Emerson 8700 Series, Справочное руководство

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Reference Manual
00809-0100-4793, Rev CA
August 2004
5-7
Rosemount 8742C
Table 5-2. Triggered Diagnostics
Symptom Probable Cause Corrective Action
Primary Range Value
Exceed The process variable (flow rate) is greater than 12 m/s
(40 ft/s).
• Lower the process rate.
• Increase the flowtube line sizes.
Sensor High Limit
Exceeded The process variable (flow rate) is greater than 13.2
m/s (44 ft/s).
• Lower the process flow rate.
• Increase the flowtube line size.
Reverse Flow
Detected The transmitter is measuring a reversed flow signal.
The following actions can be taken if reverse flow is
unexpected.
• Verify flowtube is not installed backwards. Check flow
direction arrow on the flowtube. Confirm the direction of
process flow.
• Confirm the wiring between the flowtube and the
transmitter on the flowtube is not reversed.
Corresponding terminal block numbers in the flowtube
and transmitter must be connected.
• Verify twisted shielded cable is being used.
• Siphon effect or leaky valve may cause reverse flow.
Empty Pipe Detected The flowtube is not full or fluid. The process variable is
zero. The following actions can be taken if empty pipe
detection is unexpected.
• Verify flowtube is full.
• Increase process fluid conductivity above 50
microsiemens/cm.
• Properly connect the wiring between the flowtube and
the transmitter on the flowtube. Corresponding terminal
block numbers in the flowtube and transmitter must be
connected.
• Perform flowtube electrical resistance tests. Confirm the
resistance reading between coil ground (ground symbol)
and coil (1 and 2) is infinity. Confirm the resistance
reading between electrode ground (17) and an electrode
(18 or 19) is greater than 2 kohms and rises. For more
detailed information, consult the flowtube product
manual.
To turn off empty pipe diagnostic, go to the diagnostic screen
in the transducer block properties.
High Process Noise
Detected The signal to noise ratio is less than 25.
• Increase transmitter coil drive frequency to 37.5 Hz and,
if possible, perform Auto Zero function.
• Verify flowtube is electrically connected to the process
with grounding electrode, grounding rings with grounding
straps, or lining protector with grounding straps.
• If possible, redirect chemical additions downstream of
the magmeter.
• Verify process fluid conductivity is above 10
microsiemens/cm.
To turn off high process noise detection, go to the diagnostic
screen in the transducer block properties.
Coil Drive Open
Circuit Transmitter has detected an open coil circuit condition.
• Perform flowtube electrical resistance tests. Confirm the
resistance reading between coil ground (ground symbol)
and coil (1 or 2) is infinity. Confirm the resistance reading
between electrode ground (17) and an electrode (18 or
19) is greater than 2 kohms and rises. For more detailed
information, consult the flowtube product manual.
• Verify transmitter electronics with Rosemount 8714
reference standard. The dial on the 8714 should be set
at 9.1 m/s (30 ft/s). The transmitter should be set up with
the nominal flowtube calibration number
(1000015010000000) and 5 Hz coil drive frequency.
• Properly connect the wiring between the flowtube and
the transmitter on the flowtube. Corresponding terminal
block numbers in the flowtube and transmitter must be
connected.