CN104048777B - Temperature value and resistance value conversion method for NTC-type thermistor - Google Patents

Abstract

The invention discloses a temperature value and resistance value conversion method for an NTC-type thermistor. According to the method, parameters in an empirical formula are obtained through software in a fitting mode according to a corresponding table of the temperature value and the resistance value supplied by a thermistor manufacturer, the temperature value or the resistance value is substituted in the empirical formula, and the corresponding temperature value or the resistance value is worked out and is implemented through computer programming in an engineering application; the empirical formula of the relation between the resistance value and the temperature value of the NTC-type thermistor is that . By means of the new empirical, the method can be directly applied to engineering, the error compared with the actual detecting data is small within the larger temperature range, and meanwhile the computing amount is small.

Description

Temperature for ntc type critesistor and resistance value conversion method

Technical field

The present invention relates to the ntc type thermistor technology of temperature measuring device, especially for ntc type critesistor temperature with Resistance value conversion method.

Background technology

Ntc (negative temperature coefficient, negative temperature coefficient) type critesistor refers to its resistance The resistance that value raises with temperature and reduces, because it is temperature sensitive, precision is higher, low price, easy to use the advantages of, quilt It is widely used in various thermometric occasions.Its resistance value of ntc critesistor and temperature are in nonlinear correspondence relation, and this characteristic increases The difficulty of thermometric in practical application.Solving ntc critesistor non-linear method at present mainly has experience equation, a young waiter in a wineshop or an inn Take advantage of fitting process, hardware circuit penalty method, software checking book method etc..Method of least square needs to enter under obtaining substantial amounts of experimental data OK, workload is larger, and committed memory is also larger.The requirement to electronic devices and components for the hardware circuit penalty method is higher, multiple with circuit The increase of miscellaneous degree, also brings circuit additive error simultaneously.Software checking book method is widely adopted in actual applications, but it is right The storage-space requirement of hardware is larger, and its inquiry velocity is relatively slow, if being used in combination interpolation rule inquiry velocity more Slowly, the corresponding table that most of producers provide only is accurate to 1 °, and therefore its precision is also poor.Traditional expression resistance value and temperature it Between the formula of relation be exponential equation, concrete formula is as follows:

$r_t=r_{t0}{e}^{b(\frac{1}{t}-\frac{1}{t0})}---\left(1\right)$

In formula: r_tIt is the resistance value that temperature is during t (k), r_t0It is the resistance value that temperature is during t0, b is critesistor constant.

But this exponential equation is under wider temperature range, the nonlinearity erron of introducing is larger, in unmodified feelings Substantially can not directly use under condition.

The equation that another is widely used in calculating ntc critesistor is the steinheart-hart containing 3 coefficients Equation and its curved-edge polygons, concrete formula is as follows:

$\frac{1}{t}=c_0+c_1{\mathrm{lnr}}_t+c_2{\left({\mathrm{lnr}}_t\right)}^2---\left(2\right)$

In formula: c₀, c₁, c₂For constant, rt is the resistance value that temperature is during t (k).

This curved-edge polygons relative indices error in equation is less, but the equation is that 2 rank exponential equations are more complicated.Therefore its Parameter fitting difficulty is larger, and in engineer applied operand also than larger.The curved-edge polygons of steinheart-hart also have 3 Rank and the form of 4 ranks, equation excessively complexity is it has not been convenient to use in engineering.Therefore traditional empirical equation also less in reality Middle application, in order to solve the contradiction between error and formula complexity, has document to propose the methods such as disjunction matching.

Although said method can be used for realizing the conversion of resistance and temperature, all there is conversion speed slowly, or It is a lot of problem of the higher grade of error.

Content of the invention

The present invention is to solve above-mentioned technical problem it is proposed that a kind of relatively simple temperature for ntc type critesistor With resistance value conversion method, this process employs a kind of new empirical equation, the parameter in formula is obtained by approximating method, should Method can directly use in engineering, and it is less with measured data error within the scope of larger temperature, and amount of calculation is relatively simultaneously Little.

Technical scheme is as follows:

Temperature and resistance value conversion method for ntc type critesistor it is characterised in that:

The temperature value table corresponding with resistance value being provided according to critesistor producer first, simulates empirical equation using software In parameter, then bring temperature value or resistance value into using empirical equation, you can to calculate corresponding temperature value or electricity Resistance, is realized by computer programming in engineer applied；Wherein, the pass between the resistance value of ntc type critesistor and temperature value System, is expressed as follows by empirical equation:

$r=10\·e^{(a+\frac{b}{t+c})}---\left(3\right)$

In formula: r is the resistance value that temperature is during t, t is kelvin degree.

Empirical equation in this method is to develop from traditional exponential equation, with formula in background technology (1) The main distinction is that t has added constant term c as denominator, and constant a and b is without being bound by the pass of temperature and critesistor constant System, under specific parameter setting, equation of the present invention can be equal to exponential equation.Parameter a, b, c are carried with producer by empirical equation For tables of data obtained using software matching, there is no specific physical significance.

In practical engineering application, a should be obtained using origin software matching manufacturer data in advance, b, c, in fit procedure The matching initial value of a, b, c need to be calculated and arranged according to the parameter that producer provides, if arbitrarily setting initial value is likely to result in Calculate and do not restrain, that is, software can not calculate correct result.Then parameter is substituted into empirical equation 3, and empirical equation 3 is carried out Programming, finally inputs r or t, you can in a program to export corresponding t or r.

It is an advantage of the current invention that:

The method being calculated with respect to traditional utilization index formula, within the scope of bigger temperature with measured data more It coincide；

Method with respect to being calculated using high-order formula, the formula that this method utilizes is more succinct, fitting parameter The amount of calculation of amount of calculation and equation is all less, and arithmetic speed is faster；

Less with respect to the computer stored space of the higher occupancy of look-up table precision, in engineer applied, arithmetic speed is more Hurry up；The speed of look-up table depends on the size write with data volume in table of software algorithm, and in table, the bigger result of data volume is more smart Really, but software lookup speed is slower, and it is bigger to take Computer Storage space.

Brief description

Fig. 1 is the observed temperature and resistance plot being obtained according to table 1 in the embodiment of the present invention；

Fig. 2 is index equation curve and measured curve comparison diagram in the embodiment of the present invention；

Fig. 3 is empirical equation curve and measured curve comparison diagram in the embodiment of the present invention；

Fig. 4 is the error pair of temperature that rule of thumb formula, exponential formula calculate and measured value in the embodiment of the present invention Than figure.

Specific embodiment

Taking the 103f3435rt model ntc critesistor of thinking electronic industrial formula as a example. The resistivity-temperature characteristics table that this model critesistor producer provides is shown in Table 1.

Table 1

First with origin software to parameter a, b, c are fitted, and are drawn according to the data in subordinate list 1 and obtain as Fig. 1 Shown observed temperature and resistance curve (with manufacturer data as measured data).

Nonlinear fitting function, self-defined input equation formula y=10 exp (a+b/ (x+ is utilized in origin software C)), wherein x is equal to temperature t, and y is equal to resistance r, and a, b, c are set to variable.The initial value of a, b, c can carry according to referring to producer For 25 ° when parameter set, for example can according to setting a=-b25/t25, b=b25, c=0, now then according to table 1, a =-3435/298.15=-11.521, b=3435, c=0.When initial value is arranged as previously mentioned, equation expression formula of the present invention is y =10 exp (- b25/t25+b25/x), with the finger brought into according to parameter t0=t25=25 DEG C r0=r25=10k b=b25 Number equation is identical, sees formula (1), thus it is also seen that exponential equation is a kind of special circumstances of equation of the present invention.According to Above-mentioned parameter sets, and draws exponential equation curve and producer's measured curve contrast is as shown in Figure 2.

As seen from Figure 2, directly using exponential equation, and substitute into after the provided parameter of manufacturer calculated, equation is asked The curve obtaining differs larger with measured curve, and particularly in low temperature range, equation income value is very big with actual value error, substantially Engineer applied can not directly be carried out.Setting a, using the initial value of exponential function during b, c initial value, primarily to avoid origin to exist Produce software error and be unable to matching because initial value is too poor when matching.Origin software nonlinear fitting instrument inputs After good formula and initial parameter values, click on matching button till reduced chi-sqr (residual sum of squares (RSS)) no longer changes, Obtain a=-13.36422, b=4741.1285, c=56.6196.The therefore temperature of 103f3435rt critesistor and ohmmeter Reach formula as follows:

$r=10\·e^{(-13.36422+\frac{4741.1285}{t+56.6196})}---\left(5\right)$

Wherein: r/k ω is resistance value during t/k for temperature.

Formula (5) is programmed (c language etc. can be used in engineer applied to computer or single-chip microcomputer using excel It is programmed), in input table 1 in excel, temperature value can get resistance value, draws Equation for Calculating curve obtained bent with actual measurement Line comparison diagram is as shown in Figure 3.

Equation for Calculating curve and measured curve essentially coincide as seen from Figure 3, precision higher can direct engineer applied, Record critesistor resistance value first and then substitution formula 5 just can calculate temperature.With actual measurement under identical resistance value The temperature that temperature deducts calculating obtains error, and Fig. 4 depicts temperature and the error of measured value that empirical equation calculates, and makees simultaneously Go out exponential formula and calculate error in data as a comparison.

By Fig. 4 it can also be seen that the formula error of present aspect is very little, within the scope of very big temperature, error is all close 0, and traditional exponential equation then error is larger.

Claims (3)

1. be used for temperature and the resistance value conversion method of ntc type critesistor it is characterised in that: first according to critesistor producer The temperature value table corresponding with resistance value providing, simulates constant term a, b and the c in empirical equation using software, then utilizes warp Test formula and calculate corresponding temperature value or resistance value, realized by computer programming in engineer applied；Wherein, ntc type heat Relation between the resistance value of quick resistance and temperature value, is expressed as follows by empirical equation:

$r=10\·e^{(a+\frac{b}{t+c})}$

In formula: r is the resistance value that temperature is during t, t is kelvin degree.

2. the temperature for ntc type critesistor according to claim 1 and resistance value conversion method it is characterised in that: Described software is origin software.

3. the temperature for ntc type critesistor according to claim 1 and resistance value conversion method it is characterised in that: Simulate constant term a, b using software, the matching initial value of c need to be calculated and set according to the parameter that critesistor producer provides Put.