DigitalFlow™ XGM868i Service Manual
21
Chapter 3. Diagnostics
3.3.2 Pipe Problems
Pipe-related problems may result either from a failure to observe the installation instructions, as described in the
Startup Guide
, or from improper programming of the meter. By far, the most common pipe problems are the following:
1.
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
, of the
Startup Guide
for more details on proper installation practices.
2.
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 GE, 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,
Initial Setup
, of the
Startup Guide
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 flowmeter. For a GE 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. See Appendix C,
Measuring P and L Dimensions
, of the
Startup Guide
for
a thorough discussion of this topic.
3.
Signal strength above 75.
The XGM868i is supplied with a signal preamplifier. However, this amplifier may not be necessary for high
pressure applications. If the meter has a signal strength above 75, bypass the preamp and connect the coax cable
directly to the transducers.
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