Data Drift; Flow Conditions; Low Flow Rates; Flow Data Scatter And Damping - Siemens SITRANS F Operating Instructions Manual

Section 5
1010PFM-3G

Data Drift

Drift is a defined as a long-term cyclical flow deviation resulting from variation of liquid temperature or
liquid sonic velocity. Drift is more noticeable when combined with a poor signal-to-noise ratio. System
1010P 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

FLOW CONDITIONS

Very rarely are real-world flow conditions uniform and predictable. Therefore, the operating system
provides a considerable degree of control over the stability/agility of the flow rate output. The System 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 1010P 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. The System 1010P's response speed is
ideal for tracking fast flow transients. However, if this performance is unnecessary, it also includes
controls to smooth its response time to suit any application.

System 1010P Damping and Slewing Controls

The meter 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
5-4