Accuracy of Pt100 sensors and Pt100 resistance thermometers
Pt100 sensors are known for their high accuracy, linearity and long-term stability in temperature measurement. They are manufactured as thin-film (chip) sensors or as so-called wire-wound sensors, in which a platinum wire is wound around a ceramic or glass core.In practice, Pt sensors are normally installed in a protection fitting with mechanical and electrical connections and are then referred to as Pt100 resistance thermometers.
Die Genauigkeit von Pt100-Sensoren wird durch verschiedene Faktoren beeinflusst, darunter die Qualität des Platinwiderstands, die Kalibrierung des Sensors und die Kompensation von externen Einflüssen The accuracy of Pt100 sensors is influenced by various factors, including the quality of the platinum resistor, the calibration of the sensor and the compensation of external influences (see page Measurement errors).
In the past, the accuracy of Pt100 sensors was defined in 2 classes (A and B) according to DIN. These were valid for Pt100 sensors and Pt100 resistance thermometers.
No distinction was made between thin-film sensors and wire-wound sensors.
Customer demand for more accurate sensors prompted some manufacturers to introduce additional, non-standardized accuracy classes to supplement the DIN standard:
They were called 1/3 DIN , 1/10 DIN or 3 DIN.
In non-European countries, other standards are also used to calculate accuracy (e.g. ASTM E 1137).
The increasing market demand for more accurate sensors and the possibilities of better measuring methods led to the adaptation of DIN EN 60751.
New accuracy classes have been defined and a distinction made between Pt100 sensors and Pt100 resistance thermometers.
- Accuracy class for Pt100 sensors Thin-film sensors show a different, temperature-dependent behavior at higher temperatures than wire-wound sensors.
- Thin-film Sensors
F01 / F0,15 / F0,3 /, F0,6 - Wire-wound sensors
W01 / W0,15 / W0,3 / W0,6 - Accuracy classes Pt100 resistance thermometers As practice has shown, a Pt100 resistance thermometer does not necessarily have the accuracy class of the built-in Pt100-Sensors.
For this reason, separate accuracy classes have been defined for thin-film sensors and wire-wound sensors, which differ only in the valid temperature range of the accuracy class.
The accuracy of Pt100 resistance thermometers is therefore defined in 4 separate accuracy classes (AA, A, B, C)
The previously known accuracy classes (A, B) have been supplemented by the new classes (AA and C).
These accuracy classes are also only defined for a limited temperature range, which is different for thin-film sensors and wire-wound sensors.
Calculation formulas for accuracy of Pt100 sensors
The measurement deviation can be calculated using the following formulas.Pt100-thin-film sensors
- Class: F0,1:
Calculation formula: tF= ± (0,1 + 0,0017 * t) valid for temperatures from 0 to +150 °C - Class: F0,15:
Calculation formula: tF= ± (0,15 + 0,002 * t) valid for temperatures from -30 to +300 °C - Class: F0,3:
Calculation formula: tF= ± (0,30 + 0,005 * t)
valid for temperatures from -50 to +500 °C
- Class: F0,6:
Calculation formula: tF= ± (0,60 + 0,01 * t)
valid for temperatures from -50 to +600 °C
t= Measured temperature without sign (+ or -)
tF= Measuring error in °C
Pt100-wire-wound sensors
- Class W0,1:
Calculation formula: tF= ± (0,1 + 0,0017 * t) valid for temperatures from -100 to +350 °C - Class W0,15:
Calculation formula: tF= ± (0,15 + 0,002 * t) valid for temperatures from -100 to +450 °C - Class W0,3:
Calculation formula: tF= ± (0,30 + 0,005 * t)
valid for temperatures from -196 to +660 °C
- Class W0,6:
Calculation formula: tF= ± (0,60 + 0,01 * t)
valid for temperatures from -196 to +660°C
t= Measured temperature without sign (+ or -)
tF= Measuring error in °C
Calculation formulas for accuracy of Pt100 resistance thermometers
The measurement deviation can be calculated using the following formulas.- Class AA:
Calculation formula: tF= ± (0,1 + 0,0017 * t) with thin-film sensor: valid for temperatures from 0 to +150 °C
with wire-wound sensor valid for temperatures from -50 to +250 °C - Class A:
Calculation formula: tF= ± (0,15 + 0,002 * t) with thin-film sensor: valid for temperatures from -30 to +300 °C
with wire-wound sensor valid for temperatures from -100 to +450 °C - Class B:
Calculation formula: tF= ± (0,30 + 0,005 * t)
with thin-film sensor: valid for temperatures from -50 to +500 °C
with wire-wound sensor valid for temperatures from -196 to +600 °Cbr>
- Class C:
Calculation formula: tF= ± (0,60 + 0,01 * t)
with thin-film sensor: valid for temperatures from -50 to +600 °C
with wire-wound sensor valid for temperatures from -196 to +600 °C
t= Measured temperature without sign (+ or -)
tF= Measuring error in °C
Example of Pt100 resistance thermometer with wire-wound sensor:
Class AA
Class A
Class B
Class C
-196 °C
---
---
±1,28 °C
±2,56 °C
-100 °C
---
±0,35 °C
±0,80 °C
±1,60 °C
-50 °C
±0,19 °C
±0,25 °C
±0,55 °C
±1,10 °C
-30 °C
±0,15 °C
±0,21 °C
±0,45 °C
±0,90 °C
0 °C
±0,10 °C
±0,15 °C
±0,30 °C
±0,60 °C
+100 °C
±0,27 °C
±0,35 °C
±0,80 °C
±1,60 °C
+150 °C
±0,36 °C
±0,45 °C
±1,05 °C
±2,10 °C
+200 °C
±0,44 °C
±0,55 °C
±1,30 °C
±2,60 °C
+250 °C
±0,53 °C
±0,65 °C
±1,55 °C
±3,10 °C
+300 °C
---
±0,75 °C
±1,80 °C
±3,60 °C
+400 °C
---
±0,95 °C
±2,30 °C
±4,60 °C
+450 °C
---
±1,05 °C
±2,55 °C
±5,10 °C
+500 °C
---
---
±2,80 °C
±5,60 °C
+600 °C
---
---
±3,30 °C
±6,60 °C
red values are not defined for thermometers with thin-film sensors
Download table of permissible measuring errors according to DIN EN 60751
Download table measurement error class AACalibration of Pt100 temperature sensors
The manufacturer's information on the measuring accuracy refers to the units as delivered.Despite the good long-term stability of the Pt100 sensor, an increased measurement deviation can occur during operation in the event of improper use or difficult operating conditions.
In ISO 9000 ff certified companies it is therefore stipulated that Pt100 resistance thermometers used in industrial processes must be regularly maintained and calibrated. The frequency of calibration of resistance thermometers is determined by the plant operator. Calibration can be carried out with suitable calibrators, by the manufacturer or by an independent certified calibration laboratory.
Suitable calibration devices for the simple dry calibration of temperature sensors are offered, for example, by the SIKA company Link to Sika Calibrators.
However, not only the Pt100 resistance thermometer should be checked, but also the downstream evaluation devices or display units should be checked regularly.