3-10 Troubleshooting and Customer Support 5707070-A
Advanced Energy
®
SUSPENDED PARTICLE TEST FOR DOPPLER SIGNALS
Particles in a liquid may be either in suspension or dissolved. Dissolved particles will
not reflect Doppler signals because there is no physical dimension nor density
difference to return the sound to the receiver.
Suspended particles generally will return the Doppler signal if there are enough
present and their size is sufficient to meet the requirements of the transmitted
frequency. Materials such as wood pulp, algae, moss, onion skins, fine sand, or other
materials that do not meet the 35 ppm/ 40 micron/ 0.2% density difference minimum
requirements will not reflect sounds. Instead, the signal simply passes through this
material as if it were water. Usually these materials have a specific gravity of 0.999 or
1.001. This is almost exactly the same as water itself and therefore will neither rise nor
fall in the solution. These materials will move about almost anywhere in the solution
controlled only by the motion of the liquid itself.
A simple test requires a clear glass container and a sample of the liquid you wish to
measure with the Doppler sensors. Stir the liquid and watch it for about 3 to 5 minutes.
If the visible particles in suspension neither rise nor fall, they are most likely the same
specific gravity as water and may not reflect Doppler signals. If these particles are the
same specific gravity as water, but do have a membrane or shell around them that is at
least 0.2% density difference than the water molecules, than the signals should be
strong enough for the Doppler to report correct flow readings.
If the particles rise or fall in the solution, they should provide adequate sonic
reflection as long as they meet the specified quantity, size, and density requirements
for the Doppler (see “Specifications and Reference Information” on page 4-1 for more
information).
