The EN2000 A3 and A3R is a speed monitoring and protection instrument. It is used to measure rotational speed and zero (reverse) speed of rotating machinery, to monitor rotational speed variation caused by faults and to protect the unit.  EN2000A3 is applied to various rotating machinery, such as turbine generator, gas turbine, hydro generator, compressor, motor, fan, centrifugal machine, etc.; EN2000A3/R can be used by rotating machinery which might produce reverse rotational speed. RS-485 communication interface is also provided.