Liquid Controls SP4000 - Manual (Page 100)

97
SP4000 Flow Computer
7. Principle Of Operation
7.1 General:
The SP4000 Flow Computer uses several internal calculations to compute the com-
pensated flow based on specific data input. Several computations are performed to
arrive at the uncompensated flow, 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 flowmeters are supplied by the manufacturers with a 4-20 mA output span
which is already in flow units. The SP4000 permits the user to enter this flowmeter
information directly. However, closely associated with this information is the density
that was assumed during flowmeter 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 flow 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
designated 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 fluids.
7.3 Flow Equations:
Flow Input Computation:
Linear
Input Flow = [% input span • (flow FS - flow low scale)]+ flow low scale
Square Law without External SQRT Extractor
delta P = [(% input span) • ( flow FS - flow low scale)] + flow low scale
Square Law with External SQRT Extractor
delta P = [(% input span) 2 • ( flow FS - flow low scale)] + flow 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