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Vishay BCcomponents
NTC Thermistors, Accuracy Line
Document Number: 29049
Revision: 10-Oct-03
For technical questions contact: nlr.europe@vishay.com
www.vishay.com
73
R
T
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, A
1
, B
1
, C
1
and D
1
are constant values
depending on the material concerned; see table below.
R
ref
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
°
C to +25
°
C
.
DETERMINATION OF THE
RESISTANCE/TEMPERATURE DEVIATION
FROM NOMINAL VALUE
The total resistance deviation is obtained by combining the
‘R
25
-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 R
25
-value of 10 k
has a value of 32.56 k
between
1.17 and +1.17
°
C.
R (T)
R
=
ref
e
×
A
B T
C T
2
D T
3
+
+
+
(
)
T (R) = A
1
B
1
ref
R
ln
C
1
ln
2
ref
R
D
1
ln
3
ref
R
+
+
+
1
–
Z
1
100
+
1
100
+
1
–
×
=
100
×
%
T
TC
=
Z
1
100
+
1
100
+
1
–
×
100%
×
1.05
1.0089 1
×
{
}
100%
5.9˙
5.93%
≈
(
)
=
×
=
T
TC
5.08
1.167
°
C
1.17
≈
°
C
)
(
=
=
=
PARAMETERS FOR DETERMINING NOMINAL RESISTANCE VALUES
Notes
1.
Temperature < 25
°
C.
2.
Temperature
≥
25
°
C.
B
25/85
-VALUE
(K)
A
B
(K)
C
(10
5
K
2
)
D
(10
6
K
3
)
A
1
(10
3
)
B
1
(10
4
K
1
)
C
1
(10
6
K
2
)
D
1
(10
7
K
3
)
2880
2990
3041
3136
3390
3528
(1)
3528
(2)
3560
3740
3977
4090
4190
4370
4570
9.094
10.2296
11.1334
12.4493
12.6814
12.0596
21.0704
13.0723
13.8973
14.6337
15.5322
16.0349
16.8717
17.6439
2251.74
2887.62
3658.73
4702.74
4391.97
3687.667
11903.95
4190.574
4557.725
4791.842
5229.973
5459.339
5759.15
6022.726
229098
132336
102895
402687
232807
7617.13
2504699
47158.4
98275
115334
160451
191141
194267
203157
27.4482
25.0251
0.516652
31.96830
15.09643
5914730
247033800
11992560.91
7522357
3730535
5414091
3328322
6869149
7183526
3.354016
3.354016
3.354016
3.354016
3.354016
3.354016
3.354016
3.354016
3.354016
3.354016
3.354016
3.354016
3.354016
3.354016
3.495020
3.415560
3.349290
3.243880
2.993410
2.909670
2.933908
2.884193
2.744032
2.569355
2.519107
2.460382
2.367720
2.264097
2.095959
4.955455
3.683843
2.658012
2.135133
1.632136
3.494314
4.118032
3.666944
2.626311
3.510939
3.405377
3.585140
3.278184
4.260615
4.364236
7.050455
2.70156
8.05672
0.719220
7.71269
1.786790
1.375492
0.675278
1.105179
1.034240
1.255349
1.097628