Panametrics PanaFlow XMT1000, User Manual, Page: 30 / 80

3.2 Diagnostics
3.2.1 Introduction
This section explains how to troubleshoot the XMT1000 if
problems arise with the electronics enclosure, the flowcell, or
the transducers. Indications of a possible problem include:
• Display of an error message on the LCD display screen,
Vitality PC software, or HART.
• Erratic flow readings
• Readings of doubtful accuracy (i.e., readings which
are not consistent with readings from another flow
measuring device connected to the same process).
If any of the above conditions occurs, proceed with the
instructions presented in this section.
3.2.2 Flowcell problems
If preliminary troubleshooting with the error code messages
and/or the diagnostic parameters indicates a possible
flowcell problem, proceed with this section. Usually, flowcell
problems are either fluid problems or pipe problems . Read
the following sections carefully to determine if the problem
is indeed related to the flowcell. If the instructions in this
section fail to resolve the problem, contact Panametrics
for assistance.
3.2.2a Fluid problems
Most fluid-related problems result from a failure to observe
the flow meter system installation instructions. Refer to
chapter 1, installation , to correct any installation problems.
If the physical installation of the system meets the
recommended specifications, it is possible that the fluid
itself may be preventing accurate flow rate measurements.
The fluid being measured must meet the following
requirements:
•
The fluid must be homogeneous, single-phase,
relatively clean and flowing steadily. Although a low
level of entrained particles may have little effect on
the operation of the XMT1000, excessive amounts
of solid or gas particles will absorb or disperse the
ultrasound signals. This interference with the ultrasound
transmissions through the fluid will cause inaccurate
flow rate measurements. In addition, temperature
gradients in the fluid flow may result in erratic or
inaccurate flow rate readings.
• The fluid must not cavitate near the flowcell.
Fluids with a high vapor pressure may cavitate near
or in the flowcell. This causes problems resulting
from gas bubbles in the fluid. Cavitation can usually
be controlled through proper installation design.
• The fluid must not excessively attenuate ultrasound
signals. Some fluids, particularly those that are very
viscous, readily absorb ultrasound energy. In such a
case, an error code message will appear on the display
screen to indicate that the ultrasonic signal strength is
insufficient for reliable measurements.
The fluid sound speed must not vary excessively.
The XMT1000 will tolerate relatively large changes in the
fluid sound speed, as may be caused by variations in
fluid composition and/or temperature. However, such
changes must occur slowly. Rapid fluctuations in the fluid
sound speed, to a value that is considerably above the
limit programmed into the XMT1000, will result in erratic
or inaccurate flow rate readings. Refer to chapter 2,
programming , and make sure that the appropriate
sound speed limit is programmed into the meter.
3.2.2b Pipe problems
Pipe-related problems may result either from a failure
to observe the installation instructions, as described in
chapter 1, installation , or from improper programming
of the meter (see chapter 2, programming, for details).
By far, the most common pipe problems are the following:
•
The collection of material at the transducer location(s).
Accumulated debris at the transducer location(s) will
interfere with transmission of the ultrasound signals.
As a result, accurate flow rate measurements are not
possible. Realignment of the flowcell or transducers often
cures such problems, and in some cases, transducers
that protrude into the flow stream may be used. Refer
to chapter 1, installation , for more details on proper
installation practices.
• Inaccurate pipe measurements. The accuracy of the flow
rate measurements is no better than the accuracy of the
programmed pipe dimensions. For a flowcell supplied
by Panametrics, the correct data will be included in the
documentation. For other flowcells, measure the pipe
wall thickness and diameter with the same accuracy
desired in the flow rate readings. Also, check the pipe
for dents, eccentricity, weld deformity, straightness and
other factors that may cause inaccurate readings.
Refer to chapter 2, programming , for instructions on
programming the pipe data.
In addition to the actual pipe dimensions, the path
length (P) and the axial dimension (L), based on
the actual transducer mounting locations, must be
accurately programmed into the flow meter. For a
Panametrics flowcell, this data will be included with the
documentation for the system. If the transducers are
mounted onto an existing pipe, these dimensions
must be precisely measured.
• The inside of the pipe or flowcell must be relatively clean.
Excessive build up of scale, rust or debris will interfere with
flow measurement. Generally, a thin coating or a solid
well-adhered build up on the pipe wall will not cause
problems. Loose scale and thick coatings (such as tar or
oil) will interfere with ultrasound transmission and may
result in incorrect or unreliable measurements.
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