Rosemount 8712 - Page 70

Reference Manual
00809-0100-4664, Rev BA
January 2010
Rosemount 8712
4-32
Manually Configure Digital Signal Processing (DSP)
The 8712 transmitter includes digital signal processing capabilities that can be
used to condition the output from the transmitter by enabling noise rejection.
See Appendix D: "Digital Signal Processing" for a more information on the
DSP functionality.
Enable/Disable DSP
When ON is selected, the Rosemount 8712 output is derived using a running
average of the individual flow inputs. Signal processing is a software
algorithm that examines the quality of the electrode signal against
user-specified tolerances. This average is updated at the rate of 10 samples
per second with a coil drive frequency of 5 Hz, and 75 samples per second
with a coil drive frequency of 37Hz. The three parameters that make up signal
processing (number of samples, maximum percent limit, and time limit) are
described below.
Samples
0 to 125 Samples
The number of samples function sets the amount of time that inputs are
collected and used to calculate the average value. Each second is divided
into tenths (1/10) with the number of samples equaling the number of 1/10
second increments used to calculate the average.
For example, a value of:
1 averages the inputs over the past 1/10 second
10 averages the inputs over the past 1 second
100 averages the inputs over the past 10 seconds
125 averages the inputs over the past 12.5 seconds
% Limit
0 to 100 Percent
The maximum percent limit is a tolerance band set up on either side of the
running average. The percentage value refers to deviation from the running
average. For example, if the running average is 100 gal/min, and a 2 percent
maximum limit is selected, then the acceptable range is from 98 to 102
gal/min.
Values within the limit are accepted while values outside the limit are analyzed
to determine if they are a noise spike or an actual flow change.
Time Limit
0 to 256 Seconds
The time limit parameter forces the output and running average values to the
new value of an actual flow rate change that is outside the percent limit
boundaries. It thereby limits response time to flow changes to the time limit
value rather than the length of the running average.
Field Comm. 1, 4, 4, 2
Field Comm. 1, 4, 4, 2, 1
Field Comm. 1, 4, 4, 2, 2
Field Comm. 1, 4, 4, 2, 3
Field Comm. 1, 4, 4, 2, 4