07-12-2012, 04:52 PM
Resistance Temperature Detector
Resistance Temperature Detector.pdf (Size: 3.29 MB / Downloads: 35)
a) The application of the tendency of electrical conductors to increase their electrical
resistance with rising temperature was first described by Sir William Siemens at the
Bakerian Lecture of 1871 before the Royal Society of Great Britain.
b) The necessary methods of construction were established by Callendar, Griffiths, Holborn
and Wein between 1885 and 1900.
c) RTD = Resistance Temperature Detector or PRT.
• (Platinum Resistance Thermometer).
• Resistor made from platinum, nickel, or copper. Most common material is platinum
due to purity and consistency/predictability (linear R vs. T).
Introduction:
a) Resistance thermometers
resistive thermal devices
correlating the resistance of the RTD element with temperature.
b) Most RTD elements consist of a length of fine coiled wire wrapped around a
ceramic or glass core. The element is usually quite fragile, so it is often placed
inside a sheathed probe to protect it.
Theory:
a) The simplest resistance thermometer configuration uses two wires. It is only used when
high accuracy is not required, as the resistance of the connecting wires is added to that of
the sensor, leading to errors of measurement.
b) This configuration allows use of 100 meters of cable. This applies equally to balanced
bridge and fixed bridge system
As they are almost invariably made of platinum, they are often called platinum resistance
thermometers (PRTs). They are slowly replacing the use of thermocouples in many industrial
applications below 600 °C, due to higher accuracy and repeatability
Applications of RTD:
a) Pharmaceuticals
b) Fuel custody transfer
c) Chemical
d) Tire /rubber