Flowcell Problems; Fluid Problems - GE DigitalFlow DF868 Service Manual

Chapter 3. Diagnostics

3.4 Flowcell Problems

If preliminary troubleshooting with the Error Code Messages and/or the Diagnostic Menu indicates a possible flowcell
problem, proceed with this section. Flowcell problems fall into two categories:
•
liquid problems
•
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 the factory for assistance.

3.4.1 Fluid Problems

Most fluid-related problems result from a failure to observe the flowmeter system installation instructions, as described
in the Startup Guide. Refer to Chapter 1, Installation, of the Startup Guide 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:
1. The fluid must be homogeneous, single-phase and relatively clean. Although a low level of entrained particles may
have little effect on the operation of the Model DF868, 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.
2. 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.
3. 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
code message will appear on the display screen to indicate that the ultrasonic signal strength is insufficient for
reliable measurements.
4. The fluid sound speed must not vary excessively.
The Model DF868 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 different from that programmed into the Model DF868, will result in
erratic or inaccurate flow rate readings. Refer to Chapter 2, Initial Setup, of the Startup Guide and make sure that
the appropriate sound speed is programmed into the meter.
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