FAQ: Answers to questions about SONTEC products

FAQ results (8)
How does a resistance thermometer work?
With a resistance thermometer, the electrical resistance of a sensor changes with the temperature. With this type of sensor, a distinction is made between PTC (positive temperature coefficient) and NTC (negative temperature coefficient). With PTC sensors, the electrical resistance increases with rising temperature. Platinum sensors (Pt100 / Pt500 / Pt1000) or KTY sensors usually fall under this type of sensor. The Pt100 sensors are described in DIN EN 60751. The PTC sensors are opposite NTC sensors. Here, the electrical resistance decreases with increasing temperature. NTC sensors are not standardised.
What are “PTC sensors”?
At high temperatures, PTC sensors conduct electricity worse than at cold temperatures. They are also known as PTC resistors.
What are “NTC sensors”?
At high temperatures, NTC sensors conduct electricity better than at cold temperatures. They are also known as NTC resistors.
Why should Pt100 measuring elements with tolerance class A/AA be operated with at least a 3 or 4-wire circuit?
For 2-wire circuit, the internal resistance of the supply should be added to the measured value. The result is usually a shift (“offset”) of the measured value. It is possible to measure the supply resistance at room temperature and its adjustment, but the temperature-dependent resistance of the inner conductor of the supply would show as an error in the measured value.
What minimum immersion depths are indicated as a rough guide for protection tubes to minimise to heat conduction errors?
- With gaseous medium 15 ... 20x protection tube diameter - With liquid medium 5 ... 10x protection tube diameter - With solid medium 3 ... 5x protection tube diameter
How is the accuracy of Pt100 divided into classes?
Class AA: ΔT/T= ±(0.1+0.0017*t) Class A: ΔT/T= ±(0.15+0.002*t) Class B: ΔT/T= ±(0.3+0.005*t)
What does “1/3 DIN” mean with resistance thermometers?
The term 1/3 Din and 1/5DIN are not standardised. DIN EN 60751 was revised in 2009. The new tolerance class AA was created based on the term 1/3 DIN (class B).
What is galvanic isolation?
An isolation of the signal between the input and output sides.

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