Endress+Hauser FMD72 Deltabar Metallic Electronic dP

FMD72 electronic differential pressure with metallic process membranes

The Endress+Hauser FMD72 applies the electronic differential pressure idea of the Deltabar FMD7x line to media where a metal diaphragm is the better choice. Two sensor modules are mounted at the lower and upper tapping points of a vessel, each with its own fully welded stainless steel membrane and a small silicone oil fill, and a single transmitter combines their digital signals into a level, volume or mass value. Output is 4–20 mA with superimposed HART. Seven Star LLC supplies the FMD72 in Oman and the GCC as an independent supplier in Muscat, and can match the sensor ranges and connections to your tanks.

Compared with the ceramic FMD71, the FMD72 starts at the 400 mbar cell, tolerates lower process temperatures and offers more flush and hygienic connection styles. The membrane is AISI 316L (1.4435) as standard, with Alloy C available on request.

Endress+Hauser FMD72 technical specifications

How the FMD72 sensors and transmitter work together

When process pressure deflects the metal membrane, the oil behind it carries the force to a silicon measuring element with a Wheatstone bridge. Each sensor module converts the bridge voltage to a digital value. The sensors are separate from the transmitter, so there is no capillary and no oil-filled line between the two tapping points. That removes the temperature-driven error that long capillaries add to conventional diaphragm seal systems, which the manufacturer lists as a main advantage of the design.

The transmitter reads the HP sensor (hydrostatic plus head pressure) and the LP sensor (head pressure only), subtracts them and applies the level, volume or mass calculation. It reports both pressures, both sensor temperatures and the electronics temperature through HART, which is helpful when you need to separate a process change from a sensor fault.

FMD72 sensor ranges and overload limits

The maximum differential span equals the URL of the HP sensor. Because the HP module in a closed vessel carries head pressure on top of the hydrostatic load, size it with that sum in mind. The datasheet recommends keeping the ratio between level and head pressure at or below 1:10 to avoid large errors.

Where the FMD72 fits in the Deltabar family

Pick the FMD72 over the FMD71 when the medium attacks ceramic, when the process drops below −25 °C, or when a flush or hygienic metal connection is needed. Pick the FMD71 when the lowest ranges (100 and 250 mbar) or an oil-free ceramic cell are preferred. The FMD78 sits in another branch: a Deltabar S with two diaphragm seals joined by capillaries to a single transmitter, used where process temperatures reach 400 °C or where a remote seal is mandatory. All three produce a level or differential pressure signal, but their sensor concepts and ordering codes differ.

FMD72 selection and ordering checklist

• Gauge or absolute cells, with the HP range covering hydrostatic plus head pressure.
• Reference accuracy: standard (G) or Platinum (D); note that 400 mbar cells only offer the standard class.
• Process connection family: internal membrane thread, flush thread, flange, clamp or hygienic type, with the material the datasheet lists for it.
• Process temperature, which differs for internal, flush and hygienic membrane connections.
• Delta ferrite certificate (option KF) if a limited ferrite content is required; hygienic connections allow the tighter figure.
• Housing material and cable entry (M20, G½ or NPT½), plus hazardous-area approval from the Ex documentation.
• Optional test certificates such as 3.1 material, NACE MR0175, helium leak, pressure and PMI tests.

Installing, commissioning and maintaining the FMD72

Fit the HP sensor at the lower connection and the LP sensor above the highest level, then mount the transmitter on a wall or pipe with its bracket. Keep the cable between sensors and transmitter intact and shorten it only with the supplied kit. Allow flush connections to sit properly in the tapping so the membrane is not shielded by a dead leg.

Perform the position adjustment on the differential value after mounting, set the span and density, and check that the loop reads as expected using the 4–20 mA test terminal. Write protection can be set by switch, software or remotely. Later, compare the two sensor temperatures and pressures against expectation: a gap that should not exist points to blockage, plugging or a damaged membrane on one side.

FMD72 in Oman and GCC industries

Plants in Oman and the GCC use the FMD72 on pressurised and vacuum vessels, tall columns, chemical day tanks and process vessels that see strong sun and cold nights. The all-metal membrane copes with media that would be unsuitable for ceramic, and the flush connections reduce clogging with sticky or crystallising liquids. For hygiene-sensitive services such as food, beverage and water treatment, the hygienic flush connections and the delta ferrite option are relevant. The IP66/68 housing resists dust and humid coastal air.

Information to send with an FMD72 RFQ

• Medium, density and process temperature, including cleaning or sterilising cycles.
• Tank height between tappings, operating pressure and any vacuum.
• Sensor ranges for HP and LP, gauge or absolute.
• Connection type, nominal size, pressure rating and wetted material.
• Hazardous-area class, housing material and cable thread.
• Certificates and tag text required.

Documents and quotation

The Endress+Hauser Technical Information that covers the Deltabar FMD71 and FMD72 is attached on this page as a datasheet, including the range tables and connection data referred to here.

For a quotation on the FMD72, send the part number, the sensor ranges and the connection details. Seven Star LLC will confirm availability and delivery to Oman and the GCC.