CN102768078B - Automatic resistance compensation method for temperature-measuring conductors for two-wire thermal resistor - Google Patents
Automatic resistance compensation method for temperature-measuring conductors for two-wire thermal resistor Download PDFInfo
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- CN102768078B CN102768078B CN201210223047.5A CN201210223047A CN102768078B CN 102768078 B CN102768078 B CN 102768078B CN 201210223047 A CN201210223047 A CN 201210223047A CN 102768078 B CN102768078 B CN 102768078B
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- 239000004020 conductor Substances 0.000 title claims abstract description 22
- 238000000034 method Methods 0.000 title claims abstract description 19
- 238000009529 body temperature measurement Methods 0.000 claims abstract description 16
- 239000003990 capacitor Substances 0.000 claims abstract description 13
- 238000005070 sampling Methods 0.000 claims description 27
- 238000006243 chemical reaction Methods 0.000 claims description 3
- 238000012795 verification Methods 0.000 claims description 2
- 238000005259 measurement Methods 0.000 abstract description 2
- 230000001052 transient effect Effects 0.000 abstract 1
- 230000000694 effects Effects 0.000 description 5
- 238000010586 diagram Methods 0.000 description 3
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- 230000009286 beneficial effect Effects 0.000 description 1
- 238000001514 detection method Methods 0.000 description 1
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- 238000002474 experimental method Methods 0.000 description 1
- 239000000463 material Substances 0.000 description 1
- 230000005855 radiation Effects 0.000 description 1
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Abstract
The invention relates to an automatic resistance compensation method for temperature-measuring conductors for a two-wire thermal resistor. Capacitors are connected to two ends of a thermal resistor in parallel according to characteristics of the capacitors. Before powering on, capacitance is zero, namely no charge is carried, capacitive reactance is smallest, power-on transient current is high, and short-circuit occurs nearly. After a time of powering on, the capacitors are fully charged, and the capacitive reactance is largest and causes disconnection. A constant current source is used to supply power. An acquisition circuit acquires voltages of the two-wire thermal resistor respectively when the capacitors are fully charged and powerless, the two voltages are subtracted from each other, voltage drop due to two wire resistance values is removed, and an accurate value of the thermal resistor is obtained by calculating. The automatic resistance compensation method for temperature-measuring conductors for the two-wire thermal resistor is applicable to various temperature measurements in industrial field, precision is greatly improved as compared with that of common two-wire temperature measurement, a certain level of requirements are met, hardware resources can be saved, and the method is simple, efficient, economic and highly reliable and is applicable to various measurements in industrial fields.
Description
Technical field
The present invention relates to a kind of temperature measurement technology, particularly a kind of method of two-wire system Thermistor Temperature Measurement conductor resistance auto-compensation.
Background technology
Temperature is one of production process parameters the most frequently used in current commercial production, and measuring method and the device of therefore studying temperature are significant.Practical temperature sensor kind is a lot, take radiation temperature measurement abroad as main (accounting for 2/3), domestic thermopair and the thermal resistances (accounting for 98%) of adopting more.
The lead-in wire of thermal resistance mainly contains two-wire system, three-wire system and three kinds of modes of four-wire system at present.
Two-wire system: respectively connect mode that a wire draws resistance signal at the two ends of thermal resistance two-wire system.This lead-in wire method is very simple, but certainly exists lead resistance R owing to connecting wire, and the size of resistance R is relevant with the factor of the material of wire and length, and therefore this lead-in wire mode is only applicable to the occasion that measuring accuracy is lower.
Three-wire system: the one end at the root of thermal resistance connects a lead-in wire, the mode that the other end connects two lead-in wires is called three-wire system, this mode conventionally supports the use with electric bridge, can eliminate preferably the impact of lead resistance, is the most frequently used lead resistance in industrial process control.
Four-wire system: the mode that respectively connects two wires at the root two ends of thermal resistance is called four-wire system, wherein two lead-in wires, for thermal resistance provides steady current I, convert voltage signal U to R, then by another two lead-in wires, U are caused to secondary instrument.This lead-in wire mode can be eliminated the Resistance Influence of lead-in wire completely, is mainly used in high-precision temperature detection.
Therefore, not only there is the impact of conductor resistance on thermal resistance resistance in traditional two-wire system thermal resistance resistance measuring method, but also exist the temperature causing because of temperature variation to float.
Summary of the invention
The present invention be directed to two line system temp measuring accuracy low and be subject to the problem that extraneous thermal effect is large, a kind of method of two-wire system Thermistor Temperature Measurement conductor resistance auto-compensation has been proposed, utilize capacitor charge and discharge principle and function of the MCU, the ingenious thermoelectricity resistance that accurately calculates.
Technical scheme of the present invention is: a kind of method of two-wire system Thermistor Temperature Measurement conductor resistance auto-compensation, specifically comprises the steps:
1) set up sample circuit: circuit is comprised of interior single-chip microcomputer and constant current source with A/D conversion, and constant current source output connects two-wire system thermal resistance, and the A/D port of single-chip microcomputer connects two-wire system thermal resistance, an electric capacity in parallel at thermal resistance two ends, this electric capacity is sampling capacitance;
2) sampling: set the A/D converter sampling time, the port of constant current source switch is controlled in single-chip microcomputer output, first ports-settings is 1, close constant current source, to the discharge lag time, ports-settings is 0, open constant current source, to constant current source Current rise to the specified working current time, A/D converter starts sample voltage value, sampled value is assigned to V1, and then time delay is to the duration of charging, A/D converter gathers for the second time, collection value is for the second time assigned to V2, single-chip microcomputer calculates the voltage V3=V1-V2 on thermal resistance, voltage obtains thermal resistance resistance divided by constant current source output constant current value,
3) the V1 value capacitance verification: replace electric capacity with a shorting stub, A/D converter collects actual V1 value, comparison step 2), as two values are different, return to step 1) and changes after capacitor's capacity, repeating step 2) sampling, until two values are identical.
The described sampling capacitance duration of charging is less than the specified working current time of rising to of constant current source.
In described constant current source, single-chip microcomputer is selected MC9S12XS128 single-chip microcomputer, the A/D converter of inner 12 successive approximations.
Beneficial effect of the present invention is: the method for two-wire system Thermistor Temperature Measurement conductor resistance auto-compensation of the present invention, can be applicable in the various temperature surveys of industry spot, comparing common two line system temp measuring accuracy improves greatly, reach certain class requirement, can save hardware resource, simply, efficiently, economy, reliability is high, can be applicable in the various temperature surveys of industry spot.
Accompanying drawing explanation
Fig. 1 is that the method for two-wire system Thermistor Temperature Measurement conductor resistance auto-compensation of the present invention realizes circuit diagram;
Fig. 2 is constant current source powered on moment capacitance short-circuit isoboles in the method for two-wire system Thermistor Temperature Measurement conductor resistance auto-compensation of the present invention;
Fig. 3 is the method constant current source of the two-wire system Thermistor Temperature Measurement conductor resistance auto-compensation of the present invention electric capacity isoboles that opens circuit that powers on after certain hour;
Fig. 4 is the method program process flow diagram of two-wire system Thermistor Temperature Measurement conductor resistance auto-compensation of the present invention.
Embodiment
The method of two-wire system Thermistor Temperature Measurement conductor resistance auto-compensation is based on acquisition system, adds a sampling capacitance being skillfully constructed, and system is used the simplest equipment to solve a complicated problem.
As Fig. 1 circuit diagram, comprise by interior singlechip group and constant current source with A/D conversion and forming, constant current source output connects two-wire system thermal resistance and powers to it, the A/D port of single-chip microcomputer connects two-wire system thermal resistance, a capacitor C in parallel at thermal resistance two ends, this capacitor C is referred to as sampling capacitance, electric capacity is equivalent to one and contains electric container, it is capacitive to the impedance of electric current, therefore be called capacitive reactance, a key property of capacitive reactance is exactly to be directly proportional to current electric capacity, and the current electric capacity of electric capacity is larger, capacitive reactance is larger, just larger to the impedance of electric current; The current electric capacity of electric capacity is less, and capacitive reactance is less, just less to the impedance of electric current.Electric capacity is before powering on, and being equivalent to electric capacity is zero, is not with any electric charge, and capacitive reactance is at this moment also minimum, energising immediate current is very large, is almost equivalent to short circuit, after a period of time that powers on, owing to being full of electric charge on electric capacity, capacitive reactance is at this moment maximum, has played the effect of opening circuit.
This scheme is controlled the open and close of constant current source by the I/O mouth of single-chip microcomputer.When opening constant current source, current flowing on thermal resistance loop, owing to just powering on, is not with any electric charge in capacitor C, be almost equivalent to short circuit, and its isoboles as shown in Figure 2, is exactly two voltage sums on conductor resistance so utilize the voltage V1 that A/D samples; At constant current source, open after a period of time, on electric capacity, be full of electric charge, be equivalent to open circuit, isoboles as shown in Figure 3, total be exactly the voltage in two conductor resistances of the voltage V2 at this moment sampling by A/D again and thermal resistance resistance, by single-chip microcomputer, can calculate the voltage V3 on thermal resistance, i.e. V3=V2-V1.What the present invention adopted is constant current source, and the voltage calculating on thermal resistance has also just been known the resistance of thermal resistance, has so just eliminated the impact of conductor resistance on thermal resistance resistance, thereby has made temp measuring system more accurate.
Program circuit of the present invention as shown in Figure 4.First master routine is set bus clock, for transformation period of A/D provides clock reference.Afterwards A/D converter is carried out to initialization, i.e. the setting to registers such as the working method of A/D converter, switching time, precision.Then to the I/O mouth of single-chip microcomputer, be that PA0 mouth is set to delivery outlet, and be first set as 1, the object of doing is like this to close constant current source, and time delay 100ms, allows capacitor discharge arrive zero charge afterwards.After electric capacity is discharged, PA0 is set as 0, opens constant current source.And then time delay 20us, object is in order to allow constant current source rise to specified working current 1mA.Carry out A/D sampling again, the value of adopting is assigned to V1, V1 is exactly the voltage on the conductor resistance that measures of the short-circuiting effect of electric capacity powered on moment.Then at time delay 100ms, allow electric capacity be full of electricity, make electric capacity form the effect that opens circuit, finally carry out A/D sampling again, the value of adopting is assigned to V2, V2 is exactly the voltage in conductor resistance and thermal resistance all-in resistance.Like this, just can learn the voltage V3=V1-V2 on thermal resistance.
Image data is as table 1-5, and table 1 is worked as C=22uf, the sampling code value of V1 during t=5.3us; Table 2 is worked as C=22uf, the sampling code value of V1 during t=10.6us; Table 3 is worked as C=22uf, the sampling code value of V1 during t=21.2us; Table 4 is worked as C=47uf, the sampling code value of V1 during t=21.2us; Table 5 is worked as C=680uf, the sampling code value of V1 during t=31.8us.
Table 1
|
|
0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
Table 2
|
|
0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
Table 3
| V1 | 5 | 5 | 5 | 5 | 5 | 8 | 5 | 5 | 8 | 5 |
Table 4
| V1 | 4 | 4 | 4 | 4 | 4 | 4 | 5 | 4 | 4 | 4 |
Table 5
| V1 | 10 | 10 | 10 | 10 | 10 | 10 | 10 | 10 | 10 | 10 |
When experimental data gathers, with a shorting stub, replace electric capacity, can collect like this V1 value actual correct on conductor resistance, V1=4V.
From experimental data, can find out, when capacitance is 22uf and 47uf, while only having be greater than 21.2us time delay, just can adopt data, that is to say, the rise time 10.6us<t<21.2us of constant current source.Meanwhile, the value that capacitance C adopts when larger is larger compared with the value error of hour adopting than capacitance C, thus can not choose larger electric capacity in order to obtain larger capacitor charging time, otherwise easily produce larger error.Through too much group experiment contrast, the value that system is adopted when capacitance C=47uf is the most accurately, and capacitor C is full of the rise time that the electric time is less than constant current source, and the effect of measurement is fine.So native system adopts the sampling capacitance of 47uf.
Can find, having used the electric capacity of appropriate electrical capacitance, still there is certain error in the data value of adopting simultaneously.This is that what to adopt due to the data sampling of native system is the A/D converter of 12 successive approximations carrying of MC9S12XS128 single-chip microcomputer inside, and the reference voltage of sampling is 5V, so the minimum analog quantity changing value that can detect is 1/2
12, the sampling resolution that is to say native system is 5/2
12=1.221mV.
The V1=4 of code value accurately that systematic survey obtains, but the code value of sampling is sometimes 5, that is to say minimum one that between actual value and exact value, differs as A/D, the sampling resolution that maximal value of native system absolute error is A/D.The range of native system is
.According to accuracy of instrument computing formula:
Claims (2)
1. a method for two-wire system Thermistor Temperature Measurement conductor resistance auto-compensation, is characterized in that, specifically comprises the steps:
1) set up sample circuit: circuit is comprised of interior single-chip microcomputer and constant current source with A/D conversion, and constant current source output connects two-wire system thermal resistance, and the A/D port of single-chip microcomputer connects two-wire system thermal resistance, an electric capacity in parallel at thermal resistance two ends, this electric capacity is sampling capacitance;
2) sampling: set the A/D converter sampling time, the port of constant current source switch is controlled in single-chip microcomputer output, first ports-settings is 1, close constant current source, to the sampling capacitance discharge lag time, ports-settings is 0, open constant current source, to constant current source Current rise to the specified working current time, A/D converter starts sample voltage value, sampled value is assigned to V1, and then time delay is to the sampling capacitance duration of charging, A/D converter gathers for the second time, collection value is for the second time assigned to V2, single-chip microcomputer calculates the voltage V3=V1-V2 on thermal resistance, voltage obtains thermal resistance resistance divided by constant current source output constant current value,
3) the V1 value capacitance verification: replace electric capacity with a shorting stub, A/D converter collects actual V1 value, comparison step 2), as two values are different, return to step 1) and changes after capacitor's capacity, repeating step 2) sampling, until two values are identical.
2. the method for two-wire system Thermistor Temperature Measurement conductor resistance auto-compensation according to claim 1, is characterized in that, described single-chip microcomputer is selected MC9S12XS128 single-chip microcomputer, the A/D converter of inner 12 successive approximations.
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| CN108709656A (en) * | 2018-07-23 | 2018-10-26 | 昆明理工大学 | A method of eliminating circuit and its thermometric that thermal resistance is used for lead resistance when thermometric |
| CN111811670B (en) * | 2020-07-07 | 2022-02-01 | 九阳股份有限公司 | Temperature detection circuit of plug-in type sensor and cooking utensil |
| CN112649107B (en) * | 2020-11-17 | 2023-11-17 | 惠州拓邦电气技术有限公司 | Temperature detection circuit, temperature detection method and electric tool |
| CN113432743B (en) * | 2021-06-21 | 2022-06-03 | 力高(山东)新能源技术有限公司 | Acquisition circuit and method for improving acquisition precision of temperature sensor |
| CN113820030B (en) * | 2021-09-18 | 2022-07-15 | 中国科学院长春光学精密机械与物理研究所 | Resistor resistance error correction method |
Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4205327A (en) * | 1978-03-13 | 1980-05-27 | Rosemount Inc. | Two wire current transmitter with adjustable current control linearization |
| US4623266A (en) * | 1985-09-24 | 1986-11-18 | Rosemount Inc. | Cold junction compensation for thermocouple |
| CN101806640A (en) * | 2010-04-20 | 2010-08-18 | 杭州和利时自动化有限公司 | Measurement system of thermal resistance signal |
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2012
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Patent Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4205327A (en) * | 1978-03-13 | 1980-05-27 | Rosemount Inc. | Two wire current transmitter with adjustable current control linearization |
| US4623266A (en) * | 1985-09-24 | 1986-11-18 | Rosemount Inc. | Cold junction compensation for thermocouple |
| CN101806640A (en) * | 2010-04-20 | 2010-08-18 | 杭州和利时自动化有限公司 | Measurement system of thermal resistance signal |
Non-Patent Citations (2)
| Title |
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| 李颖.热电阻引线电阻补偿电路.《中国计量》.2003,第67-68页. |
| 热电阻引线电阻补偿电路;李颖;《中国计量》;20031231;第67-68页 * |
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Inventor after: Xu Yaoliang Inventor after: Qin Rongxun Inventor after: Zhao Wanjian Inventor after: Wang Bo Inventor after: Zhou Qicong Inventor after: Chu Shichong Inventor after: Shi Yaxing Inventor before: Xu Yaoliang Inventor before: Qin Rongxun Inventor before: Zhao Wanjian Inventor before: Wang Bo |
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Granted publication date: 20140226 |