NTC Thermistors Summary

NTC Thermistors
Summary
Issue date:
April 2011
• All specifications are subject to change without notice.
• Conformity to RoHS Directive: This means that, in conformity with EU Directive 2002/95/EC, lead, cadmium, mercury, hexavalent chromium, and specific
bromine-based flame retardants, PBB and PBDE, have not been used, except for exempted applications.
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NTC Thermistors
Summary
FEATURES
TDK NTC thermistors are high-quality thermistors that have been
manufactured from carefully selected high-quality materials. TDK
uses unique fine ceramics manufacturing and precision machining
to manufacture its high quality thermistors.
• Small, compact, and highly responsive to temperature changes.
• Tightly controlled B constant for predictable and accurate
temperature measurement.
• Highly reliable.
• The chip type, the glass diode type, and the resin coated type
are prepared according to the applications. Moreover, it is
possible to correspond widely as an assembly product which
makes the best use of these features.
APPLICATIONS
TDK NTC thermistors are widely used as the followings.
Field
Applications
Intake-air temperature sensors, exhaust-air
temperature sensors, cooling-water temperature
sensors, lubricating-oil temperature sensors
Oil fan heaters, solar heating systems, air
conditioners
Automobile
Air conditioning
Office automation
equipment
Medical
instruments
Cooking
appliances
Home medical
electronics
Household
appliances
Information and
Telecommunications
Copier-facsimiles, computer equipment
Clinical thermometers, intravenous injection
temperature regulators, neonatal incubators
Microwave ovens, steam ovens, electric crock pots,
electric ranges, electric ovens
Electronic clinical thermometers, warm washing
toilets, electric curling irons
Refrigerators, irons, electric water-heaters, electric
tea-pots, electric coffee-makers, washing machines,
TVs, video cassette recorders, stereo sets, radios
Cellular phones, chargeable battery pack, personal
computers
PHYSICAL PROPERTIES OF NTC THERMISTORS
INITIAL RESISTANCE
Thermistor resistance is a function of absolute temperature as indicated by the following relationship:
1
1 ............................................................ (1)
–
R=R0 • expB
T
T0
(
)
Here R0, R(kΩ) are the respective resistance values when the surrounding temperature is T0, T(K). B is the thermistor constant(B
constant below).
B CONSTANT
The B constant is found from the following equation:
B=
2.3026(logR–logR0)
1 – 1
T T0
.......................................................(2)
This B characteristic is indicated by the slope of the linear plot of
log R-1/T 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 measurements.
Resistance-temperature characteristics (Fig.1)
450 400 350 300
Temperature(˚C)
250
200
150
100
100
20kΩ /200˚C
10
Resistance (kΩ)
NTC(Negative Temperature Coefficient) Thermistors are
manufactured from sintered metal oxides. Each thermistor consists
of a combination of two to four of the following materials:
Manganese, Nickel, Cobalt and Copper.
These semiconductor resistors exhibit decreasing resistance
characteristics with increasing temperature, and have a low
thermal time constant resulting in an extremely high rate of
resistance change to accurately track the temperature.
Conformity to RoHS Directive
3.3kΩ/100˚C
1
1.4
1.6
1.8
2
2.2
1 × 10 3 (K)
T
2.4
2.6
2.8
3
TEMPERATURE COEFFICIENT
The relationship between temperature coefficient α and B becomes:
B
1 dR
α= •
= – 2 ×100(%/°C) ..............................................(3)
T
R dT
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 coefficient found at 20°C (293.15K) becomes –4%/°C.
HEAT DISSIPATION COEFFICIENT
Temperature rises due to thermal energy formed as electrical current flows through the thermistor. The thermistor temperature T0 is
then related to the surrounding temperature Ta and the electrical
input W:
W=k(T0–Ta)=V•I(mW) ............................................................(4)
k=
W
(mW/°C) ...............................................................(5)
T0 –Ta
This k value is the heat dissipation coefficient, which represents
the additional electrical power (mW/°C) needed to raise the thermistor 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 naturally important to lower the applied electrical current as much as
possible in order to reduce measurement error resulting from self
heating.
• Conformity to RoHS Directive: This means that, in conformity with EU Directive 2002/95/EC, lead, cadmium, mercury, hexavalent chromium, and specific
bromine-based flame retardants, PBB and PBDE, have not been used, except for exempted applications.
• All specifications are subject to change without notice.
004-04 / 20110428 / eb221_ntc_sum.fm
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VOLTAGE - CURRENT CHARACTERISTIC
The voltage - current characteristic indicates the drop in voltage as
electrical current through the thermistor is gradually increased.
Voltage-current characteristics (Fig.2)
100
5
4
10
3
Voltage (V)
2
1
1
0.1
Ta=25˚C (in still air)
No.1 5kΩ
2 10kΩ
3 20kΩ
4 50kΩ
5 100kΩ
10
100
1
Current (mA)
HEATING TIME CONSTANT
The time period required to heat up a thermistor from a certain
temperature T0 over a target temperature rise is called the heating
time constant. Various types of heating time constants are indicated by the symbols shown in Table 1 as determined by the percent change from T0 toward the target temperature. The standard
change is typically taken to be 63.2%.
Thermal time constants (Fig.3)
70
Heating
Th
40
Tc
30
20
(T0 –Ta)
×0.368
Temperature (˚C)
50
T0
(T0 –Ta)
×0.632
60
Room temperature Ta
Cooling
10
0
τ
2τ
3τ
4τ
5τ
6τ
7τ
Table 1 Heating time constant and temperature change ratio
Code
τ
2τ
3τ
4τ
5τ
6τ
7τ
Rate of change (%) for T0 -Ta
63.2
86.5
95.0
98.2
99.4
99.8
99.9
• All specifications are subject to change without notice.
004-04 / 20110428 / eb221_ntc_sum.fm
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PRODUCT IDENTIFICATION
NTC D S 3H G 202 J C 3
(1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11)
(12)
• Chip type: Please refer to the NTCG Series catalog (eb221_ntcg).
• Assembled products: Please refer to the NTCGP/NTCDP Series catalog (eb225_ntcdp).
(1) This code denotes NTC thermistors.
(6) Nominal resistance
This code indicates the resistance value existing at the specified ambient temperature by two significant digits followed by
the digit 0(zero).
(Example)
(2) Structural classification code
D
G
Glass sealed diode shape
Multilayer element
(3) Assembly classification code
S
C
E
D
A
B
Z
470Ω
5kΩ
10kΩ
150kΩ
Without processing
Short cut lead wire
Kinked lead wire
Kinked lead wire with insulation tube
Folded radial lead wire
Folded radial lead wire with insulation tube
Others
(7) Nominal resistance tolerance
Tolerance is identified by the following codes.
(4) B constant(Resistance temperature characteristics)
This code indicates the value of B constant using a combination
of one numeric and one alphabetic character.
Numeric code
1
2
3
4
5
B constant(K)
1000
2000
3000
4000
5000
Alphabetic code
A
B
C
D
E
F
Note: Although B constants are
G
expressed as 1A, 1B, 2A, 2B, etc.
H
using these two tables, the
alphabetic characters do not denote J
tolerances;they have the meaning
K
shown in the example below.
L
M
(Example)
N
1A=1000(K)
P
1A=1050(K)
That is, the alphabetic character(in Q
this example, A) indicates the range R
of values that can be specified by the S
thermistor user.
T
U
V
B constant(K)
0 to 50
51 to 100
101 to 150
151 to 200
201 to 250
251 to 300
301 to 350
351 to 400
401 to 450
451 to 500
501 to 550
551 to 600
601 to 650
651 to 700
701 to 750
751 to 800
801 to 850
851 to 900
901 to 950
951 to 999
(5) B constant tolerance
This code indicates tolerances using the following code.
Code
F
G
H
J
K
471
502
103
154
Tolerance(%)
±1
±2
±3
±5
±10
Code
F
G
H
J
Tolerance(%)
±1
±2
±3
±5
(8) Ambient temperature for nominal resistance
Ambient temperatures for specified nominal-resistance values
are indicated using the following codes.
Code
A
B
C
D
E
F
G
X
Ambient temperature(°C)
–20
0
25
100
200
300
20
Others
(9) Dimensional code
3
4
5
3018(3.0×ø1.8mm)
4020(4.0×ø2.0mm)
Resin dip shape
(10) Plating specification code of lead wire
N
S
Ni
Sn
(11) Packaging style
B
T
K
Bulk
Taping(Tape width: 52mm)
Taping(Tape width: 26mm)
(12) TDK internal code
• All specifications are subject to change without notice.
004-04 / 20110428 / eb221_ntc_sum.fm
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PERFORMANCE AND TEST METHODS
ELECTRICAL CHARACTERISTICS
Item
Resistance value
B constant
Heat dissipation
constant
Thermal time constant
Withstand voltage
Rated power
Test method
Measure the value at a power level such that the influences of spontaneous heat generation
can be negligible at the specified ambient temperature.
Using the following expression, calculate the value from the resistances at the two specified
ambient temperatures.
B=2.3026
Specifications
The measured values must stay
within the specified limits.
The measured values must stay
within the specified limits.
(logR – logR2)
1
1
–
T
T0
This constant denotes the power level(mW/°C) that is needed to increase the thermistor
temperature by 1°C. It is calculated by the energy consumption at any two temperatures
and previously measured resistance-temperature characteristic values using the following
expression.
W
(mW/°C)
k=
T0– Ta
The measured values must stay
within the specified limits.
Abruptly change the ambient temperature of the thermistor and measure the time until it
reaches 63.2%(1τ) of the temperature difference.
Apply the specified voltage to the electrically insulated section of the thermistor under the
specified conditions.
Measure the maximum power level at which any increment in thermistor temperature stays
within 0.2°C due to spontaneous heat generation.
The measured values must stay
within the specified limits.
No abnormalities must occur.
The measured values must stay
within the specified limits.
MECHANICL CHARACTERISTICS
Item
Tensile strength of
terminal
Bending strength of
terminal
Test method
Secure the thermistor body, and then apply a tensile force to it under the specified conditions
and maintain this state for the specified time.
Secure the thermistor body and then apply loads to it under the specified conditions. Repeat
this procedure the specified number of times.
Vibration resistance
Apply vibration under the specified conditions. Repeat this procedure the specified times.
Shock resistance
Apply shock under the specified conditions. Repeat this operation the specified number of
times.
Solderability
Solder the thermistor terminals under the specified conditions and check their solderability.
Resistance to soldering
heat
Apply a thermal soldering shock to the thermistor under the specified conditions, then leave
the thermistor in a standard state for the specified time(one hour or more), before
measurement.
Specifications
Damage must not occur.
Damage must not occur.
Measured values must stay
within the specified limits.
Measured values must stay
within the specified limits.
Measured values must exceed
the specified limits.
Measured values must stay
within the specified limits.
ENVIRONMENTAL TESTS
Item
Low temperature
storage
High temperature
storage
Heat cycle
Heat shock
Moisture resistance
High temperature
loading
Test method
Allow the thermistor to stand in air at the minimum permissible operating temperature for the
specified time. Place and maintain the thermistor in a normal condition for one hour or more
before measurements.
Allow the thermistor to stand in air at the maximum permissible operating temperature for the
specified time. Place and maintain the thermistor in a normal condition for one hour or more
before measurements.
Cycle the thermistor at the minimum permissible operating temperature, the maximum
permissible operating temperature, and room temperature for the specified time. Repeat this
cycle for the specified number of times. Subsequently, place and maintain the thermistor in a
normal condition for one hour or more before measurements.
Cycle the thermistor at the minimum permissible operating temperature and the maximum
operating temperature for the specified time respectively. Repeat this cycle for the specified
number of times. Subsequently, place and maintain the thermistor in a normal condition for
one hour or more before measurements.
Allow the thermistor to stand in air at the specified temperature and relative humidity for the
specified times. Subsequently, place and maintain the thermistor in a normal condition for
one hour or more before measurements.
Apply the specified electrical load to the thermistor at the maximum permissible operating
temperature for the specified time. After that, place and maintain the thermistor in a normal
condition for one hour or more before measurements.
Specifications
Measured values must stay
within the specified limits.
Measured values must stay
within the specified limits.
Measured values must stay
within the specified limits.
Measured values must stay
within the specified limits.
Measured values must stay
within the specified limits.
Measured values must stay
within the specified limits.
• The test conditions and the specified values are decided individually.
• All specifications are subject to change without notice.
004-04 / 20110428 / eb221_ntc_sum.fm