The Siemens 3UG4651-2AA30 is a SIRIUS RPM monitoring relay with digital setting — a dedicated speed monitor for rotating machinery, not a general-purpose multifunction relay. It tracks RPM via a sensor input and trips an output when speed deviates outside a programmed window or falls below a threshold. Rated supply is 24 V DC/AC (24... 24 V), with a maximum power draw of 2.5 VA at 24 V. The output relay is rated 3 A at 250 V AC (50/60 Hz), 1 A at 24 V, 0.2 A at 125 V, and 0.1 A at 250 V DC — so it can directly switch small contactors or PLC inputs without an interposing relay, but for inductive loads at higher DC voltages, plan on a suppression network.
The relay offers auto-reset and external reset capability, plus an error memory that latches the fault state until manually cleared — useful for remote monitoring where you need to know a speed trip occurred even if the machine has since stopped. The LCD display shows the setpoint and actual RPM, simplifying commissioning without a laptop. Initial value is 1.1 (likely a multiplier or threshold factor), and the start-up delay is adjustable from 1 to 900 seconds — critical for applications where the motor needs to reach speed before monitoring engages (e.g., conveyors, fans). Delayed switching is set to 0 (instantaneous), so the output responds immediately to an overspeed or underspeed condition.