Intra Automation digiflow 515, Installation And Operating Manual

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Gas- and Steam Flowcomputer DigiFlow 515 Operating Manual
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6.5 Correction of The Nonlinearity
6.5.1 Correction for the frequency input
Known nonlinearities of a flow measuring instrument can be corrected.
12 frequencies and scale factors are available to this. Data on the flowmeter non-linearity can usually be sup-
plied by the flowmeter manufacturer in the form of a Calibration Certificate, and is the result of individual tests
on flowmeter over a range of flowrates. The certifikate will list a number of flowrates or frequencies with the
measured k-factor at each flowrate.
The following diagram shows an example for the different scaling factors at various frequencies of an arbi-
trary flow measuring instrument. The broad black turn stands for the current scaling factor of the set, and the
narrow line is for the approximation in the flow calculator.
Scaling Factor
Frequency
Factor 4
Factor 3
Factor 2
Factor 1
Factor 5
Factor 6
F6 F5 F4 F3 F2 F1 F max
The curve between the single dots was won by linear interpolation, except for factor 1 which maintains a con-
stant value between Frequency 1 and the maximum input frequency.
During Calibration, the user have to enter a frequency and the corresponding k-factor for each of maximimum
12 points.
If a frequency with 0Hz is entered, the program doesn't expect any further correction data. If all 12 correction
points are used, the 12th frequency is set on 0Hz automatically.
6.5.2 Linearization for the analog input
Is only a flow signal to the flow calculator connected, a linearization can be programmed for this to compen-
sate for deviations of flow signal and actual flow. Up to 12 Dots can be entered, between worth be interpo-
lated linearly. The correction is done at the standardized device signal ( 0 1 ) , so that measure begin and
measure end are not affected. Programming of corrections points start with ‘1’, if a ‘0’ is entered no further
inputs are accepted.
The flow correction is defined as:
Q Span A
C
= ⋅
Note:
The sqare root relationship for conventional differential pressure flow devices is handled separately and not by the liear-
ity correction described in this section
.