Positive Temperature Coefficient (PTC) sensor
A Positive Temperature Coefficient (PTC) sensor provides the airflow sensing function. PTC sensors remain at a low, relatively constant level of resistance over a wide temperature range then abruptly increase resistance logarithmically at an elevated temperature known as an anomaly temperature. As the transition is approached, a slight temperature rise causes a dramatic increase in resistance.

Power supplied to the PTC sensor will cause it to self–heat to a high resistance condition. Sufficient airflow will cool the sensor to its low resistance level. Insufficient airflow allows the sensor to self–heat and reach a high resistance state. This resistance change and accompanying decrease in current is used to trigger an output transistor or SCR.

Definitions for the Temperature vs. Velocity Curve (at right)
No–Fault: Operation points within this region represent the normal state. (i.e. sufficient airflow to cool sensor to its low resistance level.)
Fault: Operating points within this region represent the anomaly state. (i.e. Insufficient airflow allows sensor to reach high resistance state.)

•	Solid–state
•	High reliability
•	Commercial or military grades
•	Variety of switching modes

The Klixon 2SE solid–state vane switch has advanced, state-of-the-art airflow sensing. Successor to electromechanical vane types, the 2SE is designed to sense and protect against the loss of airflow in power supplies, data processing units, or any other commercial or military electronic equipment where it is necessary to recognize the loss or reduction of airflow.

30 VDC maximum

400 milliamps maximum

SPST or DPST

Automatic or Manual

Normally open or closed

Approximately 20 grams

Approximately 3 watts

100,000 cycles

10°C to 50°C (50°F to 120°F)

Up to 150°C (300°F)

10G, 10–500 Hz per MIL-STD-202, Method 202, Condition A

100G, for 6ms per MIL-STD-202, Method 213, Condition C

10 days per MIL-STD-202, Method 106

48 Hours per MIL-STD-202, Method 101, Condition B