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Temperature Sensor Calculator

Calculate the expected output of platinum RTDs and standard thermocouples.

1

RTD input

IEC 60751 platinum curve, α = 0.00385

Calculate from
2

Expected RTD output

Pt100 · −200 to 850 °C

Sensor resistance138.506 Ω
Temperature100.000 °C
Temperature212.000 °F
Sensor resistance138.506 Ω
Resistance at terminals138.506 Ω
Sensitivity at this point0.379 Ω/°C
Show calculation

R(t) = R₀[1 + At + Bt² + C(t − 100)t³]

IEC

Platinum RTDs
Callendar–Van Dusen coefficients used by IEC 60751.

NIST

Thermocouples
ITS-90 reference functions from NIST SRD 60.

Nominal reference values only. Verify sensor standard, wiring, calibration data, and instrument configuration before field use.

Equation guide

RTD resistance and thermocouple millivolt calculations

Platinum RTDs change resistance predictably with temperature. This calculator uses the IEC 60751 Callendar–Van Dusen relationship for the 0.00385 platinum curve and supports Pt50, Pt100, Pt200, Pt500, and Pt1000 sensors.

Thermocouples generate a small voltage from the temperature difference between the measuring and reference junctions. Type B, E, J, K, N, R, S, and T conversions use NIST ITS-90 reference functions, with cold-junction compensation applied separately.

Platinum RTD at or above 0 °C

R(t) = R₀(1 + At + Bt²)

For IEC 60751: A = 3.9083 × 10⁻³ °C⁻¹ and B = −5.775 × 10⁻⁷ °C⁻².

Platinum RTD below 0 °C

R(t) = R₀[1 + At + Bt² + C(t − 100)t³]

C = −4.183 × 10⁻¹² °C⁻⁴. R₀ is the nominal resistance at 0 °C.

Two-wire lead resistance

Rterminal = Rsensor + 2Rlead

Three- and four-wire circuits are shown as compensated, assuming the measurement system correctly cancels lead resistance.

Thermocouple cold-junction compensation

Emeasured = Ehot − EreferenceEhot = Emeasured + Ereference

Reference functions convert between temperature and EMF; the voltage is not linear across the complete thermocouple range.

Worked example: Pt100 at 100 °C

Using the IEC 60751 equation above zero:

Nominal resistanceR₀ = 100 Ω
Calculated sensorR(100) ≈ 138.506 Ω
2-wire, 0.25 Ω/leadTerminal ≈ 139.006 Ω

RTD and thermocouple FAQs

What resistance should a Pt100 have at 0 °C?

A standard Pt100 has a nominal resistance of 100 Ω at 0 °C. A Pt1000 has 1,000 Ω at 0 °C. Actual acceptance depends on sensor class and tolerance.

Why does a two-wire RTD read high?

The instrument measures the sensor plus both lead resistances. Three-wire circuits compensate when lead resistances are closely matched, while four-wire measurement provides the best lead-resistance cancellation.

Why is cold-junction compensation required?

A thermocouple measures a temperature difference rather than an absolute temperature. Compensation accounts for the temperature where the thermocouple metals connect to the measuring instrument.

Can one thermocouple equation cover every type?

No. Each thermocouple type has its own coefficients and valid temperature segments. The conversion also varies nonlinearly across the range.