Yokogawa 202 Field Mounting Rate Totalizer User Manual
Page 14
Operation
10
3.3 FILTERING
Frequency fluctuations caused by pulsating flow through a flowmeter can interfere
with the precision of the rate. For this reason, the Model 202D has a digital filter
which will average out these fluctuations and enable accurate readings.
The degree of filtering of the input signal can be adjusted depending on the
amount 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 means that highly accurate and stable
readings can be obtained.
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
response.
The following graph shows the time to reach 90% and 99% of a new reading for a
step change in input signal.