Choosing the Right Temperature Sensor: Thermocouples, RTDs, and Infrared

Temperature is one of the most measured physical variables in industry — influencing product quality, process efficiency, and safety. Three of the most widely used sensor types are Thermocouples, Resistance Temperature Detectors (RTDs), and Infrared (IR) Sensors. Each has its own measurement principle, strengths, and ideal use cases.

Thermocouples (TCs)

Principle Two dissimilar metals joined at one end produce a voltage proportional to temperature (Seebeck effect).

Advantages

• Wide temperature range (–200 °C to +1800 °C depending on type)
• Rugged and vibration‑resistant
• Fast response time
• Simple, relatively low cost

Limitations

• Lower accuracy than RTDs
• Output drift over time, especially at high temperatures
• Requires reference junction compensation

Typical Applications

• Furnaces, kilns, exhaust systems, gas turbines
• Harsh, high‑temperature industrial environments

Resistance Temperature Detectors (RTDs)

Principle Resistance of a metal (typically platinum) increases predictably with temperature.

Advantages

• High accuracy and stability
• Excellent repeatability
• Suitable for precision process control
• Good operating range (–200 °C to +600 °C)

Limitations

• Higher cost than thermocouples
• Slower response (depending on construction)
• More fragile in extreme vibration or shock

Typical Applications

• Food & beverage processing, pharmaceuticals
• Laboratory measurements, calibration standards
• HVAC control, environmental chambers

Infrared Temperature Sensors (IR)

Principle Measure thermal radiation emitted by an object, without direct contact.

Advantages

• Non‑contact — ideal for moving, hot, or hazardous targets
• Instant response time
• Can measure very high temperatures (up to ~3000 °C in specialized models)
• No risk of contaminating the product

Limitations

• Accuracy affected by emissivity, dust, steam, or optical obstructions
• Limited to surface temperature
• Narrow measurement spot (may require alignment)

Typical Applications

• Steel and glass manufacturing
• Electrical maintenance (hot spots)
• Food processing conveyor lines
• Medical diagnostics (forehead thermometers)

Selection Logic: From Process Needs to Sensor Choice

A structured selection process helps balance technical performance, cost, and maintenance:

1. Define Measurement Target

• Is it surface or internal temperature?
• Static or moving object? Contact possible?

2. Consider Temperature Range & Environment

• Extreme heat → Thermocouple or specialized IR
• Moderate precision process → RTD
• Moving/hazardous target → IR

3. Match Accuracy Requirements

• Laboratory & calibration → RTD
• Industrial monitoring where ±2–3 °C is acceptable → TC or IR

4. Account for Response Time

• Rapid temperature changes → Thermocouple or IR
• Stable processes → RTD

5. Assess Installation & Maintenance

• Harsh vibration → TC
• Limited access → IR (no wiring to process point)
• Long‑term stability → RTD

Quick Reference Table

*depends on model and optics

Final Thoughts

No single sensor type wins in all situations. Thermocouples excel in extreme conditions, RTDs deliver unmatched precision, and Infrared sensors make the impossible possible with contactless measurement. Understanding your process, constraints, and required performance will point you toward the right choice — and ensure accuracy, reliability, and efficiency in the long run.