Why Choose the Finder 72.51.0.240.0002 Liquid Level Control Relay?
The Finder 72.51.0.240.0002 is a multifunctional conductive liquid level control relay designed for automatic tank filling, emptying, pump control and liquid level monitoring. Part of the Finder 72 Series, this compact electronic relay uses conductive sensing electrodes to detect liquid levels in tanks, wells, reservoirs and industrial process vessels.
Featuring a wide-range 110–240 V AC/DC power supply, one 6 A changeover output contact and an extended 5–450 kΩ adjustable sensitivity range, the Finder 72.51.0.240.0002 provides flexible monitoring of conductive liquids, including liquids with relatively low electrical conductivity.
With six selectable operating functions, 0.5 s or 7 s switching delays, dual LED status indication and compact 35 mm DIN rail mounting, this level control relay offers a practical solution for water treatment, pumping stations, irrigation, industrial automation and building water management systems.
Key Advantages
- Wide-range 110–240 V AC/DC supply provides flexibility across industrial and commercial electrical installations.
- Extended 5–450 kΩ sensitivity adjustment supports monitoring of conductive liquids with varying electrical resistance.
- Six selectable operating functions accommodate filling, emptying and window level monitoring.
- Selectable 0.5 s or 7 s delays help prevent unnecessary switching caused by splashing, turbulence and temporary level changes.
- One 6 A changeover contact provides a flexible switching output for control circuits, alarms and suitable electrical loads.
- Two- or three-electrode arrangements support single-level and minimum/maximum level control.
- Integrated sensitivity adjustment allows the relay to be configured for the conductivity of the monitored liquid.
- Dual LED indicators provide convenient power supply and output status information.
- Reinforced insulation separates the power supply, sensing electrodes and output contact circuits.
- Compact 17.5 mm housing helps conserve space inside electrical control cabinets.
- 35 mm DIN rail mounting enables straightforward panel installation.
- Suitable for use with compatible Finder conductive liquid sensing electrodes and accessories.
Key Features
- Finder 72 Series Type 72.51 level control relay.
- Electronic level monitoring for electrically conductive liquids.
- 110–240 V AC/DC nominal supply voltage.
- 88–264 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.
- Selectable filling and emptying control modes.
- Window monitoring for detecting liquid level conditions.
- 0.5 s short delay and 7 s long delay.
- Supports suitable two- and three-electrode configurations.
- Front-mounted operating function and sensitivity selectors.
- LED indication for supply voltage and output relay status.
- 6 kV impulse insulation between specified internal circuits.
- Silver tin oxide (AgSnO2) output contacts.
- IP20 protection rating.
- 35 mm DIN rail mounting in accordance with EN 60715.
- Compact modular housing with box-clamp terminal connections.
- Suitable for automatic water level regulation and industrial pump control systems.
Technical Specifications
- Manufacturer: Finder
- Series: 72 Series
- Type: 72.51
- Model: 72.51.0.240.0002
- Product type: Conductive liquid level control relay
- Detection principle: Conductive electrode sensing
- Nominal supply voltage: 110–240 V AC/DC
- Operating supply range: 88–264 V AC/DC
- AC supply frequency: 50/60 Hz
- Rated AC power consumption: 2 VA
- Rated DC power consumption: 1 W
- Output contact configuration: 1 CO (SPDT)
- Rated output current: 6 A
- Maximum peak output current: 15 A
- Rated contact voltage: 250 V AC
- Maximum switching voltage: 400 V AC
- Rated AC-1 load: 1,500 VA
- Rated AC-15 load at 230 V AC: 250 VA
- Single-phase motor rating at 230 V AC: 0.185 kW
- DC-1 breaking capacity at 24 V DC: 3 A
- DC-1 breaking capacity at 110 V DC: 0.35 A
- DC-1 breaking capacity at 220 V DC: 0.2 A
- Contact material: Silver tin oxide (AgSnO2)
- Adjustable sensitivity range: 5–450 kΩ
- Number of operating functions: 6
- Filling functions: FL and FS
- Emptying functions: EL and ES
- Window monitoring functions: WL and WS
- Short switching delay: 0.5 s
- Long switching delay: 7 s
- Electrode input terminals: B1, B2 and B3
- Electrode configurations: Two-electrode or three-electrode operation
- Maximum electrode cable length: 200 m, subject to cable capacitance limits
- Maximum specified cable capacitance: 100 nF/km
- Impulse insulation rating: 6 kV (1.2/50 µs) between specified circuits
- Status indication: Supply voltage LED and output status LED
- Operating temperature range: −20 to +60 °C
- Protection rating: IP20
- Mounting type: 35 mm DIN rail
- DIN rail standard: EN 60715
- Terminal construction: Box-clamp terminals
- Housing width: 17.5 mm
- EAN: 8012823465623
How the Finder 72.51 Conductive Level Controller Works
The Finder 72.51.0.240.0002 monitors liquid levels by detecting electrical conductivity between sensing electrodes installed inside a tank, reservoir, well or process vessel. When the liquid reaches a sensing electrode, the conductive path allows the relay to identify the corresponding level condition and change the state of its output contact according to the selected operating function.
This sensing method is particularly useful for applications involving water and other conductive liquids where automatic filling, emptying or level monitoring is required. Unlike mechanical float switches, conductive electrodes do not rely on a moving float mechanism, although correct electrode positioning, material selection and installation remain essential.
The 5–450 kΩ adjustable sensitivity is a defining feature of the 72.51.0.240.0002 version. Compared with the standard 5–150 kΩ model, the extended sensitivity range enables monitoring of liquids with higher electrical resistance and correspondingly lower conductivity.
The relay also incorporates electrical isolation between the supply, sensing electrodes and output contacts. Its wide-range 110–240 V AC/DC supply makes it particularly convenient for installations where a separate 24 V control supply is not available.
Six Selectable Filling, Emptying and Window Functions
The Finder 72.51.0.240.0002 provides six operating functions selected using the front-mounted function selector. Each function combines a particular level monitoring arrangement with a short or long switching delay.
- FL – Filling, Long: Automatic filling control with a 7 s delay.
- FS – Filling, Short: Automatic filling control with a 0.5 s delay.
- EL – Emptying, Long: Automatic emptying control with a 7 s delay.
- ES – Emptying, Short: Automatic 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.
The filling and emptying functions allow the relay to control suitable pumping or valve systems according to the detected liquid level. Window monitoring provides an additional option for applications requiring detection of a defined level condition.
The selectable delay helps reduce unwanted output switching caused by liquid movement, splashing and temporary changes in electrode contact.
Important: After changing the operating function, the relay must be disconnected from its power supply and then powered on again to apply the new selection.
Electrode Selection and Liquid Compatibility
The Finder 72.51.0.240.0002 is intended for conductive liquids such as drinking water, rainwater, seawater, wastewater and other liquids with sufficient electrical conductivity. It can also be used with certain conductive food and beverage liquids where the electrode materials and installation arrangement are suitable.
The relay is generally not suitable for non-conductive liquids such as petrol, oil, paraffin or highly purified demineralised water. Reliable operation depends on the actual electrical conductivity of the liquid and the correct adjustment of the sensing sensitivity.
Compatible accessories include Finder suspended electrodes, fixed sensing electrodes, electrode holders and associated probe components. Suitable two- or three-electrode arrangements can be selected according to the required level control function and tank construction.
For longer installations, the manufacturer's guidance specifies electrode cable lengths up to 200 m, subject to cable capacitance and correct wiring practices.
Typical Applications
- Automatic filling and emptying of water storage tanks.
- Liquid level monitoring in wells, reservoirs and cisterns.
- Industrial pump control and pumping stations.
- Water treatment and wastewater management systems.
- Rainwater harvesting and storage installations.
- Agricultural irrigation and water distribution systems.
- Swimming pools, fountains and water features.
- Industrial process tanks containing suitable conductive liquids.
- Food and beverage production systems with compatible conductive liquids.
- High-level and low-level alarm circuits.
- Building services and commercial water management systems.
- Electrical control panels and industrial automation installations.
- Retrofit applications requiring a wide-range AC/DC supply.
