Principle Of Operation; General; Orifice Flowmeter Considerations; Flow Equations - Omega FC-21 User Manual

FC-21 Flow Computer

7. Principle Of Operation

General

7.1 General:
Operation
The FC-21 Flow Computer uses several internal calculations to compute the
compensated flow based on specific data input. Several computations are performed
to arrive at the uncompensated flow, temperature, density and viscosity. This information
is then used to compute the Corrected Volume Flow or Mass Flow.
Orifice Flowmeter

7.2 Orifice Flowmeter Considerations:

Considerations
Head class flowmeters are supplied by the manufacturers with a 4-20 mA output span
which is already in flow units. The FC-21 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 orifice 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.
The Factory will be preparing application information for several common fluid types.

Flow Equations

7.3 Flow Equations:
Input Flow Computation:
Input Flow Computation:
Input Density Computation:
Linear or External SQRT
Input Flow = [% input span * (flow FS - flow low scale)]+ flow low scale
Orifice
Input Flow = [(√% input span) * ( flow FS - flow low scale)] + flow low scale
General Case
Tf = [% input span * (temp FS - Temp low scale)] + temp low scale
RTD Case
Tf = f(measured input resistance)
Temperature Transmitter
density = reference density * (1 - Therm.Exp.Coef. * (Tf-Tref))
Density Transmitter
density = [% input span * (density FS - density low scale)] + density low scale
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