A-33
Appendix A Maintenance and Troubleshooting of this Device
A5 Supplemental description of parameters
This section describes the parameters related to pressure frequency index diagnosis and their effect
on clogging diagnosis.
The following description is intended to provide information for users who want to know the
function of each parameter in detail. For the general configuration procedures, see sections A2 to 4.
A5-1 Pressure frequency filter constant
The Press Freq Filter Constant determines the strength of the high pass filter used to suppress
decreases in the pressure frequency index due to causes other than clogging of the connecting
pipes. The default setting at the time of shipment from the factory is “0,” meaning that the filter is
not used. However, if the pressure frequency index is used for clogging diagnosis, setting the filter
constant to cut out low-frequency fluctuations is recommended. In particular, when SP is selected
for Press Freq Index Sensor Selection, setting the filter constant is strongly recommended. For
clogging diagnosis, the generally recommended filter constant value range is 0.12 to 0.18.
The larger this parameter, the stronger the filtering effect. In this case, it will be difficult for the
index value to become small for a reason other than clogging. However, if the filtering is too severe,
it is difficult to detect changes in frequency that occur when the connecting pipe is clogged, so
diagnosis performance deteriorates. The smaller the parameter, the smaller the filtering effect. In
this case, there is little deterioration of diagnosis performance using the filter. However, if filtering
is too weak, the value of the index can easily become small for reasons other than clogging. As a
result, false alarms can occur.
When low-frequency fluctuation is very large (as a rough guideline, when the width of low-
frequency fluctuation is more than 10 times greater than the standard deviation under normal
operating conditions), it is difficult to eliminate this effect even when the filter is used.
The Fcut (Hz) and Tcu (t s) (inverse value of cutoff frequency) of this filter are as follows. c is the
filter constant. Ts is the sampling interval selected in the Press Freq Index Sensor Selection, and it is
any of 0.12 (s), 0.24 (s), and 0.36 (s).
Fcut =
1
cos
−1
(
1−
c
2
)
2πTs 2 (c+1)
Tcut =
2πTs
cos
−1
(
1−
c
2
)
2 (c+1)
A5-2 Sensor selection
One of the following can be selected for Press Freq Index Sensor Selection.
DP, 120ms factory default
DP, 240ms
DP, 360ms
SP, 360ms only with a differential pressure gauge
A5-2-1 P sampling interval
When DP is selected for Press Freq Index Sensor Selection, 120, 240, or 360 ms can be selected
for the P sampling interval. Normally, a shorter sampling interval is advantageous for clogging
diagnosis. The reason for this is that changes in pressure fluctuation caused by clogging become
apparent at higher frequencies. (For details, see the “Principle” section.) The sampling interval must
be short for perception of changes in high frequency. Generally, the shorter the sampling interval,
the better the performance of clogging diagnosis. However, with a shorter sampling interval, low
frequencies are difficult to measure. Therefore, if the frequency of the pressure fluctuation is low
initially, lengthening the sampling interval will make diagnosis easier.
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