Protective circuit for protection of an appliance, in particular an electric motor, against thermal overloading

Abstract

The invention relates to a protective circuit (1) for protection of an appliance, in particular of an electric motor, against thermal overloading, comprising a first and a second terminal (2, 3) for connecting a temperature detection element (4, 11); a detection unit (6) for detecting whether a resistance value of the temperature detector element (4, 11), which is connected between the first and the second terminals (2, 3), is in a first or a second resistance range; a short-circuit detector for identifying whether there is a short circuit between the first and the second terminals (2, 3); signalling outputs (8, 9) for emitting signal messages to an evaluation unit (14) when the detected resistance value is in the second resistance range and / or when a short circuit has been identified by the short-circuit detector (10); and a third terminal (12), which is connected to the second terminal via a predetermined resistance.

Description

technical field [0001] The invention relates to a protection circuit for protection against thermal overload of a device, especially an electric motor. Background technique [0002] In order to prevent the thermal overload of the motor, in addition to using a thermal overload relay that identifies the thermal overload of the motor according to the power consumption of the motor, a thermistor protection circuit that can detect and analyze the temperature of the motor winding is also used. Various temperature detection elements are used here, such as temperature sensors, especially PTC thermistors (PTC: Positive Temperature Coefficient), PT100 sensors and KTY sensors, the resistance of which changes as a function of the detected temperature. As long as the motor winding is in a non-problematic temperature range, the resistance of this type of temperature detection element will always be in the first range. The second resistance range whose resistance value is greater than the...

AI Technical Summary

Problems solved by technology

So so far, the protection circuit set for the temperature sensor cannot be used in combination with the thermal switching element at the same time

[0007] Conventional known protective circuits are either protective circuits for evaluating temperature sensors, which do not have a short-circuit detection function and are therefore also suitable for evaluating thermal switching elements, or circuits for thermistors, which include short-circuit detection and therefore not suitable for analyzing thermal switching elements

Images