CN110333003B - NTC temperature linearization sampling circuit - Google Patents
NTC temperature linearization sampling circuit Download PDFInfo
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- CN110333003B CN110333003B CN201910587882.9A CN201910587882A CN110333003B CN 110333003 B CN110333003 B CN 110333003B CN 201910587882 A CN201910587882 A CN 201910587882A CN 110333003 B CN110333003 B CN 110333003B
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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
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- Indication And Recording Devices For Special Purposes And Tariff Metering Devices (AREA)
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Abstract
The invention discloses an NTC temperature linearization sampling circuit, which comprises a resistance voltage division circuit, a voltage comparison circuit and a trigger, wherein the resistance voltage division circuit is connected with the voltage comparison circuit; the voltage comparison circuit comprises a first comparator and a second comparator; the positive input ends of the first comparator and the second comparator are connected in common, and are connected with the output end of the trigger through a feedback resistor and are grounded through a capacitor; the output end of the first comparator is connected to the threshold end of the trigger, and the output end of the second comparator is connected to the trigger end of the trigger; the power supply voltage is divided by the resistor voltage dividing circuit and then is respectively connected to the reverse input end of the first comparator and the reverse input end of the second comparator. The circuit converts the relationship between the resistance and the temperature of the NTC which is originally a transcendental function into a linear relationship, thereby greatly improving the precision of temperature acquisition by applying the NTC; the circuit is flexible and convenient to control, and parameter setting is concise.
Description
Technical Field
The invention relates to an NTC temperature linearization sampling circuit, and belongs to the technical field of sampling circuits.
Background
The current methods for collecting temperature are as follows: physical thermometer, electronic thermometer, PT linear resistor; thermocouples are also used industrially to collect changes in equipment temperature; all of these methods of temperature acquisition do not leave a common requirement: it is desirable that the temperature collected be uniform and linear, so that the temperature collected helps to improve our predictability of temperature changes; meanwhile, the control precision of the temperature of various equipment at all levels is improved. At present, the linear temperature sensor DS18B20 which is more commonly used adopts a single-bus design, although the precision is higher, because of technical protection, no temperature collector which is comparable with the precision exists in China at present. The application field of the temperature collector is very wide, and the measurement of temperature parameters cannot be avoided in daily life, production and various products of all levels.
Ntc (negative Temperature coefficient) is used as a semiconductor resistor device, and the resistance and Temperature variation relationship is as follows:
wherein: rtIs the resistance value R of NTC at t DEG C0Is the resistance value T at 0 deg.C of NTCt273+ T is the Kerr temperature at T DEG C, T0273+0 is the kelvin temperature at 0 ℃ and B is the NTC kelvin constant. The formula (1) shows that: the NTC resistance value and temperature relationship is a transcendental function relationship, which is a serious nonlinear relationshipAnd (4) sexual relations. The acquired temperature is also nonlinear, so the NTC cannot be used to acquire temperature fundamentally.
Disclosure of Invention
The technical problem to be solved by the invention is to overcome the defects of the prior art, solve the problem of non-linearity of NTC temperature sampling and design an NTC temperature linear sampling circuit.
In order to solve the technical problems, the technical scheme adopted by the invention is as follows:
an NTC temperature linearization sampling circuit is characterized by comprising a resistance voltage division circuit, a voltage comparison circuit and a trigger;
the voltage comparison circuit comprises a first comparator and a second comparator; the positive input ends of the first comparator and the second comparator are connected in common, and are connected with the output end of the trigger through a feedback resistor and are grounded through a capacitor; the output end of the first comparator is connected to the threshold end of the trigger, and the output end of the second comparator is connected to the trigger end of the trigger;
the power supply voltage is divided by the resistor voltage dividing circuit and then is respectively connected to the reverse input end of the first comparator and the reverse input end of the second comparator.
Further, the resistance voltage division circuit comprises a first resistor and a second resistor which are connected between the power supply VCC and the ground in series, and the first resistor and the second resistor are connected to the reverse input end of the second comparator after voltage division.
Further, the resistance voltage division circuit comprises a third resistor and a fourth resistor which are connected between the power supply VCC and the ground in series, and the third resistor and the fourth resistor are connected to the reverse input end of the first comparator after voltage division.
Further, the resistance value of the first resistor is the resistance value of the NTC at zero degree, and the resistance value of the second resistor is the resistance value of the NTC at the current temperature.
Further, the NTC collected temperature is converted into K x ln (R)0/Rt) The linear relation is formed, K is a setting constant, R0 is a resistance value of the NTC at zero degree, and Rt is a resistance value of the NTC at the current temperature;
total time of charging and discharging of capacitor and RC x ln (R)0/Rt) Proportional ratio, and K x ln (R) is calculated by using the relation0/Rt)；
In the formula, R is the resistance value of the feedback resistor, C is the capacitance value of the capacitor, R0 is the resistance value of the NTC at zero degree, and Rt is the resistance value of the NTC at the current temperature.
Further, the output end of the trigger outputs a period and K x ln (R)0/Rt) A proportional square wave signal;
in the formula, K is a setting constant, R0 is a resistance value of the NTC at zero degrees, and Rt is a resistance value of the NTC at the current temperature.
Further, the flip-flop adopts an LM555CN circuit.
Further, the first comparator and the second comparator both employ TLC393CD chips.
Furthermore, one of the first resistor and the second resistor is a precision fixed resistor, and the other resistor is a precision thermistor.
Furthermore, the third resistor and the fourth resistor are both precision fixed resistors.
The invention achieves the following beneficial effects:
the invention provides an NTC temperature linear sampling circuit, which converts the relationship between resistance and temperature of an NTC which is originally a transcendental function into a linear relationship, thereby greatly improving the precision of temperature acquisition by applying the NTC; the circuit is flexible and convenient to control, and parameter setting is concise. And due to the application of a linear compensation algorithm, the precision of the NTC temperature acquisition system is far beyond that of a digital temperature sensor, and the application range of the NTC is greatly expanded.
The invention adopts a logarithmic linearization hardware circuit to better solve the problem of the nonlinearity of NTC temperature sampling, improves the precision of the temperature sampling, and has the theoretical relative error about:
the temperature sensor completely meets the requirements of daily life and industrial production on temperature acquisition, and can be said to be a novel analog temperature sensor which can be comparable with a digital temperature sensor.
Drawings
FIG. 1 is a diagram of an NTC linearized sampling circuit according to this embodiment;
FIG. 2 is a graph of capacitance charge and discharge;
fig. 3 is a graph of temperature in degrees celsius.
Detailed Description
The invention is further described below with reference to the accompanying drawings. The following examples are only for illustrating the technical solutions of the present invention more clearly, and the protection scope of the present invention is not limited thereby.
As can be seen from the analysis of the NTC resistance and temperature variation relation formula (1), the temperature collected by the NTC can be converted into K × ln (R)0/Rt) Linear relationship, K being a setting constant, RtIs the resistance value R of NTC at t DEG C0Is the resistance value at the NTC temperature of 0 ℃. So that K x ln (R) is calculated accurately if necessary0/Rt) The calculation of the logarithmic function is critical, and the value of K can be determined by circuit setting or self-learning.
In the RC circuit, when the capacitor is charged and discharged, the voltage at two ends of the capacitor and the charging and discharging time are in an exponential relation, so that the charging and discharging time of the capacitor and the voltage at two ends are in a logarithmic relation0/Rt) The linearized sampling circuit is shown in fig. 1.
The linear sampling circuit mainly comprises a resistance voltage division circuit, a voltage comparison circuit and a trigger.
Resistance bleeder circuit: the comparator voltage divider comprises a resistor R0 (precision fixed resistor) and a resistor Rt (precision thermistor) which are connected in series between a power supply VCC and the ground, and a resistor R4 (precision fixed resistor) and a resistor R5 (precision fixed resistor) which are connected in series between the power supply VCC and the ground, and obtains the reference voltage turned by the comparator through resistor voltage division. The common junction of the resistor R0 and the resistor Rt is connected to the inverting input terminal of the second voltage comparator U1B, and the common junction of the resistor R4 and the resistor R5 is connected to the inverting input terminal of the first voltage comparator U1A.
Wherein, the resistor R0 is a precision fixed resistor, and the resistor Rt is a precision thermistor; the resistance value of the resistor R0 is the resistance value of the NTC at zero degree, and the resistance value of the resistor Rt is the resistance value of the NTC at the current temperature; the resistor R4 and the resistor R5 are both precision fixed resistors and have the value range of 30k to 300 k.
A voltage comparison circuit: including a first comparator U1A and a second comparator U1B. The positive input terminals of the first comparator U1A and the second comparator U1B are connected in common, and are connected to the output terminal OUT of the flip-flop through a feedback resistor R3, and are also connected to ground through a capacitor C1. The output terminal of the first comparator U1A is connected to the threshold terminal THR of the flip-flop U2, and the output terminal of the second comparator U1B is connected to the trigger terminal TRI of the flip-flop U2 for triggering the flip-flop U2.
In this example, TLC393CD chips were used for both comparators.
In this embodiment, the flip-flop U2 employs a general LM555CN circuit, the LM555CN circuit can conveniently constitute various flip-flops or astable circuits, and the period and K × ln (R × ln) can be obtained at pin 3 of the output terminal OUT of the LM555CN0/Rt) A proportional square wave signal.
The operation process of the linear sampling circuit is as follows:
when the circuit is initially powered on, the voltage on the capacitor C1 is zero, the output end of the second comparator U1B outputs low level, the 2-pin trigger end TRI of the trigger U2 is triggered, the 3-pin output end OUT outputs high level, and the capacitor C1 starts to be charged through the feedback resistor R3;
when the voltage at the two ends of the capacitor C1 is charged to be higher than VCC/2, the output end of the first comparator U1A outputs high level, a 6-pin threshold end THR of the trigger U2 is triggered, so that a 3-pin output end OUT outputs low level, and the capacitor C1 discharges through the feedback resistor R3;
when the voltage across the capacitor C1 is discharged to be lower than
When the output end of the second comparator U1B outputs low level, the 2-pin trigger end TRI of the trigger U2 is triggered to enable the 3-pin output end OUT to output high level, and the capacitor C1 is charged through the feedback resistor R3; the operation is repeated in a circulating way.
Calculation of the charge-discharge time of the capacitor:
(1) capacitor charging time Δ t:
in the charging process of the capacitor C1, the voltage at two ends of the capacitor C1 changes exponentially along with the charging time t, and the charging power supply voltage of the circuit is set to be U0Then the voltage across the capacitor: u (t) ═ U0(1-e-t/RC) In the formula, R is equivalent to the resistance of a resistor R3 in the linear sampling circuit, and C is equivalent to the capacitance of a capacitor C1 in the linear sampling circuit.
Then the capacitor voltage is decreased by the time period t1 to t2
Is charged to
Time required: t is equal to t2-t1。
The following is the derivation of Δ t and resistance R0、RtThe relationship (2) of (c).
In the linearized sampling circuit reference diagram, the voltage across capacitor C1 is represented by:
is charged to
The required time Δ t ═ t2-t1(for convenience of description, U may be provided in this embodiment0＝VCC＝1)；
Firstly, the voltage at the two ends of the capacitor C1 is charged from zero to
The required time is t1，
The graph of the charge and discharge of the capacitor is shown in fig. 2 (wherein the output of the 3-pin output terminal OUT of the flip-flop U2 is a square wave).
Because:
secondly, the voltage across the capacitor C1 is charged from zero to
The required time is t2，
And because:
therefore: time of capacitor charging
(2) Capacitor discharge time Δ t':
the voltage across capacitor C1 is determined by:
is discharged to
The required time is recorded as Δ t ═ t'2-t'1(ii) a Because the capacitor is discharged; voltage across capacitor: u (t) ═ U0×e-t/RC(ii) a Therefore, it is not only easy to use
And because:
therefore: discharge time of capacitor
Total time Δ t +. Δ t' ═ RC × ln (R) of capacitor charging and discharging0/Rt)
Namely the total charging and discharging time of the capacitor of the linear sampling circuit and RC multiplied by ln (R)0/Rt) Proportional to K x ln (R) and of course0/Rt) The NTC temperature is in direct proportion to the total charging and discharging time of the capacitor of the linear sampling circuit; can be very muchThe total time of charging and discharging of the capacitor of the linear sampling circuit is calculated conveniently, the temperature sampling value of the NTC can be obtained through setting, and the numerical value is obviously linear.
The NTC temperature linear sampling circuit is adopted in the invention to solve the problem of non-linearity of NTC temperature sampling, improve the precision of temperature sampling, and greatly expand the application range of NTC, so that the NTC temperature linear sampling circuit is a novel analog temperature sensor which can be compared favorably with a digital temperature sensor.
Example 1
The reference diagram of the linear sampling circuit shown in fig. 1 is taken as a main module, the module takes zero degree as a reference, the difference between the current temperature and the zero degree is collected, and the measured temperature is recorded as t (R)0) (ii) a In the same way, a linear sampling circuit is arranged to convert R in the original module0Is changed to R50The module collects the difference between the current temperature and 50 degrees based on 50 degrees, and the measured temperature is recorded as t (R)50)。
Due to the fact that
And
equal; and are all expected to be equal to 25, the hardware circuits are adjusted so that their count values are all equal to 25, that is, the temperature distance difference from the normal temperature of 25 degrees to the two reference points is all equal to 50-25-0; time of actual measurement t (R)0)+t(R50) And possibly not equal to 50, by means of a linear compensation algorithm, make up for t (R)0) Calculating a compensated temperature t (Rt) instead of t (R)0)；
The compensation algorithm is as follows:
the actual compensation effect is shown in the following table 5-1:
TABLE 5-1 actual Compensation Effect
As can be seen from the compensation calculation result data in the table above, the measurement accuracy is greatly improved through the calculation of the linear compensation algorithm, and the theoretical basis of the linear compensation algorithm is the data linear fusion of the multi-point reference.
Temperature t and K x ln (R)0/Rt) The graph is as shown in FIG. 3:
the circuit of the system adopts two linear sampling modules, double counting is needed, and therefore a double setting (self-learning) process is also needed, namely, at 25 ℃, charging and discharging parameters are adjusted, so that t (R) is enabled0)、t(R50) Are all equal to 25 degrees, further improving the sampling accuracy.
Basic working steps of the circuit are as follows:
1. counting the periodic signals generated by the two modules (double counting);
2. double tuning, a self-learning process can be realized by software, and two coefficients of 25/t (R) are determined0) And 25/t (R)50)；
3. Linear compensation, which is to perform compensation calculation according to the linear compensation algorithm;
4. and displaying the result (nixie tube dynamic display).
The above description is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, several modifications and variations can be made without departing from the technical principle of the present invention, and these modifications and variations should also be regarded as the protection scope of the present invention.
Claims (7)
1. An NTC temperature linearization sampling circuit is characterized by comprising a resistance voltage division circuit, a voltage comparison circuit and a trigger;
the voltage comparison circuit comprises a first comparator and a second comparator; the positive input ends of the first comparator and the second comparator are connected in common, and are connected with the output end of the trigger through a feedback resistor and are grounded through a capacitor; the output end of the first comparator is connected to the threshold end of the trigger, and the output end of the second comparator is connected to the trigger end of the trigger;
the power supply voltage is divided by the resistor voltage dividing circuit and then is respectively connected to the reverse input end of the first comparator and the reverse input end of the second comparator;
the resistance voltage division circuit comprises a first resistor and a second resistor which are connected between a power supply VCC and the ground in series, and the first resistor and the second resistor are connected to the reverse input end of the second comparator after voltage division;
the resistance voltage division circuit comprises a third resistor and a fourth resistor which are connected between a power supply VCC and the ground in series, and the third resistor and the fourth resistor are connected to the reverse input end of the first comparator after voltage division;
the resistance value of the first resistor is the resistance value of the NTC at zero degree, and the resistance value of the second resistor is the resistance value of the NTC at the current temperature.
2. The NTC temperature linearized sampling circuit of claim 1,
converting the NTC collected temperature in centigrade into K x ln (R)0/Rt) The linear relation is formed, K is a setting constant, R0 is a resistance value of the NTC at zero degree, and Rt is a resistance value of the NTC at the current temperature;
total time of charging and discharging of capacitor and RC x ln (R)0/Rt) Proportional ratio, and K x ln (R) is calculated by using the relation0/Rt)；
In the formula, R is the resistance value of the feedback resistor, C is the capacitance value of the capacitor, R0 is the resistance value of the NTC at zero degree, and Rt is the resistance value of the NTC at the current temperature.
3. The NTC temperature linearized sampling circuit of claim 2, wherein the output of the flip-flop has a period of K x ln (R) and output of the flip-flop0/Rt) A proportional square wave signal;
in the formula, K is a setting constant, R0 is a resistance value of the NTC at zero degrees, and Rt is a resistance value of the NTC at the current temperature.
4. The NTC temperature linearization sampling circuit of claim 1, wherein the flip-flop is an LM555CN circuit.
5. The NTC temperature linearized sampling circuit of claim 1, wherein the first comparator and the second comparator both use TLC393CD chips.
6. The NTC temperature linearization sampling circuit of claim 1, wherein one of the first resistor and the second resistor is a precision fixed resistor, and the other resistor is a precision thermistor.
7. The NTC temperature linearization sampling circuit of claim 1, wherein the third resistor and the fourth resistor are both precision fixed resistors.
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