Resistance Temperature Detectors (RTDs): An Overview

Resistance thermometers, commonly known as Resistance Temperature Detectors (RTDs), are highly accurate and reliable sensors used to measure Temperature by correlating the resistance of the RTD element with Temperature. They are widely used in applications where precision and stability are critical. Unlike thermocouples, RTDs operate based on the predictable change in electrical resistance of certain metals—most notably platinum—with Temperature.

RTDs are valued for their excellent repeatability, long-term stability, and accurate linear output over a broad Temperature range. They are commonly employed in laboratory, industrial, and commercial settings for Temperature monitoring and control, especially in processes requiring consistent and precise measurements.

Working Principle

The working principle of an RTD is rooted in the positive Temperature coefficient of electrical resistance exhibited by metals like platinum, nickel, or copper. As the Temperature increases, the resistance of the RTD element also increases in a known and repeatable manner.

An RTD element typically consists of a fine wire wrapped around a ceramic or glass core. The resistance is measured using a Wheatstone bridge or similar circuit, and the corresponding Temperature is derived based on standardized resistance-Temperature characteristics (such as the DIN EN 60751 standard for platinum RTDs).

Due to their stable and accurate behavior, RTDs are widely used where precise Temperature monitoring is essential, such as in power plants, refineries, chemical plants, and aerospace applications.

Model S7 – Manufactured by Ajmer Thermotech Pvt. Ltd.

Ajmer Thermotech Pvt. Ltd., an ISO 9001:2015 and CE certified company, manufactures and supplies the Model S7 RTD, a melt bolt-style Temperature sensor featuring mineral insulated (M.I.) construction. Specifically designed for high-Temperature and high-pressure environments such as plastic and rubber extrusion processes, the Model S7 ensures accurate and responsive Temperature monitoring where direct contact with molten materials is required.

The melt bolt design allows the RTD to be threaded directly into machinery or tooling, providing reliable thermal contact with the melt stream. Its mineral insulated construction enhances mechanical strength, flexibility, and vibration resistance while maintaining excellent thermal conductivity and electrical insulation.

The Model S7 is built using high-purity platinum sensing elements and is available in 2-wire, 3-wire, or 4-wire configurations. It can be customized with a variety of thread sizes, bolt lengths, lead wire types, and sheath materials to meet specific process requirements. Ideal for use in extrusion, injection molding, and die casting, the Model S7 offers long service life, robust performance, and high measurement precision in challenging production environments.