Data Sheet

-92-
182. Resistor Temperature Effects
Build the circuit shown on the left and turn on the switch (62). Press
the press switch (61) and you will see the star LED (70) and colorful
LED (72) light. Release the press switch (61) and the star LED (70)
and colorful LED (72) will stay bright for a while and then turn dim.
Actual resistance of a resistors can vary based on temperature. At
higher temperatures, electrons become more free to move around
and this reduces resistance. At lower temperatures electrons are less
free to move around which increases resistance. Again, for the need
for very high accuracy resistors, it becomes necessary to specify the
Temperature Coefcient of Resistance (TCR) of the resistor. TCR is
usually expressed in Parts Per Million per degree Centigrade (often
just referred to as PPM). This tells you how much the resistance of the
resistor can change for every degree change in temperature.
183. 6-Band Resistors
Replace the 10kW resistor (44) in project #182 with the 100kW resistor
(45) and then turn on the switch (62). Press the press switch (61) and
you will see the star LED (70) and colorful LED (72) light. Release the
press switch (61) and the star LED (70) and colorful LED (72) will stay
bright for several seconds before turning dim. When high accuracy is
needed for resistor values, it can become important to specify how the
resistance of the resistor changes with temperature. Because of this,
6-band resistors have been introduced that provide a band to specify
the TCR. See the gure below. This would be a 316*102 = 31,600W
resistor that would be accurate to within 1% (31,284W to 31,916W)
with 50ppm change per degree Centigrade.
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