Pt100 - Temperatur Sensors

Accuracy of Pt100 - temperature sensors

Pt100 sensors are known for their high accuracy, linearity and long-term stability in temperature measurement.
The accuracy of Pt100 sensors is influenced by various factors, including the quality of the platinum resistor. platinum resistor, the calibration of the sensor and the compensation of external influences. (see page errors).
Most Pt100 sensors have an accuracy class according to the DIN EN 60751 standard. In non-European countries other standards are used (e.g. ASTM E 1137), which specify other accuracies or accuracy classes for Pt100 sensors.
The DIN EN standard specifies the accuracy of Pt100 temperature sensors in so-called classes.
The Pt100 sensor accuracy class for the Pt100 sensor is determined by the manufacturer.
With some manufacturers or Pt100 sensor types (e.g. chip sensors), the measuring accuracy is sometimes limited to a certain measuring range span.

Download table of permissible measuring errors according to DIN EN 60751

Calculation formulas for accuracy of Pt100 sensors

The measurement deviation can be calculated using the following formulas.

• Class A:
  Calculation formula: t_F= ± (0,15 + 0,002 x t)
  valid for temperatures from -200...+650 °C in 3- or 4-wire connection
• Class B:
  Calculation formula: t_F= ± (0,30 + 0,005 x t)
  alid for temperatures from -200...+850 °C
  
  t= Measured temperature without sign (+ or -)
  t_F= Measuring error in °C

Example:

	Class A	Class B			Class A	Class B
-200 °C	0,55 °C	1,30 °C		+400 °C	0,95 °C	2,30 °C
-100 °C	0,35 °C	0,80 °C		+500 °C	1,15 °C	2,80 °C
0 °C	0,15 °C	0,30 °C		+600 °C	1,35 °C	3,30 °C
+100 °C	0,35 °C	0,80 °C		+700 °C	---	3,80 °C
+200 °C	0,55 °C	1,30 °C		+800 °C	---	4,30 °C
+300 °C	0,75 °C	1,80 °C

Some manufacturers of Pt100 sensor elements, have extended these tolerance ranges according to the requirements of the market.
For example:

• 1/3 DIN B
  Berechnungformel: t_F= ± (0,1+0,005 x t)
oder
• 3-fach DIN B
  Berechnungsformel: t_F= ± (0,9+0,005 x t)
  
  t= gemessene Temperatur ohne Vorzeichen
  t_F= Messfehler in °C

Calibration 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 www.sika-instruments.co.uk/products/temperature/temperature-calibrators/.
However, not only the Pt100 resistance thermometer should be checked, but also the downstream evaluation devices or display units should be checked regularly.