What it is and what it does
The Omron 61F-GP-NL AC24 4KM is a High/Low Level controller from the 61F series, designed for conductive liquid level detection. It operates on a 24VAC supply and uses the conductivity of the liquid between probes to sense high and low levels, switching a relay when the setpoint is reached. The key spec here is the 4 km maximum distance between the controller and the sensor probes — that's the '4KM' suffix. This means the sensing head can be placed a long way from the control panel, useful for large tanks, remote sumps, or distributed water/wastewater sites where running a separate power supply to the sensor location isn't practical. Sensitivity is adjustable from 0 to 0.5 kOhm, so it can be tuned for different liquid conductivities — from relatively conductive tap water down to low-conductivity fluids like deionized water or certain process chemicals. The SPDT (2 Form C) relay contacts are rated 3A at 250VAC, enough to drive a small pump contactor or alarm directly.
Mounting and wiring
Socketable mounting via an 11-pin octal base. The plug-in design allows swapping the controller without rewiring. Termination style is Plug In, 11 Pin (Octal).