Operation
3-28
3.12.2 Resistor temperature coefficient testing
Temperature coefficient is the rate of change of resistance
with respect to temperature, typically expressed as ppm/°C
(parts per million per degree centrigrade).
For example, a resistor that measures exactly 100Ω at 25°C
with a temperature coefficient of 100ppm/°C should not
change more than 10mΩ per °C of temperature change. That
resistor measured at 35°C should read between 99.900 and
100.100Ω (100Ω±100mΩ).
Temperature coefficient is calculated from the following
equation:
where:
TC = temperature coefficient in ppm/°C
∆R = change in resistance (reference resistance – test re-
sistance)
R = actual resistance at the reference temperature
∆T = change in temperature (reference temperature – test
temperature)
Typically, several samples of a particular resistor from a ven-
dor will be tested to verify the specifications. The tempera-
ture coefficient is usually checked at several temperature
points to ensure its integrity over a range of temperatures.
Evaluation of resistors can be done with a Model 2001-TC-
SCAN card in a DMM to make temperature and 4-terminal
resistance measurements. Temperature coefficients are cal-
culated with respect to the resistance measurement made at
a reference temperature. Thermal EMFs generated by con-
nections in the test circuit are cancelled by the offset-com-
pensated ohms feature of the DMM.
Figure 3-6 shows a system that can test accuracy and temper-
ature coefficient of up to seven resistors that have the same
specifications (resistance and temperature coefficient.)
The thermocouple is connected to channel 2, while a short is
connected to channel 3 to allow for offset compensation. The
HI terminals of the resistors are connected to channels 3-10,
while the LO terminals are connected to the DMM LO ter-
minals.
TC
∆
R()10
6
()
R()
∆
T()
--------------------------=
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