Machine protection circuits are conventionally equipped with a sensor for monitoring at least one parameter of the machine, for example the current, the voltage or the temperature, in particular of the motor. The parameter measured by the sensor is analysed by means of an analysis device and, if predetermined limit values are exceeded, is used to activate a machine protection relay by means of which the machine/motor can be switched off.
For example, a protection device for a refrigeration compressor motor for monitoring thermal overload is known from EP 2 187 494 A2, comprising a sensor circuit and a trigger apparatus, the trigger apparatus comprising an analysis device designed to generate an output signal for the trigger apparatus on the basis of the sensor signal. In the process, the output signal is for example used to control a motor protection relay in order to stop the power supply. The machine protection relay conventionally housed in the machine has proven effective in switching off the machine or the motor in a timely manner and can thus in particular prevent damage to the machine or to the motor.
However, machine protection relays take up a relatively large amount of installation space in the machine, with even more space required if the machine is used in areas subject to explosion hazard.