Safety device, system and method for monitoring an electric motor

A safety device (10) configured to monitoring an electric motor (101), said electric motor (101) being connected to a power supply line (100), characterized in that said safety device (10) comprises a control unit (12) having:

• at least one first input channel (16) configured to be connected to a power supply line (100) of the electric motor (101) to detect a voltage and a frequency on said power supply line (100) and to transmit at least one first work signal (W) correlated to said detected voltage and frequency, wherein said voltage is correlated to a state of stopped or running engine and said frequency is correlated to the rotation speed of said electric motor (101),
• switching means (15) configured to transmit a control signal (CF, CV),
• at least one first processing unit (17) connected to said first input channel (16) and to said switching means (15) and configured to control said switching means (15) generating at least one first activation signal (AV, AF) according to said at least one first work signal (W),
• wherein said control signal (CF, CV) is transmitted in response to said at least one first activation signal (AV, AF),
• wherein said at least one first processing unit (17) is configured to compare said at least one first work signal (W) with at least one predetermined frequency threshold (F) and with at least one predetermined voltage threshold (V), and
• wherein said first input channel (16) comprises at least one first measurement unit (19) connected to said at least one first processing unit (17) and first amplification means (18) configured to be connected to said power supply line (100) and to transmit to said first measurement unit (19) at least one first intermediate voltage signal (IV) and at least one first intermediate frequency signal (IF), said first measurement unit (19) being configured to measure said at least one first intermediate voltage signal (IV) and said at least one first intermediate frequency signal (IF) and to transmit said at least one first work signal (W) to said at least one first processing unit (17).