Flow Conditions; Low Flow Rates; Flow Data Scatter And Damping; Fue1010En Damping And Slewing Controls - Siemens SITRANS F Instruction Manual

Section 5
1010ENFM-3B
.4

FLOW CONDITIONS

Very rarely are real-world flow conditions uniform and predictable. Therefore, the FUE1010EN operating
system provides a considerable degree of control over the stability/agility of the flow rate output. The
FUE1010EN 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 flowmeters 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 perfor-
mance 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. FUE1010EN's response speed is ideal for
tracking fast flow transients. However, if this performance is unnecessary, you can smooth the
FUE1010EN's response time to suit any application.

FUE1010EN Damping and Slewing Controls

FUE1010EN 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 track-
ing 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 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 extends
the time constant and the resulting output is smooth data.

5.4.3 NOTES ON LIQUID CONDITIONS

Successful transit-time flow measurement depends on sonic transmit signals traveling through liquid
and arriving at the receive transducer without excessive attenuation. Receive signals can be scattered by
liquids carrying dispersed particulate matter, either of a solid, non-homogeneous or gaseous nature.
This is especially true if the dispersed material is of different sonic impedance than the base liquid.
Liquids that contain an excess of gas bubbles or mineral solids may prove to be unsatisfactory transit-
time applications.
5-4