The Omron 61F-GD AC110/220 is a chassis-mount liquid level controller from the 61F series, configured as a High/Low Level type. It operates on a dual-rated 110/220VAC supply and provides SPDT (2 Form C) relay contacts rated at 5A at 220VAC. Sensitivity is adjustable across 0 ~ 1.8kOhm, which covers conductive liquids from clean water to mildly contaminated process fluids. The control-to-sensor distance can run up to 1km, making it suitable for remote tank farms or elevated reservoirs where the controller sits in a panel and the probes are field-run.
The 0 ~ 1.8kOhm sensitivity range is the key selection parameter: it determines the conductivity threshold at which the relay switches. At the low end (0 Ohm), the controller triggers on near-short conditions (highly conductive liquids like saltwater); at the high end (1.8kOhm), it still detects relatively resistive fluids like deionized water or light slurries. The SPDT contact form (2 Form C) gives both a normally-open and normally-closed set of contacts per relay, so you can wire separate alarm and pump-control circuits off the same controller without adding interposing relays. The 5A at 220VAC contact rating handles direct switching of small pumps up to about 1/3 HP; anything larger should drive a contactor coil through the relay.
This class of level controller is standard in water and wastewater treatment, cooling tower sump control, condensate return systems, and chemical batching where conductive probes sense liquid presence. The 1km maximum distance between controller and sensor means the probes can be field-mounted at the tank while the controller lives in a central panel — common in large tank farms or elevated storage where running the controller supply voltage to the tank is impractical. The screw terminals and chassis-mount form factor suit permanent panel installations where the controller is wired into a terminal block rather than plugged into a socket.