A-17
Appendix A Maintenance and Troubleshooting of this Device
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).
• For the both-side clogging simulation test, close the valves of the connecting pipes on both
the high and low pressure sides.
• For the one-side clogging simulation test (high pressure side), open the valve of the
connecting pipe on the high pressure side and close only the valve on the low pressure side.
• For the one-side clogging simulation test (low pressure side), close the valve of the
connecting pipe on the high pressure side and open the valve on the low pressure side.
(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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