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Endress+Hauser FMD633 Smart Diaphragm Differential Pressure Transmitter


The Deltabar S transmitter is used for the following differential pressure measurement tasks:
• Flowrate (volumetric or mass flow) in connection with primary devices in gases, vapours and liquids
• Level, volume or mass flow measurement in liquids
• Differential pressure monitoring of filters and pumps

Features and Benefits
• High accuracy
− Linearity better than 0.1 % of set span
− With “platinum” version, linearity better than 0.05 % of set span
− Long-term drift better than 0.1 % per year or 0.25 % per 5 years
• Process temperatures up to 120 °C as standard
• Universal modularity for differential pressure and process pressure (Deltabar S – Cerabar S), e.g.
− Replaceable display
− Sensor modules
− Universal electronics for process pressure and differential pressure
• Simple and easy operation via 4…20 mA, HART protocol or connection to PROFIBUS-PA or Foundation Fieldbus
• Zero and span freely adjustable with or without referential pressure
• Self-monitoring from sensor to electronics
• Wide variety of software functions such as characteristic curves, diagnostic codes, totalizer etc.


Diaphragm seal systems should be used if the process media and the device should be separated.

Diaphragm seal systems offer clear advantages in the following instances:
• In the case of high process temperatures
• In the case of process media that crystallise
• In the case of corrosive or highly various process media or process media with solids content
• In the case of heterogeneous and fibrous process media
• If good and rapid measuring point cleaning is necessary
• The measuring point is exposed to vibration (e.g. better view of display).

Design and Operation Mode

Diaphragm seals are separating equipment between the measuring system and the process medium.

A diaphragm seal system consists of:
• A diaphragm seal in a one-sided system, e.g. FMD 630 or two diaphragm seals, in a two-sided system, e.g. FMD 633
• Capillary tube
• Fill fluid and
• A differential pressure transmitter.

The process pressure acts via the diaphragm seal membrane on the liquid-filled system, which transfers the process pressure via the capillary tube onto the sensor of the differential pressure transmitter.

Endress+Hauser delivers all diaphragm seal systems as welded versions. The system is hermetically sealed, which ensures the highest reliability.