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Especially the machine-building industry often asks me which is the right measuring element for them. This is the reason why I would like 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 regions of Pt100, Pt1000 and NTC
Resistance thermometers on the basis of 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 employed 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 when compared to NTC could possibly be reduced to this 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). Due to material- and production-specific criteria, a standardisation of semiconductor elements such as NTC isn’t 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 in addition to a high measurement accuracy and linearity. High measurement accuracy and linearity are also possible with an NTC, but only in a very limited temperature range. While Pt100 and Pt1000 sensors in thin-film technology are ideal for temperatures up to 500�C, the standard NTC can be utilized 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 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 case of higher temperatures.
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In case of high quantities, using 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 use of a Pt1000 manufactured in thin-film technology is really a perfect compromise between your costs on the 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 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. Further information are available on the WIKA website.
Find out more about the functionality of resistance thermometers with Pt100 and Pt1000 sensors in the following video: