Imagine monitoring a large HVAC system with sensors throughout a building. If temperature readings become skewed due to wiring issues, the resulting energy waste and comfort loss could be substantial. In long-distance temperature measurement, selecting the right RTD (Resistance Temperature Detector) sensor is crucial—particularly when choosing between 100Ω and 1000Ω models. This analysis explores the key differences to help avoid common selection pitfalls.

RTDs measure temperature by detecting changes in electrical resistance of metals—typically platinum—as temperature varies. Two standard options exist: 100Ω and 1000Ω RTDs, indicating their resistance values at 0°C (32°F). While operating on identical principles, their performance differs significantly in practical applications.

In HVAC systems where sensors may be located far from control units, signal transmission becomes critical. Wire resistance inherently affects measurement accuracy, making the 1000Ω RTD the superior choice for such scenarios.

The sensitivity comparison reveals why: 100Ω RTDs typically show 0.21Ω/°F sensitivity, while 1000Ω RTDs demonstrate approximately 2.1Ω/°F—a tenfold increase. This means each 1°F change produces a 2.1Ω variation in 1000Ω RTDs compared to just 0.21Ω in 100Ω models.

Consider a typical installation using 100 feet of 18-gauge wire in a two-wire RTD configuration (creating a 200-foot loop). With 18-gauge wire resistance at 0.664Ω/100 feet, total wire resistance becomes 1.328Ω.

For 100Ω RTD: The error calculation shows 1.328Ω / 0.21Ω/°F ≈ 6.3°F potential deviation—an unacceptable margin for precise climate control.

For 1000Ω RTD: The same calculation yields 1.328Ω / 2.1Ω/°F ≈ 0.63°F error—a tenfold improvement in accuracy.

This demonstrates how 1000Ω RTDs minimize wire resistance effects through their higher base resistance, producing more stable and reliable signals over distance.

• Enhanced sensitivity: Ten times more responsive to temperature changes than 100Ω models
• Reduced error: Significantly less affected by wire resistance in long-distance installations
• Improved signal integrity: Stronger output resists electrical interference more effectively

Despite the advantages of 1000Ω RTDs for distance applications, certain situations may warrant 100Ω models:

• Short-distance installations where wire resistance becomes negligible
• Legacy systems requiring specific 100Ω compatibility
• Budget-sensitive projects with relaxed accuracy requirements

• Installation distance: Favor 1000Ω models for runs exceeding 50 feet
• Precision needs: Critical applications demand 1000Ω sensors
• System compatibility: Verify controller specifications
• Budget constraints: Balance cost against performance requirements

For most HVAC and building automation systems involving extended sensor runs, 1000Ω RTDs deliver superior measurement accuracy and system reliability. Proper sensor selection ensures efficient energy use, optimal comfort conditions, and precise environmental control.