What it is and what it does
The Siemens 3RT1916-2DH21 is a SIRIUS timing relay — a dedicated OFF-delay timer that clips onto a DIN rail and controls when a downstream load drops out after the control signal is removed. Its adjustable time range of 0.5... 10 s covers common delay-on-release applications like fan run-down, conveyor brake sequencing, or post-lubrication cycles. The relay accepts a wide supply voltage of 90... 240 V AC (50/60 Hz) or DC, which simplifies stocking across panels with different line voltages.
Key ratings and what they mean for fit
The OFF-delay function means the relay's output remains energized for the set time after the input signal drops — critical for loads that must not stop abruptly. The minimum ON period of 35 ms ensures the timing circuit stabilizes before the delay starts. Recovery time of 150 ms is the minimum interval before the relay can be re-triggered after a timing cycle; if your process cycles faster than that, this relay will miss a pulse. Basic insulation per IEC 60947-1 and pollution degree 3 means the relay is rated for industrial environments with conductive dust or occasional condensation — standard for a control cabinet, not for clean-room or wet-area placement without an enclosure. The IP20 rating at the terminals means finger-safe but not sealed; the relay belongs inside a panel, not in a washdown zone.
Mounting and integration
Clip-on mounting snaps onto a standard 35 mm DIN rail. Dimensions of 45 mm wide × 38 mm deep × 38 mm high keep it compact for dense panel layouts. Mounting position is unrestricted — any orientation works, which helps when fitting into existing wireways or tight sub-panels. Wire termination accepts solid or stranded conductors from 18 to 14 AWG, matching typical control-circuit wiring.