CN110333003A - NTC temperature linearity sample circuit - Google Patents
NTC temperature linearity sample circuit Download PDFInfo
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- CN110333003A CN110333003A CN201910587882.9A CN201910587882A CN110333003A CN 110333003 A CN110333003 A CN 110333003A CN 201910587882 A CN201910587882 A CN 201910587882A CN 110333003 A CN110333003 A CN 110333003A
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- Prior art keywords
- comparator
- resistance
- ntc
- resistor
- sample circuit
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01K—MEASURING TEMPERATURE; MEASURING QUANTITY OF HEAT; THERMALLY-SENSITIVE ELEMENTS NOT OTHERWISE PROVIDED FOR
- G01K7/00—Measuring temperature based on the use of electric or magnetic elements directly sensitive to heat ; Power supply therefor, e.g. using thermoelectric elements
- G01K7/16—Measuring temperature based on the use of electric or magnetic elements directly sensitive to heat ; Power supply therefor, e.g. using thermoelectric elements using resistive elements
- G01K7/22—Measuring temperature based on the use of electric or magnetic elements directly sensitive to heat ; Power supply therefor, e.g. using thermoelectric elements using resistive elements the element being a non-linear resistance, e.g. thermistor
- G01K7/24—Measuring temperature based on the use of electric or magnetic elements directly sensitive to heat ; Power supply therefor, e.g. using thermoelectric elements using resistive elements the element being a non-linear resistance, e.g. thermistor in a specially-adapted circuit, e.g. bridge circuit
- G01K7/25—Measuring temperature based on the use of electric or magnetic elements directly sensitive to heat ; Power supply therefor, e.g. using thermoelectric elements using resistive elements the element being a non-linear resistance, e.g. thermistor in a specially-adapted circuit, e.g. bridge circuit for modifying the output characteristic, e.g. linearising
Abstract
The invention discloses a kind of NTC temperature linearity sample circuits, including resistor voltage divider circuit, voltage comparator circuit and trigger；Voltage comparator circuit includes first comparator and the second comparator；The positive input of first comparator and the second comparator connects altogether, and connect through a feedback resistance with trigger output end, while through a capacity earth；The output end of first comparator is connected to the threshold values end of trigger, and the output end of the second comparator is connected to the triggering end of trigger；Supply voltage is respectively connected to the reverse input end of first comparator and the reverse input end of the second comparator after resistor voltage divider circuit divides.NTC is originally used for the resistance surmounted function and temperature relation by the circuit, is converted into linear relationship, substantially increases the precision using NTC temperature collection；The circuit control is flexible and convenient, and parameter tuning is succinct.
Description
Technical field
The present invention relates to a kind of NTC temperature linearity sample circuits, belong to sample circuit technical field.
Background technique
Temperature collection usual way has at present: using physical temperature meter, electronic thermometer, PT linear resistance；Industrially
Also using the variation of thermocouple acquisition device temperature；All methods of these temperature acquisitions all be unable to do without a common requirement:
Wish acquisition temperature be it is uniform, linear, the temperature acquired in this way helps to improve our foresight to temperature change；Together
Control precision of the Shi Tigao to all types device temperature.Linear temperature sensor DS18B20 more common at present, it is using single
Bus design, though precision is higher, because of technical protection, the temperature sampler that China compares favourably with this not yet at present.Temperature is adopted
The wide range of applications of storage all be unable to do without temperature ginseng in the product of daily life, production and all types
Several measurements.
NTC (Negative Temperature Coefficient) be used as a kind of semiconductor resistor device, resistance with
The variation relation of temperature are as follows:
Wherein: RtResistance value, R when for NTC temperature being t DEG C0Resistance value, T when for NTC temperature being 0 DEG Ct=273+t is
Kai Er temperature at t DEG C, T0Kai Er temperature when=273+0 is 0 DEG C, B are NTC Kai Er constant.From formula (1): the electricity of NTC
Resistance value and temperature relation are that one kind surmounts function relationship, are serious non-linear relation.And acquire temperature be also it is nonlinear, because
This, can not basically use NTC temperature collection.
Summary of the invention
The technical problem to be solved by the present invention is to overcome the deficiencies of existing technologies, solve the non-thread of NTC temperature sampling
Property problem, and design a kind of NTC temperature linearity sample circuit.
In order to solve the above technical problems, The technical solution adopted by the invention is as follows:
A kind of NTC temperature linearity sample circuit, characterized in that including resistor voltage divider circuit, voltage comparator circuit and touching
Send out device；
Voltage comparator circuit includes first comparator and the second comparator；First comparator and the forward direction of the second comparator are defeated
Enter end to connect altogether, and is connect through a feedback resistance with trigger output end, while through a capacity earth；The output end of first comparator
It is connected to the threshold values end of trigger, the output end of the second comparator is connected to the triggering end of trigger；
Supply voltage is respectively connected to the reverse input end and the second ratio of first comparator after resistor voltage divider circuit divides
Compared with the reverse input end of device.
Further, resistor voltage divider circuit includes the first resistor and second resistance being connected between power supply VCC and ground, the
The reverse input end of the second comparator is connected to after one resistance and second resistance partial pressure.
Further, resistor voltage divider circuit includes the 3rd resistor being connected between power supply VCC and ground and the 4th resistance, and
The reverse input end of first comparator is connected to after three resistance and the 4th electric resistance partial pressure.
Further, the resistance value when resistance value of first resistor is NTC zero degree, when second resistance is NTC Current Temperatures
Resistance value.
Further, it converts the NTC Celsius temperature acquired to and K × ln (R0/Rt) linear, K is that adjusting is normal
Number, the resistance value that R0 is NTC when being zero degree, resistance value when Rt is NTC Current Temperatures；
The total time of the charge and discharge of capacitor and RC × ln (R0/Rt) directly proportional, K × ln (R is calculated conducive to this relationship0/
Rt)；
In formula, R is the resistance value of feedback resistance, and C is the capacitance of capacitor, and resistance value when R0 is NTC zero degree, Rt works as NTC
Resistance value when preceding temperature.
Further, the output end output period of the trigger and K × ln (R0/Rt) directly proportional square-wave signal；
In formula, K is adjusting constant, the resistance value that R0 is NTC when being zero degree, resistance value when Rt is NTC Current Temperatures.
Further, trigger uses LM555CN circuit.
Further, first comparator and the second comparator are all made of TLC393CD chip.
Further, in first resistor and second resistance, one of resistance is accurate fixed resistance, another resistance is
Accurate thermistor.
Further, 3rd resistor and the 4th resistance are accurate fixed resistance.
Advantageous effects of the invention:
The present invention provides a kind of NTC temperature linearity sample circuit, which is originally used for NTC the resistance surmounted function
With temperature relation, it is converted into linear relationship, substantially increases the precision using NTC temperature collection；The circuit control is flexible and convenient,
Parameter tuning is succinct.In addition the application of linear compensation algorithm, makes the far super digital temperature sensing of the precision of NTC temperature acquisition system
Device greatly expands the application range of NTC.
The present invention preferably solves the non-linearity problems of NTC temperature sampling using logarithmic linearization hardware circuit, mentions
The high precision of temperature sampling, theoretical relative error is about are as follows:Fully meet daily life and industry
Produce the requirement to temperature acquisition, it may be said that be a novel analog temperature sensing that can be compared favourably with digital temperature sensor
Device.
Detailed description of the invention
Fig. 1 is the present embodiment NTC linearisation sample circuit figure；
Fig. 2 is capacitor charge and discharge curve graph；
Fig. 3 is Celsius temperature curve graph.
Specific embodiment
The invention will be further described below in conjunction with the accompanying drawings.Following embodiment is only used for clearly illustrating the present invention
Technical solution, and not intended to limit the protection scope of the present invention.
By the analysis of the variation relation formula (1) of NTC resistance and temperature it is found that the NTC Celsius temperature acquired can be converted to
With K × ln (R0/Rt) linear, K is adjusting constant, RtResistance value, R when for NTC temperature being t DEG C0It is 0 for NTC temperature
DEG C when resistance value.So if needing accurately to calculate K × ln (R0/Rt) numerical value, logarithmic function therein calculating is to close
The numerical value of key, K is adjusted by circuit or self study is assured that.
In RC circuit, when capacitor charge and discharge, the voltage at capacitor both ends and charge and discharge time are exponential relationship, then capacitor
The charge and discharge time and the voltage at both ends be logarithmic relationship, the present invention exactly dexterously utilizes this relationship, to calculate K × ln
(R0/Rt) numerical value, linearisation sample circuit it is as shown in Figure 1.
The linearisation sample circuit mainly includes resistor voltage divider circuit, voltage comparator circuit and trigger.
Resistor voltage divider circuit: including the resistance R0 (accurate fixed resistance) being connected between power supply VCC and ground and resistance Rt
(precision is fixed by (accurate thermistor) and the resistance R4 being connected between power supply VCC and ground (accurate fixed resistance) and resistance R5
Resistance), by electric resistance partial pressure, obtain the reference voltage of comparator overturning.Wherein, the total contact of resistance R0 and resistance Rt is connected to
The total contact of reverse input end in second voltage comparator U1B, resistance R4 and resistance R5 are connected to first voltage comparator U1A
In reverse input end.
Wherein, resistance R0 is accurate fixed resistance, and resistance Rt is accurate thermistor；The resistance value of resistance R0 is NTC zero degree
When resistance value, the resistance value when resistance value of resistance Rt is NTC Current Temperatures；Resistance R4 and resistance R5 is accurate fixed electricity
Resistance, value range is between 30k to 300k.
Voltage comparator circuit: including first comparator U1A and the second comparator U1B.First comparator U1A and second compares
The positive input of device U1B connects altogether, and connect through a feedback resistance R3 with trigger output end OUT, while also connecing through capacitor C1
Ground.The output end of first comparator U1A is connected to the threshold values end THR of trigger U2, and the output end of the second comparator U1B is connected to
The triggering end TRI of trigger U2, for triggering trigger U2.
Two comparators are all made of TLC393CD chip in the present embodiment.
Trigger U2 uses general LM555CN circuit in the present embodiment, and LM555CN circuit can be formed very easily respectively
Kind trigger or astable circuit, 3 feet available period and K × ln (R in the output end OUT of LM555CN0/Rt) directly proportional
Square-wave signal.
The linearisation sample circuit course of work is as follows:
When circuit initial power-on, the voltage on capacitor C1 is zero, and the second comparator U1B output end exports low level, triggering
The 2 foot triggering end TRI of trigger U2 make its 3 foot output end OUT export high level, start to give capacitor C1 by feedback resistance R3
Charging；
When the voltage at the both ends capacitor C1 is charged to higher than VCC/2, the output end of first comparator U1A exports high level,
Trigger trigger U2 6 foot valve value end THR, make its 3 foot output end OUT export low level, capacitor C1 by feedback resistance R3 into
Row electric discharge；
When the tension discharge at the both ends capacitor C1 is to being lower thanWhen, the output end of the second comparator U1B exports low again
Level triggers the 2 foot triggering end TRI of trigger U2, so that its 3 foot output end OUT is exported high level, gives further through feedback resistance R3
Capacitor C1 charging；It loops back and forth like this.
The calculating of the charge and discharge time of capacitor:
(1) capacitor charging time △ t:
During the charging process, the voltage at the both ends capacitor C1 changes capacitor C1 with charging time t exponentially rule, if circuit
Charge power supply voltage is U0, then the voltage at capacitor both ends: u (t)=U0(1-e-t/RC), in formula, in R and linearisation sample circuit
Resistance R3 resistance value is suitable, and C is suitable with the capacitor C1 capacitance in linearisation sample circuit.
So within the period of charging time t1 to t2, capacitance voltage byIt is charged toThe required time: △ t=t2-t1。
Derive △ t and resistance R below0、RtRelationship.
In linearisation sample circuit with reference in figure, the voltage at the both ends capacitor C1 by:It is charged toRequired time △ t=t2-t1(for convenience of U can be set in description the present embodiment0=VCC=1)；
The voltage at the both ends capacitor C1 first is charged to by zeroNeeding the time is t1,
Capacitor charge and discharge curve graph such as Fig. 2 (wherein the 3 foot output end OUT output of trigger U2 is square wave).
Cause are as follows:
Secondly the voltage at the both ends capacitor C1 is charged to by zeroNeeding the time is t2,
And because are as follows:
So: capacitor charging time
(2) capacitor discharge time △ t':
The voltage at the both ends capacitor C1 by:It discharges intoThe required time is denoted as △ t'=t
'2-t'1；Because capacitor discharges；The voltage at capacitor both ends: u (t)=U0×e-t/RC；So
And because are as follows:
So: capacitor discharge time
The total time △ t+ △ t'=RC × ln (R of capacitor charge and discharge0/Rt)
The total time of i.e. above-mentioned linearisation sample circuit capacitor charge and discharge and RC × ln (R0/Rt) directly proportional, it can also wait certainly
It is same as and K × ln (R0/Rt) directly proportional, so the Celsius temperature of NTC acquisition and above-mentioned linearisation sample circuit capacitor charge and discharge
Total time is directly proportional；The total time that linearisation sample circuit capacitor charge and discharge can very easily be calculated, by adjusting
The temperature sampling value of NTC is acquired, numerical value is clearly linear.
The present invention solves the non-linearity problems of NTC temperature sampling using NTC temperature linearity sample circuit, improves
The precision of temperature sampling greatly expands the application range of NTC, it may be said that a to compare favourably with digital temperature sensor
Novel analog temperature sensor.
Embodiment 1
It with reference to figure is main module using linearisation sample circuit shown in FIG. 1, which is on the basis of zero degree, and acquisition is current
The difference of temperature and zero degree measures temperature and is denoted as t (R0)；One linearisation sample circuit is set in the same way, by former module
In R0It is changed to R50, which is then to be acquired Current Temperatures and 50 degree of difference on the basis of 50 degree, measured temperature and be denoted as t (R50)。
Due toWithIt is equal；And all expectation is equal to 25, so passing through adjusting
Hardware circuit makes their count value be equal to 25, that is, 25 degree to two reference points of room temperature temperature distance difference all etc.
In 50-25=25-0；T (R when actual measurement0)+t(R50) and, by linear compensation algorithm, t (R may be made up not equal to 500)
Measurement error, calculate compensated temperature t (Rt) instead of t (R0)；
Backoff algorithm is as follows:
Practical compensation effect is as shown in following table 5-1:
The practical compensation effect of table 5-1
It can be seen that the calculating by linear compensation algorithm from the compensation calculation result data of upper table, make its measurement accuracy
It greatly improves, the theoretical foundation of linear compensation algorithm is the data linear fusion of multiple spot reference.
Celsius temperature t and K × ln (R0/Rt) curve graph such as Fig. 3:
This system circuit uses two pieces of linearisation sampling modules, needs to carry out double-counting, therefore is also required to double adjustings and (learns by oneself
Practise) process, i.e., at 25 degree, adjusting charge-discharge parameter, the t (R made0)、t(R50) 25 degree are equal to, it is adopted to further increase
Sample precision.
The groundwork step of circuit:
1, (double-counting) is counted to periodic signal caused by two modules；
2, double adjustings can realize self study process with software, determine two coefficient 25/t (R0) and 25/t (R50)；
3, linear compensation compensates calculating by above-mentioned linear compensation algorithm；
4, result (charactron Dynamically Announce) is shown.
The above is only a preferred embodiment of the present invention, it is noted that for the ordinary skill people of the art
For member, without departing from the technical principles of the invention, several improvement and deformations can also be made, these improvement and deformations
Also it should be regarded as protection scope of the present invention.
Claims (10)
1. a kind of NTC temperature linearity sample circuit, characterized in that including resistor voltage divider circuit, voltage comparator circuit and triggering
Device；
Voltage comparator circuit includes first comparator and the second comparator；The positive input of first comparator and the second comparator
It connects, and is connect through a feedback resistance with trigger output end, while through a capacity earth altogether；The output end of first comparator connects
To the threshold values end of trigger, the output end of the second comparator is connected to the triggering end of trigger；
Supply voltage is respectively connected to the reverse input end and the second comparator of first comparator after resistor voltage divider circuit divides
Reverse input end.
2. NTC temperature linearity sample circuit according to claim 1, characterized in that resistor voltage divider circuit includes series connection
Second is connected to after first resistor and second resistance between power supply VCC and ground, first resistor and second resistance partial pressure to compare
The reverse input end of device.
3. NTC temperature linearity sample circuit according to claim 1, characterized in that resistor voltage divider circuit includes series connection
3rd resistor and the 4th resistance between power supply VCC and ground are connected to first after 3rd resistor and the 4th electric resistance partial pressure and compare
The reverse input end of device.
4. NTC temperature linearity sample circuit according to claim 2, characterized in that the resistance value of first resistor is NTC zero
Resistance value when spending, resistance value when second resistance is NTC Current Temperatures.
5. NTC temperature linearity sample circuit according to claim 4, characterized in that
It converts the NTC Celsius temperature acquired to and K × ln (R0/Rt) linear, K is adjusting constant, and R0 is that NTC is zero
Resistance value when spending, resistance value when Rt is NTC Current Temperatures；
The total time of the charge and discharge of capacitor and RC × ln (R0/Rt) directly proportional, K × ln (R is calculated conducive to this relationship0/Rt)；
In formula, R is the resistance value of feedback resistance, and C is the capacitance of capacitor, and resistance value when R0 is NTC zero degree, Rt is that NTC is currently warm
Resistance value when spending.
6. NTC temperature linearity sample circuit according to claim 5, characterized in that the output end of the trigger is defeated
Period and K × ln (R out0/Rt) directly proportional square-wave signal；
In formula, K is adjusting constant, the resistance value that R0 is NTC when being zero degree, resistance value when Rt is NTC Current Temperatures.
7. NTC temperature linearity sample circuit according to claim 1, characterized in that trigger is using LM555CN electricity
Road.
8. NTC temperature linearity sample circuit according to claim 1, characterized in that first comparator and second compares
Device is all made of TLC393CD chip.
9. NTC temperature linearity sample circuit according to claim 2, characterized in that in first resistor and second resistance,
One of resistance is accurate fixed resistance, another resistance is accurate thermistor.
10. NTC temperature linearity sample circuit according to claim 3, characterized in that 3rd resistor and the 4th resistance are equal
For accurate fixed resistance.
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