What it is and what it does
The Siemens 3UG5651-1CW31 is a digital monitoring relay from the SIRIUS 3UG5 family, purpose-built for speed monitoring of rotating machinery. It measures rotational speed from 0.1 to 2200 r/min and triggers on overshoot or undershoot conditions, making it a direct fit for conveyor drives, fans, pumps, and any shaft where loss of speed or overspeed protection is required. Supply voltage is universal — 24 to 240 V AC/DC, 50/60 Hz — so it works across control voltages without a separate power supply module. Both ON delay and tripping delay are adjustable from 0.1 to 999.9 s, which gives you time to handle start-up transients or brief load dips without nuisance trips. Outputs are two changeover contacts (2 C/O) via screw terminals, rated for general-purpose switching. The relay carries a SIL 1 / PL c functional safety classification, meaning it can be used in low-risk safety-related applications where a single fault is tolerable.
Lifecycle and sourcing posture
RoHS compliance is effective from 01 June 2023, and the part contains lead above 0.1% w/w (CAS 7439-92-1) per REACH Article 33, which is typical for electronic components with solder joints. No special export restrictions apply (AL: N / ECCN: N).
What the ratings mean for fit
The 0.1–2200 r/min range covers everything from slow conveyor shafts to moderate-speed fans and spindle drives. If your application runs below 0.1 r/min (e.g., a very slow agitator) or above 2200 r/min (high-speed centrifuge), this relay will not pick up the signal — you would need a different sensor or a higher-range model. The universal supply (24–240 V AC/DC) means you can wire it directly to a 24 VDC PLC output or a 230 VAC control transformer without a separate power module. Just confirm the supply is within that range and clean; the relay handles both AC and DC internally. Adjustable ON delay and tripping delay (0.1–999.9 s) let you mask start-up acceleration and brief load variations. For example, a conveyor that takes 5 seconds to reach full speed can have an ON delay set to 6 s, preventing an undershoot alarm during ramp-up.
Mounting and wiring note
Packaged dimensions are 127 x 111 x 38 mm — a compact footprint that fits standard DIN-rail enclosures. Screw terminals accept solid or stranded wire; strip length and torque follow standard Siemens terminal practice (typically 7 mm strip, 0.5–0.6 Nm). The two changeover contacts are electrically isolated from the input circuit, so you can wire them to separate control systems (e.g., one contact to the PLC, the other to a warning light) without cross-talk.