How to select a resistance temperature detector (RTD) based on your temperature measurement range? Keep this selection guide handy!

Accurate Temperature Measurement Starts with Choosing the Right One

Temperature measurement is crucial in daily industrial production, and resistance temperature detectors (RTDs), as the "kings of temperature measurement" in the medium and low temperature range, directly impact the performance and reliability of the entire system if chosen correctly. Faced with a dazzling array of RTD types, how do we select the most suitable product for different temperature measurement ranges? Today, let's explore this issue from the customer's perspective.

Overview of RTD Temperature Measurement Ranges

RTDs are sensors that measure temperature based on the characteristic of the resistance value of a metal conductor changing with temperature. They are characterized by high measurement accuracy and stable performance.

Different types of RTDs have their specific temperature measurement ranges: common platinum RTDs (such as Pt100) generally have a temperature measurement range of -200℃ to 850℃, while copper RTDs (such as Cu50) are typically suitable for a range of -40℃ to 140℃, and are prone to oxidation above 150℃.

RTD Selection Guide for Different Temperature Measurement Ranges

1. Ultra-Low Temperature Measurement (-200℃ to 0℃)

For ultra-low temperature measurements, platinum RTD Pt100 is the preferred choice. Its accuracy reaches ±0.15℃, providing stable and reliable measurement results even in extreme environments. The resistance of Pt100 is approximately 18.52Ω at -200℃ and 100Ω at 0℃.

2. Medium and Low Temperature Measurement (0℃～400℃)

This range is the most common industrial temperature measurement range. Depending on specific needs, the following can be selected:

Platinum Resistance Temperature Detector (Pt100): High accuracy, good stability, suitable for most industrial scenarios.

Copper Resistance Temperature Detector (Cu50): High cost-effectiveness, 50% cheaper than platinum resistance temperature detectors, but the operating temperature should not exceed 150℃, otherwise it is easily oxidized.

Sheathed Platinum Resistance Temperature Detector: Suitable for applications with vibration or requiring rapid response; thermal response time can be less than 5 seconds.

3. High Temperature Measurement (400℃～850℃)

Pt100 can still operate at temperatures above 400℃, but a model suitable for high temperatures must be selected. For high-temperature scenarios above 500℃, thermofitted platinum resistance thermometers (RTDs) can be considered, capable of measuring temperatures up to 650℃. In some extreme cases, switching to thermocouples may even be necessary.

Selection Considerations for Special Operating Conditions

Besides temperature range, the actual application environment must also be considered:

Corrosive Media: Corrosion-resistant RTDs should be selected, typically made of PTFE or with a ceramic coating, resistant to strong acids and corrosion.

Explosive Environments: In flammable and explosive environments such as chemical plants and coal mines, explosion-proof RTDs (suitable for Bla-B3c hazardous areas) must be selected, with explosion-proof junction box design limiting the explosion risk to the junction box.

High Voltage/Vibration Scenarios: Armored RTDs are the best choice, with a withstand pressure of over 50MPa and good impact resistance.

Surface Temperature Measurement: For surface temperature measurement of bearings, molds, etc., end-face type RTDs should be selected, with their sensing element in close contact with the end face for rapid surface temperature capture.

Balancing Accuracy and Response Speed

Different applications have different requirements for accuracy and response speed:

Laboratory Environment: High-precision Class A Pt100 should be selected, with an error of only ±0.15℃.

Industrial Fast Response: Armored RTDs are ideal, with a thermal response time of less than 5 seconds.

Long-Distance Transmission: PT1000 RTDs (1000Ω resistance at 0℃) are particularly suitable for long-distance temperature monitoring systems due to their higher signal strength and better signal-to-noise ratio.

Installation and Wiring Precautions

Proper installation and wiring are crucial for measurement accuracy:

Installation Depth: When measuring pipe temperature, the insertion depth should be ≥ 8 times the pipe diameter; for large spaces such as flues, 1 meter insertion is sufficient.

Wiring Method: Three-wire connection is preferred in industry, effectively eliminating lead wire errors; four-wire connection is used for ultra-high precision measurements in laboratories.

Installation Direction: It should be installed as vertically as possible on horizontal or vertical pipes to ensure accurate and reliable temperature measurement.