Gas- and Steam Flowcomputer
DigiFlow 515
Operating Manual
19
6.4 Filtering of The Flow Input
Reading the instantaneous measurand correctly often is impossible because of the frequency fluctuations or
output current fluctuations of the flow measuring instrument created by the pulsating flow.
Therefore the flow calculator is provided with a digital filter which average out these fluctuations of the flow
signal and facilitates through this a more precisely reading of the measured values.
The following diagram shows an input signal pulsating and the effect of the filter on this signal.
unfiltered
Flow
filtered
Time
As guideline to the degree of filteringto be used, the following table shows the response to a step change in
input.
The value AF is the entered filter constand.
The times, after the value reported on the display 90 or 99% of the at the ending worth reaches, is indicated
in seconds. For the value AF = 1 therefor no filtering is executed.
AF
90%
99%
1 0 0
2 1 2
4 2 4
6 3 6
10 5 11
15 8 17
20 11 22
25 14 28
35 20 40
45 25 51
60 34 69
75 43 86
90 52 103
99 57 113
Table 1:
Response time in seconds on a volatile modification of the input signal
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