Caution & Terms
thermal sensors
Precautions for the
Thermal Sensors
Particulars Common to Thermal Sensors
• Excessive voltage such as ESD, could damage thermal sensors.
• Water drops from condensation or impure substances that adheres
between the electrode wires may cause insulation deficiency and
lower the resistance value of the thermal sensors. Be aware when
using this product.
• Avoid applying thermal shocks with large temperature difference in
order to maintain the accuracy of the thermistor.
• Some of the thermal sensors use special temperature sensing films.
Contact us if the sensors are constantly operated under high
temperature environment.
Platinum Thin-Film Thermal Sensors
• Welding is recommended to connect the lead wires of SDT101B,
SDT310P, SDT310MTM and SDT310AP since they are heat
resistant lead wires. Select the flux for stainless-steel when
soldering. Wash the flux with hot water after the soldering to
remove the residue completely.
• The 3-wire or 4-wire method is recommended for implementing high
precision temperature measuring for both SDT101 and SDT310 series.
• When molded or placed in a metal tube filled with resin, the
resistance value may change depending on the kind of resins used.
Terms and Definitions
Thermistor
• Thermally sensitive resistors, constructed from temperature
sensitive semi-conductive materials, with predictable, large variation
in resistance due to change in temperature. There are two kinds of
thermistors characterized by resistance change
• PTC (Positive Temperature Coefficient): Resistance increases with
a rise in temperature.
• NTC (Negative Temperature Coefficient): Resistance decreases
with a rise in temperature.
Resistance Value
High
PTC
NTC
Low
thermal
protection
Refer to the precautions of common matters for all products
in the beginning of this catalog.
Low
High
Temperature (°C)
Rated Power
• The maximum wattage which can be continuously applied to
a resistor at the rated ambient temperature.
Critical Resistance Value
• The maximum nominal resistance value at which the rated power
can be applied without exceeding the maximum working voltage.
• The rated voltage is equal to the maximum working voltage at the
critical resistance value.
Maximum Working Voltage
• Maximum D.C. or A.C. voltage that can be continuously applied
to a resistor or a thermosensor. However, the maximum value of
the applicable voltage is the rated voltage at the critical resistance
value or lower.
Overload Voltage
• Allowable voltage which is applied for 5 sec. according to the short
time overload test. Overload voltage shall be 2.5 times of rated
voltage or max. overload voltage, whichever is lower.
Curie Temperature (PTC)
• The temperature at which the resistance value starts to increase
rapidly. It is also called the switching temperature.
Resistance-Temperature Characteristic of a Thermistor (NTC)
• The relationship between a zero load resistance and a temperature or
a temperature range. It can be expressed using the following formula:
R = R0 exp {B(1/T−1/T0)}
R : Resistance Value at Temperature T (K)
R0 : Resistance Value at Temperature T0 (K)
B : B Constants T (K)=t (°C)+273.15
B Constant of a Thermistor (NTC)
• Size of change in the resistance between any two temperatures
within a specified range is calculated using the following formula:
R : Resistance Value in T (K)
R1 : Resistance Value in T1 (K)
B (K) = lnR−lnR1
1/T−1/T1
T : Standard Temperature (K)
T1 : Regulated Temperature (K)
Thermal Dissipation Constant
• The necessary power which is needed to increase the temperature
of the element 1℃ by self heating and is expressed with the following
formula:
W : Electrical input power (W)
δ(W/°C) = W/(T1−T) T : Standard Temperature (℃)
T1 : Self heating temperature generated
by applied power (°C)
Temperature Coefficient of Resistance (T.C.R.)
• Relative variation of resistance between two given temperatures
when temperature is changed by 1K, which is calculated by the
following formula.
1
T.C.R. (ppm/°C)＝ R−R0 x
x106
R0
T−T0
R : Resistance value (Ω) at T
R0 : Resistance value (Ω) at T0
T : Measured test temperature (°C)
T0 : Measured base temperature (°C)
Rated Temperature
• Maximum ambient temperature at which the power rating may be
applied continuously. The rated ambient temperature refers to the
temperature around the resistor mounted inside the equipment,
not to the air temperature outside the equipment.
Derating Curve
• Plot that expresses the relation between ambient temperature
and the maximum allowable power, which is generally expressed
in percentage.
Thermal Time Constant
• Time needed for a sensor’s temperature to change 63.2% when the
ambient temperature of a sensor is rapidly changed by a condition
in which self heat generation can be ignored.
External Conductor
• A conductor connected to a temperature sensor that is located
outside of the protective body.
Internal Conductor
• A conductor connected to a temperature sensor that is located
inside of the protective body.
Specifications given herein may be changed at any time without prior notice. Please confirm technical specifications before you order and/or use.
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KOA Speer Electronics, Inc. • 199 Bolivar Drive • Bradford, PA 16701 • USA • 814-362-5536 • Fax: 814-362-8883 • www.koaspeer.com