Document Number: 29049 For technical questions contact: nlr.europe@vishay.com www.vishay.com
Revision: 12-Apr-05 73
2381 640 3/4/6....
NTC Thermistors, Accuracy Line Vishay BCcomponents
RT VALUE AND TOLERANCE
These thermistors have a narrow tolerance on the B-value,
the result of which provides a very small tolerance on the
nominal resistance value over a wide temperature range. For
this reason the usual graphs of R = f(T) are replaced by
Resistance Values at Intermediate Temperatures Tables,
together with a formula to calculate the characteristics with a
high precision.
FORMULAE TO DETERMINE NOMINAL
RESISTANCE VALUES
The resistance values at intermediate temperatures, or the
operating temperature values, can be calculated using the
following interpolation laws
(extended “Steinhart and Hart”):
(1)
(2)
where:
A, B, C, D, A1, B1, C1 and D1 are constant values
depending on the material concerned; see table below.
Rref is the resistance value at a reference temperature (in
this event 25 °C).
T is the temperature in K.
Formulae numbered (1) and (2) are interchangeable with an
error of max. 0.005 °C in the range 25 °C to 125 °C and
max. 0.015 °C in the range −40 °Cto+25°C.
DETERMINATION OF THE
RESISTANCE/TEMPERATURE DEVIATION
FROM NOMINAL VALUE
The total resistance deviation is obtained by combining the
‘R25-tolerance’ and the ‘resistance deviation due to
B-tolerance’.
When:
X=R
25-tolerance
Y = resistance deviation due to B-tolerance
Z = complete resistance deviation,
then: or Z ≈X+Y.
When:
TC = temperature coefficient
∆T = temperature deviation,
then:
The temperature tolerances are plotted in the graphs on the
previous page.
Example: at 0 °C, assume X = 5%, Y = 0.89% and
TC = 5.08%/K (see Table ), then:
A NTC with a R25-value of 10 kΩ has a value of 32.56 kΩ
between −1.17 and +1.17 °C.
(T) R=ref e×ABT⁄CT
2
⁄DT
3
⁄+++(
T (R) = A1B1
R
Rref
----------ln C1ln2R
Rref
----------D1ln3R
Rref
----------
+++
⎝⎠
⎛⎞
1–
Z1
X
100
----------
+
⎝⎠
⎛⎞
1Y
100
----------
+
⎝⎠
⎛⎞
1–×= 100×%
∆TZ
TC
--------
=
Z1
5
100
----------
+ 1
0.89
100
-----------
+1–×
⎩⎭
⎨⎬
100%×=
1.05 1.0089 1–×
100% 5.9345% 5.93%≈
=×·
=
∆TZ
TC
--------5.93
5.08
----------- 1.167 °C 1.17≈ °C)(== =
Notes
1. Temperature < 25 °C.
2. Temperature ≥25 °C.
PARAMETERS FOR DETERMINING NOMINAL RESISTANCE VALUES
B25/85
(K) NAME
TO L . B
VALU
E %
AB
(K)
C
(105K2)
DA
1
(10−3)
B1
(10−4K−1)
C1
(10−6K−2)
D1
(10−7K−3)
1 2880
mat O. with Bn = 2880K
3
-9.094 2251.74 229098 -27448200 3.354016 3.495020 2.09596E-06 4.26062E-07
2 2990
mat P. with Bn = 3990K
3
-10.2296 2887.62 132336 -25025100 3.354016 3.415560 4.95546E-06 4.36424E-07
3 3041
mat Q. with Bn = 3041K
3
-11.1334 3658.73 -102895 516652 3.354016 3.349290 3.68384E-06 7.05046E-08
616652
4 3136
mat R. with Bn = 3136K
3
-12.4493 4702.74 -402687 3196830 3.354016 3.243880 2.65801E-06 -2.70156E-0
5 3390
mat S. with Bn = 3390K
3
-12.6814 4391.97 -232807 1509643 3.354016 2.993410 2.13513E-06 -8.05672E-0
63528
(1
mat I. with Bn = 3528K
0.5
-12.0596 3687.667 -7617.13 -5914730 3.354016 2.909670 1.63214E-06 7.1922E-08
3528
(2
-21.0704 11903.95 -2504699 247033800 3.354016 2.933910 3.49431E-06 -7.71269E-0
7 3560
mat H. with Bn = 3560K
0.75
-13.0723 4190.574 -47158.40 -11992560. 3.354016 2.884190 4.11803E-06 1.78679E-07
83740
mat B. with Bn = 3740K
2
-13.8973 4557.725 -98275 -7522357 3.354016 2.744030 3.66694E-06 1.37549E-07
93977
mat A. with Bn = 3977K
0.75
-14.6337 4791.842 -115334 -3730535 3.354016 2.569850 2.62013E-06 6.38309E-08
10 4090
mat C. with Bn = 4090K
1.5
-15.5322 5229.973 -160451 -5414091 3.354016 2.519110 3.51094E-06 1.10518E-07
11 4190
mat D. with Bn = 4190K
1.5
-16.0349 5459.339 -191141 -3328322 3.354016 2.460380 3.40538E-06 1.03424E-07
12 4370
mat E. with Bn = 4370K
2.5
-16.8717 5759.15 -194267 -6869149 3.354016 2.367720 3.58514E-06 1.25535E-07
13 4570
mat F. with Bn = 4570K
1.5
-17.6439 6022.726 -203157 -7183526 3.354016 2.264100 3.27818E-06 1.09763E-07