Advantages and Disadvantages of Resistance Temperature Detectors (RTDs)

This article explores the pros and cons of using Resistance Temperature Detectors (RTDs). We’ll delve into their benefits and drawbacks, offering a clear understanding of when and where they excel, and where they might fall short.

Introduction to RTDs

An RTD, or Resistance Temperature Detector, is a type of temperature sensor that relies on the principle that a metal’s electrical resistance changes with temperature. Specifically, RTDs have a positive temperature coefficient, meaning their resistance increases as the temperature goes up.

The typical operating range for an RTD is quite broad, spanning from -250°C to a scorching 1000°C.

Figure 1: A typical voltage versus temperature curve of an RTD.

It’s worth noting the sensitivity and linearity when comparing RTDs to other temperature sensors:

• Sensitivity Order: Thermistor > RTD > Thermocouple
• Linearity Order: RTD > Thermocouple > Thermistor

Advantages of RTDs

Let’s look at the reasons why RTDs are often a preferred choice for temperature measurement:

• High Stability: RTDs are known for their exceptional stability over time. This means they’re less prone to drifting and provide consistent readings.
• High Accuracy: They offer very accurate temperature measurements, making them ideal for applications that demand precision.
• Good Linearity: RTDs exhibit a more linear relationship between resistance and temperature compared to thermocouples. This simplifies calibration and signal processing.

Disadvantages of RTDs

While RTDs have many advantages, they also have some limitations:

• Passive Devices: RTDs are passive devices, meaning they require an external current source to function.
• Higher Cost: They tend to be more expensive than other types of temperature sensors like thermocouples and thermistors.
• Self-Heating: When a current passes through the RTD to measure its resistance, the sensor will inevitably heat up a bit. This “self-heating” effect can introduce some error, especially at higher currents.
• Less Rugged: Compared to thermocouples, RTDs are generally more delicate and less rugged, making them vulnerable in harsh environments.
• Small Resistance Change: The change in resistance with temperature, while linear, can be quite small. This can require more sensitive measurement circuitry.