Engineering ToolBox - Resources, Tools and Basic Information for Engineering and Design of Technical Applications!

RTD Resistance Temperature Sensor

Thermal resistive sensor - a basic introduction.

Sponsored Links

RTDs are manufactured from metals whose resistance increases with temperature. Within a limited temperature range, the resistivity increases linearly with temperature. Each metals specific, and unique resistivity, can be determined experimentally. This resistance is directly proportional to a metal wire's length, and inversely proportional to the cross-sectional area.

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

RTD Resistance Temperature Sensors - Coefficients of Resistance
MaterialTemperature Coefficient 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

The chemical stability, availability in pure form, and highly reproducible electrical properties, has made Platinum the metal of choice for RTD's which are made of either IEC/DIN-grade platinum or reference-grade platinum. The difference lies in the purity of the platinum. The IEC/DIN standard is pure platinum that is intentionally contaminated with other platinum

The RTD sensors can be made small enough to have response times of a fraction of a second.

To measure the resistance of an RTD a small electric current (about 1 mA) must flow through the sensor to create the necessary voltage drop. The current causes the platinum element in the RTD to heat up above the temperature of the RTD's environment (Also called Joule heating). The heating is proportional to the electric power (P = I2 R) in the RTD and the heat transfer between the RTD sensing element and the RTD environment. If the RTD is in a poor heat transfer medium (e.g., air), it will heat up more than if it is in a fluid, such as water. The electrical current will heat the sensor and may influence the measurement.

Tolerances for RTD's should meet the standards of ASTM E1137 Grade A or B and IEC 751 Class A or B.

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.
Sponsored Links

Related Topics

Related Documents

Sponsored Links

Search

Search is the most efficient way to navigate the Engineering ToolBox.

Engineering ToolBox - SketchUp Extension - Online 3D modeling!

3D Engineering ToolBox Extension to SketchUp - add parametric components to your SketchUp model

Add standard and customized parametric components - like flange beams, lumbers, piping, stairs and more - to your Sketchup model with the Engineering ToolBox - SketchUp Extension - enabled for use with older versions of the amazing SketchUp Make and the newer "up to date" SketchUp Pro . Add the Engineering ToolBox extension to your SketchUp Make/Pro from the Extension Warehouse !

Translate this Page

Translate this page to Your Own Language .

About the Engineering ToolBox!

Privacy Policy

We don't collect information from our users. More about

Citation

This page can be cited as

  • The Engineering ToolBox (2003). RTD Resistance Temperature Sensor. [online] Available at: https://www.engineeringtoolbox.com/rtd-termal-resistive-d_498.html [Accessed Day Month Year].

Modify the access date according your visit.

3D Engineering ToolBox - draw and model technical applications! 2D Engineering ToolBox - create and share online diagram drawing templates! Engineering ToolBox Apps - mobile online and offline engineering applications!

Unit Converter

















































2.19.10

Sponsored Links
.