This document discusses resistance temperature detectors (RTDs), which are devices that measure temperature by measuring the resistance of an electrical wire. It describes how an RTD works by explaining that the resistance of the wire increases with increasing temperature in a linear and repeatable manner. It then discusses the different types of RTDs, focusing on wire-wound and thin film RTDs, and explains their constructions. Finally, it covers the different wiring configurations for RTDs, comparing 2-wire, 3-wire, and 4-wire configurations and how each handles lead wire resistance.

1. HINDUSTHAN COLLEGE OF ENGINEERING & TECHNOLOGY
RESISTANCE TEMPERATURE
DETECTOR
Department of Biomedical Engineering

2. INTRODUCTION
• A Resistance Temperature Detector (also known as a Resistance
Thermometer or RTD) is an electronic device used to determine the
temperature by measuring the resistance of an electrical wire.
• This wire is referred to as a temperature sensor.
• If we want to measure temperature with high accuracy, an RTD is the
ideal solution, as it has good linear characteristics over a wide range of
temperatures.
• The resistance increases as the temperature of the sensor increases.

3. INTRODUCTION
• The resistance vs temperature relationship is well known and is
repeatable over time.
• An RTD is a passive device.
• It does not produce an output on its own.
• External electronic devices are used to measure the resistance of the
sensor by passing a small electrical current through the sensor to
generate a voltage.
• The variation of resistance of the metal with the variation of the
temperature is given as,

4. INTRODUCTION
• The variation of resistance of the metal with the variation of the
temperature is given as,
Where, Rt and R0 are the resistance values at toC and t0
oC temperatures. α
and β are the constants depends on the metals.

5. WORKING
• In RTD devices; Copper, Nickel and Platinum are widely used metals.
• These three metals are having different resistance variations with
respective to the temperature variations.
• That is called resistance-temperature characteristics.

6. CONSTRUCTION

7. TYPES OF RTD
• In Wire-wound RTD uses platinum wire wound
around a ceramic or glass bobbin.
• The construction keeps the platinum wire loose and
lets it expand and contract freely with a change in
temperature.
• This minimizes long-term stress-induced resistance
change, but has very poor resistance to vibration and
is primarily limited to lab use.

8. TYPES OF RTD
• In Thin Film, the bifilar winding is wound around the
bobbin and then sealed with molten glass, ceramic
cement, or another high-temperature, non-conductive
coating.
• This construction helps protect the wire from
vibration, but it is prone to long-term stress induced
resistance change when the bobbin and platinum wire
have different temperature coefficients of expansion.

9. WIRING CONFIGURATIONS
• A 2-wire configuration is the simplest but
the least accurate configuration.
• This constructions result in leadwire
resistance getting added to the element
resistance.
• 2-wire RTD’s are mostly used with short lead
wires or where close accuracy is not required.

10. WIRING CONFIGURATIONS
• 3-wire construction is most commonly used in
industrial applications where the third wire provides a
method for removing the average lead wire resistance
from the sensor measurement.
• It works by measuring the resistance between #1 & #2
(R 1+2) and subtracting the resistance between #2 & #3
(R 2+3) which leaves just the resistance of the RTD bulb
(R b).
• This method assumes that wires 1,2 & 3 are all the
same resistance.

11. WIRING CONFIGURATIONS
• True 4-wire resistance measurement will effectively
cancel leadwire resistance error even if all 4 wires
are not the same.
• It is used primarily in the laboratory where close
accuracy is required.
• This method assumes that wires 1,2 & 3 are all the
same resistance.
• The 4-wire circuit is a true 4-wire bridge, which
works by using wires 1 & 4 to power the circuit and
wires 2 & 3 to read.