tidu271

www.ti.com
Table 5. RTD Class and Tolerance Information
Theory of Operation
(1)
(2)
TEMPERATURE RANGE of TOLERANCE RESISTANCE at ERROR OVER
TOLERANCE CLASS VALIDITY (1) ERROR at 100°C
VALUES 0°C WIRE-WOUND
(DIN-IEC 60751)
(°C)
WIRE-WOUND THIN-FILM
(°C) (Ω) RANGE (°C)
AAA (1/10 DIN) (2) 0 to 100 0 to 100 ±(0.03 + 0.0005 × T) 100 ± 0.012 0.08 0.08
AA (1/3DIN) –50 to 250 0 to 150 ±(0.1 + 0.0017 × T) 100 ± 0.04 0.27 0.525
A –100 to 450 –30 to 300 ±(0.15 + 0.002 × T) 100 ± 0.06 0.35 1.05
B –196 to 600 –50 to 500 ±(0.3 + 0.005 × T) 100 ± 0.12 0.8 3.3
C –196 to 600 –50 to 600 ±(0.6 + 0.01 × T) 100 ± 0.24 1.6 6.6
Manufacturers may choose to guarantee operation over a wider temperature range than DIN-IEC60751 provides.
AAA (1/10DIN) is not included in the DIN-IEC-60751 specification but is an industry accepted tolerance class for highperformance
measurements.
The relationship between the resistance and temperature of platinum RTD is defined by a nonlinear
mathematical model known as the Callendar-Van Dusen (CVD) equations. The coefficients in the
Callendar-Van Dusen equations are defined by the IEC-60751 standard.
For T > 0°C, the CVD equation is a second-order polynomial as given in Equation 14:
RTD (T) = R 0 × [1 + A (T) + B (T) 2 ] (14)
For T < 0°C, the CVD equation expands to a fourth-order polynomial as given in Equation 15:
RTD (T) = R 0 × [1 + A (T) + B (T) 2 + C (T) 3 (T – 100)] (15)
The linear approximation model is as follows:
RTD (T) = R 0 × [1+ α (T)]
where
• T = Temperature of RTD element in °C
• RTD (T) = resistance of RTD element as a function of temperature
• R 0 is the resistance of the RTD element at 0°C
• α = Sensitivity of RTD element = 0.00385 Ω/Ω/°C
• A = 3.9083 × 10 –3 °C –1
• B = –5.7750 × 10 –7 °C –2
• C = –4.1830 × 10 –12 °C –4 25
TIDU271–May 2014
Submit Documentation Feedback
Temperature Sensor Interface Module for Programmable Logic Controllers
(PLC)
Copyright © 2014, Texas Instruments Incorporated