Description
Differential Pressure Flow Measurement: SITRANS FP230
With the SITRANS FP product line Siemens offers a complete solution for differential pressure flow measurements. This well-established technology is suitable for all kinds of applications – liquids, dry or humid gases and steam. Due to the robust though variable design it has been and still is one of the main technologies for flow measurement in various industries.
Overview---SITRANS FP230
When the line diameter constricts within the pressure device, the flow rate generates a differential pressure. A differential pressure transmitter then converts this differential pressure into a proportional current signal or flow value. A calculation of the primary differential pressure device determines the assignment of differential pressure to flow.
Primary differential pressure devices are suitable for single-phase media such as gas, steam and liquids without solid components.
Benefits---SITRANS FP230
- Suitable for universal use across the globe and widely accepted in all industries
- Very robust and can use to the wide range of nominal diameters
- Suitable for high temperature and pressure ranges
- Low uncertainty of measurement
- No wet calibration required as they use an internationally standardized flow rate measurement procedure
- Differential pressure transmitter can use over a long distance from the measuring location
- Differential pressure method is well known and has a large installed base
- SITRANS P differential pressure transmitter is easy to parameterize again if process data change. Engineers adapt them by recalculating and assigning new parameters to the transmitter. Or, in the case of an orifice plate with annular chamber, we use a new orifice plate.
Application
- Technical gases
- Compressed air
- Fresh and combustion air
- Steam/Heat quantities
- Heat transfer fluids
- Water
Design
Basics: Orifices for flow measurement
Engineers usually differentiate orifice plates by their type of installation, type of differential pressure tapping, and the shape of the orifice. The orifice bore, a defined circular opening, creates the characteristic differential pressure. According to ISO 5167 - 2, it is usually a square - edged concentric type, and engineers position it in the middle of the pipe.
The main features are a sharp edge, a cylindrical bore of a certain length and a conical bevel tapering to the rear. Alternatively, the relevant standards provide for deviating designs, which are used for applications with highly viscous (e.g. quarter-circle nozzles) or contaminated media (e.g. segment orifices).
The standard design is permitted by the standard for an inner diameter of the pipe between 50 mm and 1000 mm. For pipes with smaller inside diameters, standards such as ISO 15377-TR or ASME MFC-14M which go beyond these standards must be taken into account. Orifice plates for pipes with small inside diameters are usually designed as meter tubes.
In order to reduce the uncertainties of these meter tubes, technicians can calibrate the devices on a flow test bench if required on request.
Types of differential pressure tappings
The differential pressure can be tapped in different ways:
Corner tapping
Engineers place an opening in the corner of a carrier ring directly in front of and behind the orifice plate to measure upstream and downstream pressure. They route both pressure signals through these openings to the outside.
Corner tapping with annular chamber
An annular chamber holds the orifice plate. Technicians measure upstream and downstream pressure through an annular gap opening between the carrier ring and the orifice plate. They average both pressure signals over the entire circumference and route them outside.
Flange tapping
Two so - called orifice flanges hold the orifice plate. Technicians measure upstream and downstream pressure signals through flange taps that they drill into the flanges.
Tapping with distance D, D/2
An annular chamber holds the orifice plate. We measure upstream and downstream pressure through an annular gap opening between the carrier ring and the orifice plate. We average both pressure signals over the entire circumference and route them outside.
Designs
- Standard orifice plate with corner pressure tappings (7ME171)
- Standard orifice plate with annular chamber (7ME172)
- Orifice meter run (7ME173)
- (7ME174)Orifice plate
- Orifice plate with orifice flanges (7ME175)
Mounting arrangements
For more information on installation position and piping, please see the Operating Instructions "SITRANS FPS200" on SIOS.
Integration
Installers place the orifice plate between two flanges in the pipeline. They use condensation pots (for steam) and initial shut - off valves to direct the differential pressure of the high - pressure side and low - pressure side through differential pressure lines to a manifold and then to the differential pressure transmitter. For fluids with pressure and temperature fluctuations it makes sense to take an additional measurement of the pressure and temperature in order to correct the flow signal of the transmitter in a subsequent correction computer.
Selection of mounting point
The flow measuring regulations EN ISO 5167 not only consider the design of primary differential pressure devices, but also assume that their installation is in accordance with the standard so that the specified tolerances can be retained. The required inlet and outlet pipe sections according to ISO 5167 can be found in the calculation protocol of the respective orifice plate.
Configuration of the pipeline should allow for standardized installation (required inlet and outlet pipe section). Particular attention must be paid to ensure that the primary device can be fitted in a sufficiently long straight section of pipe. Bends, valves and similar should be fitted sufficiently far upstream of the primary device to prevent them having a detrimental effect. Primary devices with a large diameter ratio are particularly sensitive to interferences.
Design of measuring point
The design of the measuring point depends on the medium and on the spatial conditions. The designs for gas and water only differ with regard to the position of the tapping sockets (see section "Tapping sockets"); condensation pots are provided for steam applications.
Orifice meter runs
On lines with small nominal diameters (DN 10 to DN 50), the wall roughness and diameter tolerances of the pipes influence the measurements more than those with larger nominal diameters. We can counteract these influences by using orifice meter runs with inlet and outlet pipe sections made of precision pipes and fitted. To get exact measurements with orifice meter runs, we can determine the flow coefficient C through calibration.
Options
Further versions that are available on request:
- Other types of primary differential pressure device: nozzles, venturi nozzles, classic venturi tubes etc.
- Nominal diameters and nominal pressures to EN, ASME and other standards
- Other lengths, special lengths
- Other materials
- Sealing face with recess or groove
- Flushing rings
- Other tapping sockets, multiple tappings
- Material acceptance test certificates or cold water pressure tests
To obtain the most competitive quote, please contact our ANTLETS team.
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