Basic Concepts RESISTENCE OF ANY METAL CHANGES WITH

Basic Concepts Ø RESISTENCE OF ANY METAL CHANGES WITH ITS TEMPERATURE CHANGE. Ø RTDs ARE Positive Temperature Co-efficient Device i. e. Their effective resistance increases with the increase in temperature Ø RTDs are sensors used to measure temperature by correlating the resistance of the RTD element with temperature. Ø 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.

Ø The RTD element is made from a pure material whose resistance at various temperatures has been documented. The material has a predictable change in resistance as the temperature changes; it is this predictable change that is used to determine temperature Ø The RTD is one of the most accurate temperature sensors. Not only does it provide good accuracy, it also provides excellent stability and repeatability. Ø RTDs are also relatively immune to electrical noise and therefore well suited for temperature measurement in industrial environments, especially around motors, generators and other high voltage equipment. 10/29/2021 2

2 Wire PT 100 provides one connection to each end of the sensor. This construction is suitable particularly where the changes in lead resistance due to ambient temperature changes can be ignored.

3 Wire PT 100 provides one connection to one end and two to the other end of the sensor. Connected to an instrument designed to accept three-wire input, compensation is achieved for lead resistance and temperature change in lead resistance. This is the most commonly used configuration

Common Resistance Material for RTDs Ø Ø Platinum (most popular and accurate) Nickel Copper Balco (rare) Tungsten (rare 10/29/2021 ` Ø 5

Typical Design

RTD Element The RTD element is the simplest form of RTD. It consists of a piece of wire wrapped around a ceramic or glass core. Because of their compact size, RTD elements are commonly used when space is very limited. 10/29/2021 7

A surface element is a special type of RTD element. It is designed to be as thin as possible thus providing good contact for temperature measurement of flat surfaces.

RTD Probes The RTD probe is the most rugged form of RTD. A probe consists of an RTD element mounted inside a metal tube, also known as a sheath. The sheath protects the element from the environment. 10/29/2021 9

RTD PROBES (Thermowell)