RTD

From HwB

RTD = Resistive Temperature Device

Common type of RTD is Pt-100, which is a temperature sensor made from platinum. Resistance varies with temperature. 100Ω at 0 °C.

Contents

Pt-100

Temperature Resistance
Pt-100
α=0.003750 °C-1
Pt-100
α=0.003850 °C-1
°C Ω Ω
-200 19.9 18.5
-100 61.2 60.3
0 100 100
100 138 139
200 174 176
300 209 212
400 243 247
500 275 281
600 307 314
700 337 345
800 366 376
850 380 390

Callendar-Van Dusen Equation

Given from RTD manufacturer:

Alpha, α
Delta, δ
Beta, β

Calculated from α, δ & β:

A = <math>\alpha + \frac{\alpha \times \delta}{100}</math>

B = <math>-\frac{\alpha \times \delta}{100^2}</math>

C = <math>-\frac{\alpha \times \beta}{100^4}</math>

Given:

RT = Resistance (Ω) at T°C
R0 = Resistance (Ω) at 0°C (100 Ω for Pt-100)
T = Temperature in °C

Temperature according to ITS-90 (International Temperature Scale of 1990.

Calculated

RT = R0 x (1 + A x T + B x T² + (T-100 °C) x C x T³) for T < 0 °C
RT = R0 x (1 + A x T + B x T²) for T > 0 °C

Callendar-Van Dusen Constants

Constants

The purity of the metal will determine the constants.

Given Calculated
Alpha, α Delta, δ Beta, β A B C
°C-1 °C °C °C-1 °C-2 °C-4
0.003750 1.605 0.16 0.381 x 10-3 -6.02 x 10-7 -6.0 x 10-12
0.003850 1.4999 0.10863 3.908 x 10-3 -5.775 x 10-7 -4.183 x 10-12
0.003902 1.52 0.11 3.96 x 10-3 -5.93 x 10-7 -4.3 x 10-12
0.003911 3.9692 × 10-3 –5.8495 × 10-7 –4.233 × 10-12
0.003916 3.9739 × 10-3 –5.870 × 10-7 –4.4 × 10-12
0.003920 3.9787 × 10-3 –5.8686 × 10-7 –4.167 × 10-12
0.003928 3.9888 × 10-3 –5.915 × 10-7 –3.85 × 10-12

Alpha, α, is sometimes known as TCR

0.003850 is according to IEC 751-2 standard. Made from 99.99% pure platinum.

Typical data

Standard Typical data
α Tolerance R0
BS EN 60751 1996 0.003850 °C-1 ±0.05%, ±0.03%, ±0.02%, ±0.01% 100 Ω
DIN 43760 1980 0.003850 °C-1 ±0.05% (1/2 DIN B), ±0.03% (1/3 DIN B), ±0.02% (1/5 DIN B), ±0.01% (1/10 DIN B) 100 Ω
IEC 60751:1995 0.003850 °C-1 ±0.05%, ±0.03%, ±0.02%, ±0.01% 100 Ω
JIS C1604 - 1981 (Japanese Industrial Standard) 0.003916 °C-1 ±0.15ºC, ±0.2ºC, ±0.5ºC 100 Ω or 50 Ω
US Standard Curve 0.003916 °C-1 ±0.1 ohms 100 Ω or 50 Ω
BS 2G 148 (British Aircraft Industry) 0.003900 °C-1 ±0.1% (at 0ºC) 130 Ω

Graph

Temperature vs Resistance

Gnuplot Plot

Non linearity

This graph shows the affect of B & C in the Callendar-Van Dusen equation. Percentage error if the RTD would have been assumed to be linear.

Gnuplot Plot

Standards

  • IEC 60751:1995
  • BS EN 60751 1996
  • DIN 43760 1980
  • BS 2G 148

Sources

Contributors