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Understanding resistance temperature detectors: What you need to know

Resistance temperature detectors (RTDs) are composed of realizing materials such as Copper, Nickel, or Platinum and offer greater accuracy and stability than thermocouples in the below 600°C range.

These sensors are also used in furnaces, heaters, ovens, and other thermal process control applications.

RTDs are also ideal for monitoring pressure, flow rate, level, and other process variables which require precise measurement because of their fast response time and repeatable output.

For instance, when the correct mixture of air and fuel is blended in an engine’s combustion chamber, the engine has to maintain a specific temperature to ensure maximum efficiency – this is where a resistance temperature detector comes into play.

The RTD can accurately measure the temperature inside the chamber and provide the fuel-air mixture at optimum levels.

How is a resistance temperature detector made?

Generally, the wire is coiled around a form on a mica cross frame to reduce the size and improve the thermal conductivity to hasten the reaction time and achieve a high heat transfer rate. In industrial RTDs, the coil is defended by a stainless steel sheath or a guard tube.

This minimizes the physical strain when the wire expands and increases in length due to temperature changes. If the strain on the wire increases, the tension will also go up, causing undesirable changes in the wire’s resistance.

This ensures that the resistance changes with temperature, not any other factor. This is also beneficial in maintaining RTDs while the plant is still running. Mica is interposed between the steel sheath and the resistance wire for better electrical insulation.

As the strain on the wire is limited, it should be carefully wound over the mica sheet.

How does RTD works?

The elementary concept of a resistance temperature detector sensor is straightforward. All metals are composed of a specific resistivity that increases with the metal’s temperature. This resistance can be measured and utilized to acquire temperature readings.

RTD sensors are used widely in industrial production and sensitive temperature procedures due to their accuracy and endurance to high temperatures, vibrations, and shock. A low amount of DC current is applied to activate the sensor and keep it from overheating.

When the sensor is integrated into an operation, it is recommended to use a thermowell. This is a sealed-end cylinder that is attached to the process stream. The process passes the heat to the thermowell wall and the sensor.

A thermowell is a thermal conductive protrusion placed in the process line so that sensing devices can be set up without creating a hole in the line.

Most resistance temperature detector sensors have a protective covering of stainless steel or Inconel that guards the sensing element from the surroundings. The sensor has a part that can be inserted into the measurement space, and it is linked to the device that takes readings through the termination wires.

What are the differences between RTDs and Thermocouples?

In terms of environmental factors

The majority of temperature measurements are taken in areas where there are harsh, oxidizing, and reducing atmospheres. Apart from these uncomfortable states, noise, shaking, and electricity exist.

RTDs are encased in protective coverings, which make them resistant to rough, hazardous conditions. To give an extra layer of defense, RTDs can be coated with PTFE polytetrafluoroethylene, which is helpful in pressurized systems and plating baths.

Thermocouples, having metallic exteriors, can also cope with corrosive and oxidizing environments. When exposed thermocouple junctions are used, one must take extra caution.

In terms of costs

RTDs permit a larger range of temperatures to be read than thermocouples. However, this comes at a higher cost.

Whereas thermocouples are much more affordable, costing only two-thirds of the cost of a resistance temperature detector. This cost savings can add up if you use multiple temperature sensors in multiple places.

In terms of stability

In contrast to thermocouples, a resistance temperature detector is far more stable.

This makes them the preferred choice for applications where reliability is critical.

Moreover, unlike thermocouples, RTDs do not produce electromagnetic fields (EMFs), which can change over time due to oxidation, corrosion, and metallurgical changes in the sensing elements.

As such, RTDs offer a much more reliable and consistent performance compared to thermocouples; once a thermocouple begins to drift, the effect is irreversible. This makes RTDs the ideal choice for applications requiring accurate data over extended periods.

With their superior performance.

In terms of accuracy

When it comes to accuracy, there is a clear winner in the field of temperature-measuring devices, the resistance temperature detector. In industrial applications, RTDs offer readings that can be trusted with an accuracy of up to 0.1C.

This precision is far greater than what thermocouples can produce, which usually have an accuracy of 1C. This difference in accuracy makes RTDs the ideal choice for any situation that requires consistent and reliable measurements.


The resistance temperature detector from Tempsens is one of the best options available. It provides precise measurements in various applications and is designed for long-term performance.

It also features a high-temperature accuracy rating, ensuring accurate readings even in harsh conditions. Moreover, these detectors are robust and reliable, with long service life and minimal maintenance requirements.

Because of its superior design, it is trusted by industry professionals.


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