Why Choose the Finder 72.51.0.024.0000 Liquid Level Control Relay?
The Finder 72.51.0.024.0000 is a versatile 24 V AC/DC liquid level control relay designed for monitoring and regulating electrically conductive liquids in tanks, reservoirs, sumps and industrial process systems. Part of the Finder 72 Series, this modular monitoring relay provides automatic filling, emptying and level supervision functions for water management, pumping installations and industrial automation.
Featuring an adjustable sensitivity range of 5–150 kΩ, the Finder 72.51.0.024.0000 can be configured to detect different conductive liquids using external sensing electrodes. Its six selectable operating functions include filling, emptying and window monitoring, with a choice of 0.5 s or 7 s switching delay to help prevent unnecessary operation caused by splashing, waves or temporary changes in liquid level.
With a 24 V AC/DC supply, 6 A changeover output contact, adjustable sensitivity and front-panel LED indicators, this Finder liquid level relay offers a practical solution for automated tank control. Its compact DIN rail mounting design and compatibility with Finder liquid level electrodes make it suitable for electrical control panels, industrial machinery and commercial pumping systems.
Key Advantages
- 24 V AC/DC operation for compatible low-voltage industrial control systems.
- Adjustable 5–150 kΩ sensitivity for monitoring a range of conductive liquids.
- Six selectable operating functions for filling, emptying and window level monitoring.
- Selectable 0.5 s or 7 s delay to reduce unwanted switching caused by liquid movement.
- 6 A changeover output contact for suitably rated electrical loads and control circuits.
- Single-level and dual-level monitoring using appropriate electrode arrangements.
- LED indicators provide convenient supply and output status information.
- Reinforced insulation between the supply, electrode inputs and output contacts.
- IP20 protection rating for installation inside suitable electrical enclosures.
- Compact DIN rail mounting for efficient control panel installation.
- Compatible with selected Finder 072 Series electrodes, probes and electrode holders.
- Suitable for automatic pump control, tank level regulation and liquid level alarm systems.
Key Features
- Finder 72 Series liquid level monitoring relay.
- Type 72.51 conductive liquid level controller.
- 24 V AC/DC rated supply voltage.
- 50/60 Hz AC supply frequency.
- 19.2–26.4 V AC/DC operating voltage range.
- 5–150 kΩ adjustable sensitivity range.
- Six selectable functions: FL, FS, ES, EL, WL and WS.
- Filling and emptying control for automatic pump operation.
- Window monitoring for liquid level supervision.
- 0.5 s or 7 s selectable switching delay.
- One changeover contact (SPDT / 1 CO).
- 6 A rated output current at 250 V AC.
- 1,500 VA AC-1 rated switching load.
- 250 VA AC-15 rated switching load at 230 V AC.
- Front-panel power supply and output status LEDs.
- Two-electrode or three-electrode operation.
- Maximum electrode cable length of 200 m, subject to cable capacitance requirements.
- IP20 protection rating.
- Operating temperature range of −20 to +60 °C.
Technical Specifications
- Manufacturer: Finder
- Series: 72 Series
- Model: 72.51.0.024.0000
- Product type: Conductive liquid level control relay
- Relay type: 72.51
- Monitoring principle: Electrical conductivity between sensing electrodes
- Rated supply voltage: 24 V AC/DC
- AC supply frequency: 50/60 Hz
- Operating voltage range: 19.2–26.4 V AC/DC
- Supply consumption: 2 VA AC / 1 W DC
- Adjustable sensitivity: 5–150 kΩ
- Number of selectable functions: 6
- Filling functions: FL and FS
- Emptying functions: EL and ES
- Window monitoring functions: WL and WS
- Selectable delay: 0.5 s or 7 s
- Output contact arrangement: 1 changeover (1 CO / SPDT)
- Rated output current: 6 A
- Rated contact voltage: 250 V AC
- Maximum peak contact current: 15 A
- Maximum switching voltage: 400 V AC
- Rated load (AC-1): 1,500 VA
- Rated load (AC-15 at 230 V AC): 250 VA
- Single-phase motor rating at 230 V AC: 0.185 kW
- DC-1 switching current at 24 V DC: 3 A
- DC-1 switching current at 110 V DC: 0.35 A
- DC-1 switching current at 220 V DC: 0.2 A
- Contact material: Silver tin oxide (AgSnO2)
- Minimum switching load: 500 mW
- Minimum switching voltage/current: 10 V / 5 mA
- Power-on activation time: Less than 3 s
- Power supply indication: LED
- Output status indication: LED
- Electrode arrangements: Two or three sensing electrodes
- Maximum electrode cable length: 200 m
- Maximum specified electrode cable capacitance: 100 nF/km
- Impulse withstand voltage between isolated circuits: 6 kV
- Protection rating: IP20
- Operating temperature: −20 to +60 °C
- Mounting type: DIN rail mounting
- Connection terminals: A1, A2, B1, B2, B3, 11, 12 and 14
- Compatible accessories: Finder 072 Series sensing electrodes, probes and electrode holders
Reliable Conductive Liquid Level Monitoring and Automatic Pump Control
The Finder 72.51.0.024.0000 uses an electrical conductivity sensing principle to monitor the level of liquid inside a tank or reservoir. External electrodes are installed at the required detection points, allowing the relay to identify when the liquid reaches or falls below a particular level. The relay then operates its changeover output according to the selected control function.
Its 24 V AC/DC supply makes it suitable for industrial automation systems using a compatible low-voltage control supply. The relay can be incorporated into pump control panels, process control equipment and electrical cabinets where reliable level detection is required without continuous manual intervention.
The 5–150 kΩ adjustable sensitivity range allows the relay to be configured for different electrically conductive liquids. Suitable applications include monitoring mains water, well water, rainwater, seawater, wastewater and various conductive process liquids. Sensitivity should be adjusted according to the conductivity of the liquid, the electrode arrangement and the installation conditions.
The Finder 72.51 provides six selectable functions. The FL and FS modes control filling, the EL and ES modes control emptying, while the WL and WS modes provide window level monitoring. Each function offers either a 7 s or 0.5 s delay, enabling the installer to choose the response appropriate to the application.
In filling mode, the relay can control a pump or valve to replenish liquid when the level falls below a selected threshold. In emptying mode, it can operate a pump to remove liquid from a sump or tank when the level rises. Window monitoring provides a further option for supervising liquid levels within a defined range.
The relay supports two-electrode and three-electrode sensing configurations. This allows it to be used for single-level detection or applications requiring minimum and maximum level supervision. Compatible Finder electrodes and accessories provide installation flexibility for different tank designs and operating environments.
Its 6 A changeover output can operate suitably rated control circuits, indicators, alarms and electrical loads. For pumps or motors exceeding the relay's direct switching capability, the output should operate an appropriately rated contactor or motor starter. The front-panel LEDs provide convenient visual confirmation of supply and output status during commissioning and maintenance.
The Finder 72.51.0.024.0000 is designed for conductive liquids and should not be used for direct detection of non-conductive liquids such as oil, petrol or demineralised water. The correct sensing technology must be selected according to the liquid being monitored.
Typical Applications
- Automatic water tank filling and emptying systems.
- Industrial liquid level monitoring and regulation.
- Water treatment and distribution installations.
- Wastewater pumping and sump level control.
- Reservoir and cistern level supervision.
- Industrial pump start and stop control circuits.
- Tank overflow prevention and low-level alarm systems.
- Rainwater collection and storage systems.
- Agricultural irrigation and water storage equipment.
- Industrial process tanks containing conductive liquids.
- Food and beverage processing installations with suitable conductive liquids.
- Building services and commercial pumping systems.
- PLC-connected liquid level monitoring circuits.
- OEM pump control equipment and electrical panel manufacturing.
