Rtd Termal Resistive

Reference data and engineering information about rtd termal resistive for miscellaneous applications.

rtdtermalresistive

Overview

Engineering reference data for Rtd Termal Resistive in miscellaneous.

Key Formulas

Unit Conversion

$y = x \cdot k$

Multiply by conversion factor.

Linear Interpolation

$y = y_1 + \frac{(x - x_1)(y_2 - y_1)}{x_2 - x_1}$

Estimate between two known points.

Percentage

$p = \frac{\text{part}}{\text{whole}} \times 100\%$

Part as fraction of whole.

Symbol	Description	Unit
$x$	Input value	—
$y$	Output value	—
$k$	Conversion factor	—

Temperature Coefficients of Resistance for Common Materials
Material	Temperature Coefficient (α)(1/°C, Ω/Ω°C)
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

Platinum is the preferred metal for RTDs due to its chemical stability, availability in a highly pure form, and reproducible electrical properties. RTD elements can be made small enough for fast response times (a fraction of a second).

Self-Heating Effect

Measuring an RTD's resistance requires a small current (typically ~1 mA) to generate a measurable voltage drop. This current dissipates power as heat within the sensor ( $P = I^2R$ ), causing its temperature to rise above the ambient environment—a phenomenon known as Joule heating. The degree of self-heating depends on the power dissipated and the heat transfer efficiency between the sensor and its surroundings (e.g., it is greater in still air than in a moving fluid).

Standards & Specifications

ASTM Standards for RTDs

*ASTM E1137: Standard Specification for Industrial Platinum Resistance Thermometers (defines Grade A and B tolerances).
*ASTM E644: Standard Test Methods for Testing Industrial Resistance Thermometers.
*ASTM E1652: Specification for insulating powders used in metal-sheathed RTD manufacturing.

*ASTM E1594: Guide for the Expression of Temperature.
*ASTM E344: Terminology Relating to Thermometry and Hygrometry.
*ASTM E563: Practice for Preparation and Use of Freezing Point Reference Baths.
*ASTM E1502: Guide for Using Freezing Point Cells for Reference Temperatures.
*ASTM E1750: Guide for Use of Water Triple Point Cells.
*DIN IEC 751: German standard for platinum resistance thermometers.
*DIN 43760: German standard for nickel resistance thermometers.

References

Original Source

Source: engineeringtoolbox.com