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Chapter 3 Starting and Stopping this Device
- P Sampling Interval
Select the sampling interval for the differential pressure and pressure value that is used to
calculate the pressure frequency index value when [DP Sensor] is selected for [Sensor Selection].
The options are 120, 240, and 360 ms.
The shorter the fluctuation detection cycle is, the higher the upper limit on detectable frequencies
becomes. However, a short fluctuation detection interval results in the lower limit being raised. A
longer fluctuation detection cycle lowers the upper limit on detectable frequencies but allows the
detection of lower frequencies.
To detect phenomena resulting from high frequencies, as in the case of clogging of connecting
pipes, it is generally better if the fluctuation detection cycle is as short as possible. However, if the
original pressure fluctuation frequency is low, it may go out of the range of detectable frequencies,
making it difficult to detect fluctuation. Therefore, when setting the sampling interval, it is
necessary to take into consideration the pressure fluctuation frequency under normal conditions
and the frequency domain in which abnormalities occur.
(iv) Filter adjustments
The pressure frequency index is intended to detect abnormalities in a process. However, if the
pressure and flow rate naturally change slowly over a period of 40 seconds to five minutes (low-
frequency fluctuation), the index may fall to a low value even if the process is normal. Since such
fluctuation in pressure and flow rate can occur in a normal process, a fall in the index may wrongly
suggest an abnormality, or it may not be possible to correctly detect actual abnormalities.
To prevent false recognition of abnormalities resulting from a reduction in the index value,
high pass filtering is performed to remove the low-frequency component before the number of
fluctuations is counted.
The strength of the filter (filter coefficient) can be set.
Press Freq Filter Constant: The possible setting range is between 0.0 and 1.0.
The factory default is 0.0.
Increase the filter coefficient to remove more low-frequency components, and decrease the
coefficient for the opposite effect. Note that increasing the coefficient decreases the filter’s ability to
detect abnormalities.
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