Data Drift; Aeration; Slurries; Two-Phase Liquids - Siemens SITRANS F FUH1010 Series Operating Instructions Manual

Section 5
response capability of some conventional meters. This performance level is required for de-
tecting very fast and short transients or for a fast-response servo control loop application.

Data Drift

Drift is a defined as a long-term cyclical deviation resulting from variation of liquid tempera-
ture or liquid sonic velocity. Drift is more noticeable when combined with a poor signal-to-
noise ratio. System 1010BX is carefully designed to minimize the effects of drift. There are no
drift-prone analog phase-locked loop devices in the primary detection circuits. In addition,
we use only the most stable plastics or steel to construct our transducers.
5.4

AERATION

Undissolved gases, having very low sonic impedance, may cause sonic beam scattering. In
large quantities, they can reduce the sonic signal strength. Small bubbles, caused by cavita-
tion, usually provoke more signal loss than an equal quantity of large gas bubbles. Usually, the
problem can be alleviated by eliminating the cause. Aeration may be caused by a mixing tank,
throttling valve cavitation, or air suction upstream of the transducer location.
System 1010BX can operate successfully with a larger amount of aeration than any
other transit-time meter.
It measures and reports the aeration level as the analog output, Vaer %. This represents the
relative degree of aeration detected within the liquid stream. Its computer reports the Vaer
level until it impedes operation and forces a Fault Alarm. The Vaer output accommodates
applications requiring an aeration indicator. The aeration percentage can be used as an alarm
relay set-point. You can set the aeration alarm setpoint such that it trips before aeration
reaches a level that impairs measurement.
NOTE: Before performing the installation routine, allow enough time for the liquid
to "flush" out all air trapped in the pipe.
5.5

SLURRIES

High-density undissolved solids (e.g., sand slurry) may cause application problems if present
in sufficient quantity to scatter the sonic beam significantly. Low-density solids, such as or-
ganic materials, coal slurries and unaerated sewage sludge, are usually adequate sonic con-
ductors and their sonic impedance is very close to most liquids. Excessive mineral solids though
could trigger the aeration alarm.
5.6

TWO-PHASE LIQUIDS

Two-phase liquids (e.g., oil and water) cause some sonic beam scattering. However, these
usually conduct sonic beams sufficiently for proper operation (unless heavy aeration is present
also). Two-phase liquids with large quantities of different components, such as sand or free
gas, could prove to be too attenuative for transit-time operation.
5.7

VISCOUS LIQUIDS

Highly viscous liquids tend to "absorb" some of the energy of the sonic beam. This causes a
reduction of signal amplitude when compared to low viscosity liquids. However, most high
viscosity liquids are sufficiently conductive for acceptable operation. A low Valc % value usu-
ally indicates low sonic conductivity.
Siemens Hardware
5-3
1010BXFM-3