5-4
1010PVNFM-3A
Section 5
Data Drift
Drift is a defined as a long-term cyclical flow deviation resulting from the variation of liquid
temperature or liquid sonic velocity. Drift may be more noticeable when combined with a poor
signal-to-noise ratio. System 1010 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 addi-
tion, we use only the most stable plastics or steel to construct our transducers.
5.4 FLOW CONDITIONS
Very rarely are real-world flow conditions uniform and predictable. Therefore, the 1010 oper-
ating system provides a considerable degree of control over the stability/agility of the flow
rate output. System 1010 is significantly more agile in tracking pressure wave induced Vs
transients, and will recover from mistracking more quickly and smoothly than any other com-
peting transit-time flowmeter.
5.4.1 LOW FLOW RATES
Our 1010 Systems provide a flow resolution and measurement range that surpasses any
other type of flowmeter. Therefore, it operates superbly for low or high flow rate applications.
However, with our clamp-on systems, using the highest resolution when measuring a low flow
rate may cause natural data scatter to become a high percentage of the reading. Since it is data
scatter, it will not contribute any error to a totalizer reading accumulating for at least several
minutes. However, if the flow rate is extremely low (e.g., under 0.25 ft/sec) the minute zero
drift retained by the system may cause an observable performance decline. Therefore, if your
application involves extremely low flow velocities, and your line size is 2" or under, our 992DFT
or 1011FT Flow Tubes might serve you best.
5.4.2 FLOW DATA SCATTER AND DAMPING
The transit-time flowmeter’s ability to respond to the extremely fast flow fluctuations that
characterize “real” flow may surprise you. Most conventional flowmeters cannot detect these
rapid flow fluctuations since they are subject to unavoidable mechanical inertia. System 1010’s
response speed is ideal for tracking fast flow transients. However, if this performance is un-
necessary, you can smooth the System 1010’s response time to suit any application.
System 1010 Damping and Slewing Controls
System 1010 can detect and display minute flow fluctuations that are always present, though
not usually detectable by typical flowmeters. This rapid response accommodates applications
that require the tracking of fast flow transients.
Time Average is our recommended filter that controls the output damping (the number of
samples averaged together to produce the instrument’s primary rate output). It integrates the
instantaneous flow rate over a selectable time period. Time Average function is very useful
when stability in flow readings are essential.
It allows the user to enter a value in seconds that the flow computer uses to integrate its
response to flow changes. Do not confuse this with the update speed of analog outputs. This
occurs every 0.2 seconds, regardless of the time average that you select. One practical applica-
tion is to set the time average damping so that the meter maintains a smooth output when it is
installed downstream from devices (e.g., a positive displacement pump) that may cause regu-
lar surges in the liquid flow.
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