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Chapter 9. Diagnostics and Troubleshooting
208 Transport® Model PT878 Portable Liquid Flowmeter User’s Manual
9.3 Flowcell Problems
Flowcell problems fall into two categories: fluid problems and pipe
problems. Read the following sections carefully to determine if such
problems exist.
9.3.1 Fluid Problems
Most fluid-related problems can be solved by proper design of the
flowmeter installation and the proper choice of transducer frequency.
Contact the factory if you cannot solve a fluid-related problem.
Certain fluid properties may prevent proper flow measurement. Some fluid
properties that cause problems are listed below.
1. THE FLUID MUST BE HOMOGENOUS, SINGLE PHASE,
RELATIVELY CLEAN, and FLOWING STEADILY. Solid particles
and gas bubbles absorb and disperse ultrasound. Although, in some
cases, solids and gases have little effect on the operation of the
TransPort, excessive amounts will prevent ultrasound transmission
through the fluid and interfere with proper flow measurement.
Temperature gradients may also cause a problem.
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 ATTENUATE ULTRASOUND
EXCESSIVELY. Some fluids, particularly those that are very viscous,
absorb ultrasound energy. In these cases an “E1” will display on the
screen to indicate that the ultrasonic signal is not of sufficient strength
for reliable measurements.
4. THE FLUID SOUNDSPEED MUST NOT VARY EXCESSIVELY.
The TransPort will tolerate relatively wide, but slow, changes in fluid
soundspeed due to changes in fluid composition and temperature.
However, if you are measuring a fluid that is considerably different
from the fluid programmed into the TransPort, you may have to adjust
the meter for the new fluid. Refer to Chapter 3, Programming Site Data,
on page 37.