GE DigitalFlow DF968, Service Manual

Page: 39 / 78

March 2008
3-6 Diagnostics
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
D,
Measuring P and L Dimensions , of the Startup Guide for a
thorough discussion of this topic.
3. 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.