CN105910733A - AT (Automatic Transmission)-used NTC (Negative Temperature Coefficient) temperature sensor analysis method - Google Patents

Abstract

The invention discloses an AT (Automatic Transmission)-used NTC (Negative Temperature Coefficient) temperature sensor analysis method. Comparative analysis is carried out according to effective parameters provided by an NTC temperature sensor product selection guide, and based on an analysis result on the NTC temperature sensor R-T features and a material constant, an NTC temperature sensor type best matched with the actual working condition application is thus determined. According to the actual applications of a certain automatic transmission, the R-T (resistance vs temperature) features of the NTC temperature sensor are analyzed, the using precision of the sensor is evaluated according to the main working temperature range of a hydraulic pressure system oil way on the basis, AD (Analogue Digital) circuit features of a TCU system are analyzed at the same time, errors of the temperature measurement system are finally confirmed, the AT can accurately monitor the system temperature during the operation process, and stable, quick and accurate control is thus realized.

Description

A kind of analysis method of AT NTC temperature sensor

Technical field:

The present invention relates to a kind of analysis method, be specifically related to a kind of analysis method of AT NTC temperature sensor.

Background technology:

Hydraulic automatic speed variator (Automatic Transmission) is the one of automatic commercial-vehicle gearbox, mainly should It is used under the operating modes such as city bus.The action of the mechanical parts such as variator internal clutch, brake is dependent on hydraulic oil and carries out , hydraulic oil is fluid torque-converter (Torque Convert) pump impeller, the Transfer Medium of turbine torque, for brake, clutch The medium of strength transmission, lubrication, the medium of retarder work are provided during work.The oil temperature of hydraulic system is crucial performance ginseng Number, be variator operationally need monitoring significant variable.The control system making AT obtains under different operating modes accurately, stablizes Temperature signal be non-the normally off key.

Needing to carry out according to system requirements the selection of temperature sensor in actual applications, the most common temperature passes Sensor is broadly divided into two kinds, PTC (Positive Temperature Coefficient) positive temperature coefficient sensor and NTC (Negative Temperature Coefficient) negative temperature coefficient sensor, the characteristic of PTC sensor is that resistance is with temperature Degree rises and increases, and NTC temperature sensor is the most contrary.When carrying out the type selecting of concrete sensor, concern is primarily with sensing The certainty of measurement of device, but due to non-linear in whole operating temperature range of both sensors, sensor cannot be whole Unified precision is ensured in temperature range.

Summary of the invention:

Present invention aims to the deficiencies in the prior art, it is provided that the analysis of a kind of AT NTC temperature sensor Method.

For reaching above-mentioned purpose, the present invention adopts the following technical scheme that and realizes:

A kind of analysis method of AT NTC temperature sensor, according to having that NTC temperature sensor product type selection handbook provides Effect parameter is analyzed contrast, based on to NTC temperature sensor R T characteristic and the analysis result of material constant, so that it is determined that with The NTC temperature sensor model of the optimal coupling of actual condition application.

The present invention is further improved by: based on the analysis knot to NTC temperature sensor R T characteristic and material constant Really, calculating and the analysis of following three parts are carried out respectively:

Calculate the temperature coefficient α, temperature coefficient α of NTC temperature sensor by for follow-up system temperature analysis of measurement errors Foundation is provided；

The definition of temperature coefficient α is: NTC temperature sensor at the percentage ratio of every degree Celsius of lower change in resistance, %/DEG C, its Computing formula is as follows:

$\mathrm{\α}=\frac{1}{R_T}\×\frac{dR}{dT}\×100$

Wherein, R_TIt it is the resistance of sensor under absolute temperature T；

In actual applications this formula is converted into:

$\mathrm{\α}=\frac{1}{R_T}\×\frac{\mathrm{\Δ}R}{\mathrm{\Δ}T}\×100$

Δ T: the temperature gap between adjacent temperature spot, unit DEG C；

Δ R: the resistance difference between adjacent temperature spot, unit Ohn；

By the resistance that can find NTC temperature sensor under every degree Celsius that the R-T parameter of NTC temperature sensor is tabled look-up Value, can obtain Δ R and Δ T by the resistance at adjacent temperature is done difference, thus the temperature coefficient α under obtaining every degree Celsius；

Measurement temperature-time to sensor responds and is analyzed simultaneously, to understand NTC temperature sensor in reality application In time expression behaviour；

When analyzing this characteristic, the R-T characteristic of NTC temperature sensor need to be taken out a mathematical relationship, it may be assumed that transmission letter Number H (S), when we input certain external signal to this function, sensor mathematical relationship based on himself is calculated One output signal, the typical sensor function of the NTC temperature sensor being currently known is first-order system:

$H\left(s\right)=\frac{1}{\mathrm{\τ}s+1}$

Wherein, s is the independent variable of Laplace function；

τ is time constant；

This sensor function is loaded the value that step signal can try to achieve the time response of its correspondence；

The AD sample circuit of NTC temperature sensor is carried out performance evaluation, understands operation principle and the filtering of sample circuit Characteristic；

Typical NTC temperature sensor sampling circuit is bleeder circuit, i.e. NTC temperature sensor R_ntc and pull-up resistor R1 carries out dividing potential drop to voltage source VCC_ref:

$V_{in}=VCC\_ref\×\frac{R\_ntc}{R1+R\_ntc}$

Resistance R_ntc of NTC temperature sensor changes along with the change of temperature, so Vin can reflect in real time accordingly Voltage；

When the filtering characteristic of analytical sampling circuit, network function H (j ω) analytic process need to be used:

$H\left(j\mathrm{\ω}\right)=\frac{\stackrel{\·}{R}}{\stackrel{\·}{E}}$

Wherein,The Stable State of Sine vector of circuit；

The sinusoidal input vector of circuit；

By the analysis of circuit network function being tried to achieve the cut-off frequency f of this circuit_c, the size of cut-off frequency reflects The capacity of resisting disturbance of circuit, the namely filtering characteristic of circuit；

Analysis result by three above part so that NTC temperature sensor has been had more by user in actual applications For comprehensively understanding, the systematic measurement error for subsequent step provides parameter foundation simultaneously.

The present invention is further improved by: NTC temperature sensor temperature coefficient-α and to AD sample circuit filtering characteristic Analysis result, carry out systematic overall analysis of measurement errors, obtain final temperature measurement system error characteristics.

Relative to prior art, the present invention has a following beneficial effect:

When choosing temperature sensor, product manual the most only can describe the service precision of product qualitatively, but in reality Border needs the requirement of actual working condition according to measurand to carry out the temperature range paid close attention to determining quantitative analysis to judge to pass in using Whether the certainty of measurement of sensor meets the requirement of system, and the R-T characteristic that the present invention proposes from NTC temperature sensor goes out Sending out, according to the material constant Beta of sensor, temperature coefficient Alpha can calculate the error under sensor arbitrary temp point, from And the measured value of accurate analyte sensors.

When the measurement error of the system of analysis, it is considered that the certainty of measurement of system is equal to the precision of sensor itself, And have ignored the error that sensor interface circuitry brings, cause correctly finding error source.

Typical AD (Analogue Digital) filtering characteristic of interface circuit, the certainty of measurement of sensor are entered by the present invention Go analysis, on this basis, sensor and interface circuit are considered as an entirety, by resistance, the electricity of analysis interface circuit The error in source, finally gives measurement system error characteristics in whole operating temperature range.According to above method to NTC temperature Sensor, the specificity analysis of AD interface circuit, make understanding these parts table in systems that our energy is relatively sharp Existing, thus stability, the reliability for AT control system provides and ensures.

In sum, the present invention is according to the actual application of certain automatic gear-box, the R-T to NTC temperature sensor (resistance vs temperature) characteristic is analyzed, and passes according to the prevailing operating temperatures ranging assessments of hydraulic system oil circuit on this basis The service precision of sensor, is analyzed the AD circuit characteristic of TCU system simultaneously, thus finally confirms temperature measurement system Error, makes AT can accurately monitor system temperature in running, thus realizes stable, quick.Control accurately.

Accompanying drawing illustrates:

Fig. 1 NTC temperature sensor R-T curve；

Fig. 2 NTC temperature sensor 100&NTC temperature sensor-2057 sensor R-T curve；

Fig. 3 NTC temperature sensor-1000 sensor temperature coefficient vs senor operating temperature；

The step response of Fig. 4 NTC temperature sensor-1000 sensor；

Fig. 5 typical case's AD interface circuit；

The frequency response curve of Fig. 6 filter circuit；

Fig. 7 AD circuit temperature measurement error.

Detailed description of the invention:

Below in conjunction with drawings and Examples, the present invention is made further instructions.

R-T (the resistance vs temperature) characteristic of NTC temperature sensor is the sensor that resistance declines along with temperature rising, as Shown in Fig. 1.(in Fig. 1 as a example by certain brand NTC temperature sensor-1000 model sensor), this product resistance when-40 DEG C For 33487.4Ohm, resistance when 150 DEG C is 19.31Ohm.

Typical NTC temperature sensor R-T characteristic relation is:

$R_T=R_{25}{e}^{\left\{B(\frac{1}{T}-\frac{1}{298.15})\right\}}\mathrm{...}\left(1\right)$

Wherein, R_TResistance of sensor under absolute temperature T, unit-Ohm；

R₂₅Resistance of sensor under 25 degrees Celsius, unit-Ohm；

B sensor material constant Beta, unit Kelvin K；

T absolute temperature T, unit-Kelvin K.

Understand according to formula (1), resistance R when being aware of sensor 25 DEG C₂₅And sensor material constant Beta (B) After, the resistance under arbitrary temp T can be tried to achieve, make the control system can be according to R_TValue calculates corresponding temperature.

When making a concrete analysis of the characteristic of NTC temperature sensor, 3 key parameters of main consideration:

● material constant Beta (β) Material Coefficient；

● temperature coefficient Alpha (α) Temperature Coefficient；

● thermal response time Thermal Constant Time.

(1) B material constant:

Resistance and the temperature of sensor is found after the R-T characteristic of NTC temperature sensor is carried out lot of experiments Mathematical relationship be approximately exponential function:

$R_T={\mathrm{Ae}}^{\left(\frac{\mathrm{\β}}{T}\right)}\mathrm{...}\left(2\right)$

R_TResistance of sensor under absolute temperature T；

T absolute temperature T, unit Kelvin K；

A-linear coefficient；

β index coefficient, is the temperature vs resistance coefficient determined by sensor self material.

The equation can accurately represent temperature and the value relatable of NTC temperature sensor in certain temperature range, But owing to NTC temperature sensor is the most not an ideal element, if should by this mathematical model When being used in a wider temperature range, it finds that the parameter (β β) in the equation cannot describe whole temperature accurately In the range of R-T relation, found by measurement in actual applications, β β value is not in the whole temperature range of sensor Changeless, but can change along with the variation of ambient temperature residing for NTC temperature sensor, measurement result shows β β value meeting Reduce along with the rising of temperature.

In order to describe sensor R-T characteristic in certain temperature range the most accurately, can basis Two actual temperature measuring point (R₁, T₁) and (R₂, T₂) calculate the material constant Beta (B) of sensor, describe more with this For R-T characteristic curve accurately:

$R_1={\mathrm{Ae}}^{\left(\frac{\mathrm{\β}}{T_1}\right)}\mathrm{...}\left(3\right)$

$R_2={\mathrm{Ae}}^{\left(\frac{\mathrm{\β}}{T_2}\right)}\mathrm{...}\left(4\right)$

$B=ln\frac{R_1}{R_2}\×\left(\frac{1}{\frac{1}{T_1}-\frac{1}{T_2}}\right)\mathrm{...}\left(5\right)$

Material constant Beta is the parameter that sensor is the most crucial, and it is the eyeball (R concrete by two₁, T₁)、(R₂, T₂) calculate and get, illustrating a kind of build-in attribute of sensor, the size of this value is by the material of sensor self Matter, the characteristic such as processing technology determines, once sensor production completes, and Beta value will not change.

The size of Beta value illustrates sensor at temperature spot T₁With T₂Between R-T characteristic, i.e. in this temperature range pass The change in resistance rule of sensor, this value is the biggest, represents that the resistance of sensor changes along with the change of temperature spot the most obvious, Beta value carry out sensor ratio compared with time be an important reference frame:

As a example by two real sensor parameters of certain brand:

The NTC temperature sensor 1000 resistance when 25 DEG C and 100 DEG C is respectively 1000Ohm, 69.24Ohm；

The NTC temperature sensor 2057 resistance when 25 DEG C and 100 DEG C is respectively 2057Ohm, 187.53Ohm；

5. calculate according to formula and can try to achieve:

B₁₀₀₀=4032.6K

B₂₀₅₇=7179.1K

Two sensors R-T characteristic between 25 DEG C to 100 DEG C is drawn, such as Fig. 2 according to Beta value

Observing Fig. 2 can find, it is the most precipitous that the resistance of NTC temperature sensor-2057 declines along with the rising of temperature, I.e. slope is bigger.This explanation is during variations in temperature, and the rate of change of resistance is bigger, and this makes the measurement system can be the cleverest Quick, catch the change of unit temperature clearly.

Calculating NTC temperature sensor, when the rate of change of the resistance of any temperature spot T, refers to another ginseng Number-temperature coefficient-α.

(2) α temperature coefficient:

The definition of α is: sensor is at the percentage ratio of every degree Celsius of lower change in resistance:

R_TIt it is the resistance of sensor under absolute temperature T；

This formula would generally be converted in actual applications:

$\mathrm{\α}=\frac{1}{R_T}\×\frac{\mathrm{\Δ}R}{\mathrm{\Δ}T}\×\mathrm{100...}\left(7\right)$

Typical case's application is as follows:

Understanding the NTC temperature sensor-1000 resistance when 25 DEG C by inquiry product sensor handbook is 10000Ohm, α is-4.39%/DEG C, finding that sensor resistance in certain medium is 12000Ohm if measured, examination calculates medium temperature now 7. degree, then can be calculated according to such as formula:

Then corresponding for 12000Ohm medium temperature is 25 DEG C-0.456 DEG C=24.554 DEG C

Temperature coefficient α illustrates the percentage ratio of sensor change in resistance at different temperatures, can calculate phase by this parameter Answer the temperature value under resistance, more crucially can calculate correspondence according to sensor resistance error Δ R under unit temperature Temperature error Δ T.

Owing to R-T (the resistance VS temperature) characteristic of NTC temperature sensor is nonlinear, therefore temperature coefficient is passing Also it is nonlinear in the whole working range of sensor.Knowable to 3, the value of α is relatively big at low-temperature space, and the value of Δ R under every Δ T is described Relatively big, along with this value of rising of temperature can reduce.

(3) T.C-thermal time constant (Thermal Time Constant):

When measuring certain medium temperature with sensor, can sensor quickly respond the change of ambient temperature, is Whether the dynamic response of we same concern, i.e. sensor meets the demand of system.When analyzing dynamic response, can root Judge according to the transfer function H (s) of sensor.Show according to substantial amounts of test data, the biography of NTC temperature sensor Delivery function H (s) is a typical first-order system:

$H\left(s\right)=\frac{1}{\mathrm{\τ}s+1}\mathrm{...}\left(8\right)$

Wherein, s is the independent variable of Laplace function；τ is time constant；

The time constant determining τ transmission function according to first-order system response time.

I.e. sensor is issued to the time of steady-state value 63.2% at Stepped Impedance Resonators r (t)=1 (t).By Laplce's inversion Change to try to achieve sensor output under time domain and respond and be:

$h\left(t\right)=1-e\frac{-t}{\mathrm{\τ}}\mathrm{...}\left(9\right)$

Understand according to formula (9), (τ=4.84 × 10 in Fig. 4 when sensor is at the time point of 1 τ^-3), it is output as 0.632, i.e. reach the 63.2% of steady-state value ' 1 ', illustrated that the value of timeconstantτ here is exactly the thermal time constant of sensor T.C.General sensor supplier can be given product under certain medium from temperature spot A to the thermal time constant of temperature spot B, i.e. should Response time under operating mode, but in actual applications due to measured medium, the difference of temperature spot A, B, concrete response time is Different, so tentatively can be judged by the thermal time constant of the transfer function model elder generation simulation calculation sensor of sensor Whether sensor meets the requirement of system under this operating mode, is verified by experimental test the most again.

When having grasped above 3 parameters of every money NTC temperature sensor product, then can the most comprehensively understand this product Concrete property, provide for follow-up system matches and support.

After determining the concrete model of sensor, the AD circuit by TCU is needed to be acquired by the signal of sensor Being read out for application layer program, typical case's AD interface circuit is as follows,

VCC_ref: upper pull-up voltage；

R1: divider resistance；

R2: filter resistance:

R_ntc temperature sensor: NTC temperature sensor

C1: filter capacitor；

ADC: analog-digital converter (Analogue Digital Convertor).

AD circuit operation principle is as follows: NTC temperature sensor shows different resistances in different ambient temperatures Value (characteristic is as shown in Figure 1), then the value of Vin can change along with the change of temperature:

$V_{in}=VCC\_ref\×\frac{R\_ntc}{R1+R\_ntc}\mathrm{...}\left(10\right)$

V_inThe R of rear end₂And C₁Forming basic RC low-pass filter circuit, here we need to analyze this circuit simultaneously Frequency response, to understand filtering characteristic, is calculated by the network function H (j ω) of circuit,

$H\left(j\mathrm{\ω}\right)=\frac{\stackrel{\·}{R}}{\stackrel{\·}{E}}$

::Stable State of Sine for circuit is vectorial,For the sinusoidal input vector of circuit, can try to achieve according to vector method:

$H\left(j\mathrm{\ω}\right)=\frac{\frac{1}{{\mathrm{j\ωC}}_1}}{\frac{1}{{\mathrm{j\ωC}}_1}+R_2}=\frac{1}{1+{\mathrm{j\ωR}}_2{C}_1}=\frac{1}{\sqrt{1+{\mathrm{\ω}}^2{R}_2^2{C}_1^2}}\∠-{\mathrm{arctan\ωR}}_2{C}_1$

$\left|H\left(j\mathrm{\ω}\right)\right|=\frac{1}{\sqrt{1+{\mathrm{\ω}}^2{R}_2^2{C}_1^2}}$

The angular frequency of RC filter circuit is understood according to above formula The then cut-off frequency of circuitIllustrate that the signal higher than 33Hz can be attenuated when by this circuit, root Understanding according to the definition by frequency, the power of these signals can decay more than half.

By the analysis of filter circuit cut-off frequency being helped the characteristic of our apparent understanding AD interface circuit.

Can be to the certainty of measurement of system after the characteristic of the R-T characteristic and AD interface circuit of having understood NTC temperature sensor It is analyzed:

In the ideal situation, V_outV should be equal to_in, i.e. the front-end port of ADC should capture NTC temperature sensor accurately Magnitude of voltage, but in actual applications, V_Ref, R₁, R₂Value be not preferable, these values have error in actual applications, So can be to V_in、V_outImpacting, according to these error amounts, we can analyze the measurement error of AD circuit.

When analyzing this error, what we calculated is the maximum error of measuring of circuit, i.e. according to V_Ref, R₁, R₂Three variablees The systematic measurement error that caused of maximum error.

Error definition according to resistance understands, and the error of resistance is made up of three parts: initial error, ageing error, And temperature drift.The resistance error parameter that here we use is as follows:

Table 1 resistance error table

Then R₁、R₂Error amount R '₁、R′₂It is respectively as follows:

R′₁=R₁× (1+1%+1%+ (T-25 × 100 ÷ 10⁶)

R′₂=R₂× (1+5%+10%+ (T-25 × 250 ÷ 10⁶)

T Celsius temperature DEG C

Upper pull-up voltage V_RefIt is to be provided by the power module on TCU, understands V by inquiry chip handbook_RefError V′_ref=V_ref± 2%

According to R '₁、R′₂、V′_refThe V under arbitrary temp T can be calculated_out:

$V_{out}=\frac{R_{NTC}}{R_{NTC}+R_1^{\′}}\×V_{ref}^{\′}-R_2^{\′}\×I_{leakage}$

I_leageFor the leakage current (leakage current can be obtained by inquiry chip handbook) on ADC, this electric current stream Through R '₂Time can cause V_inBetween V_outPressure drop, therefore this factor need to be considered in the lump,

Obtain V_outAfter need the NTC temperature sensor resistance R ' corresponding under this magnitude of voltage of inverse_NTC, by formula 10. Understand

$R_{NTC}^{\′}=\frac{V_{out}\×R_1}{V_{\mathrm{Re}f}-V_{out}}$

Further according to NTC temperature sensor temperature coefficient α calculate Δ T, the temperature error values under the most each temperature spot,

$\mathrm{\Δ}T=\frac{\mathrm{\Δ}R}{R_T}\×\frac{100}{\mathrm{\α}}=\frac{R_{NTC}^{\′}-R_{NTC}}{R_{NTC}}\×\frac{100}{\mathrm{\α}}$

By R '₁、R′₂、V′_ref、α、I_leageValue bring into respectively and can draw AD system in the whole operating temperature range of sensor Interior curve of error, as it is shown in fig. 7, according to said method, i.e. obtained the measurement error of whole system.

Claims (3)

1. the AT analysis method of NTC temperature sensor, it is characterised in that: according to NTC temperature sensor product type selection hands The actual parameter that volume provides is analyzed contrast, based on to NTC temperature sensor R T characteristic and the analysis result of material constant, So that it is determined that the NTC temperature sensor model most preferably mated with actual condition application.

The analysis method of a kind of AT NTC temperature sensor the most according to claim 1, it is characterised in that: based on to NTC Temperature sensor R T characteristic and the analysis result of material constant, carry out calculating and the analysis of following three parts respectively:

The temperature coefficient α, temperature coefficient α that calculate NTC temperature sensor will provide for follow-up system temperature analysis of measurement errors Foundation；

The definition of temperature coefficient α is: NTC temperature sensor at the percentage ratio of every degree Celsius of lower change in resistance, %/DEG C, it calculates Formula is as follows:

$\mathrm{\α}=\frac{1}{R_T}\×\frac{dR}{dT}\×100$

Wherein, R_TIt it is the resistance of sensor under absolute temperature T；

In actual applications this formula is converted into:

$\mathrm{\α}=\frac{1}{R_T}\×\frac{\mathrm{\Δ}R}{\mathrm{\Δ}T}\×100$

Δ T: the temperature gap between adjacent temperature spot, unit DEG C；

Δ R: the resistance difference between adjacent temperature spot, unit Ohn；

By the resistance that can find NTC temperature sensor under every degree Celsius that the R-T parameter of NTC temperature sensor is tabled look-up, logical Cross and the resistance at adjacent temperature is done difference can obtain Δ R and Δ T, thus the temperature coefficient α under obtaining every degree Celsius；

The measurement temperature-time of sensor is responded simultaneously and be analyzed, to understand NTC temperature sensor in actual applications Time expression behaviour；

When analyzing this characteristic, the R-T characteristic of NTC temperature sensor need to be taken out a mathematical relationship, it may be assumed that transfer function H (S), when we input certain external signal to this function, sensor mathematical relationship based on himself is calculated one Output signal, the typical sensor function of the NTC temperature sensor being currently known is first-order system:

$H\left(s\right)=\frac{1}{\mathrm{\τ}s+1}$

Wherein, s is the independent variable of Laplace function；

τ is time constant；

This sensor function is loaded the value that step signal can try to achieve the time response of its correspondence；

The AD sample circuit of NTC temperature sensor is carried out performance evaluation, understands operation principle and the filtering characteristic of sample circuit；

Typical NTC temperature sensor sampling circuit is bleeder circuit, i.e. NTC temperature sensor R_ntc and pull-up resistor R1 pair Voltage source VCC_ref carries out dividing potential drop:

$V_{in}=VCC\_ref\×\frac{R\_ntc}{R1+R\_ntc}$

Resistance R_ntc of NTC temperature sensor changes along with the change of temperature, so Vin can reflect corresponding electricity in real time Pressure；

When the filtering characteristic of analytical sampling circuit, network function H (j ω) analytic process need to be used:

$H\left(j\mathrm{\ω}\right)=\frac{\stackrel{\·}{R}}{\stackrel{\·}{E}}$

Wherein,The Stable State of Sine vector of circuit；

The sinusoidal input vector of circuit；

By the analysis of circuit network function being tried to achieve the cut-off frequency f of this circuit_c, the size of cut-off frequency reflects circuit Capacity of resisting disturbance, the namely filtering characteristic of circuit；

Analysis result by three above part so that NTC temperature sensor has been had the most complete by user in actual applications The understanding in face, the systematic measurement error for subsequent step provides parameter foundation simultaneously.

The analysis method of a kind of AT NTC temperature sensor the most according to claim 2, it is characterised in that: NTC temperature passes Sensor temperature coefficient-α and the analysis result to AD sample circuit filtering characteristic, carry out systematic overall analysis of measurement errors, Obtain final temperature measurement system error characteristics.