Out here in the grease, when you need a compact brain for a pump skid or a small conveyor section, the Zelio Logic SR3B261B is a modular smart relay that doesn't need a whole PLC rack. It gives you 16 discrete inputs on 24 V AC, a real-time clock that keeps time for ten years off battery, and a self-check that runs program memory verification every time you power it up. That clock drift runs about 12 minutes a year over the 0–55 °C range, six seconds a month at 25 °C—tight enough for timed cycle control. Cycle time lands between 6 and 90 ms, depending on the program size, and the ladder response on a discrete input is a fixed 50 ms—predictable, no surprises. The backup time on the clock is rated ten years at 25 °C, so you can cycle the panel and not lose your time-of-day schedule.
The compliance paperwork is all there: IEC 61131-2 for the hardware, EMC Directive per EN 55022 Class B for conducted and radiated emissions, plus low-voltage directive and environmental standards IEC 60068-2-6 and -27 for vibration and shock.
Screw terminals accept 0.2 to 2.5 mm² solid or stranded, or two 0.2 to 1.5 mm² solid in one clamp. Torque to 0.5 N·m—four and a half pound-inches. The front panel carries an IP40 rating; the terminals are IP20. Mount it in a standard enclosure, keep it under 2000 m altitude, and it'll handle 95% humidity without condensation. Supply voltage is 20.4 to 28.8 V AC/DC, 50/60 Hz. It pulls 7.5 VA base, 10 VA with extensions. Discrete input current is 4.4 mA at 24 V. Each input guarantees a 1 state above 14 V and a 0 state below 2 V, so standard 24 V sensors work without a fight.