PT100 Resistance to Temperature Calculator
Convert PT100 RTD sensor resistance measurements (Ω) directly into Celsius (°C) and Fahrenheit (°F) values using precision IEC 60751 equations.
PT100 Resistance to Temperature Calculator
How to Use Resistance to Temperature Calculator PT100
Determining the temperature of a process or piece of electrical equipment using platinum RTD sensors is highly efficient. When configuring PLC analog input modules (such as Siemens S7 RTD cards) or temperature transmitters (such as Rosemount 3144P), instrumentation technicians frequently need to verify resistance readings. Follow these technical steps to use our calculator:
- 1Input the measured resistance. Enter the resistance value in ohms (Ω) measured across the PT100 terminals.
- 2Set the decimal precision. Select the desired number of decimal places for formatting your temperature output.
- 3Run the calculation. Click the Calculate Temperature button to execute the quadratic solver.
- 4Verify the range status. Read the calculated temperature in both Celsius (°C) and Fahrenheit (°F) and check the PT100 status card.
- 5Reset for new calculation. Click the Reset button to clear all inputs and start again.
Practical industrial examples include verifying RTD sensors connected to PLC systems, diagnosing temperature transmitters in a 4-20mA loop configuration, and calibrating high-precision laboratory thermal baths.
How to Calculate Resistance to Temperature Calculator PT100
For temperatures equal to or greater than 0°C, the relation between the electrical resistance and temperature of a platinum RTD is defined by the Callendar-Van Dusen equation under the international IEC 60751 standard. Converting the measured resistance back into temperature requires solving a quadratic equation.
Callendar-Van Dusen Standard Formula
Where:
- R = Measured electrical resistance of the PT100 sensor (Ω)
- R0 = Nominal resistance at 0°C, which is exactly 100 Ω
- T = Calculated temperature in Celsius (°C)
- A = 3.9083 × 10−3 °C−1
- B = −5.775 × 10−7 °C−2
To determine the temperature, we rearrange the formula into standard quadratic form: B × T2 + A × T + (1 − R / 100) = 0. Solving for temperature (T) yields the following equation:
Step-by-Step Engineering Worked Example
Given Parameters:
- Measured Resistance (R): 138.50 Ω
- Nominal Resistance (R0): 100 Ω
- Coefficient A: 0.0039083
- Coefficient B: −0.0000005775
Step 1 — Calculate (1 − R / R0)
1 − (138.50 / 100) = 1 − 1.3850 = −0.3850
Step 2 — Calculate 4 × B × (1 − R / R0)
4 × (−5.775 × 10−7) × (−0.3850) = 8.8935 × 10−7
Step 3 — Compute A2
A2 = (3.9083 × 10−3)2 = 1.52748 × 10−5
Step 4 — Subtract the Terms Under the Square Root
1.52748 × 10−5 − 8.8935 × 10−7 = 1.438545 × 10−5
Step 5 — Take the Square Root
√(1.438545 × 10−5) = 0.003792816
Step 6 — Solve for Temperature (T)
T = (−0.0039083 + 0.003792816) / (2 × −5.775 × 10−7)
T = −0.000115484 / −0.000001155 = 99.986°C
Final Verified RTD Temperature Results
- Calculated Temperature in Celsius: 100.00°C (rounded to 2 decimal places)
- Calculated Temperature in Fahrenheit: 212.00°F
- PT100 Status: Valid PT100 range
This calculation confirms that a measured resistance of 138.50 Ω corresponds to an operating temperature of approximately 100°C. For back-calculation purposes, you can consult our PT100 temperature to resistance calculator. To analyze current or voltage in the sensor loop, you can refer to our resistance to voltage calculator, resistance to current calculator, or resistance to power calculator.
Resistance to Temperature Calculator PT100 Chart
The following reference table presents the relationship between operating temperature (°C) and nominal electrical resistance (Ω) for platinum PT100 RTD sensors, calculated in compliance with the IEC 60751 standard curve.
| Temperature (°C) | Resistance (Ω) |
|---|---|
| 0 °C | 100.00 Ω |
| 10 °C | 103.90 Ω |
| 20 °C | 107.79 Ω |
| 30 °C | 111.67 Ω |
| 40 °C | 115.54 Ω |
| 50 °C | 119.40 Ω |
| 60 °C | 123.24 Ω |
| 70 °C | 127.08 Ω |
| 80 °C | 130.90 Ω |
| 90 °C | 134.71 Ω |
| 100 °C | 138.50 Ω |
| 150 °C | 157.33 Ω |
| 200 °C | 175.86 Ω |
| 250 °C | 194.10 Ω |
| 300 °C | 212.05 Ω |
| 350 °C | 229.72 Ω |
| 400 °C | 247.09 Ω |
| 450 °C | 264.18 Ω |
| 500 °C | 280.98 Ω |
| 550 °C | 297.49 Ω |
| 600 °C | 313.71 Ω |
| 650 °C | 329.64 Ω |
| 700 °C | 345.28 Ω |
| 750 °C | 360.64 Ω |
| 800 °C | 375.70 Ω |
| 850 °C | 390.48 Ω |
Note: All values in the table are calculated using IEC 60751 platinum RTD characteristics. In actual field conditions, check your sensor wiring tolerance class (Class A, B, or 1/10 DIN) to determine the exact measurement uncertainty.
Frequently Asked Questions (FAQs)
Converting PT100 resistance to temperature is typically done using standardized conversion tables or equations like the Callendar-Van Dusen formula. Since the relationship is slightly non-linear, these tools provide the precise temperature in Celsius for any measured resistance value in ohms.
A standard PT100 sensor has a resistance of approximately 109.73 ohms at 25 degrees Celsius. Because its base resistance is 100 ohms at 0 degrees Celsius, the resistance steadily increases by roughly 0.385 ohms for every single degree Celsius increase in the surrounding ambient temperature.
The term PT100 comes from its construction and properties. "PT" stands for platinum, which is the precious metal used to make the sensor's delicate wire element. The number "100" refers to its nominal electrical resistance of exactly 100 ohms at a freezing temperature of zero degrees Celsius.
The most common standard alpha value for industrial PT100 sensors is 0.00385 ohms per ohm per degree Celsius. This temperature coefficient defines how much the sensor's resistance changes with temperature and is essential for ensuring highly accurate conversions across a wide thermal range.
PT100 sensors generally provide significantly better accuracy, stability, and repeatability over time compared to thermocouples. However, thermocouples are often preferred for measuring extremely high temperatures, responding much faster to temperature changes, and withstanding harsh vibrations.