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Section 5
1020NFM-1D
5.4
FLOW CONDITIONS
Very rarely are real-world flow conditions uniform and predictable. Therefore, the 1020 operating sys-
tem provides a considerable degree of control over the stability/agility of the flow rate output. System
1020 is significantly more agile in tracking pressure wave induced Vs transients, and will recover from
mistracking more quickly and smoothly than any other competing transit-time flowmeter.
5.4.1 LOW FLOW RATES
Our 1020 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 1020's response speed is ideal for
tracking fast flow transients. However, if this performance is unnecessary, you can smooth the Sys-
tem 1020's response time to suit any application.
System 1020 Damping and Slewing Controls
The 1020 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 a filter that controls the output damping (the number of samples averaged together to
produce the instrument's primary rate output). It allows you 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 application 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
regular surges in the liquid flow.
SmartSlew is a digital signal processing method that generates a variable time constant based on the
real-time assessment of collected data. When the flow data exhibits a steady trend, SmartSlew ex-
tends the time constant - resulting in very smooth data output. SmartSlew instantaneously reduces the
time constant whenever the trend of flow changes, even for a short duration. The flow output quickly
follows the slewing of actual flow. SmartSlew thus provides excellent data without sacrificing the fast
response required for precise flow control. Feel free to experiment with time average damping and
slewing factors to discover which settings optimize the collected data. With SmartSlew enabled, you
can create very smooth output graphs without losing the ability to respond to fast flow transients that
may be undetectable with the fixed time average filter enabled.
5-4
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