Electric motors intrinsically safe control - has zener or safety barrier and temperature dependent current limiters

摘要

Intrinsically safe control for electric motors comprises a zener (or safety) barrier with current limiting resistors, a microfuse and with zener diodes in transverse limbs/branches of the circuit, auxiliary apparatus, transformer, rectifier and a relay to switch the electric motor. These latter, taken together, form the non-intrinsically safe part of the current circuit, while the intrinsically safe part comprises a control circuit starting at the output of the zener barrier. Part of the current limiting resistance is made temperature dependent and is in heat-conducting connection with the windings being temperature monitored of the controlled motor.