JUMO MAERA S25 Hydrostatic Level Probe

Low-cost submersible level probe for tanks and sumps

The JUMO MAERA S25 (type 401015) is a hydrostatic level probe for continuous level measurement of liquids in ventilated tanks, covering filling heights from 2.5 to 10 metres of water column through four ranges between 0 and 0.25 bar and 0 and 1 bar. A piezoresistive silicon cell with a stainless steel separating membrane senses the pressure of the liquid column, and a protective hose in the cable compensates air-pressure changes automatically.

JUMO lists heating oil and diesel tanks and AUS32 (AdBlue, DEF, ARLA 32) among the media. The probe is 25 mm in diameter, weighs 90 g without cable and is rated IP68, submersible to 20 m, with a medium temperature of 0 to 50 C. It is not suited to outdoor installation of the cable end without protection, and the data sheet marks it as suitable for indoor installation.

Technical specifications

How to order

The code reads 401015/000, then the range (451 to 454), the output (405 current or 412, 415, 418, 420 voltage), the process connection (567 G 1/4 inside, 659 open at the bottom, 707 M3 inside), connection material 20, electrical connection 11 (attached cable), the protective hose (1 PE and 2 PA, both not UV resistant, or 3 PA UV resistant) and the cable length. Extra code 691 gives improved moisture and vibration protection.

Listed stock versions are 401015/000-451-405-567-20-11-1-005/000 (part no. 00557854), 401015/000-452-405-567-20-11-1-010/000 (00560384) and 401015/000-453-405-567-20-11-1-010/000 (00560386).

Installing the probe

Hang the probe from its cable so it points straight down, a short distance above the tank floor, and keep the ventilation hose end dry; for the moisture-prone end, the data sheet describes accessories for local pressure compensation with tank or wall mounting. The 4 to 20 mA signal runs on two wires and can feed a controller such as the JUMO dTRANS AS 02 or a PLC.

The data sheet asks the user to check the durability of the wetted materials against the medium. For titanium or chloride-containing media see the MAERA S29 SW, and for foaming or viscous liquids the front-flush S29.

Selection checks for the MAERA S25

First work out the deepest liquid level the probe will see, measured from where the probe will hang, and pick the smallest of the four ranges that still covers it with some margin. Then convert the liquid density into the calculation: the ranges are stated in metres of water column, so a lighter liquid such as diesel gives a lower pressure for the same height, and the signal span should be planned on that basis.

Confirm that the tank is vented, since the probe measures relative pressure against the atmosphere through its cable hose. Check the medium temperature against the 0 to 50 °C limit throughout the year, and confirm with the medium data that the wetted stainless steel and hose materials are compatible. Choose the output that matches the receiving device, and a cable length that reaches from the probe position to a dry junction point without joins inside the tank.

Installation and commissioning

Lower the probe slowly so it does not strike the tank floor or internal pipework, and fix the cable at the top so the probe hangs at a known, repeatable height. Keep it away from inlet streams, pump suction points and mixers, where flow and turbulence can disturb the reading, and avoid places where sludge collects on the floor. In tanks with strong movement, a still pipe or guide tube can help keep the probe steady.

Terminate the cable in a junction box or enclosure that keeps the ventilation hose end dry and protected from dust and insects. At commissioning, record the reading with the tank at a known level, compare it with a dip measurement and set the scaling in the controller or PLC accordingly, allowing for the distance between the probe and the tank floor.

Oman and GCC conditions to plan for

Many diesel and water tanks in Oman stand outdoors or in hot, partly open buildings. The data sheet describes the probe as suitable for indoor installation and notes that most hose versions are not UV resistant, so cable runs on outdoor tanks should be routed through conduit or shaded trays rather than left exposed to the sun. Liquids in sun-exposed tanks can also warm up during long summer days, so check that the medium stays within the stated temperature range.

Wind-blown sand and dust can block or contaminate the open end of the ventilation hose, and humid air near the coast can lead to condensation inside it, which affects the pressure reference. Keep the hose end inside a sealed or protected enclosure, and consider the pressure compensation accessories mentioned in the data sheet for moisture-prone locations.

Routine maintenance

At planned intervals, raise the probe, inspect the cable and hose for cuts or crushing, and gently clean deposits from the protective cap area using water or a cleaning agent compatible with the materials. Do not poke the membrane with tools. After refitting, check the reading against a manual level measurement and adjust the controller scaling if the probe height has changed.

Documents and quotation

The manufacturer document (JUMO MAERA S25 data sheet 401015 (EN)) is attached to this page as a PDF. Send the complete type code or part number you need through the quotation form and we will reply with availability and delivery terms; please confirm the range, cable length and protective hose against the plant specification before ordering. More in Level Instrumentation.