Finder 72.51.0.024.0002 – 72 Series Level control monitoring relays

Why Choose the Finder 72.51.0.024.0002 Liquid Level Control Relay?

The Finder 72.51.0.024.0002 is a compact, multifunctional conductive liquid level control relay designed for automatic filling, emptying and liquid level monitoring in tanks, reservoirs, wells and industrial process installations. Part of the Finder 72 Series monitoring relay range, this electronic controller uses conductive electrodes to detect liquid levels and operate pumps, valves or associated control equipment.

Featuring a 24 V AC/DC supply, one 6 A changeover output contact and an extended 5–450 kΩ adjustable sensitivity range, the Finder 72.51.0.024.0002 provides flexible monitoring of conductive liquids with different electrical characteristics. The extended sensitivity range makes this particular version especially useful where the liquid has relatively low conductivity.

With six selectable operating functions, 0.5 s or 7 s selectable delay times, dual LED status indicators and a slim 17.5 mm DIN rail housing, the relay provides a versatile solution for water management, pump automation, liquid storage and industrial level control applications.

Key Advantages

• Automatic liquid level monitoring for conductive liquids in tanks, wells and reservoirs.
• 24 V AC/DC supply provides compatibility with common industrial control systems.
• Extended adjustable sensitivity of 5–450 kΩ accommodates liquids with different conductivity levels.
• Six selectable operating functions provide flexible filling, emptying and window monitoring.
• Selectable 0.5 s or 7 s delay helps prevent unnecessary switching caused by turbulence, splashing or temporary level fluctuations.
• One 6 A changeover contact supports connection to suitable control loads, pump contactors and alarm circuits.
• Two LED indicators provide clear power supply and relay output status information.
• Reinforced electrical insulation between the supply, electrodes and output contacts supports reliable circuit separation.
• Two- or three-electrode operation allows single-level or minimum/maximum level control.
• 35 mm DIN rail mounting simplifies installation inside electrical control cabinets.
• 17.5 mm housing width helps minimise panel space requirements.
• Suitable for integration with compatible Finder conductive level electrodes and accessories.

Key Features

• Finder 72 Series Type 72.51 modular level control relay.
• Designed specifically for conductive liquid level detection.
• 24 V AC/DC nominal supply voltage.
• 19.2–26.4 V AC/DC operating supply range.
• One changeover (1 CO / SPDT) output contact.
• 6 A rated output current at 250 V AC.
• 5–450 kΩ adjustable electrode sensitivity.
• Six operating functions: FL, FS, ES, EL, WL and WS.
• Filling and emptying modes for automatic liquid level regulation.
• Window monitoring for detecting levels within a defined range.
• 0.5 s short delay or 7 s long delay, selected through the operating function.
• Compatible with two- and three-electrode sensing arrangements.
• Separate LED indicators for power supply and output relay status.
• Front-mounted rotary selectors for function and sensitivity adjustment.
• 6 kV impulse insulation rating between specified internal circuits.
• IP20 protection rating.
• 35 mm DIN rail mounting according to EN 60715.
• Compact housing with screw-type electrical terminals.
• Suitable for compatible conductive liquids including water, wastewater and certain liquid food products.

How the Finder 72.51 Conductive Level Controller Works

The Finder 72.51.0.024.0002 detects liquid levels by measuring electrical conductivity between electrodes positioned inside a tank, well or other vessel. When a conductive liquid reaches the relevant electrode, it completes a low-energy sensing path, allowing the relay to determine whether the monitored level has been reached.

Unlike a mechanical float switch, conductive electrode sensing does not require a moving float mechanism inside the liquid. This makes the relay useful for installations where electrode-based monitoring is preferred, provided that the liquid has sufficient electrical conductivity and is compatible with the selected probes.

The 5–450 kΩ sensitivity adjustment is an important feature of this specific model. It enables the controller to respond to a broader range of liquid conductivities than the standard 5–150 kΩ version, making it particularly useful for applications involving relatively low-conductivity liquids.

Six Selectable Filling, Emptying and Window Functions

The Finder 72.51.0.024.0002 provides six operating modes, selected using the front-mounted rotary function selector. These modes allow the same relay to be configured for different liquid level control requirements.

• FL – Filling, Long: Filling control with a 7 s delay.
• FS – Filling, Short: Filling control with a 0.5 s delay.
• EL – Emptying, Long: Emptying control with a 7 s delay.
• ES – Emptying, Short: Emptying control with a 0.5 s delay.
• WL – Window, Long: Window level monitoring with a 7 s delay.
• WS – Window, Short: Window level monitoring with a 0.5 s delay.

Filling and emptying functions can be used to maintain liquid levels between defined limits, while window monitoring provides an alternative method of detecting liquid level conditions. The selectable delays help reduce unwanted output changes caused by waves, splashing and temporary disturbances.

Important: The manufacturer specifies that the relay must be disconnected from its power supply and then powered on again after changing the operating function.

Liquid Compatibility and Electrode Selection

The Finder 72.51.0.024.0002 is intended for electrically conductive liquids. Typical compatible media include mains water, well water, rainwater, seawater, wastewater, milk and other conductive liquid products where the electrode materials are suitable for the application.

The controller is not suitable for non-conductive liquids such as oils, fuels, paraffin or demineralised water that does not provide sufficient conductivity. Suitability must be assessed according to the liquid's actual electrical conductivity, chemical composition and installation conditions.

Compatible Finder accessories include suspended electrodes, fixed electrodes, electrode holders and conductive level sensors. Electrode selection should consider the vessel construction, liquid characteristics, cable length and the required minimum and maximum monitoring levels.

Typical Applications

• Automatic filling and emptying of water storage tanks.
• Water level monitoring in wells, cisterns and reservoirs.
• Pump control and dry-running prevention in appropriately designed systems.
• Industrial wastewater and sewage level monitoring.
• Water treatment and distribution installations.
• Rainwater harvesting and storage systems.
• Irrigation systems and agricultural water management.
• Swimming pool and fountain water level control.
• Liquid level monitoring in food and beverage processing.
• Industrial process tanks containing suitable conductive liquids.
• High-level and low-level alarm circuits.
• Commercial building water management systems.
• Electrical control panels and automated pumping stations.