Yokogawa EJX930A - Manual (Page 145)

A8-1
IM 01C25T02-01E
Appendix 8. Advanced Diagnostics
A8.1 Multi-sensing Process
Monitoring
Multi-sensing process monitoring function (option
code: /DG1) provides the advanced diagnostics
to detect the abnormal conditions in process
environment such as an impulse line etc. by using
the EJX multi-sensing technology and its unique
algorithm. There are following two functions.
 Impulse Line Blockage Detection (ILBD)
The fluctuation change of differential pressure and
static pressure is monitored by a silicone resonant
sensor and detects a potential blockage condition.
The differential pressure transmitter provides also a
result of which pressure-side was plugged.
 Heat Trace Monitoring
The flange temperature is calculated by two
temperature sensors built in the EJX. The
temperature change enables to detect the heat
trace breakage or the abnormal temperature due to
the failure.
A8.2 Impulse Line Blockage
Detection (ILBD)
ILBD is carried out by using statistical analysis
derived from the measured values of process
fluctuations that exist in a fluid. An alarm on the
EJX LCD display or an analog alert is generated if
certain blockage level is reached. EJX provides the
following results as blockage detection.
(1) A Blocking and B Blocking
These are blockage detections derived from
the fluctuation value change of differential
pressure/pressure. With a differential pressure
transmitter, each result indicates that both or
single side is plugged.
(2) Low Side Blocking
It is a low-pressur-side blockage detection
derived from the change of VALUE_BLKF* or
low-pressure-side fluctuation value.
(3) High Side Blocking
It is a high-pressure-side blockage detection
derived from the change of VALUE_BLKF* or
low-pressure-side fluctuation.
*: VALUE_BLKF indicates blockage degree
characterized by a comparison of the high- and
low-pressure-side fluctuation values. For the
details, refer to A8.2.1.
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
change 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,
you need to 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
• A pressure transmitter is used and the pressure
drops to nearly the low-cut value.
• Even though the pressure is constant, the flow
decreases after a reference value is obtained.
• 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.