ASME MFC-16-2007 pdf download
ASME MFC-16-2007 pdf download.Measurement of Liquid Flow in Closed Conduits With Electromagnetic Flowmeters.
5 FLOWMETER DESCRIPTIONS 5.1 Flowmeter Primary Theflowmeterprimarymustbedesigned andselected to be an integral portion of the piping system (see para. 6.8.2). It consists of the following: (a) a flowtube with a nonconductive inside surface (b) a means for integrating it into the pipeline (c) electromagnetic field coils (d) two or more sensing electrodes thatmaybe wetted or nonwetted (see Fig. 4) (e) a housing to protect the coils and electrodes from damage and moisture Itmayalsoinclude groundingelectrodes orgrounding rings. They are used to ground the process and the flowmeter primary together, as required by the applica- tion, piping system, or design ofthe flowmeter. Noncon- ductive piping systems or piping systems with a nonconductive liner in particular require some method of grounding the process to the flowmeter. Some special application flowmeter primaries are independently powered from regular AC circuits. These flowmeter primaries must contain the needed circuitry for this power arrangement. These special application flowmeter primaries have power requirements beyond that available from normal application flowmeter sec- ondaries. Flowmeter primaries come in a variety of sizes depending on the flow rate. Some inside diameters are as small as 1 mm (0.04 in.) while others can be over 2 500 mm (100 in.). Flanges are the most common method of attaching the flowmeter primary to the pipeline. Other attachment methods include victaulic couplings or tri-clamp con- nections. Another variation of the flowmeter primary is a wafer flowmeter that is installed between the pipeline flanges. ISO 13359 specifies overall length (lay length face to face) for flanged electromagnetic flowmeters. The lay lengths specified in ISO 13359 are for lower-pressure 4 systems ratherthan higher-pressure systems. The manu- facturer shall provide a reasonable clearance between the rear face of the flange and the meter housing for installation and removal. 5.2 Flowmeter Secondary The flowmeter secondary consists of the electronic transmitter and its housing, which may be mounted either integral with the flowmeter primary, or remotely. If the flowmeter secondary is mounted remotely from the flowmeter primary, it may be necessary to have a separate electrical connection housing, terminals, and preamplifier mounted on the flowmeter primary. The flowmeter secondary measures: the emf v voltage at the electrodes of flowmeter primary, provides the output from the meter, and in most cases provides power to the coils. The coils may be either AC or pulsed-DC powered, depending on the design of the meter. The output from the flowmeter secondary may include one or more of the following: an analog signal (i.e., 4-20 mA DC), a pulse output (frequency), or a digi- tal signal. The outputs can be scaled to represent units of flow. The digital signal can be used to connect to one of the various bus protocols (manufacturer dependent). Otheroptional outputs include solid-state ormechanical contact closures that can be used for totalizing or system control. Some designs also offer the option of visual indication of flow rate and/or totalized flow in numeri- cal or graphical form. 6 APPLICATION CONSIDERATIONS 6.1 Process Liquid 6.1.1 Liquid Electrical Conductivity. If the electrical conductivity of the liquid is uniform, and above a speci- fied minimum value, the meter output will generally be independent of the liquid conductivity. The minimum liquid conductivity required for the flowmeter to func- tion should be obtained from the manufacturer. Ifthe conductivity gradient is not uniform throughout the meter, flow measurement errors will occur. Nonho- mogeneous flow streams must be mixed sufficiently to assure uniform electrical conductivity throughout the measurement region. Heterogeneous liquids, such as a slurries or pulp stocks, composed of small particles uni- formly distributed in a liquid, may be considered an electrically homogeneous liquid. 6.1.2 Noisy Flow Signal. Excessive flow signal noise may be encountered in the following situations: (a) when measuring the flow of a slurry or pulp stock (b) when triboelectric effects are present (see para. 6.2.4) (c) with large variations in liquid conductivity (d) with air entrained in the liquid (e) with incomplete chemical mixing
