The Omron 61F-GP-ND AC120 is a conductive-type level controller that detects liquid presence by sensing resistance between probes. It's set up as a High/Low level controller, meaning it can manage both fill-to-a-level and drain-to-a-level sequences in a tank. The sensitivity adjustment spans 0 to 1.3 kOhm, so you tune it to the conductivity of whatever liquid you're monitoring — clean water at one end, something with higher resistivity further up the scale. Power it with 120VAC, and the relay output gives you a SPDT (2 Form C) contact rated 3A at 250VAC. That's enough to kick a contactor or alarm directly without an interposer relay. The socketable 11-pin octal base means replacement is a pull-and-plug job — no rewiring when the controller itself needs swapping. The control-to-sensor distance is rated up to 1 km, so the probes can be a long way from the controller.
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