A-3
Appendix A Maintenance and Troubleshooting of this Device
A2 Configuration using a pressure gauge
A2-1 Clogging and the pressure frequency index
The pressure frequency index varies depending on clogging in the connecting pipe. Generally, the
pressure frequency index becomes smaller as clogging progresses. Normally, the pressure frequency
index does not become larger.
A2-2 Points to note regarding the diagnosis of clogging
When the pressure frequency index is used to diagnose clogging in the connecting pipe, observe
the cautions shown below.
If the fluctuation is very small or its frequency is low, clogging cannot be diagnosed. This is because
the pressure must include a sufficient number of fluctuations for the pressure frequency index to be
calculated accurately. Specific examples are listed below.
• There is no fluid flow, or flow velocity is very slow.
• Fluid viscosity is high.
Variation in the pressure frequency index does not always mean that clogging in the connecting
pipe has occurred. The index may vary due to other factors, such as the following.
• A change in the operating conditions of the pump, compressor, etc. (ON/OFF, number of units,
RPM, etc.)
• Air bubbles entering the process piping or connecting pipe
• A change in the viscosity of the process fluid
• Flow velocity variation caused by valve hunting
Note that whether or not the cause is clogging can be inferred by comparing the pressure frequency
index and the standard deviation with their values when conditions are normal. If the standard
deviation increases at the same time that the pressure frequency index decreases, it is probable that,
rather than a decrease in high-frequency fluctuation due to clogging, there has been an increase in
low-frequency fluctuation due to some other cause.
Depending on the material that causes clogging, it is possible that variation in the index will be too
small for an alarm to be activated. For example, if the clog is made of something like gravel, where
there are gaps, the pressure fluctuation can be transmitted through the gaps, and there will not be
much change in the index.
If the frequency of pressure fluctuation is abnormal from the beginning, as is a case where the
connecting pipe was clogged from the start, it may not be possible to diagnose the clogging. Do the
setup procedures (A2–4) when the connecting pipe is operating normally.
Even if clogging occurs suddenly, the pressure frequency index will not change immediately. This
is because it takes a few minutes to calculate the frequency of the pressure fluctuation with a high
level of accuracy.
If the transmitter is installed in an environment subject to heavy vibration, the pressure frequency
index may be affected, preventing correct diagnosis.
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