Main technical parameters of NTC Thermistor __ thermistor

Original http://blog.sina.com.cn/s/blog_605538500101bd3p.html

0 Power resistor value RT (Ω)

RT refers to the resistance value measured by measuring power that causes the change in the resistance value to be negligible in relation to the total measurement error when the specified temperature T is used. Olympian Sincerity

The relationship between resistance value and temperature variation is:

RT = RN EXPB (1/t–1/tn)

RT: NTC thermistor resistance at temperature T (K).
RN: NTC thermistor resistance at rated temperature TN (K).
T: The specified temperature (K).
The material constant of the B:NTC thermistor, also known as the Thermosensitive index.
Exp: the index (e = 2.71828) with natural number e as the base. ）。

The equation is an empirical formula, only in the limited range of the rated temperature TN or the rated resistor resistance RN, because the material constant B itself is also a function of the temperature T.

Rated 0 Power resistor value R25 (Ω) Olympian sincerity

According to national standards, the rated 0 power resistance is the NTC thermistor at the benchmark temperature of 25 ℃ measured resistance value R25, this resistance value is the NTC thermistor nominal resistance value. The NTC thermistor is commonly referred to as the value of the resistance.

Material constant (thermosensitive index) B value (K)

The B value is defined as:

RT1: The 0 Power resistance value when the temperature T1 (K).
RT2: The 0 Power resistance value when the temperature T2 (K).
T1, T2: Two specified temperatures (K).

For the commonly used NTC thermistor, the B value range is generally between 2000K ~ 6000K.

0 Power resistance temperature coefficient (αt)

The relative variation of the NTC thermistor 0 Dynamic Power resistance value at the specified temperature is the ratio of the temperature variation to the change.

Αt: The temperature coefficient of 0 power resistance at temperature T (K).
RT: Temperature T (K) when the 0 power resistance value.
T: Temperature (T).
B: Material constants.

Dissipation coefficient (δ)

At the specified ambient temperature, the NTC thermistor dissipation coefficient is the ratio of the dissipation power variation of the resistor to the corresponding temperature change of the resistor.

Δ: NTC thermistor dissipation coefficient, (mw/k).
P:NTC thermistor consumption Power (MW).
When the T:NTC thermistor consumes power P, the corresponding temperature changes (K) of the resistor body.

Thermal time constant (TAU)

Under 0 power conditions, when the temperature changes, the temperature of the thermistor varies from two to 63.2% of the temperature difference, the thermal time constant is proportional to the heat capacity of NTC thermistor, and inversely proportional to its dissipation coefficient.

Tau: Thermal Time constant (S).
Thermal capacity of C:NTC thermistor.
Δ: The dissipation coefficient of NTC thermistor.

Rated Power PN

In the prescribed technical conditions, the thermal resistor long-term continuous work of the allowable power consumption. Under this power, the resistance body temperature does not exceed its maximum operating temperature.

Maximum operating temperature Tmax

Under the prescribed technical conditions, the thermal resistor can be a long-term continuous operation of the maximum allowable temperature. That

t0-ambient temperature.

Measuring power PM

In the specified ambient temperature, the resistance of the resistive body under the measured current heating can be neglected when compared with the total measurement error.
General requirements for resistance changes greater than 0.1%, then the measurement power PM is:

Resistance temperature characteristics

The temperature characteristics of NTC thermistor can be approximated by the following formula:

In-style:
RT: Temperature T when zero power resistance value.
A: The coefficients relating to the physical properties and geometrical dimensions of the thermistor material.
B:b value.
T: Temperature (k).
The more accurate expression is:

In-style: RT: thermistor in temperature T when the 0 power resistance value.
T: For absolute temperature value, K;
A, B, C, D: for a specific constant. Basic characteristics of thermistors -resistance-temperature characteristics

The resistance-temperature characteristics of the thermistor can be approximately expressed in type 1.

(Type 1) R=ro Exp {B (i/t-i/to)}

R	: The resistance value of temperature T (K)
Ro	: The resistance value when temperature T0 (K)
B	: B Value
*t (K) = T (ºc) +273.15

But in fact, the thermistor's B value is not constant, the size of the change due to the composition of the material, the largest or even up to 5k/°c. Therefore, the application of 1 o'clock in a large temperature range, there is a certain error between the measured value.

Here, if the B-value in Type 1 is calculated as the function of the temperature as shown in type 2, the error between the measured values can be reduced and the approximate equivalence can be considered.

(Type 2) Bt=ct2+dt+e

C, D, and e are constants in the formula.
In addition, the fluctuation of B value caused by different production conditions can cause the constant e to change, but the constant C and D will not change. Therefore, when discussing the fluctuation of B value, only the constant e can be considered.


• calculation of constants C, D, E
Constants C, D, E can be 4 (temperature, resistance) data (T0, R0). (T1, R1). (T2, R2) and (T3, R3), calculated by means of 3~6.
First, the B1,B2,B3 is derived from Model 3 based on the resistance values of the T0 and T1,T2,T3, which are then introduced into the following various samples.




• Calculation example of resistance value

According to the resistance-temperature characteristic table, the resistance value of the thermistor at 25°c is 5 (KΩ), and the B-value deviation is (K) of the resistor in the 10°c~30°c.

• Steps

(1) According to the resistance-temperature characteristics of the table, the constant C, D, E. T o=25+273.15 t 1=10+273.15 t 2=20+273.15 t 3=30+273.15

(2) substituting bt=ct2+dt+e+50 for BT.

(3) Substituting the numeric value into R=5exp {(bti/t-i/298.15)} for R.
*t:10+273.15~30+273.15

• resistance-temperature characteristics shown in Figure 1
resistance temperature coefficient

The so-called resistance temperature coefficient (α) refers to the change rate of 0 load resistance at any temperature when the temperature changes to °c (K). The relationship between the resistance temperature coefficient (α) and the B value can be obtained by the Formula 1 differential.



Here the minus sign (-) before Alpha indicates that the zero-load resistance decreases when the temperature rises.

heat dissipation coefficient (jis-c2570)

Heat dissipation coefficient (δ) is the power required to heat a thermistor element through its own heat to increase its temperature by a thermal equilibrium state.
In thermal equilibrium, the relationship between temperature T1, ambient temperature T2 and consumption power p is shown in the following form.



The value of the product catalogue is the typical value under the following measurement conditions.

(1)	At 25°c, still in the air.
(2)	The axial pin and the warp pin type are determined in the factory state.

rated Power (jis-c2570)

At the rated ambient temperature, the maximum power of continuous load can be run.
Product Catalog record value is at 25°c for the rated ambient temperature, the value calculated from the next formula.

(type) rated Power = heat dissipation factor X (maximum operating temperature -25) maximum running power

Maximum operating power =tx heat dissipation coefficient ... (3.3)
This is the use of thermistor for temperature detection or temperature compensation, the temperature of their own heating up the allowable value of the corresponding power. (Not defined in JIS.) When the allowable temperature rises t°c, the maximum operating power can be calculated by the lower formula. Thermal response time constants for ambient temperature changes (jis-c2570)

Refers to the time required for a thermistor element to produce a temperature change of 63.2% of the temperature difference between the initial temperature and the final temperature when the ambient temperature of the thermistor changes dramatically at 0 load state.

When the ambient temperature of the thermistor changes from T1 to T2, the following relationship between the time t and the thermistor temperature T exists.

t=	(T1-T2) exp (-t/τ) +t2 ... (3.1)
	(T2-T1) {1-exp (-t/τ)}+t1 ..... (3.2)

Constant tau is called thermal response time constant.
T=τ (T-T1)/(T2-T1) = 0.632.

In other words, as described in the above definition, the time required for a thermistor to produce a temperature change of 63.2% of the initial temperature difference is the thermal response time constant.

The relationship between the time and the temperature change rate of thermistor is shown in the following table.




The Product catalog record value is a typical value under the following conditions of measurement.

(1)	When ambient temperature changes from 50°c to 25°c in the stationary air, the temperature of the thermistor changes to the time required for 34.2°c.
(2)	The axial pin and radial pin type are determined in the factory state.

It should be noted that the heat dissipation coefficient and thermal response time constant vary with ambient temperature and assembly conditions.

　

　

NTC negative temperature coefficient thermistor r-t characteristics

B the same value, different resistance r-t characteristic curve diagram