5-3
1010PVNFM-3A
Section 5
5.3.4 OVERVIEW OF SYSTEM PERFORMANCE
Our system performance specifications are based on acceptable liquid sonic conductivity and
other pertinent application conditions. The diversity that characterizes liquid flow, makes it
impossible for us to cover all possible application conditions that have the potential to reduce
performance. Performance within specifications depends primarily on the receive signal’s sig-
nal-to-noise ratio and amplitude. The information below may point to application conditions
that could reduce system performance below its normally high level.
5.3.5 ACCURACY
Although system accuracy is exceptional over a wide turndown ratio, at extremely low flow
rates, a small zero offset becomes a high percentage of actual flow. Obviously, the ultimate
accuracy will be obtained by performing an on-site flow calibration. A flow calibration can
increase system accuracy to between 0.3% to 0.5%, depending on application conditions.
Two common data-entry mistakes may reduce performance. If you enter an incorrect liquid
viscosity value, you could compromise the intrinsic flow profile compensation curve. Incor-
rectly identifying the transducers will reduce accuracy. Measured sonic velocity (Vs) errors
will usually reveal this problem and by simply returning to the appropriate menu cells, enter-
ing the correct values, and then repeating the transducer installation it will resolve it.
5.3.6 REPEATABILITY
Some applications require repeatability rather than absolute accuracy. System 1010 features
excellent repeatability specifications since its digital “no moving parts” design avoids the ad-
verse effects of hysteresis and other wear mechanisms typical of mechanical devices.
5.3.7 DATA STABILITY
Two main factors influence the system’s data stability:
Data Scatter and Drift.
Data Scatter
Data scatter is a rapid variation in flow readings (within a span of about 0.1 to 5 seconds).
Minimal data scatter (approximately 0.01 to 0.03 ft/sec) is a natural by-product of digital com-
putation that extracts the extremely small difference in the up vs. down sonic transit time.
Minimal data scatter will not influence the integrated flow total over periods as short as
several minutes. Naturally, it will be a greater percentage of the reading when the meter
measures extremely low flow rates. Poor liquid sonic conductivity may attenuate sonic signal
to a level that increases data scatter. You should check the signal level (Valc %) item on the
Diagnostic Menu. Usually, this is indicated by a low Valc % value (less than 30).
System 1010 does not exhibit inertia since it has no moving parts. In addition, it takes read-
ings ten times per second. Therefore, it can detect and track very brief flow fluctuations that
are beyond the response capability of some conventional meters. This performance level is
required for detecting very fast and short flow transients or for a fast-response servo control
loop application. However, you can use the damping and slewing controls to smooth the out-
put response if you want the system to ignore rapid flow fluctuations or data scatter.
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