C-3
Appendix C
This software technique, known as signal processing, “qualifies”
individual flow signals based on historic flow information and
three user-definable parameters, plus and on/off control. These
parameters are:
1. Number of samples: The number of samples or discrete input
values included in the running average. Adjustable between 0
and 125 samples, it is this number of previous inputs that are
averaged together to arrive at the average value. Because the
output stage of the 8732C circuit is updated twelve times each
second, regardless of coil drive mode, twelve samples equals one
second (i.e., 0 to 120 samples = 0 to 10 seconds). Factory Preset
Value = 90 samples (7.5 seconds).
2. Maximum Percent Limit: The tolerance band set up on either side
of the running average, referring to percent deviation from the
average. Values within the limit are accepted while value outside
the limit are scrutinized to determine if they are a noise spike or
an actual flow change. Factory Preset Value = 2 percent.
3. Time Limit: Forces the output and running average values to the
new value of an actual flow rate change that is outside the
percent limit boundaries, thereby limiting response time to real
flow changes to the time limit value rather than the length of the
running average. Factory Preset Value = 2 seconds.
How Does It Really Work?
The best way to explain this is with the help of an example, plotting
flow rate versus time
.
x
: Input flow signal from flowtube.
o
: Average flow signals and transmitter output, determined by the
“number of samples” parameter.
Tolerance band, determined by the “percent limit” parameter.
– Upper value = average flow + [(percent limit/100) average flow]
– Lower value = average flow – [(percent limit/100) average flow]
FIGURE C-1. Signal Processing.
871
2-
029
2A
Flow
Rate
Max
%
Limit
Time Limit
12 Samples = 1 Second
Time
Содержание 8732C
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