Yokogawa 415 Steam and Gas - Manual (Page 33)

3.4 FILTERING
Frequency fluctuations caused by pulsating flow through a flowmeter, often make
the Rate impossible to read with any precision.
The Flow Computer `as a digital filter which will average out these fluctuations
and enable the Rate to be read to four digit accuracy. The ability to select a
suitable filtering level means that highly accurate and stable readings can be
obtained without excessive lag. When the Rate is retransmitted via the 4-20mA
output, the filtering will also average out any fluctuations on the output.
The diagram below shows a pulsating signal input together with the effect of
filtering.
As a guideline to the degree of filtering to be used, the following table shows the
response to a step change in input. The value, A, is the filter constant which is
programmed during the Calibration routine. The times for the display value to
reach 90% and 99% of full swing are given in seconds, for different values of A.
Operation 31
Filtered Response
Time
Unfiltered Response
Rate