ES749 Flow Computer
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7. Principle Of Operation
7.1 General:
The ES749 Flow Computer uses several internal calculations to compute the compen-
sated ow based on specic data input. Several computations are performed to arrive at
the uncompensated ow, temperature, pressure, density and viscosity. This information
is then used to compute the Corrected Volume Flow, Mass Flow or Heat Flow.
7.2 Square Law Flowmeter Considerations:
Head class owmeters are supplied by the manufacturers with a 4-20 mA output span
which is already in ow units. The ES749 permits the user to enter this owmeter in-
formation directly. However, closely associated with this information is the density that
was assumed during owmeter calibration. This information must also be input if the
user is to obtain maximum accuracy.
It is assumed that the user has the printout from a standardized sizing program for the
particular device he will be using. Such standardized printouts list all the necessary
information which the user will then be prompted for.
Several specialized ow equations are listed that are not intended for the standard
unit but to be offered to appropriate OEMs or as special order items. These are desig-
nated by a “†”.
Note concerning Fluid Information
The user will be prompted for Fluid Information during the setup of the instrument.
SeeAppendix A for the properties of several common uids.
7.3 Flow Equations:
Flow Input Computation:
Linear
Input Flow = [% input span • (ow FS - ow low scale)]+ ow low scale
Square Law without External SQRT Extractor
delta P = [(% input span) • ( ow FS - ow low scale)] + ow low scale
Square Law with External SQRT Extractor
delta P = [(% input span)
2
• ( ow FS - ow low scale)] + ow low scale
NOTE: For stacked differential pressure option, the appropriate input sensor signal is
used in calculations at all times to maximize accuracy.
General
Operation
Square Law
Flowmeter
Considerations
Flow Equations
7.3.1
Flow Input
Computation
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