Liquid Controls IT375 - Manual (Page 8)

Sponsler, Inc. Model IT375 Operation Pg. 8
3.3 FILTERING
Frequency fluctuations caused by pulsating flow through a flowmeter can interfere with the precision of the displayed
rate. For this reason, the Model IT375 has a programmable digital filter which will average out these fluctuations and
enable accurate, stable readings.
The degree of filtering of the input signal can be adjusted depending on the magnitude of fluctuation and the particular
application. Values from 1 to 99 can be programmed where 1 corresponds to no filtering and 99 corresponds to
heavy filtering. Such flexibility in filtering allows each application to be addressed on it’s merits.
When programming the degree of filtering, it is advisable to start with no filtering (the factor equals 1) and gradually
increase until a steady reading is obtained. It is important that the filtering is not too heavy because this will cause an
overdamped (slow) response to changes in the flowrate.
The following graph shows the time to reach 90% and 99% of a new reading for a step change in input signal.
Filter Factor vs Time to Reach New Reading
(for a step change in input signal)
0
20
40
60
80
100
120
0 10 20 30 40 50 60 70 80 90 100
Filter Factor
T
im
e t
o
R
each
%
o
f
N
ew
R
ead
in
g
(
seco
n
d
s)
90% of New Reading 99% of New Reading