A-25
Appendix A Maintenance and Troubleshooting of this Device
A4 Setting using a level meter
A4-1 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.
A4-2 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 and differential pressure need to include sufficient perturbation in order to calculate
the pressure frequency index with high accuracy. The following is a list of specific examples.
• There is no fluid flow, or flow velocity is very slow.
• Fluid viscosity is high.
• There is no fluctuation source due to the fact that no fluid is flowing in or out to/from the tank
or the fluid is not agitated.
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, agitator, etc. (ON/OFF, number
of units, RPM, etc.)
• A change in the viscosity of the process fluid
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 (A4–4) 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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