System and method for monitoring a failsafe function of sensors in a motor

A method for monitoring failsafe operation of at least one first and one second sensor of a servo drive system including an electric motor, the at least one first sensor, the second sensor and an automation controller, the at least one first and second sensors operating independently of each other, the at least one first and second sensors being operated to ascertain a rotational speed of the electric motor, the rotational speed being subsequently utilized for failsafe rotor position determination of the electric motor, and the at least one first sensor supplying a first output signal and the second sensor suppling a second output signal, the method comprising:

• operating the servo drive system and monitoring, by the automation controller, the failsafe operation of the at least one first sensor and the second sensor;
• forming a first product of a first current count value of the first output signal and a maximum count value of the second output signal obtained by the at least one first sensor during operation of the servo drive system;
• forming a second product of a second current count value of the second output signal and a maximum count value of the first output signal obtained by the second sensor during operation of the servo drive system;
• checking cyclically, by the automation controller, the first and second products for equality while monitoring failsafe operation of the at least one first sensor and the second sensor;
• generating a fault indication when the check is negative while operating the servo drive system and monitoring the failsafe operation of the at least one first sensor and the second sensor;
• and
• applying at least one safety function to the electric motor based on receipt of the fault indication, the safety function comprising at least one of STO, SS1, SLT, SLS and SSM.