Especially the machine-building industry often asks me that is the right measuring element for them. This is why why I would like 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.
Application regions 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. In the process 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 a minimum. As a result, the 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 provide 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. For this reason their interchange ability is limited. 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 suitable for temperatures around 500�C, the standard NTC may be used for temperatures around approx. 150�C.
Upbeat 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 following 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 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. Due to the 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 use of NTC sensors continues to be justified because of cost reasons. For small to medim-sized lots, I would recommend the use 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 following table, I’ve 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
?
++
++
+
?
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 various 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 next video:g