Data Sheet

-93-
184. Understanding PPM
Build the circuit shown on the left and turn on the switch (62). Press the press switch
(61) and you will see the bi-directional LED (71) and colorful LED (72) light. Release the
press switch (61) and the bi-directional LED (71) and colorful LED (72) will stay bright
briey and then turn dim. Understanding how to calculate the effects of temperature on
a resistor value can be confusing as it is specied in Parts Per Million (PPM). You can
think of the PPM value of a resistor as providing the resistance tolerance per degree
Centigrade for a 1MW resistor. If a 1MW resistor was specied as 50 PPM, this would
mean the actual value of the resistor could be between 9,999,950W to 1,000,050W
for a 1 degree temperature change from the reference temperature (usually 20 or 25
degrees Celsius). Basically, for every million Ohms, a 50 PPM resistor could vary by 50
Ohms for every degree Centigrade change.
185. PPM Color Code
Replace the 1kW resistor (42) in project #184 with the 10kW resistor (44) and then turn on
the switch (62). Press the press switch (61) and you will see the bi-directional LED (71) and
colorful LED (72) light. Release the press switch (61) and the bi-directional LED (71) and
colorful LED (72) will stay bright for a little while and then turn dim. The table below shows
the color coding for the Temperature Coefcient of Resistance (TCR) for 6 band resistors.
186. 10kW Resistor Temperature Tolerance Example
Replace the 1kW resistor (42) in project #184 with the 10kW resistor (44) and then turn
on the switch (62). Press the press switch (61) and you will see the bi-directional LED
(71) and colorful LED (72) light. Release the press switch (61) and the bi-directional LED
(71) and colorful LED (72) will stay bright for a while and then turn dim. If we had a 10kW
resistor with a 6th band that is yellow, then this would mean that for every temperature
degree change from the reference, the actual resistance of the resistor could vary
by 25*10,000/1,000,000 = 0.25W. So if the resistor was used in an unusually hot
environment, say 20 degrees above the reference, then this could lead to a 20*0.25 =
5W difference in the actual resistance of the resistor.
187. 100kW Resistor Temperature Tolerance Example
Replace the 1kW resistor (42) in project #184 with the 100kW resistor (45) and then
turn on the switch (62). Press the press switch (61) and you will see the bi-directional
LED (71) and colorful LED (72) light. Release the press switch (61) and the bi-directional
LED (71) and colorful LED (72) will stay bright for a long time before turning dim. If we
had a 100kW resistor with a 6th band that is green, then this would mean that for every
temperature degree change from the reference, the actual resistance of the resistor
could vary by 20*100,000/1,000,000 = 2W. So if the resistor was used in an unusually
cold environment, say 20 degrees below the reference, then this could lead to a 20*2 =
40W difference in the actual resistance of the resistor.
Color TCR (ppm/
O
C)
Brown 100
Red 50
Orange 15
Yellow 25
Green 20
Blue 10
Violet 5
Gray 1
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