Yokogawa 414 Batch Controller Manuel d'utilisateur télécharger pdf (Page 22)

3.3.3 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 ability to select a suitable filtering level 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

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.

20 Operation

Filtered Response

Time

Unfiltered Response

Rate

1 2 ... 17 18 19 20 21 22 23 24 25 26 27 ... 50 51

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Yokogawa 414 Batch Controller Manuel d'utilisateur Page 22