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Operation 17
HP289
3.3.2 Filtering
Frequency fluctuations caused by pulsating flow through a flowmeter,
often makes the Rate impossible to read with any precision.
The Batch Controller has a digital filter which will average out these
fluctuations and enable the Rate to be read to four digit accuracy. The
degree of filtering is fully configurable which means that highly
accurate and stable readings can be obtained without excessive lag.
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 set during the configuration process. The times for
the display value to reach 90% and 99% of full swing are given in
seconds for different values of A.