R = k L / A (1) where R = resistance (ohm, Ω) k = constant of proportionality or resistivity of the material (ohm, Ω) L = length of conductor (m) A = cross sectional area of conductor (m2) Resistivity and temperature can be expressed as
kt = ko [1 + α (t – to)] (2) where kt = resistivity at temperature t (ohm, Ω) ko = resistivity at standard temperature to (ohm, Ω) α = temperature coefficient of resistance (1/oC, Ω/ΩoC) t = temperature (oC) to = standard temperature (oC)Combining (1) and (2):
R / Ro = α t + 1 (3)Resistance Temperature Coefficients
Material | Temperature Coefficient of Resistance – α – (1/oC, Ω/ΩoC) |
---|---|
Nickel | 0.0067 |
Iron | 0.002 to 0.006 |
Tungsten | 0.0048 |
Aluminum | 0.0045 |
Copper | 0.0043 |
Lead | 0.0042 |
Silver | 0.0041 |
Gold | 0.004 |
Platinum | 0.00392 |
Mercury | 0.0009 |
Manganin | +- 0.00002 |
Carbon | -0.0007 |
Electrolytes | -0.02 to -0.09 |
Thermistor | -0.068 to 0.14 |
ASTM Standards Related to Resistance Temperature Detectors
- E 644-98 Standard Test Methods for Testing Industrial Resistance Thermometers
- E 1137-97 Standard Specification for Industrial Platinum Resistance Thermometers
- E 1652-00 Standard Specification for Magnesium Oxide and Aluminum Oxide Powder and Crushable Insulators Used in the Manufacture of Metal-Sheathed Platinum Resistance Thermometers, Base Metal Thermocouples, and Noble Metal Thermocouples
ASTM Standards Related to Temperature and Calibration:
- E 1594-99 Standard Guide for the Expression of Temperature
- E 344-01a…Terminology Relating to Thermometry and Hygrometry
- E 563-97 Standard Practice for Preparation and Use of Freezing Point Reference Baths
- E 1502-98 Standard Guide for the Use of Freezing Point Cells for Reference Temperatures
- E1750-02 Standard Guide for Use of Water Triple Point Cells
DIN – German Industrial Standards Organization
- DIN 43760 references nickel precision
- DIN IEC 751 reference platinum precision resistance thermometers.