Especially the machine-building industry often asks me which is the proper measuring element for them. This is the reason why I want to explain in the following paragraphs the differences between your 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.
Application areas of Pt100, Pt1000 and NTC
Resistance thermometers on the basis of Pt100, Pt1000 (positive temperature coefficient PTC) and NTC (negative temperature coefficient) are used all around 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 the very least. As a result, the price difference when compared to NTC could 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.
Advantages and disadvantages of the different sensors
The platinum elements Pt100 and Pt1000 provide benefit of meeting international standards (IEC 751 / DIN EN 60 751). Because of material- and production-specific criteria, a standardisation of semiconductor elements such as for example NTC isn’t possible. For this reason their interchange ability is bound. Further benefits of platinum elements are: better long-term stability and better behaviour over temperature cycles, a wider temperature range in addition to a high measurement accuracy and linearity. High measurement accuracy and linearity are also possible having an NTC, but only in a very limited temperature range. While Pt100 and Pt1000 sensors in thin-film technology are ideal for temperatures around 500�C, the typical NTC may be used for temperatures up to 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 taken into account. For copper cable with a cross-section of 0.22 mm2, the following guide value applies: 0.162 ?/m ? 0.42 �C/m for Pt100. Alternatively, a version with Pt1000 sensor could be chosen, with that your 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 much 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 use of NTC sensors is still justified due to cost reasons. For small to medim-sized lots, I would recommend the use of a platinum measuring resistor. Triggers 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 following table, I’ve compiled the strengths and weaknesses of the various measuring elements in an overview for you:
Strengths and weaknesses of different sensors
NTC
Pt100
PT1000
Ni1000
KTY
Temperature range
?
++
++
+
?
Accuracy
?
++
++
+
?
Linearity
?
++
++
+
++
Long-term stability
+
++
++
++
+
International standards
?
Promising +
++
+
?
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 different 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: