Motor protection based on PTC sensors is one of the most effective
and reliable protective measures against thermal overload in electrical
machines. The protection unit is composed of the INT69 motor
protector and the PTC sensors. Due to its compact construction, the
INT69 is suitable for installation in electrical devices or in the terminal
boxes of electrical machines.
At the measuring circuit input of the INT69, it is possible to connect up
to nine DIN 44081, DIN 44082 conform PTC sensors. Sensors with
different nominal response temperatures may be used. Thus it is
possible to monitor several measuring points with only one INT69
If the temperature in one of the monitored parts or sections reaches the
nominal response temperature of the respective PTC sensor, the
sensor becomes highly resistive and the motor protector switches off.
The device switches itself on again after cooling back down.
The relay's switching output is a potential-free changeover contact.
This circuit works in accordance with the closed-circuit principle, i.e.
even in the event of a sensor or cable break, the relay returns to its rest
position and switches off.
The sensor, relay and supply current circuits are galvanically isolated
from each other.