ASME MFC-16-2007 pdf free download.Measurement of Liquid Flow in Closed Conduits With Electromagnetic Flowmeters.
3.1 Definitions From ASME MFC-1M
accuracy: the degree of Freedom from error; the degree of conformity of the indicated value to the true value of the measured quantity.
precision: the closeness of agreement between the results obtained by applying the experimental procedure several times under prescribed conditions. The smaller the random part of the experimental errors that affect the results, the more precise is the procedure.
rangeability (turndou’n): flowmeter rangeahility is the ratio of the maximLim to minimum floss’ rates or Reynolds number in the range over which the meter meets a specified uncertainty (accuracy).
repeatability: the closeness of agreement among a series of results obtained with the same method on identical test material, under the same conditions (same operator, same apparatus, same lahoratory and short intervals of time).
uncertainty (of nwasurcrnefltk the range within which the true value of the measured quantity can be expected to lie with a specified probability and confidence level.
3.2 Definitions for ASME MFC-16
bias: the systematic errors (i.e., those that cannot he reduced by increasing the number of measurements taken under fixed flow conditions).
flou’rnetcr primary: includes the flowtube, process connections, electromagnetic coils, and electrodes. Flowmeter primary is also known by other names such as: flow- meter primary device, primary device, primary etc.
flowmeh’r secondary: includes the electronic transmitter, measurement of the emf,, and in most cases the power for the electromagnet coils of the flowmeter primary.
linearity: linearity refers to the constancy of the meter factor over a specified range, defined by either the pipe Reynolds number or the flow rate.
meter factor: the number, determined by liquid calibration, that enables the output flow signal to be related to the volumetric flow rate under defined reference conditions.
5.2 Flowmeter Secondary
The flowmeter secondary consists of the electronic transmitter and its housing, which may be mounted either integral with the fiowmeter primary, or remotely. lithe 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 cirf. voltage at the electrodes of flowmeter primar> 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 digital 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). Other optional outputs include solid-state or mechanical contact closures that can be used for totalizing or system control. Sonic designs also oiler the option of visual indication of flow rate and/or totalized flow in numerical or graphical form.
6 APPLICATION CONSIDERATIONS
6.1 Process Liquid
6.1.1 Liquid Electrical Conductivity, lithe electrical conductivity of the liquid is uniform, and above a specified minimum value, the meter output will generally be independent of the liquid conductivity. The minimum liquid conductivity required for the flowmeter to function should he obtained from the manufacturer.
If the conductivity gradient is not uniform throughout the meter, flow measurement errors will occur. Nonhomogeneous 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 uniformly 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).