Calculator Inputs
Example Data Table
These sample values use a Pt100 platinum element with IEC coefficients and show typical resistance and local sensitivity over temperature.
| Sensor | Temperature (°C) | Resistance (Ω) | Sensitivity (Ω/°C) |
|---|---|---|---|
| Pt100 | -50 | 80.3063 | 0.4086 |
| Pt100 | 0 | 100.0000 | 0.3908 |
| Pt100 | 100 | 138.5055 | 0.3793 |
| Pt100 | 200 | 175.8560 | 0.3677 |
| Pt100 | 400 | 247.0920 | 0.3446 |
Formula Used
For temperatures at or above 0°C: R(T) = R0[1 + AT + BT2]
For temperatures below 0°C: R(T) = R0[1 + AT + BT2 + C(T - 100)T3]
Lead compensation: Relement = Rmeasured - Rlead, where the lead term depends on two-wire, three-wire, or four-wire wiring.
Linear reference: Rlinear = R0(1 + αT)
Sensitivity: dR/dT is the derivative of the Callendar-Van Dusen equation at the solved temperature.
Electrical outputs: V = IR and P = I2R using the selected excitation current and the sensor element resistance.
Inverse solving: the calculator estimates temperature by numerically solving the Callendar-Van Dusen curve from the compensated resistance value.
How to Use This Calculator
- Select a platinum sensor preset or choose a custom R0 value.
- Choose whether you want resistance from temperature or temperature from resistance.
- Enter the temperature or measured resistance, depending on your mode.
- Set the wire configuration and lead resistance per wire.
- Enter the excitation current to estimate voltage drop and self-heating power.
- Use the IEC preset coefficients or enter your own custom A, B, and C values.
- Pick a tolerance class to estimate the likely resistance band around the solution.
- Press the calculate button to show the result above the form.
- Download the result as CSV or PDF when you need documentation.
FAQs
1. What does an RTD resistance calculator do?
It converts temperature to RTD resistance or resistance back to temperature. This version also estimates lead-wire effects, sensitivity, voltage, power, tolerance bands, and linearization deviation.
2. Why is Callendar-Van Dusen used here?
It is the standard platinum RTD model for broad temperature ranges. It captures the curve shape better than a simple linear approximation, especially below freezing and at higher temperatures.
3. Why does wire configuration matter?
Lead wires add extra resistance in measurement loops. Two-wire systems include the largest error, three-wire systems partially cancel it, and four-wire systems nearly eliminate lead resistance influence.
4. What is the difference between measured and compensated resistance?
Measured resistance includes wire effects. Compensated resistance estimates the sensor element alone after subtracting the lead contribution implied by the selected wiring arrangement and lead resistance value.
5. Why does the calculator show voltage and power?
Excitation current creates a measurable voltage across the RTD. That same current also causes electrical heating, so power is useful when checking possible self-heating error in sensitive installations.
6. What does the tolerance class mean?
It estimates the allowable temperature uncertainty for common platinum RTD classes. The calculator converts that uncertainty into an approximate resistance band using the local slope at the solved temperature.
7. Can I use custom coefficients?
Yes. Choose custom coefficients when your sensor or calibration data differs from the IEC preset. This is useful for specialty elements, fitted laboratory models, or vendor-specific characterization.
8. What range is practical for this tool?
The inverse solver is limited to the common platinum range of about -200°C to 850°C. Outside that span, the standard model or sensor itself may no longer be appropriate.