1 is electrically connected with the constant current source driving circuit 2, the A/D conversion circuit 5 and the singlechip 6, the constant current source driving circuit 2 is electrically connected with the signal processing circuit 4, the signal processing circuit 4 comprises equivalent resistors of four leads connected with the temperature sensor 3, namely a first resistor, a second resistor, a third resistor and a fourth resistor, wherein the first resistor, the constant current source driving circuit 2, the second resistor and the temperature sensor 3 are sequentially connected in series through leads to form a loop, one end of the third resistor is connected between the first resistor and the temperature sensor 3 through leads, the other end of the third resistor is connected with an A/D sampling compensation line of the A/D conversion circuit 5, one end of the fourth resistor is connected between the second resistor and the temperature sensor 3 through leads, the other end of the fourth resistor is connected with a ground compensation line, the signal processing circuit 4 is connected with the single chip microcomputer 6 through the A/D conversion circuit 5, the display 7, the storage 8, the key module 9, the reset circuit 10 and the crystal oscillator circuit 11 are respectively connected with the single chip microcomputer 6, the key module 9 is connected with the data signal processing module 13 through the temperature calibration module 12, and the data signal processing module 13 is connected with the single chip microcomputer 6.
The temperature sensor 3 adopts a PT100 platinum resistance sensor, the constant current source driving circuit 2 is connected with a high-precision resistor with high temperature stability coefficient, the temperature change coefficient of the high-precision resistor is 1ppm, namely the temperature changes by 1 ℃, and the resistance value changes by 106And omega, the current output by the constant current source driving circuit 2 cannot be larger than 4 mA.
The A/D conversion circuit 5 adopts a 24-bit LTC2492 analog-to-digital converter, and the precision of the A/D conversion circuit can reach VREF/224。
The measuring method divides a temperature measuring range into a plurality of sections according to the relation that the environmental temperature change of a platinum resistor is close to linearity with the resistance value of the resistor, wherein each section is linear, the resolution ratio of PT100 can reach 1mK, a signal processing circuit 4 adopts an improved four-wire connection method, simultaneously collects the voltage of the platinum resistor and the reference voltage, and provides a stable and continuous current for the circuit by a constant current source, thereby eliminating the influence of temperature drift caused by the error of a connected lead resistor and the exciting current of the platinum resistor on temperature measurement. The data processing adopts a function approximation algorithm and a temperature correction algorithm, and two points of temperature of each section are selected for correction, so that the theoretical calculation precision can reach 0.001 ℃.
The A/D conversion circuit 5 adopts a 24-bit LTC2492 analog-to-digital converter, and the precision of the A/D conversion circuit can reach VREF/224，VREFApproximately equal to 1.1V, using the formula Rt＝R0(1+At+Bt2+C(t-100)t3) And formula Rt＝(1+At+Bt2) And solving by adopting a numerical approximation algorithm.
When the ambient temperature of the platinum resistor is changed between-200 ℃ and 800 ℃, the change of the ambient temperature and the resistance value of the resistor are close to linear relation. The resistance value R of the PT platinum resistor is specified by the national standard at 0 DEG C0The characteristic curve is shown in fig. 1, which is 100 Ω.
Platinum resistors have mainly resistance and allow two kinds of errors. Wherein, the allowable error of A is equal to + - (0.15+0.002t), the allowable error of B is equal to + - (0.30+0.005t), and t represents the temperature value.
When t is more than or equal to-200 ℃ and less than or equal to 0 ℃, the function expression of the resistance value of the platinum resistor and the temperature change is as follows:
Rt＝R0(1+At+Bt2+C(t-100)t3) (1)
when t is more than or equal to 0 ℃ and less than or equal to 850 ℃, the function expression of the resistance value of the platinum resistor and the temperature change is as follows:
Rt＝(1+At+Bt2) (2)
in the formula, RtRepresents the resistance value, R, of the platinum resistor at t DEG C0Representing the resistance of the platinum resistor at 0 deg.C, the resistor selected in the design process is Pt, R of standard Pt0Equal to ohms. A. B, C are the values: a 3.9082 × 10-3,B＝-5.80195×10-7,C＝-4.2735×10-12。
According to the principle, a numerical approximation algorithm is utilized, an array is taken and stored with the following data, the array is set to be T (K) in a program, the array has 24 data in total, and the data are as follows:
8388.608,4194.304,2097.152,1048.576,0524.288,0262.144,0131.072,0065.536,0032.768,0016.384,0008.192,0004.096,0002.048,0001.024,0000.512,0000.256,0000.128,0000.064,0000.032,0000.016,0000.008,0000.004,0000.002,0000.001。
the program adopts a loop accumulation mode, when K is equal to 1, 8388.608 is substituted into the formula (2), the resistance value is calculated, and the value R is calculatedTThe resistance value R of the platinum resistor actually measuredPT100Making a comparison, if greater than the actual measured resistance value, i.e. RT＞RPT100Then, this data is not accumulated, if it is smaller than the actually measured resistance value, i.e., RT＜RPT100Then, this data is accumulated. And circulating for 24 times once, and finally adding the T (K) values meeting the conditions to obtain a calculated value of the platinum resistance temperature.
The signal processing circuit 4 adopts an improved four-wire wiring method to ensure the measurement precision and stability. X in FIG. 51、X2、X3、X4The equivalent resistances of the four leads of the platinum resistance sensor, respectively. With R4The voltage value of the resistor is used as the reference voltage R in the design4The value is 510 Ω, and the measurement accuracy and stability of the circuit are seriously affected by the design of the reference voltage and the constant current source. Reference voltage VREFWhether the temperature is stable or not and the temperature is low are important preconditions for ensuring that the high-precision temperature measuring instrument has high precision. The mirror current source formed by the triode 8550 is used for reducing external interference and avoiding errors. On the basis, a high-precision resistor R is connected in series0Temperature variation of the high precision resistorThe coefficient of variation is 1ppm, i.e. 1 ℃ change in temperature, and the resistance change is 10-6Omega, R in this design0The value is Ω. According to the theory of electronic circuits, the current I of the platinum resistance PT sensor is as follows:
reference voltage VREFComprises the following steps:
VRef＝I×R4(4)
voltage and precision resistor R of PT sensor0The voltages of (a) are:
VPT100＝I×RPT100(5)
VR0＝I×R0(6)
finally, obtaining the voltage and the precision resistor R of the PT sensor0Is the ratio of the voltage of (a) to the voltage of (b), i.e.
Therefore, the current change of the constant current source due to temperature drift and other factors is eliminated, and the output voltage ratio and the platinum resistor form a good linear relation.
The obtained voltage signal is sampled by a 24-bit A/D converter LTC2492, and then the signal is sent to an ATmega32 single chip microcomputer which carries out data processing and stores and displays data. The stability of the designed temperature measurement of the circuit can reach 1 per thousand.
The invention uses ATmega32 single chip as the core device of the control circuit, 24-bit LTC2492 as A/D converter, the temperature sensor selects PT100, the temperature measuring width is-200-800 ℃, because the PT100 sensor allows the current not higher than 4mA, the minimum embedded depth can not be less than 200mm, the precision is as high as 1mK, the PT100 temperature is linearly changed along with the resistance value, the sampling circuit adopts the improved four-wire connection method, collects the platinum resistance voltage and the reference voltage at the same time, and uses the constant current source to provide a stable and continuous current for the circuit, and eliminates the influence of the temperature drift caused by the resistance error of the connected lead and the platinum resistance exciting current on the temperature measurement. The data processing adopts a function approximation algorithm and a temperature correction algorithm, so that high-precision temperature measurement is realized, and the theoretical calculation precision can reach 0.001 ℃.
The invention meets the measurement requirement, and the temperature measurement precision of the calibrated high-precision temperature measuring instrument reaches five thousandths of a year in the temperature measurement interval of 0-100 ℃. The temperature measurement precision is high, the temperature measurement range is wide, the price is low, and the economic value and the social value are great.
Drawings
FIG. 1 is a characteristic curve of platinum resistance;
FIG. 2 is a schematic diagram of temperature measurement;
FIG. 3 is a schematic diagram of a wide-range high-precision temperature measuring instrument based on platinum resistors and a measuring method thereof;
FIG. 4 is a four-wire wiring diagram of a platinum resistor;
FIG. 5 is a constant current source drive circuit diagram;
FIG. 6 is a schematic diagram of LTC 2492;
FIG. 7 is a circuit diagram of a key module;
FIG. 8 is a flow chart of a wide-range high-precision temperature measuring instrument based on platinum resistors and a measuring method thereof;
Detailed Description
As shown in fig. 3, a power supply circuit 1, a constant current source driving circuit 2, a temperature sensor 3, a signal processing circuit 4, an a/D conversion circuit 5, a single chip microcomputer 6, a display 7, a storage 8, a key module 9, a reset circuit 10, a crystal oscillator circuit 11, a temperature calibration module 12, and a data signal processing module 13; wherein, the power supply circuit 1 is electrically connected with the constant current source driving circuit 2, the A/D conversion circuit 5 and the singlechip 6, the constant current source driving circuit 2 is electrically connected with the signal processing circuit 4, the signal processing circuit 4 comprises equivalent resistors of four leads connected with the temperature sensor 3, namely a first resistor, a second resistor, a third resistor and a fourth resistor, wherein the first resistor, the constant current source driving circuit 2, the second resistor and the temperature sensor 3 are sequentially connected in series through leads to form a loop, one end of the third resistor is connected between the first resistor and the temperature sensor 3 through leads, the other end of the third resistor is connected with an A/D sampling compensation line of the A/D conversion circuit 5, one end of the fourth resistor is connected between the second resistor and the temperature sensor 3 through leads, the other end of the fourth resistor is connected with a ground compensation line, the signal processing circuit 4 is connected with the single chip microcomputer 6 through the A/D conversion circuit 5, the display 7, the storage 8, the key module 9, the reset circuit 10 and the crystal oscillator circuit 11 are respectively connected with the single chip microcomputer 6, the key module 9 is connected with the data signal processing module 13 through the temperature calibration module 12, and the data signal processing module 13 is connected with the single chip microcomputer 6.
The A/D conversion circuit 5 adopts a 24-bit LTC2492 analog-to-digital converter, and the precision of the A/D conversion circuit can reach VREF/224，VREFApproximately equal to 1.1V, using the formula Rt＝R0(1+At+Bt2+C(t-100)t3) And formula Rt＝(1+At+Bt2) And solving by adopting a numerical approximation algorithm.
The key module 9 includes 4 control keys, specifically 1 ESC key, 1 ↓ direction key and 1 ↓ direction key, one end of 4 control keys is grounded, and the other end is connected with an I/O port and a pull-up resistor.
As shown in fig. 1, when the temperature of the environment in which the platinum resistor is placed varies between-200 ℃ and 800 ℃, the change of the temperature of the environment in which the platinum resistor is placed and the resistance value of the resistor are approximately in a linear relationship. The resistance value R of the PT platinum resistor is specified by the national standard at 0 DEG C0The characteristic curve is shown in fig. 1, which is 100 Ω.
Platinum resistors have mainly resistance and allow two kinds of errors. Wherein, the allowable error of A is equal to + - (0.15+0.002t), the allowable error of B is equal to + - (0.30+0.005t), and t represents the temperature value.
When t is more than or equal to-200 ℃ and less than or equal to 0 ℃, the function expression of the resistance value of the platinum resistor and the temperature change is as follows:
Rt＝R0(1+At+Bt2+C(t-100)t3) (1)
when t is more than or equal to 0 ℃ and less than or equal to 850 ℃, the function expression of the resistance value of the platinum resistor and the temperature change is as follows:
Rt＝(1+At+Bt2) (2)
in the formula, RtRepresenting the resistance of platinum at t DEG CResistance value, R0Representing the resistance of the platinum resistor at 0 deg.C, the resistor selected in the design process is Pt, R of standard Pt0Equal to ohms. A. B, C are the values: a 3.9082 × 10-3,B＝-5.80195×10-7,C＝-4.2735×10-12。
According to the principle, a numerical approximation algorithm is utilized, an array is taken and stored with the following data, the array is set to be T (K) in a program, the array has 24 data in total, and the data are as follows:
8388.608,4194.304,2097.152,1048.576,0524.288,0262.144,0131.072,0065.536,0032.768,0016.384,0008.192,0004.096,0002.048,0001.024,0000.512,0000.256,0000.128,0000.064,0000.032,0000.016,0000.008,0000.004,0000.002,0000.001。
the program adopts a loop accumulation mode, when K is equal to 1, 8388.608 is substituted into the formula (2), the resistance value is calculated, and the value R is calculatedTThe resistance value R of the platinum resistor actually measuredPT100Making a comparison, if greater than the actual measured resistance value, i.e. RT＞RPT100Then, this data is not accumulated, if it is smaller than the actually measured resistance value, i.e., RT＜RPT100Then, this data is accumulated. And circulating for 24 times once, and finally adding the T (K) values meeting the conditions to obtain a calculated value of the platinum resistance temperature.
In reality, the platinum resistor temperature and the resistor do not always satisfy such a simple linear relationship, and the platinum resistor temperature and the resistor are influenced by other conditions and have deviation.
The high-precision temperature measuring instrument selects the platinum resistor as a temperature measuring sensor, and the platinum resistor adopts an improved four-wire wiring method, so that errors caused by lead resistance in temperature measurement can be effectively avoided. The constant current power supply provides a stable and continuous current for the platinum resistor, the resistance value change of the platinum resistor caused in the temperature change process is converted into an electric signal and then transmitted to the A/D converter to be converted into a digital signal, the digital signal is received, analyzed and processed by the singlechip, the calculation result is corrected, if necessary, the system can be initialized by an external key module of the singlechip, and finally, the data processed by the singlechip is displayed through a nixie tube. The working principle is shown in fig. 2.
The platinum resistor PT100 temperature sensor is manufactured according to the characteristic that a platinum resistor changes along with temperature, when the environment temperature to be detected changes, the resistance value of the platinum resistor changes along with the temperature, so that a temperature signal is converted into a resistance signal, and the resistance signal is converted into a voltage signal by detecting the voltage value of the platinum resistor. The 24-bit LTC 2492A/D converter reads the voltage of the platinum resistor PT and the voltage of the high-precision resistor, respectively, and converts the read voltage signals into digital signals. The digital signal is transmitted to an ATMEGA32 singlechip, the microprocessor analyzes and operates the digital signal according to a program which is written by taking a function approximation algorithm as a core in advance, so that the measured temperature of the environment to be measured is obtained, and finally the measured temperature is displayed through a nixie tube.
The signal processing circuit 4 adopts a four-wire wiring mode, which means that two wires are respectively connected and led at two sides of the temperature sensor 3, namely a platinum resistor, and the method is a high-precision temperature measurement method. The two-wire system wiring method is respectively externally connected with an A/D sampling compensation wire and an A/D ground compensation wire. The wire at one end of the platinum resistor converts the change of the platinum resistor into an electric signal, and the other two wires transmit the electric signal to the signal processor. The wiring mode completely eliminates the influence of lead resistance, and can be used in places with high precision and long distance. Meanwhile, the current output by the constant current source is controlled within 4mA, so that the phenomenon that the platinum resistor is overheated due to overlarge current to bring errors to measurement is avoided.
The constant current source has infinite resistance and is not influenced by temperature change, so that the constant current source is widely applied to circuit design and mainly used for providing a constant current which does not change along with load change for the designed circuit. The variation of the resistance of the platinum resistor needs to be accurately measured in a design circuit of the high-precision thermometer, so that the variation of the resistance can be converted into an electric signal and then converted into a digital signal, and the temperature of the environment to be measured is obtained. The constant current source is a precondition for accurately measuring the resistance value of the platinum resistor.
The design of the reference voltage and the constant current source seriously influences the measurement precision and the stability of the circuit. Reference voltage VREFWhether or not it is stable andthe low temperature drift is an important precondition for ensuring high precision of the high precision temperature measuring instrument in the text; meanwhile, it is also necessary to provide a stable constant current source for the platinum resistance temperature sensor adopting a four-wire system wiring mode, and the passing current of the platinum resistance temperature sensor cannot be higher than 4mA absolutely.
As shown in fig. 4, the signal processing circuit 4 adopts an improved four-wire wiring method to ensure the accuracy and stability of the measurement. X in FIG. 51、X2、X3、X4The equivalent resistances of the four leads of the platinum resistance sensor, respectively. With R4The voltage value of the resistor is used as the reference voltage R in the design4The value is 510 Ω, and the measurement accuracy and stability of the circuit are seriously affected by the design of the reference voltage and the constant current source. Reference voltage VREFWhether the temperature is stable or not and the temperature is low are important preconditions for ensuring that the high-precision temperature measuring instrument has high precision. The mirror current source formed by the triode 8550 is used for reducing external interference and avoiding errors. On the basis, a high-precision resistor R is connected in series0The temperature change coefficient of the high-precision resistor is 1ppm, namely the temperature change is 1 ℃, and the resistance value change is 10-6Omega, R in this design0The value is Ω. According to the theory of electronic circuits, the current I of the platinum resistance PT sensor is as follows:
reference voltage VREFComprises the following steps:
VRef＝I×R4(4)
voltage and precision resistor R of PT sensor0The voltages of (a) are:
VPT100＝I×RPT100(5)
VR0＝I×R0(6)
finally, obtaining the voltage and the precision resistor R of the PT sensor0Is the ratio of the voltage of (a) to the voltage of (b), i.e.
Therefore, the current change of the constant current source due to temperature drift and other factors is eliminated, and the output voltage ratio and the platinum resistor form a good linear relation.
The obtained voltage signal is sampled by a 24-bit A/D converter LTC2492, and then the signal is sent to an ATmega32 single chip microcomputer which carries out data processing and stores and displays data. The stability of the designed temperature measurement of the circuit can reach 1 per thousand.
TABLE 1 simulation data of high-precision temperature measuring instrument
According to the design circuit shown in fig. 5 and the flow chart of the system structure shown in fig. 3, the test verification of the circuit of the system simulates the test of a platinum resistor temperature sensor by changing the resistance value of a potentiometer, the resistance value of the potentiometer is measured by using a five-bit half-desktop multimeter 8808A for calibration, and part of measurement data is shown in table 1. Measuring the sampled data, V, according to the system of Table 1100Is indicative of a precision resistance R0Voltage of VPT100The resistance value of the platinum resistance sensor can be calculated by the formula (7), and then the temperature measurement value is solved by the formulas (1) and (2). Through data calculation, the average error is 1.1 per mill, and the maximum error is 4 per mill.
In order to ensure the precision and stability of measurement, a mirror current source which takes a resistance of 510 ohms as a reference voltage and consists of a triode 8550 is designed to reduce external interference and avoid errors. On the basis, an ohmic high-precision resistor is connected in series, the temperature changes by 1 ℃, and the resistance change value of the high-precision resistor is 106And one-fourth. In order to ensure the temperature measurement precision and stability of the high-precision measuring instrument designed by the invention, a voltage value is obtained by respectively taking analog voltages as ratios by using an ohmic high-precision resistor and PT. The circuit design is shown in the figure5。
The A/D conversion circuit 5 mainly functions to convert an analog signal into a digital signal, and the system is independently designed with an A/D converter. The ADC selects 0.5LSB, 1LSB ═ V voltage resolutionREF/224，VREFHas a value range of 0.1 to VCCAnd a 24-bit LTC2492, which completely meets the precision requirement of the system, and the design of the LTC2492 is shown in FIG. 6.
In order to facilitate parameter setting and temperature calibration of the high-precision thermometer, the key module 9 is specially designed, the key module 9 comprises 4 control keys, and the functions of the control keys are ESC, ENTER and two direction keys respectively. In order to realize the control function of the circuit, one end of each of the 4 control keys is grounded, and the other end of each control key is connected with an I/O port and a pull-up resistor. Each key on the keyboard is equal to a mechanical switch, when the key is pressed, the circuit is in a connected state, and at the moment, the corresponding singlechip port line is at a low level; when the key is released, the whole circuit is in a disconnected state, and the port line corresponding to the single chip microcomputer is at a high level. The circuit of the key module is shown in fig. 7.
The key module 9 adopts independent keys, can be directly connected with the I/O lines to form a single key circuit, each key is independently connected with one I/O port line and is in an independent state, and the key arrangement mode avoids influencing other I/O port lines. The design of the circuit diagram adopts low level to be effective, and when the key is disconnected, the pull-up resistor ensures that the I/O port line has high level.
The temperature calibration module 12 is mainly used for linearly calibrating the value of the measured temperature, and the error of the temperature value measured by the system mainly consists of the difference of the sensors, the difference of the constant current sources, the error caused by the analog-to-digital converter, the error generated by solving the temperature equation, and the like. The formula of the correction equation is as follows: before calculation, two parameters a and b in the equation need to be determined, the two parameters a and b can be obtained by comparing two measured values with a standard temperature value, and x is substituted into the formula: in y ═ ax + b, the solved y is the corrected result. In determining both a and b parameters, two points, 0 ℃ and 100 ℃, are preferably selected as two-point measurements.
When t is more than or equal to-200 ℃ and less than or equal to 0 ℃, the function expression of the resistance value of the platinum resistor and the temperature change is as follows:
Rt＝R0(1+At+Bt2+C(t-100)t3) (1)
when t is more than or equal to 0 ℃ and less than or equal to 850 ℃, the function expression of the resistance value of the platinum resistor and the temperature change is as follows:
Rt＝(1+At+Bt2) (2)
corrected by the system. The temperature gauge test data are shown in tables 2 and 3.
Table 2 final test data for ice-water mixtures after calibration
Table 3 boiling water final test data after calibration
According to the characteristic curve of the platinum resistor, the calculation formula of a correction equation is as follows: and y is ax + b. The numerical value of the measured temperature is linearly calibrated through a temperature calibration parameter program, and the difference of the constant current source, the error caused by the analog-to-digital converter, the error generated by solving a temperature equation and the like are comprehensively considered and can be corrected by using a linear equation. Before calculation, two parameters a and b in an equation are determined, the two parameters a and b can be obtained by a method of comparing two-point measurement values with a standard temperature value, two points of 0 ℃ and 100 ℃ are selected as two-point measurement values to solve the two parameters a and b, and x is substituted into the formula: in y ═ ax + b, the solved y is the corrected result.
According to the wide-range high-precision temperature measuring instrument based on the platinum resistor and the measuring method thereof, the measuring requirements are met by comparing the measuring data of the temperature measuring instrument before and after calibration, and the temperature measuring precision of the calibrated high-precision temperature measuring instrument reaches five thousandths of the temperature in the temperature measuring interval of 0-100 ℃. The temperature measurement precision is high, the temperature measurement range is wide, the price is low, and the economic value and the social value are great.
Claims (1)
1. The utility model provides a wide range high accuracy temperature measurement appearance based on platinum resistance which characterized in that: the temperature control circuit comprises a power supply circuit (1), a constant current source driving circuit (2), a temperature sensor (3), a signal processing circuit (4), an A/D conversion circuit (5), a single chip microcomputer (6), a display (7), a storage (8), a key module (9), a reset circuit (10), a crystal oscillator circuit (11), a temperature calibration module (12) and a data signal processing module (13); wherein, the power circuit (1) is electrically connected with the constant current source driving circuit (2), the A/D conversion circuit (5) and the singlechip (6), the constant current source driving circuit (2) is electrically connected with the signal processing circuit (4), the signal processing circuit (4) comprises equivalent resistors of four leads connected with the temperature sensor (3), namely a first resistor, a second resistor, a third resistor and a fourth resistor, wherein the first resistor, the constant current source driving circuit (2), the second resistor and the temperature sensor (3) are sequentially connected in series through leads to form a loop, one end of the third resistor is connected between the first resistor and the temperature sensor (3) through leads, the other end of the third resistor is connected with an A/D sampling compensation line of the A/D conversion circuit (5), one end of the fourth resistor is connected between the second resistor and the temperature sensor (3) through leads, the other end of the fourth resistor is connected with a ground compensation line, a signal processing circuit (4) is connected with a single chip microcomputer (6) through an A/D conversion circuit (5), a display (7), a storage (8), a key module (9), a reset circuit (10) and a crystal oscillator circuit (11) are respectively connected with the single chip microcomputer (6), the key module (9) is connected with a data signal processing module (13) through a temperature calibration module (12), the data signal processing module (13) is connected with the single chip microcomputer (6), the temperature sensor (3) adopts a PT100 platinum resistance sensor, the constant current source driving circuit (2) is connected with a high-precision resistor with a high temperature stability coefficient and a temperature variation coefficient of 1ppm, the current output by the constant current source driving circuit (2) cannot be more than 4mA, the A/D conversion circuit (5) adopts a 24-bit LTC2492 analog-to-digital converter, the precision can reach VREF/224，VREFApproximately equal to 1.1V, using the formula Rt＝R0(1+At+Bt2+C(t-100)t3) And formula Rt＝(1+At+Bt2) Using a numerical approximation algorithm to solve whenWhen the environment temperature of the PT100 platinum resistance sensor is changed between-200 ℃ and 800 ℃, the relation between the change of the environment temperature and the resistance value of the resistance is close to linearity, and the resistance value R of the PT100 platinum resistance sensor is regulated by the national standard at 0 DEG C0The PT100 PT resistance sensor mainly has two errors, namely resistance and tolerance, where a tolerance is ± (0.15+0.002t), B tolerance is ± (0.30+0.005t), where t represents a temperature value;
when t is more than or equal to-200 ℃ and less than or equal to 0 ℃, the function expression of the resistance value and the temperature change of the PT100 platinum resistance sensor is as follows:
Rt＝R0(1+At+Bt2+C(t-100)t3) (1)
when t is more than or equal to 0 ℃ and less than or equal to 850 ℃, the function expression of the resistance value and the temperature change of the PT100 platinum resistance sensor is as follows:
Rt＝(1+At+Bt2) (2)
in the formula, RtRepresents the resistance value, R, of the PT100 platinum resistance sensor at t DEG C0Representing the resistance value of the PT100 platinum resistance sensor at 0 ℃, the values of A, B, C were: a 3.9082 × 10-3,B＝-5.80195×10-7,C＝-4.2735×10-12；
According to the principle, a numerical approximation algorithm is utilized, an array is taken and stored with the following data, the array is set to be T (K) in a program, the array has 24 data in total, and the data are as follows:
8388.608,4194.304,2097.152,1048.576,0524.288,0262.144,0131.072,0065.536,0032.768,0016.384,0008.192,0004.096,0002.048,0001.024,0000.512,0000.256,0000.128,0000.064,0000.032,0000.016,0000.008,0000.004,0000.002,0000.001, respectively; the program adopts a loop accumulation mode, when K is equal to 1, 8388.608 is substituted into the formula (2), the resistance value is calculated, and the value R is calculatedTThe resistance value R of the PT100 platinum resistance sensor actually measuredPT100Making a comparison, if greater than the actual measured resistance value, i.e. RT>RPT100Then, this data is not accumulated, if it is smaller than the actually measured resistance value, i.e., RT<RPT100If so, accumulating the data; one circulation for 24 times, the mostFinally, adding the T (K) values meeting the conditions to obtain a calculated value of the temperature of the PT100 platinum resistance sensor; the measuring method of the wide-range high-precision temperature measuring instrument based on the platinum resistor divides the temperature measuring range into a plurality of sections according to the relation that the environment temperature change of the PT100 platinum resistor sensor is close to linearity with the resistance value of the resistor, wherein each section is linear, the resolution ratio of the PT100 platinum resistor sensor can reach 1mK, the signal processing circuit (4) adopts an improved four-wire connection method, namely, two sides of the temperature sensor (3), namely the PT100 platinum resistor sensor, are respectively connected with two wires, the two wires are respectively externally connected with an A/D sampling compensation wire and an A/D ground compensation wire on the two-wire connection method, wherein the wire at one end of the PT100 platinum resistor sensor converts the change of the PT100 platinum resistor sensor into an electric signal, the A/D sampling compensation wire and the A/D ground compensation wire transmit the electric signal to a signal processor, and simultaneously collect the voltage and the reference voltage of the PT100 platinum resistor sensor, and a constant current source is used for providing a stable and continuous current for the circuit, eliminating the influence of temperature drift caused by the error of the resistance of an access lead and the exciting current of the PT100 platinum resistance sensor on temperature measurement, the data processing adopts a function approximation algorithm and a temperature correction algorithm, two points of each section of temperature are selected for correction, R is1、R2、R3、R4Equivalent resistances of four leads of the PT100 platinum resistance sensor, respectively; with R4The voltage value of the resistor is used as a reference voltage, R4The value is 510 Ω; a mirror current source formed by a triode 8550; on the basis, a high-precision resistor R is connected in series0High precision resistor R0Has a temperature coefficient of variation of 1ppm, i.e., a temperature variation of 1 ℃ and a resistance variation of 10-6Ω，R0100 Ω; according to the theory of electronic circuits, the current I of the PT100 platinum resistance sensor is as follows:
reference voltage VRefComprises the following steps:
VRef＝I×R4(4)
voltage and high accuracy of PT100 platinum resistance sensorClosed resistance R0The voltages of (a) are:
VPT100＝I×RPT100(5)
VR0＝I×R0(6)
finally, the voltage and the high-precision resistance R of the PT100 platinum resistance sensor are obtained0Is the ratio of the voltage of (a) to the voltage of (b), i.e.
Sampling the obtained voltage signal through an A/D conversion circuit (5), then sending the signal to a single chip microcomputer (6), and carrying out data processing and storing and displaying data by the single chip microcomputer (6); the circuit test verification simulates the test of a PT100 platinum resistance sensor by changing the resistance value of a potentiometer, the resistance value of the potentiometer is measured by using a five-bit half-desk multimeter 8808A for calibration, part of measured data is taken, and V is calculated according to the dataR0Is to represent a high precision resistance R0Voltage of VPT100The voltage of the PT100 platinum resistance sensor is calculated by the formula (7), the resistance value of the PT100 platinum resistance sensor is calculated by the formula (1) and the formula (2), and the temperature measurement value is solved by the formula (1) and the formula (2), and the average error is 1.1 per thousand and the maximum error is 4 per thousand by data calculation;
the key module (9) comprises 4 control keys, and the functions of the key module are ESC, ENTER and two direction keys respectively; in order to realize the control function of the circuit, one end of each of the 4 control keys is grounded, and the other end of each control key is connected with an I/O port and a pull-up resistor; each key on the keyboard is equal to a mechanical switch, when the key is pressed, the circuit is in a connected state, and at the moment, the corresponding singlechip port line is at a low level; when the key is released, the whole circuit is in a disconnected state, and the port line corresponding to the singlechip is at a high level;
the temperature calibration module (12) is mainly used for carrying out linear calibration on the numerical value of the measured temperature and can be corrected by a linear equation; the formula of the correction equation is as follows: before calculation, two parameters a and b in the equation need to be determined, the two parameters a and b can be obtained by comparing two measured values with a standard temperature value, and x is substituted into the formula: in y ═ ax + b, the solved y is the corrected result; in determining both parameters a and b, two points of 0 ℃ and 100 ℃ were selected as two-point measurements.
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