PT100 and PT1000 resistance calculator
Platinum RTDs are the most repeatable common temperature sensor. Their resistance follows a well-defined polynomial.
ohm
mA
ohm
RTD resistance
157.3251ohm
- Temperature from your measured resistance
- 150.0131
- Resistance the instrument sees
- 158.3251 ohm
- Temperature error from lead resistance
- 2.559 degrees C
- Sensitivity near zero
- 0.390 83 ohm per K
- Self-heating power
- 0.1573 mW
- Voltage across the RTD
- 157.325 mV
Show the working
- Temperature = 150
- Sensor type = 100
- Or a measured resistance = 157.33
- Excitation current = 1
- Lead resistance per wire = 0.5
- Wiring = 2
- a = 3.9083e-3 = 0.003 908 3
- b = -5.775e-7 = -0.000 000 577 5
- RTD resistance = 150 >= 0 ? 100 * (1 + 0.003 908 3*150 + -0.000 000 577 5*150^2) : 100 * (1 + 0.003 908 3*150 + -0.000 000 577 5*150^2 - 4.183e-12*(150-100)*150^3) = 157.325
- lead_error_ohm = 2 * 0.5 = 1
- Resistance the instrument sees = 157.325 + 1 = 158.325
- Sensitivity near zero = 100 * 0.003 908 3 = 0.390 83
- Temperature error from lead resistance = 0.390 83 > 0 ? 1 / 0.390 83 : 0 = 2.558 66
- Temperature from your measured resistance = -0.000 000 577 5 != 0 ? (-0.003 908 3 + sqrt(0.003 908 3^2 - 4*-0.000 000 577 5*(1 - 157.33/100))) / (2*-0.000 000 577 5) : 0 = 150.013
- Self-heating power = (1/1000)^2 * 157.325 * 1000 = 0.157 325
- Voltage across the RTD = 1 * 157.325 = 157.325
Values are shown to six significant figures here; the arithmetic itself runs on exact fractions and is only rounded where a number is printed.
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The formula
- Callendar-Van Dusen above 0 C: R = R0 (1 + A t + B t^2)
- A = 3.9083e-3, B = -5.775e-7 for the standard 0.00385 platinum curve
Two-wire RTDs add the lead resistance straight into the reading. On a PT100 that is 2.6 degrees per ohm.
PT1000 is ten times less sensitive to lead resistance, which is why it dominates in two-wire installations.
Self-heating raises the sensor above the process temperature. Keep excitation to a milliamp or less in still air.