an iron-constantan (Type J) thermocouple instead of the ... extended so the
copper-to-iron junctions are made on .... This procedure works with voltmeters.
Practical Temperature Measurements* RTD
Thermistor
R
VOLTAGE TEMPERATURE
T
V or I
R
RESISTANCE
V
TEMPERATURE
T
I. C. Sensor
VOLTAGE or CURRENT
Thermocouple
RESISTANCE
TEMPERATURE
T
TEMPERATURE
T
□ Self-powered □ Most stable □ High output □ Most linear □ Simple □ Most accurate □ Fast □ Highest output □ Rugged □ More linear than □ Two-wire ohms □ Inexpensive □ Inexpensive thermocouple measurement □ Wide variety □ Wide temperature range
Disadvantages Advantages
□ Non-linear □ Expensive □ Non-linear □ T 0 0. 11 (typical) T < 0
The exact values for coefficients α , β , and δ are determined by testing the RTD at four temperatures and solving the resultant equations. This familiar equation was replaced in 1968 by a 20th order polynomial in order to provide a more accurate curve fit. The plot of this equation shows the RTD to be a more linear device than the thermocouple: Z-35
