B221_NTCCM
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NTCCM Series NTCCM1005, 1608, 2012 Types
Sensors
Temperature Sensors
NTC Thermistors
PHYSICAL PROPERTIES OF NTC THERMISTORS
INITIAL RESISTANCE
HEAT DISSIPATION COEFFICIENT
Thermistor resistance is a function of absolute temperature as
indicated by the following relationship:
Temperature rises due to thermal energy formed as electrical cur-
rent flows through the thermistor. The thermistor temperature T0 is
then related to the surrounding temperature Ta and the electrical
input W:
1
T
1
............................................................ (1)
–
R=R0 • expB
(
)
T0
Here R0, R(kΩ) are the respective resistance values when the sur-
rounding temperature is T0, T(K). B is the thermistor constant(B
constant below).
W=k(T0–Ta)=V•I(mW) ............................................................(4)
W
...............................................................(5)
W(%/°C)
k=
T0–Ta
This k value is the heat dissipation coefficient, which represents
the additional electrical power (mW/°C) needed to raise the ther-
mistor temperature by 1°C. This heat dissipation coefficient varies
with changes in the measurement and environmental conditions.
When a thermistor is used for temperature measurement, it is nat-
urally important to lower the applied electrical current as much as
possible in order to reduce measurement error resulting from self
heating.
B constant
The B constant is found from the following equation:
2.3026(logR–logR0)
R=
....................................................... (2)
1
T
1
T0
–
This B characteristic is indicated by the slope of the linear plot of
log R vrs inverse absolute temperature.
The B constant value is generally in the vicinity of 2500K to 5000K.
B constant values of 3000K to 4000K are frequently used for mea-
surements.
VOLTAGE - CURRENT CHARACTERISTIC
The voltage - current characteristic indicates the drop in voltage as
electrical current through the thermistor is gradually increased.
Resistance-temperature characteristics (Fig.1)
450 400 350 300 250
200
150
100
100
10
1
Voltage-current characteristics (Fig.2)
100
20kΩ/200°C
5
4
10
3
2
1
3.3kΩ/100°C
1
(
)
Ta=25°C in still air
No.1 5kΩ
2
3
4
5
10kΩ
20kΩ
50kΩ
100kΩ
1.4
1.6
1.8
2
1
T
2.2
2.4
2.6
2.8
3
×103 °C
(
)
0.1
1
10
100
(
)
Current mA
TEMPERATURE COEFFICIENT
The relationship between temperature coefficient α and B becomes:
1
R
dR
dT
1
T2
............................................. (3)
α=
•
=–
×100(%/°C)
The negative sign of the temperature coefficient indicates that the
temperature coefficient decreases as both thermistor resistance
and temperature rise. If B is taken as 3400K, the temperature coef-
ficient found at 20°C (293.15K) becomes –4%/°C.
Specifications which provide more details for the proper and safe use of the described product are available upon request.
All specifications are subject to change without notice.