Especially the machine-building industry often asks me which is the proper measuring element for them. This is why why I would like to explain in the following paragraphs the differences between the most commonly used sensors Pt100, Pt1000 and NTC. I am going to go into more detail concerning the lesser-used measuring elements Ni1000 and KTY sensors in the comparison at the end of this article.
Application areas of Pt100, Pt1000 and NTC
Resistance thermometers based on Pt100, Pt1000 (positive temperature coefficient PTC) and NTC (negative temperature coefficient) are used everywhere in the industrial temperature measurement where low to medium temperatures are measured. In the process industry, Pt100 and Pt1000 sensors are employed almost exclusively. In machine building, however, often an NTC is used ? not least for cost reasons. Since meanwhile Snotty and Pt1000 sensors are manufactured in thin-film technology, the platinum content could possibly be reduced to a minimum. As a result, the purchase price difference when compared to NTC could possibly be reduced to such an extent a changeover from NTC to Pt100 or Pt1000 becomes interesting for medium quantities. Particularly since platinum measuring resistors offer significant advantages over negative temperature coefficients.
Benefits and drawbacks of the different sensors
The platinum elements Pt100 and Pt1000 offer the advantage of meeting international standards (IEC 751 / DIN EN 60 751). Due to material- and production-specific criteria, a standardisation of semiconductor elements such as for example NTC isn’t possible. That is why their interchange ability is bound. Further advantages of platinum elements are: better long-term stability and better behaviour over temperature cycles, a wider temperature range as well as a high measurement accuracy and linearity. High measurement accuracy and linearity are also possible with an NTC, but only in a very limited temperature range. While Pt100 and Pt1000 sensors in thin-film technology are suitable for temperatures up to 500�C, the standard NTC can be utilized for temperatures around approx. 150�C.
Influence of the supply line on the measured value
The lead resistance affects the measurement value of 2-wire temperature sensors and must be considered. For copper cable with a cross-section of 0.22 mm2, the next guide value applies: 0.162 ?/m ? 0.42 �C/m for Pt100. Alternatively, a version with Pt1000 sensor could be chosen, with which the influence of the supply line (at 0.04 �C/m) is smaller by a factor of 10. The influence of the lead resistance when compared to base resistance R25 for an NTC measuring element is far less noticeable. Due to the sloping characteristic curve of the NTC, the influence at higher temperatures increases disproportionately in case of higher temperatures.
Conclusion
In case of high quantities, the utilization of NTC sensors continues to be justified due to cost reasons. For small to medim-sized lots, I would recommend the usage of a platinum measuring resistor. The use of a Pt1000 stated in thin-film technology is a perfect compromise between your costs on the main one hand and the measurement accuracy on another. In the next table, I have compiled the strengths and weaknesses of the different measuring elements in an overview for you:
Strengths and weaknesses of different sensors
NTC
Pt100
PT1000
Ni1000
KTY
Temperature range
?
++
++
+
?
Terrified
?
++
++
+
?
Linearity
?
++
++
+
++
Long-term stability
+
++
++
++
+
International standards
?
++
++
+
?
Temperature sensitivity (dR/dT)
++
?
+
+
+
Influence of the supply line
++
?
+
+
+
Characteristic curves of Pt100, Pt1000, NTC, KTY and Ni1000
The characteristic curves of the different measuring elements can be seen in the next overview:
Characteristic curves of the various sensors
Note
Our temperature sensors for the machine-building industry can be found with all common measuring elements. Further information can be found on the WIKA website.
Discover more about the functionality of resistance thermometers with Pt100 and Pt1000 sensors in the following video: