Especially the machine-building industry often asks me which is the right measuring element for them. This is why why I wish to explain in this posting the differences between the mostly used sensors Pt100, Pt1000 and NTC. I’ll go into greater detail concerning the lesser-used measuring elements Ni1000 and KTY sensors in the comparison at the end of this article.
Corpse of Pt100, Pt1000 and NTC
Resistance thermometers on the basis of 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 the Pt100 and Pt1000 sensors are stated in thin-film technology, the platinum content could possibly be reduced to a minimum. As a result, the price difference compared to the NTC could be reduced to this 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 NTC is not 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 may also be possible having an NTC, but only in an exceedingly limited temperature range. While Pt100 and Pt1000 sensors in thin-film technology are ideal for temperatures up to 500�C, the typical NTC can be used 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 should 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 way of a factor of 10. The influence of the lead resistance when compared to base resistance R25 for an NTC measuring element is much less noticeable. Because of 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 usage of NTC sensors continues to be justified due to cost reasons. For small to medim-sized lots, I would recommend the use of a platinum measuring resistor. The use of a Pt1000 stated in thin-film technology is a perfect compromise between the costs on the one hand and the measurement accuracy on the other. In the following table, I’ve compiled the strengths and weaknesses of the various measuring elements within an overview for you personally:
Strengths and weaknesses of different sensors
NTC
Pt100
PT1000
Ni1000
KTY
Temperature range
?
++
++
+
?
Accuracy
?
++
++
+
?
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 following overview:
Characteristic curves of the various sensors
Note
Our temperature sensors for the machine-building industry are available with all common measuring elements. More info can be found on the WIKA website.
Discover more about the functionality of resistance thermometers with Pt100 and Pt1000 sensors in the following video: