Endress+Hauser FMU41 Prosonic M Ultrasonic Level Transmitter

Endress+Hauser FMU41 Prosonic M ultrasonic transmitter for medium-height tanks

The Endress+Hauser FMU41 is a two-wire ultrasonic level transmitter from the Prosonic M family with a 2″ threaded sensor and a range of 8 m in liquids and 3.5 m in bulk solids. The FMU41 takes the same electronics and operating concept as the FMU40 but uses a larger transducer, which gives more reach and a stronger signal. Seven Star LLC, an independent supplier in Muscat, supplies the FMU41 and related level instruments in Oman and the GCC.

The type code is the simplest way to place it: FMU4x with 0 is the 1 1/2″ short-range unit, FMU41 is the 2″ thread unit with 8 m range, and FMU42 is the flanged unit for 10 m. Choose the FMU41 when a 5 m device would be too short and the vessel has a threaded nozzle.

FMU41 technical specifications

Why the FMU41 reaches further

Lower operating frequency travels better through air. The FMU41 runs near 50 kHz against about 70 kHz on the FMU40, and its sound pressure is a little lower at 143 dB, but the signal still carries to 8 m because the 110 dB threshold distance is 1.7 m instead of 1.0 m. The trade-off is a longer blocking distance of 0.35 m and a wider beam at long distance: at 8 m the beam radius reaches about 0.77 m, so internal structures near the edge of the cone should be checked.

As with every ultrasonic unit, the range is a ceiling, not a promise. Surface waves, heavy dust, a temperature difference between sensor and liquid, and a falling stream each reduce the available signal, and the data sheet gives dB allowances for each so that the usable range can be read from a chart.

How level is calculated in the FMU41

The electronics time the echo, apply sound velocity corrected by the integrated NTC sensor, and convert distance D into level from the empty distance E. Interference echo suppression hides fixed targets, and linearization turns level into volume, with preset horizontal-cylinder logic or a user table of up to 32 points. The output can be damped from 0 to 255 s, and the failure current can follow NAMUR NE43.

Wiring, supply and diagnostics of the FMU41

The FMU41 is loop powered. Terminal voltage at the device is 14 V to 36 V at 4 mA and 8 V to 36 V at 20 mA in the standard version, with a 30 V upper limit in Ex ia and Ex d versions. Power consumption lies between 51 and 800 mW. Fixed-current modes are available for solar powered installations and for multidrop operation.

• Local operation through a 4-line display in seven languages, with envelope curves on screen.
• FieldCare with Commubox FXA195 or FXA291, Field Xpert, or a Bluetooth modem for remote access.
• Cable entries G 1/2 or NPT 1/2, or an M20x1.5 gland; shielded twisted pair recommended for HART.

Where the FMU41 fits: related Endress+Hauser level parts

Within the same line, the FMU40 handles small tanks to 5 m and the FMU42 handles 10 m with a flange. Where several sensors must feed one transmitter, the FMU95 is the multi-channel option. For overfill or dry-run alarms on conductive liquids, the FTW31 and FTW32 give a separate switch point. The product page notes that for higher chemical resistance or high turbulence the manufacturer points to the FMU42 or the FDU9x sensor combinations.

FMU41 selection and ordering checklist

• Verify empty distance is within 8 m for liquids or 3.5 m for solids, and that the full level never enters the 0.35 m blocking distance.
• Check the nozzle: 2″ thread, G or NPT, and its length relative to the sensor face.
• Check pressure (0.7 to 3 bar abs) and temperature (-40 to 80 °C).
• List vapours, foam, dust and filling streams that may attenuate the signal.
• Choose housing (F12 or T12), approvals and cable entry for the hazardous area.
• Decide on accessories, such as a weather protection cover or mounting bracket.

Installing and commissioning the FMU41

Install the sensor facing straight down, off centre, with a clearance of around one sixth of the vessel diameter to the wall. Keep the beam free of pipes, heating coils and temperature probes, and do not mount two ultrasonic devices on one vessel. In a nozzle, respect the maximum nozzle length stated for the diameter. The thread may be tightened to a maximum of 20 Nm. In shafts with uneven walls, an ultrasound guide pipe of at least 100 mm diameter improves reliability.

At commissioning enter the empty distance and span, run interference echo mapping with the tank at a known level, and compare the reading against a dip or reference measurement. Revisit the mapping whenever internal fittings change.

Typical FMU41 applications in Oman and the GCC

The FMU41 is a good match for clarifier launders, wet wells and balance tanks at water treatment and desalination plants, effluent holding tanks, process water tanks, and open channels where a weir is used for flow. For outdoor roofs under strong sun add the weather cover, since heating the transducer raises the temperature difference to the liquid and eats range. Dust from cement or fertiliser can also make solids measurements challenging at the upper end of the 3.5 m limit.

Prosonic M family comparison

Information to send with an RFQ for the FMU41

• Part number FMU41 and quantity, or the nameplate order code for a replacement.
• Medium, tank height, maximum and minimum level.
• Process pressure and temperature.
• Thread standard (G or NPT) and nozzle dimensions.
• Hazardous-area classification and approvals needed.

Documents and quotation

The Technical Information for the FMU41 is attached on this page. Please compare it with the configured order code before ordering.

Send the FMU41 part number or the full order code, the quantity and the delivery location, and Seven Star LLC will confirm availability and lead time.