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iTEMP TMT182B
Sensor adjustment
Endress+Hauser
Sample calculation with Pt100, measuring range 0 to +200 °C (+32 to +392 °F), ambient
temperature +25 °C (+77 °F), supply voltage 24 V:
Measured error digital = 0.1 °C + 0.006% x (200 °C - (-200 °C)):
Measured error D/A = 0.003 % x 200 °C (360 °F)
Measured error digital value (HART):
Measured error analog value (current output): √(Measured error digital² +
Measured error D/A²)
Sample calculation with Pt100, measuring range 0 to +200 °C (+32 to +392 °F), ambient
temperature +35 °C (+95 °F), supply voltage 30 V:
Measured error digital = 0.1 °C + 0.006% x (200 °C - (-200 °C)):
Measured error D/A = 0.03 % x 200 °C (360 °F)
Influence of ambient temperature (digital) = (35 - 25) x (0.0017 % x 200 °C -
(-200 °C)), min. 0.003 °C
Influence of ambient temperature (D/A) = (35 - 25) x (0.003% x 200 °C)
Influence of supply voltage (digital) = (30 - 24) x (0.01% x 200 °C - (-200 °C)), min.
0.005 °C
Influence of supply voltage (D/A) = (30 - 24) x (0.003% x 200 °C)
Measured error digital value (HART):
√(Measured error digital² + Influence of ambient temperature (digital)² + Influence
of supply voltage (digital)²
Measured error analog value (current output):
√(Measured error digital² + Measured error D/A² + Influence of ambient
temperature (digital)² + Influence of ambient temperature (D/A)² + Influence of
supply voltage (digital)² + Influence of supply voltage (D/A)²
Sensor-transmitter matching
RTD sensors are one of the most linear temperature measuring elements. Nevertheless,
the output must be linearized. To significantly improve temperature measurement
accuracy, the device allows the use of two methods:
• Callendar van Dusen coefficients (Pt100 resistance thermometer)
The Callendar van Dusen equation is described as:
R T = R 0 [1+AT+BT²+C(T-100)T³]
The coefficients A, B and C are used to match the sensor (platinum) and transmitter in
order to improve the accuracy of the measuring system. The coefficients for a standard
sensor are specified in IEC 751. If no standard sensor is available or if greater accuracy is
required, the coefficients for each sensor can be determined specifically with the aid of
sensor calibration.
• Linearization for copper/nickel resistance thermometers (RTD)
The polynomial equation for copper/nickel is as follows:
R T = R 0 (1+AT+BT²)
The coefficients A and B are used for the linearization of nickel or copper resistance
thermometers (RTD). The exact values of the coefficients derive from the calibration
data and are specific to each sensor. The sensor-specific coefficients are then sent to the
transmitter.
Sensor-transmitter matching using one of the methods mentioned above significantly
improves the temperature measurement accuracy of the entire system. This is because the
Technical data
0.12 °C (0.22 °F)
0.06 °C (0.11 °F)
0.12 °C (0.22 °F)
0.14 °C (0.25 °F)
0.12 °C (0.22 °F)
0.06 °C (0.108 °F)
0.07 °C (0.13 °F)
0.06 °C (0.108 °F)
0.02 °C (0.036 °F)
0.04 °C (0.72 °F)
0.14 °C (0.25 °F)
0.17 °C (0.31 °F)
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