CN101922981B - Thermistor temperature detecting method based on DSP (Digital Signal Processing) - Google Patents

Abstract

The invention provides a thermistor temperature detecting method based on DSP, wherein a relational expression between T and lgR-T is obtained by utilizing the temperature of thermistor R-T characteristic detection power equipment and fitting a lgR-T curve in DSP. The method comprises the following steps of: converting the computation for lnR into the approximate operation of addition, subtraction, multiplication and division, obtaining a computing formula by adopting a high-item truncation approximate computing method, then determining a segmenting mode by adopting an error comparison method, and finally obtaining the lnR value of each segment by adopting a segmentation algorithm to realize accurate temperature computation. The temperature detecting precision is greatly improved by adopting the method; the method is simple to realize and has high operational speed; the hardware structure is simple, and the cost is saved.

Description

A kind of thermistor temperature detecting method based on DSP

Technical field

The present invention relates to a kind of temp measuring method, particularly based on the thermistor temperature detecting method of DSP.

Background technology

Temperature is controlled in other industrial control equipments such as frequency converter, UPS and often uses.Control system when temperature exceeds normal range of operation, is carried out overheating protection to equipment according to the control of temperature value decision to radiator fan, and preventing to work on causes damage to equipment.At one industrial control equipment like one of necessary design when temperature control is design of Controller in the equipment such as frequency converter, UPS.Temperature detection and control method to this type of opertaing device is complicated at present, and precision is not high, and hardware cost is high.

Summary of the invention

The technical matters that the present invention will solve is: a kind of thermistor temperature detecting method based on DSP is provided, can improves temperature detecting precision effectively.

The present invention solves the problems of the technologies described above the technical scheme of being taked to be: a kind of thermistor temperature detecting method based on DSP is characterized in that: it comprises following step:

S1) select for use thermistor as temperature sensor; Based on DSP platform building system for detecting temperature; System for detecting temperature is specially: first resistance and thermistor are in parallel, thermistor one end ground connection, and the other end and second resistance and the 3rd resistance link; The second resistance other end making alive U, the 3rd resistance other end output voltage U _Out, connect with the AD port of DSP; Described thermistor is a negative tempperature coefficient thermistor;

S2) DSP carries out the detection of AD port voltage, carries out the U that obtains after AD proofreaies and correct according to the value of the register that detects _OutValue, and the resistance of each resistance calculate the R value;

S3) obtain the R-T family curve by the thermistor instructions, R is asked denary logarithm, obtain the lgR-T curve, the lgR-T curve is carried out cubic fit obtain the relational expression between T and the lgR;

S4) in fixed DSP, the calculating of lnR is converted into the operate approximately of addition subtraction multiplication and division, takes " the high approximation technique of house " to obtain computing formula, and then adopt the error relative method to confirm segmented mode, adopt segmentation algorithm to obtain the lnR value of each segmentation at last;

S5) since with S2) R that draws corresponds to S4) and segmentation in; Draw lnR; Be updated to S3) relational expression in, calculate this moment thermistor temperature value T.

Press such scheme, described step S4) in segmentation algorithm be specially and R carried out 2 repeatedly number formulary segmentation, make R=2 ^a* 2 ^b, wherein a is greater than the integer that waits 0,0＜b＜1, so have:

2 ^a＜R=2 ^a* 2 ^b＜2 ^A+1, the span of the R that the temperature range that in the R-T curve, obtains detecting is corresponding is with the value of a foundation as segmentation; Obtain the lnR computing formula of each segmentation; This moment is because a is a constant, so the first addend item of lnR computing formula is constant, in the second addend item Be the number in 1 to 2 scope, can directly use " the high approximation technique of house " and calculate.

Press such scheme, the resistance of first resistance, second resistance and the 3rd resistance is chosen so that U _OutIn dsp chip AD end input voltage range, be as the criterion.

Principle of work of the present invention is: the characteristic of thermistor is the nonlinear function of a complicacy, is difficult to accurately obtain its relational expression, can only adopt approximate method to calculate.The R-T class of a curve is similar to the logarithmic function curve, therefore the R-T curve is asked denary logarithm, obtains the lgR-T curve, and visible lgR-T curve linear degree is higher, realizes match easily.The lgR-T curve is carried out cubic fit, and the error that calculates is very little.

Because how then calculates lnR with fixed-point algorithm and can obtain lgR in DSP.In fixed DSP, can only carry out the computing of addition subtraction multiplication and division, the operate approximately that must be converted into addition subtraction multiplication and division comes indirect calculation lnR.

$\left.\begin{array}{c}\ln (1-x)=-x-\frac{x^2}{2}-\frac{x^3}{3}-...-\frac{x^n}{n}\\ \ln (1+x)=x-\frac{x^2}{x}+\frac{x^3}{3}+...+{(-1)}^{n-1}\frac{x^n}{n}\\ \ln \left(\frac{1-x}{1+x}\right)=-2\×(x+\frac{x^3}{3}+\frac{x^5}{5}+...)\end{array}\right\}---\left(1\right),$

Make that

substitution (1) obtains

because 0＜R＜+∞, therefore the high-order term cast out more than 5 times of (2) formula obtains

$\ln R=-2\×[\frac{1-R}{1+R}+\frac{1}{3}{\left(\frac{1-R}{1+R}\right)}^3]---\left(3\right),$

When (3) condition set up of formula is and

, through (3) formula calculate error just more little.

Adopt the error relative method to confirm the R segmented mode, adopt segmentation algorithm to obtain the lnR value of each segmentation at last.

Beneficial effect of the present invention is: 1, adopt the method to make temperature detecting precision improve greatly; 2, the method realizes simply, fast operation; 3, hardware configuration is simple, practices thrift cost.

Description of drawings

Fig. 1 is based on DSP platform building system for detecting temperature structural drawing

Fig. 2 obtains the lgR-T curve for the thermistor R-T curvilinear transformation of one embodiment of the invention

Fig. 3 is the temperature error curve to obtaining after the lgR-T curve cubic fit among Fig. 2

Fig. 4 is lnR error E (lnR) figure of one embodiment of the invention

Fig. 5 is temperature error E (T) figure of one embodiment of the invention

Embodiment

Fig. 1 is based on DSP platform building system for detecting temperature structural drawing, and the bleeder circuit of using the 3.3V reference power supply is realized the voltage transitions of the resistance of thermistor, and voltage is measured through the AD mouth of DSP, and other all are accomplished remaining temperature computation in the DSP the inside.Wherein bleeder circuit is used after resistance and the thermistor parallel connection of 10K of one 1% precision the output voltage of connecting with the resistance of the 10K of 1% same precision afterwards to the AD mouth of DSP again.Carry out AD in the DSP the inside and detect the AD mouth input voltage U after voltage obtains dividing potential drop _Out

The selected thermistor of present embodiment is a negative tempperature coefficient thermistor, and its model is: NTSA0103FZ485, can satisfy-40 ℃-105 ℃ temperature detection requirement.

The concrete steps of present embodiment are:

1) DSP carries out AD mouth voltage detecting, obtains U with carrying out according to the value of the register that detects after AD proofreaies and correct _Out, calculate R value relation then and be:

$R=\frac{10\×U_{\mathrm{out}}}{U-2U_{\mathrm{out}}}---\left(4\right)$

What adopt in this step is that the resistance of 1% precision carries out dividing potential drop, and the AD of DSP detects that to have obtained the precision after the linearity correction enough good, and the error of calculation of this step is smaller.

2) obtain the R-T family curve by the thermistor instructions, it is asked denary logarithm, obtain the lgR-T curve, as shown in Figure 2.The characteristic of thermistor is the nonlinear function of a complicacy, is difficult to accurately obtain its relational expression, can only adopt approximate method to calculate.Can find out that by the left figure of Fig. 2 the R-T class of a curve is similar to the logarithmic function curve, therefore R-T curve R asked denary logarithm, obtain the lgR-T curve, like the right figure of Fig. 2, visible lgR-T curve linear degree is higher, realizes match easily.

3) the lgR-T curve is carried out cubic fit and obtains the relational expression between T and the lgR:

T＝-1.007(lgR) ³+10.64(lgR) ²-69.49(lgR)+84.80 (5)

Temperature error figure to the lgR-T curve carries out obtaining after the cubic fit is as shown in Figure 3; The difference Δ T of the temperature that temperature that horizontal ordinate is represented to calculate for specific resistance value R among the figure and desirable R-T curve are tried to achieve, ordinate represent the thermistor temp value T that specific resistance value R is corresponding.Can know by figure, when lgR calculates cubic fit calculates under the situation accurately error within 0.1 degree centigrade of scope.

4) because

comes indirect calculation to go out lgR with the operate approximately that fixed-point algorithm is converted into addition subtraction multiplication and division in DSP.

$\left.\begin{array}{c}\ln (1-x)=-x-\frac{x^2}{2}-\frac{x^3}{3}-...-\frac{x^n}{n}\\ \ln (1+x)=x-\frac{x^2}{x}+\frac{x^3}{3}+...+{(-1)}^{n-1}\frac{x^n}{n}\\ \ln \left(\frac{1-x}{1+x}\right)=-2\×(x+\frac{x^3}{3}+\frac{x^5}{5}+...)\end{array}\right\}---\left(1\right)$

Make

here 0＜R＜+∞,

arranged

$\ln R=-2\×[\frac{1-R}{1+R}+\frac{1}{3}{\left(\frac{1-R}{1+R}\right)}^3+\frac{1}{5}{\left(\frac{1-R}{1+R}\right)}^5...]---\left(2\right)$

The high-order term that following formula is cast out more than 5 times obtains:

$\ln R=-2\×[\frac{1-R}{1+R}+\frac{1}{3}{\left(\frac{1-R}{1+R}\right)}^3]---\left(3\right)$

When (3) condition set up of formula is

and

, through (3) formula calculate error just more little.Because 360＞R＞0.5 in-40＜T＜100 scopes; When R=0.5,

at this moment

$\ln R=\left.\begin{array}{c}-2\×[\frac{1}{3}+\frac{1}{3}{\left(\frac{1}{3}\right)}^3]=-0.69136\\ \ln 0.5=-0.69315\end{array}\right\}---\left(6\right)$

There is temperature computation error E (T)=0.054 degree that obtains error E=0.00179 that formula (6) is calculated in the substitution formula (5).

Make

promptly in 0.5＜R＜2 o'clock, formula (3), (5) calculate error E＜0.00179E (T)＜0.054.Make full use of these characteristics at present, make R=2 ^a* 2 ^b, wherein a is that 0＜b＜1 has greater than the integer that waits 0:

$\left.\begin{array}{c}{\log }_2\left(R\right)=(a+b)\\ \ln \left(R\right)=\ln 2*{\log }_2\left(R\right)=\ln 2*(a+b)\\ \ln \left(R\right)=a*\ln 2+b*\ln 2\end{array}\right\}$

$2^b=\frac{R}{2^a}\⇒b={\log }_2\left(\frac{R}{2^a}\right)=\frac{\ln \left(\frac{R}{2^a}\right)}{\ln 2}$

$\ln \left(R\right)=a*\ln 2+\ln \left(\frac{R}{2^a}\right)---\left(7\right)$

By 0＜b＜1, then have 1＜2 ^b＜2, promptly be Consequent can the using of event formula (7) " the high approximation technique of house " realized, and (7) formula preceding paragraph is a constant, and (7) formula has only a unknown quantity a, and how present goal displacement confirms a if arriving.

By R=2 ^a* 2 ^b, wherein a is that 0＜b＜1 obtains 2 greater than the integer that waits 0 ^a＜R=2 ^a* 2 ^b＜2 ^A+1, adopt and just can realize asking a value and 2 the R staging treating ^aBe worth.

Want detected temperatures-20 ℃ 0＜R＜102 in 105 ℃ of scopes at us, then R carried out 2 repeatedly number formulary segmentation, and calculate like following table with segmentation algorithm:

Table 1 carries out segmentation by 2 repeatedly number formulary to R

R	2 a	a	lnR
				64＜R＜＝128	64	6	6*ln2+ln(R/64)
32＜R＜＝64	32	5	5*ln2+ln(R/32)
				16＜R＜＝32	16	4	4*ln2+ln(R/16)
8＜R＜＝16	8	3	3*ln2+ln(R/8)
				4＜R＜＝8	4	2	2*ln2+ln(R/4)
2＜R＜＝4	2	1	ln2+ln(R/2)
				0＜R＜＝2	1	0	0+lnR

Calculate through staging treating like this; In the table 1 in the second addend item of computing formula R/64, R/32 etc. all be the number in 1 to 2 scope; The second addend item has proved that can directly use " the high approximation technique of house " calculates, and can accomplish very little so resulting error is calculated in above segmentation.LnR error E (lnR) figure and the temperature error E (T) that obtain through the method for the invention scheme; It is respectively like Fig. 4, shown in Figure 5; In the drawings horizontal ordinate represent the corresponding temperature value T of the thermistor resistance R that will calculate, ordinate is represented the lnR error E (lnR), the temperature error E (T) that calculate.The lnR graph of errors that curve 1 directly calculates with 3 formulas for not segmentation among Fig. 4, the lnR graph of errors of curve 2 for adopting new sectional type to calculate.Temperature error E (T) curve that curve 3 directly uses (3) formula to calculate for not segmentation among Fig. 5, temperature error E (T) curve of curve (4) for adopting new sectional type algorithm computation to draw.Clearly, adopt new sectional type computing, can reduce the sum of errors temperature error of temperature at the lnR that calculates of the following thermistor resistance R of 60 degree greatly, the precision of the lnR value that new algorithm calculates can reach the precision of temperature detection fully.If the AD of system detect and R under the reliable situation of peripheral circuit precision of U, the method for the invention accounting temperature deviation is in 0.054 degree scope.

Claims (3)

1. thermistor temperature detecting method based on DSP, it is characterized in that: it comprises following step:

S1) select for use thermistor as temperature sensor; Based on DSP platform building system for detecting temperature; System for detecting temperature is specially: first resistance and thermistor are in parallel, thermistor one end ground connection, and the other end is connected with the 3rd resistance with second resistance; The second resistance other end making alive U, the 3rd resistance other end output voltage U _Out, be connected with the AD port of DSP; Described thermistor is a negative tempperature coefficient thermistor;

S2) DSP carries out the detection of AD port voltage, carries out the U that obtains after AD proofreaies and correct according to the value of the register that detects _OutValue, and the resistance of each resistance calculate the R value;

S3) obtain the R-T family curve by the thermistor instructions, R is asked denary logarithm, obtain the lgR-T curve, the lgR-T curve is carried out cubic fit obtain the relational expression between T and the lgR;

S4) in fixed DSP, the calculating of lnR is converted into the operate approximately of addition subtraction multiplication and division, takes " the high approximation technique of house " to obtain computing formula, and then adopt the error relative method to confirm segmented mode, adopt segmentation algorithm to obtain the lnR value of each segmentation at last;

S5) since

with S2) R that draws corresponds to S4) and segmentation in; Draw lnR; Be updated to S3) relational expression in, calculate this moment thermistor temperature value T.

2. a kind of thermistor temperature detecting method based on DSP according to claim 1 is characterized in that: the segmentation algorithm described step S4) is specially and R is carried out 2 repeatedly number formulary segmentation, makes R=2 ^a* 2 ^b, wherein a is greater than the integer that waits 0,0＜b＜1, so have:

2 ^a＜R=2 ^a* 2 ^b＜2 ^A+1, the span of the R that the temperature range that in the R-T curve, obtains detecting is corresponding is with the value of a foundation as segmentation; Obtain the lnR computing formula of each segmentation; This moment is because a is a constant, so the first addend item of lnR computing formula is constant, in the second addend item

Be the number in 1 to 2 scope, can directly use " the high approximation technique of house " and calculate.

3. a kind of thermistor temperature detecting method based on DSP according to claim 1 and 2 is characterized in that: the resistance of first resistance, second resistance and the 3rd resistance is chosen so that U _OutIn dsp chip AD end input voltage range, be as the criterion.

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