04.24.08
TABLE V Temperature Coefficients
TABLE V
Temperature Coefficients
+—————————+—————————–+
| PURE METALS | TEMPERATURE COEFFICIENTS |
+—————————+————–+————–+
| | CENTIGRADE | FAHRENHEIT |
+—————————+————–+————–+
| Silver (annealed) | 0.00400 | 0.00222 |
| Copper (annealed) | 0.00428 | 0.00242 |
| Gold (99.9%) | 0.00377 | 0.00210 |
| Aluminum (99%) | 0.00423 | 0.00235 |
| Zinc | 0.00406 | 0.00226 |
| Platinum (annealed) | 0.00247 | 0.00137 |
| Iron | 0.00625 | 0.00347 |
| Nickel | 0.0062 | 0.00345 |
| Tin | 0.00440 | 0.00245 |
| Lead | 0.00411 | 0.00228 |
| Antimony | 0.00389 | 0.00216 |
| Mercury | 0.00072 | 0.00044 |
| Bismuth | 0.00354 | 0.00197 |
+—————————+————–+————–+
_Positive and Negative Coefficients._ Those conductors, in which a
rise in temperature produces an increase in resistance, are said to
have positive temperature coefficients, while those in which a rise in
temperature produces a lowering of resistance are said to have
negative temperature coefficients.
The temperature coefficients of pure metals are always positive and
for some of the more familiar metals, have values, according to
Foster, as in Table V.
Iron, it will be noticed, has the highest temperature coefficient of
all. Carbon, on the other hand, has a large negative coefficient, as
proved by the fact that the filament of an ordinary incandescent lamp
has nearly twice the resistance when cold as when heated to full
candle-power.
Certain alloys have been produced which have very low temperature
coefficients, and these are of value in producing resistance units
which have practically the same resistance for all ordinary
temperatures. Some of these alloys also have very high resistance as
compared with copper and are of value in enabling one to obtain a high
resistance in small space.