Frage:
PTC temperature sensor: What does the characteristic curve look like?
What needs to be considered when connecting PTC elements in series?
Antwort:
PTC = Positive Ttemperature Coefficient:
PTC elements are electronic components whose internal resistance increases to higher temperature values, whereby dthe increase is not linear is not linear, see diagram.
In the range of the temperature limit to be monitored (NAT = nominal Atriggerttemperature = TREF), the characteristic curve shows a very sharp increase. An increase in temperature of a few degrees is sufficient and the internal resistance of the PTC element changes from a few ohms to values above 1 kOhm. Depending on the design of the PTC element, the NAT temperature limit can be at different temperatures.
The properties of PTC elements for use as temperature sensors are defined in DIN44081/44082.
NAT = Nominals Atrigger-Ttemperature = TREF:
In the area of the temperature limit to be monitored (NAT) the PTC characteristic curve has a very steep rise. An increase in temperature of a few degrees is sufficient and the internal resistance of the PTC element rises from a few ohms to values in the kOhm range.
Depending on the design of the PTC element, the temperature limit NAT can vary The properties of PTC elements for use as PTC temperature sensors are defined in DIN 44081/44082.
Series connection of PTCs: Since the characteristic curve in the area of the NAT temperature threshold is almost vertical, it is usually possible to connect several PTC elements in series without any problems.
In this case, however, double the resistance values must be set in the evaluation electronics.
Example:
An electronic evaluation unit for PTC elements responds at a resistance value of 1200 ohms. With two PTC elements connected in series, the evaluation electronics would already trigger at a resistance value of 600 ohms per PTC element.
Due to the very steep PTC characteristic curve, a resistance value of 600 ohms corresponds to a temperature that is only slightly below the NAT temperature threshold.
Further information can be obtained from the manufacturers, e.g. , . E.G. www.ziehl.de, www.thermik.de.
Search terms: temperature measurement, PTC element (DIN44081/44082), PTC temperature sensor, PTC characteristic
