Page 288 - Mechanical Engineer's Data Handbook

276 MECHANICAL ENGINEER'S DATA HANDBOOK

7.4.6 Thermal e.m.f. for thermocouple
combinations

Thermal e.m.f, for common thermocouple combinations (reference junction at 0 "C)

E.m.f. (mV)
Temperature
Copper/ Chromel/ Iron/ Chromel/ Platinum
"F "C constantan constantan constantan alumel 10% rhodium
- 300 - 184 - 5.284 - 8.30 -7.52 -5.51 -
- 250 - 157 -4.747 - -6.71 -4.96 -
- 200 - 129 -4.111 - 6.40 - 5.76 - 4.29 -
- 150 - 101 - 3.380 - -4.68 - 3.52 -
- 100 - 73 - 2.559 - 3.94 - 3.49 -2.65 -
- 50 - 46 - 1.654 - - 2.22 - 1.70 -
0 - 18 -0.670 - 1.02 -0.89 -0.68 -
50 10 0.389 - 0.05 0.04 -
100 38 1.517 2.27 1.94 1.52 0.221
150 66 2.71 1 - 3.41 2.66 0.401
200 93 3.967 5.87 4.91 3.82 0.595
250 121 5.280 - 6.42 4.97 0.800
300 149 6.647 9.71 7.94 6.09 1.017
350 177 8.064 - 9.48 7.20 1.242
400 204 9.525 13.75 1 1.03 8.31 1.474
450 232 1 1.030 - 12.57 9.43 1.712
500 260 12.575 17.95 14.12 10.57 1.956
600 316 15.773 22.25 17.18 12.86 2.458
700 371 19.100 26.65 20.26 15.18 2.977
800 427 - 3 1.09 23.32 17.53 3.506
lo00 538 - 40.06 29.52 22.26 4.596
1200 649 - 49.04 36.01 26.98 5.726
1500 816 - 62.30 - 33.93 7.498
1700 927 - 70.90 - 38.43 8.732
2000 1093 - - - 44.91 10.662
2500 1371 - - - 54.92 13.991
3000 1649 - - - - 17.292

1.4.7 Electronic thermocouple This has a robust sheathed thermocouple connected to
thermometer a voltmeter which gives a digital or analogue readout
of temperature. It avoids many of the usual disadvan-
tages of thermocouples.
1.4.8 Resistance thermometers
Resistance thermometers are based on the fact that the
electrical resistance of a metal wire varies with tem-
perature. The metals most used are platinum and
nickel, for which the resistance increases with tempera-
ture in a linear manner.