The Omron 61F-HSL AC115 is a conductive-type level controller for detecting high or low liquid levels in a tank or vessel. It works by sensing the resistance between two or three probe electrodes — when the liquid bridges the probes, the internal relay switches. The adjustable sensitivity from 0 to 5 MOhm means you can tune it for different liquid conductivities, from clean water (low resistance) to demineralized or high-purity water (high resistance) or even some process chemicals. It runs on a 115 VAC supply and switches a SPDT (2 Form C) relay rated at 5 A at 220 VAC — enough to drive a small pump contactor or an alarm annunciator directly. The octal 8-pin base (standard 8-pin relay footprint) makes it a drop-in swap for existing level relay sockets in a panel.
Socketable design — mounts on a standard 8-pin octal relay socket (sold separately). That socket typically snaps onto DIN rail or panel-mounts with two screws. The plug-in form factor means you can swap the controller in seconds without disturbing the wiring; the base stays in the panel. Not rated for outdoor or washdown locations without an IP-rated enclosure around it.
Listed as active in production. This is a mature, widely stocked part in the 61F series — not a niche or end-of-life item. That means it's a safe choice for a BOM that needs to stay stable for the next several years.