Platinum temperature sensors: Differences and applications

A widely used and very accurate sensor element type for temperature measurement is the platinum sensor.
Platinum (Pt) sensors belong to the group of RTD sensors. RTD stands for "Resistance Temperature Detector" and refers to sensors in which the resistance is dependent on the temperature. By measuring the sensor resistance, the temperature can thus be determined.
Platinum sensors are available in two different designs: Platinum thin film sensors and wire wound platinum sensors. Platinum thin-film technology is widely used for Pt sensor elements. Thin film technology is a microstructured connection of layers of ceramics, metal and also glass. In addition to the widespread layer technology, however, some Pt sensor elements also consist of a fine platinum wire winding. This wire winding is applied to a base body made of either glass or ceramic. These sensors are called wire wound platinum sensors.
Compared to other RTDs, the platinum material in Pt sensors provides a resistance that is considered to be very stable over time. Also an advantage over other RTD sensors is the electrical resistance of the platinum sensors, which changes almost linearly with temperature over a wide temperature range. As the temperature increases, so does the resistance. This allows measurements over wide temperature ranges. Via the measurement of the voltage drop, a resistance value is provided, which is then used for the calculation of the absolute temperature. All platinum temperature sensors are standardized according to DIN EN 60751 for the temperature range -200...+850 °C. However, it should be noted that the accuracy classes are only valid for certain temperature ranges (see table). This standard specifies when which sensor must have which accuracy class in order to be designated as Pt100 or Pt1000, for example. For non-standard platinum sensors, a marking must therefore be added.
Accuracy classes according to DIN EN 60751:
With regard to the accuracy classes, it must be noted that DIN EN 60751 was adapted in 2008. Since then, the standard distinguishes between the sensor elements (the actual Pt100, Pt1000, etc. sensors) and the resistance thermometers (probes). Furthermore, the standard distinguishes again between wirewound and film resistors.
In addition, B+B also offers the accuracy class 1/10 DIN up to 350°C. This is a non-standardized class. The deviation is calculated according to the following formula:± (0.03 + 0.0005 x |T|) °C
What does the designation Pt100 or Pt1000 mean?
Probably the most common Pt sensors are the Pt100 and the Pt1000. The number after the designation "Pt" stands for the resistance at the temperature 0 °C. Thus, a Pt100 sensor has a nominal resistance of 100 Ω at a temperature of 0 °C. In conclusion, the Pt1000 sensor has a nominal resistance of 1000 Ω at 0 °C.
But what does that mean? Here is an example to illustrate:
Pt100 has at 10°C=103.9 Ω nominal resistance (resistance increases with temperature, i.e. from 0 °C to 10 °C resistance increase of 3.9 Ω)
Pt1000 has nominal resistance at 10°C=1039 Ω (resistance increases with temperature, i.e. from 0 °C to 10 °C resistance increase of 39 Ω)
Of course, besides Pt100 and Pt1000 sensors, there are also Pt200, Pt500, Pt10,000, etc. sensors. Sensors, where the number also stands for the resistance at 0 °C. The choice of which Pt sensor to use is usually based on the input of the control unit, as well as the accuracy. For example, it makes sense to use a Pt1000 sensor in a 2-wire circuit, since the lead resistance has less influence on the measurement result than with a Pt100. The reason is that the base resistance of a Pt1000 sensor is 10 times higher than that of a Pt100 sensor. Detailed explanations of the different conductor techniques for temperature sensors can be found in the next B+B application report.