Yokogawa EJX930A - Manual (Page 54)

<4. Diagnostics>
4-4
IM 01C25R02-01E
IMPORTANT
• The pressure fluctuation amplitude in fluids
must be sufficiently large for blockages to be
detected.
• If the pressure fluctuation amplitude is too
low for a reference value to be obtained,
blockages detection operation cannot be
performed with an alarm that the reference
value is invalid.
• The pressure fluctuation amplitude may
decrease due to other causes unrelated with
a blockage according to process condition. In
above case, a false alarm of an impulse line
blockage may be generated. Before taking
action in response to a blockage alarm,
consider the plant operating conditions.
 Notes for Pressure or Level
Measurement
With pressure or level measurement, the pressure
fluctuation amplitude may reduce especially for the
following cases.
 Pressure Measurement
• Operational pressure is near outside of
diagnostic range.
• Even though pressure is constant, the flow
decreases than that under normal condition.
• A source of pressure fluctuation (pump,
compressor, blower, etc.) is shut down. As
a result, the pressure fluctuation amplitude
decreases.
 Level Measurement
• A transmitter is used to measure tank level and
the flow of fluid into or out of the tank comes to
a stop.
• The agitator in the tank is shut down.
• A source of pressure variation (a compressor,
etc.) that controls the internal pressure of a
sealed (closed) tank is shut down.
Before taking action in response to a blockage
alarm, consider the plant operating conditions.