Resistance Temperature Detectors have become indispensable in present industries and applications where precision in temperature measurement is a must. The sensors boast very high accuracy, repeatability, and stability, hence making them very attractive in many fields. Let’s look into the key aspects of RTDs, their advantages, and wide-ranging applications.
What is an RTD?
An RTD is a temperature measuring device whose electrical resistance changes with temperature. For a rise in the temperature, its sensor resistance rises in a predictable and linear way. It is this unique characteristic which, therefore, enables RTDs to give very accurate and reproducible temperature measurements.
The principle of operation for an RTD is rather straightforward. As it is a passive component, another external active electronic device is needed for measuring its resistive value. This is accomplished by passing a small electrical current through the RTD sensor so that the voltage developed across it is proportional to the resistance.
Key Features and Standards
RTDs are standardized according to DIN and IEC standards, with consistent resistance-temperature relations and tolerances. The most commonly used RTD is a Platinum RTD, usually with a base resistance of 100 ohms at 0°C and referred to as Pt100. Following are the standard tolerances of RTDs:
- DIN Class A: ±(0.15 + 0.002 |T|°C)
- DIN Class B: ±(0.3 + 0.005 |T|°C)
- Class C according to DIN: ±(1.2+0.005|T|°C)
Types of RTD Elements
The performance and precision of an RTD are to a great extent decided by the type of element used. Following are the most common elements used in the construction of RTD and their features:
| Element Type | Base Resistance | Temperature Coefficient (TCR) |
| Platinum | 100 ohms at 0°C | 0.00385 |
| Nickel | 120 Ohms at 0°C | 0.00672 |
| Copper | 10 Ohms at 25°C | 0.00427 |
These advantages have led to platinum resistance temperature detectors being used in most applications, especially with high accuracy, a wide temperature range, and good stability.
Wiring Configurations
RTDs are available in several different wiring configurations to suit specific accuracy requirements, including:
- Two-Wire Configuration:
- Suitable for non-critical applications.
- Resistance of the lead wires adds to the total resistance, reducing accuracy.
- Three-Wire Configuration:
- Most common in industrial applications.
- Compensates for lead wire resistance, offering improved accuracy.
- Four-Wire Configuration:
- Provides the highest accuracy by eliminating lead wire resistance altogether.
- Often used in laboratory and precision industrial settings.
Accuracy and calibration:
The accuracy of an RTD depends upon two major factors:
- Base resistance tolerance
- Temperature coefficient tolerance
To ensure predictable operation, RTDs are driven using one of two methods: the fixed-point or comparison methods:
- Fixed-Point Calibration: This uses the freezing or melting points of pure substances for precise calibration.
- Calibration for Comparison: RTD is calibrated by comparison in a controlled environment with a standard reference thermometer.
Advantages of RTDs
- High Accuracy: Ideal for precise temperature measurements in critical applications.
- Repeatability: It provides the same results on every use.
- Wide Temperature Range: Effective in a temperature range of -200°C to 850°C.
- Stability: Ensures durability in industrial processes over a long period.
Applications of RTDs
RTDs are used across various industries due to their versatility and precision:
- Industrial Automation: This is the monitoring and control of processes at manufacturing plants.
- Health: Measuring body temperature with very high accuracy.
- Aerospace: Temperature stability in critical systems.
- Food and beverage: Maintaining unchanging temperatures at the time of processing.
- Power Generation: Monitoring temperatures in turbines and generators.
RTDs vs. Thermocouples
While thermocouples are widely applied for high temperature applications, there are some benefits of RTDs.
- Accuracy: RTDs are more accurate than thermocouples.
- Stability: RTDs hold accuracy for long periods of time.
- Temperature Range: Suitable for applications below 660°C.
Choose the appropriate RTD
The following are the factors to consider in choosing an RTD:
- Accuracy Requirements: Choose the tolerance class and wiring configuration based on your needs.
- Operating Environment: The RTD material must be capable of operating in the required temperature and physical environment.
- Compatibility: Make sure the RTD that you will choose is compatible with your measuring device. Tempsens Instruments is one of the leading companies in RTDs and thermal solutions. The company provides a variety of products suited to various industrial applications.
Endnote
Resistance Temperature Detectors are an essential tool in modern industries. With their high accuracy, stability, and versatility, they continue to replace traditional thermocouples in many applications. By understanding their features, configurations, and applications, businesses can optimize their processes and ensure reliable temperature measurements. Whether it’s industrial automation, healthcare, or aerospace, RTDs are a stepping stone to precision and better efficiency. With Tempsens Instruments, you choose a partner committed to quality and innovation in thermal solutions. Explore their range of RTDs to find the best fit for your application!
