RTD & Temperature Sensor Calculator
Calculate resistance from temperature, or determine temperature from resistance. Supports common PT100, PT1000, Ni1000, and 10k Type II sensor characteristics with Celsius or Fahrenheit temperature units.
Temperature Sensor Calculator
How to Use the Two Modes
Temperature → Resistance
Use this mode when you know the approximate sensor temperature and want to determine what resistance the sensor should have.
This is useful for checking a sensor against a resistance measurement during troubleshooting.
Resistance → Temperature
Use this mode when you have a resistance measurement from a meter and want to determine what temperature that resistance represents.
This is particularly useful when troubleshooting a temperature sensor at the controller or transmitter.
Supported Sensor Types
| Sensor | Technology | Reference Resistance | Characteristic |
|---|---|---|---|
| PT100 | Platinum RTD | 100 Ω @ 0 °C | IEC 60751 |
| PT1000 | Platinum RTD | 1000 Ω @ 0 °C | IEC 60751 |
| Ni1000 | Nickel RTD | 1000 Ω @ 0 °C | DIN 43760 |
| 10k Type II | NTC Thermistor | 10,000 Ω @ 25 °C | Beta = 3975 K |
Temperature Units
The sensor equations themselves use Celsius or absolute temperature internally, depending on the sensor model. The calculator converts Fahrenheit to Celsius before performing the sensor calculation.
When calculating temperature from resistance, the result is calculated internally in Celsius and then converted to Fahrenheit if Fahrenheit is selected.
PT100 and PT1000
PT100 and PT1000 sensors use the IEC 60751 platinum resistance characteristic.
For temperatures at or above 0 °C:
Where:
- R(t) = resistance at temperature t
- R0 = resistance at 0 °C
- A = 3.9083 × 10⁻³
- B = −5.775 × 10⁻⁷
Below 0 °C, the cubic Callendar–Van Dusen term is also included.
where:
Example: PT100 at 212 °F
212 °F is equivalent to:
A PT100 at 100 °C has a nominal resistance of approximately:
Ni1000
The Ni1000 characteristic is different from the platinum curve even though both PT1000 and Ni1000 have a nominal resistance of 1000 Ω at 0 °C.
The calculator uses the DIN 43760 polynomial implemented for this sensor family.
With:
A = 5.485 × 10⁻³
B = 6.650 × 10⁻⁶
C = 2.805 × 10⁻¹¹
D = −2.000 × 10⁻¹⁷
10k Type II Thermistor
A 10k Type II sensor is an NTC thermistor rather than an RTD. Its resistance decreases as temperature increases.
The calculator assumes:
B = 3975 K
The Beta equation is:
Temperatures in this equation are absolute temperatures in Kelvin.
Field Troubleshooting Example
Scenario
A technician is troubleshooting a PT100 temperature sensor. The controller is displaying an unexpectedly high temperature.
The technician measures:
Select:
- Sensor: PT100
- Mode: Resistance → Temperature
- Resistance: 157.3 Ω
- Unit: °F
The calculator gives approximately:
That corresponds to approximately 150 °C. If the physical process is actually around 75 °C / 167 °F, further investigation is needed.
Don't Forget Lead Resistance
The calculator determines the temperature represented by the resistance you enter. It does not know whether that resistance came entirely from the sensing element.
For example, a PT100 actually at 100 °C should have approximately:
If the wiring contributes another 2 Ω, a two-wire measurement could show approximately:
Feeding 140.505 Ω into the calculator would produce a temperature higher than the actual 100 °C sensor temperature.
2-Wire, 3-Wire, and 4-Wire Sensors
2-Wire
The meter measures the sensing element plus the resistance of both conductors. This can introduce significant error on long runs.
3-Wire
Common industrial and HVAC RTD configuration. Appropriate transmitter circuitry can compensate for much of the lead resistance when the conductors are properly matched.
4-Wire
Provides the most accurate resistance measurement because the sensing circuit can separate excitation from voltage measurement.
Common Mistakes
- Selecting PT1000 instead of Ni1000: Both are nominally 1 kΩ devices, but their curves differ.
- Assuming a 10k sensor is always the same: Thermistor curves can vary between manufacturers and sensor families.
- Ignoring lead resistance: The resistance measured at the controller may include the wiring.
- Mixing Celsius and Fahrenheit: Always verify the selected temperature unit before entering or interpreting a temperature.
- Measuring an energized circuit: Follow the manufacturer's and site's appropriate procedure before disconnecting or resistance-testing an installed sensor.
- Using the calculator as a calibration standard: Nominal sensor curves do not replace the manufacturer's calibration data or sensor tolerance specification.
Related Calculators
Engineering Note
The calculator uses nominal sensor characteristics. For actual calibration or acceptance testing, verify the sensor manufacturer's part number, tolerance class, applicable standard, wiring configuration, and specified resistance-temperature curve.