A-6
Appendix A Maintenance and Troubleshooting of this Device
A2-4-3 Clogging simulation test
If a valve such as a stop valve is connected to the connecting pipe, the valve can be utilized to
conduct the clogging simulation test. The pressure frequency index and standard deviation values
that are collected in the clogging simulation state are used to judge the possibility of diagnosis and
to adjust the parameters in later steps.
Caution
When the valve of the connecting pipe is closed completely, the transmitter cannot
measure the correct value. In addition, even when the valve is not closed completely,
the delay before the process variable follows a change in pressure may be long. (This
symptom is the same as when the damping time constant of the transmitter is made
larger.) When conducting the clogging simulation test, exercise great care so that the test
does not interfere with process safety or control.
Procedure
(1) Close the valve of the connecting pipe either completely or so that it is slightly open (with a
small amount of fluid flow).
(2) Execute Reset Press Freq Index and Reset Standard Deviation.
(3) Wait 20 minutes or more.
(4) Record the values for Pressure Frequency Index, Press Freq Index Min, Press Freq Index Max,
and the PV.
(5) Obtain the values for Standard Deviation, Standard Deviation Min, and Standard Deviation
Max as reference values, and record them.
If there are multiple operating conditions and the index value under normal operating conditions
varies depending on the operating conditions, it is recommended that the steps described above be
repeated under each operating condition.
In the clogging simulation test, the valve of the connecting pipe needs to be sufficiently closed.
The reason for this is that the low-pass filter effect due to clogging as described in “Principle”
above does not occur if the flow path resistance caused by clogging (resistance to fluid flow) is not
sufficiently high.
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