A Pt100 RTD measures 138.5 Ω. What is the approximate temperature?
A. 50°C
B. 100°C
C. 150°C
D. 200°C
View Answer:
Correct Answer: B
Explanation:
A Pt100 RTD has a resistance of 100 Ω at 0°C and follows an approximately linear relationship near ambient temperatures:
Where:
- RT = Resistance at temperature T
- R₀ = Resistance at 0°C = 100 Ω
- α = Temperature coefficient = 0.00385/°C
- T = Temperature in °C
Rearranging the formula:
Substituting the given values:
- RT = 138.5 Ω
- R₀ = 100 Ω
- α = 0.00385/°C
Temperature = (138.5 − 100) ÷ (0.00385 × 100)
Temperature = 38.5 ÷ 0.385
Temperature ≈ 100°C
Therefore, a Pt100 RTD resistance of 138.5 Ω corresponds to approximately 100°C, making Option B the correct answer.