Especially the machine-building industry often asks me which is the right measuring element for them. This is why why I want to explain in the following paragraphs the differences between your most commonly used sensors Pt100, Pt1000 and NTC. I’ll go into greater detail about 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 everywhere in 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 can be used ? not least for cost reasons. Since meanwhile the Pt100 and Pt1000 sensors are stated in thin-film technology, the platinum content could be reduced to a minimum. As a result, the purchase price difference compared to the NTC could possibly be reduced to such an extent that 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 various 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 for example NTC isn’t possible. Because of this their interchange ability is limited. Further benefits 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 up to 500�C, the typical NTC can 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 should be considered. For Disoriented 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 can be chosen, with that your 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 much less noticeable. Because of the sloping characteristic curve of the NTC, the influence at higher temperatures increases disproportionately in the event of higher temperatures.
Conclusion
In the event of high quantities, the utilization of NTC sensors is still justified due to cost reasons. For small to medim-sized lots, I recommend the use of a platinum measuring resistor. The usage of a Pt1000 manufactured in thin-film technology is really a perfect compromise between the costs on the main one hand and the measurement accuracy on the other. In the next table, I’ve compiled the strengths and weaknesses of the different 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 is seen in the next overview:
Characteristic curves of the different sensors
Note
Our temperature sensors for the machine-building industry are available with all common measuring elements. Further information 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: