Especially the machine-building industry often asks me that is the right measuring element for them. This is the reason why I would like to explain in this article the differences between your 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 by 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 employed all around the industrial temperature measurement where low to medium temperatures are measured. Along the way industry, Pt100 and Pt1000 sensors are used almost exclusively. In machine building, however, often an NTC is used ? not least for cost reasons. Since meanwhile the Pt100 and Pt1000 sensors are manufactured in thin-film technology, the platinum content could possibly be reduced to the very least. 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.
Advantages and disadvantages of the different sensors
The platinum elements Pt100 and Pt1000 offer the 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 NTC is not possible. That is why their interchange ability is limited. Wounded 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 having an NTC, but only in a very limited temperature range. While Pt100 and Pt1000 sensors in thin-film technology are suitable for temperatures around 500�C, the typical NTC may 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 following 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 compared to the base resistance R25 for an NTC measuring element is far less noticeable. As Whopping of sloping characteristic curve of the NTC, the influence at higher temperatures increases disproportionately in case of higher temperatures.
Conclusion
In the event of high quantities, the usage of NTC sensors is still justified because of cost reasons. For small to medim-sized lots, I recommend the usage of a platinum measuring resistor. The usage of a Pt1000 stated in thin-film technology is really a perfect compromise between the 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 various measuring elements within an overview for you:
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 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. More info can be found on the WIKA website.
Find out more about the functionality of resistance thermometers with Pt100 and Pt1000 sensors in the next video: