Pt100 - Temperatur Sensors

-Measuring error of Pt100 resistance thermometers-

About the site

This is a private information page about electrical temperature measurement with resistance thermometers (e.g. Pt100, Pt500, Pt1000). My experiences of many years in the field of measurement and control technology are recorded. I do not take over any liability for incorrect information and would be pleased about further suggestions and requests for additions.
Please also visit my information page about variable area flowmeters: https://schwebekö

Suppliers of Pt100

Links to selected manufacturers and suppliers of Temperature Sensors.

Measuring error

Besides the basic accuracy of the Pt100 sensor, the following additional errors may occur:

Self-heating of the Pt100

To measure the resistance of a Pt100 sensor, a current must flow through the sensor. The measuring current generates a power loss and thus heat at the sensor. The associated measurement error of a higher temperature indication depends on various influencing variables:

Line error

The line error results from the connection of the Pt100 resistor to the evaluation electronics with a 2-wire connection line (two-wire connection). The resistance of the connecting cable is included in the measurement as an error.
Particularly with long connection lines and small line diameters, this can lead to considerable measuring errors. With modern evaluation devices, the resistance of the connecting cable can be compensated, but temperature fluctuations on the cable cannot be taken into account. The resistances of the Pt100 and the connecting cable add up, resulting in the display of a higher temperature.

This can be remedied by connecting the Pt100 in 3- or 4-wire technology.
--> Top

Insulation error

Penetration of moisture into the sensor or into the insulating material between the connecting cables, leads to a measuring error (lower temperature). temperature).
The sensors are normally sufficiently protected against moisture. However, when manufacturing the measuring insert, care must be taken to use absolutely dry insulating materials and careful sealing.
--> Top

Parasitic thermoelectric voltages

When different metals are joined, a thermoelectric voltage occurs.
Such metal connections occur, for example, when extending the sensor connection wires with copper wires. Normally, the connection points have the same temperature and thus cancel each other out in terms of value. However, if different temperatures are present at the connection points, e.g. due to different heat dissipation, different thermoelectric voltages occur which lead to a voltage drop which is interpreted by the evaluation device as a change in resistance.
This results in a measurement error.
How high the measuring error is strongly depends on the evaluation device and the selected connection type (2, 3 or 4-wire). Fault detection by reversing the measuring current. The higher the difference of the measured values, the higher the thermoelectric voltage present.
--> Top