GE TransPort PT900 User Manual page 146

Chapter 8. Error Codes and Troubleshooting
8.2.2a Fluid Problems
Most fluid-related problems result from a failure to observe the flow meter system
installation instructions. Refer to Chapter 2, 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 PT900, 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 measurement point.
Fluids with a high vapor pressure may cavitate near the measurement
point. 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 PT900 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 PT900, will result in erratic or inaccurate flow rate
readings. Refer to Chapter 4, Programming, and make sure that the
appropriate sound speed is programmed into the meter.
130
®
TransPort PT900 User's Manual