Dynasonics TFXL Clamp-On Ultrasonic Flow - Manual (Page 21)

06-TTM-UM-00158 8/2012 21
will be in the Flow Rate Units. For unidirectional measure-
ments, set Max Flow to the highest (positive) fl ow rate
expected in the piping system. For bidirectional measure-
ments, set Max Flow to the highest (positive) fl ow rate
expected in the piping system.
Low Flow Cutoff is provided to allow very low fl ow rates
(that can be present when pumps are off and valves are
closed) to be displayed as zero fl ow. Typical values that
should be entered are between 1.0% and 5.0% of the fl ow
range between Min Flow and Max Flow.
Low Signal Cutoff is used to drive the fl ow meter and its
outputs to the value specifi ed in the Substitute Flow fi eld
when conditions occur that cause low signal strength. A
signal strength indication below 5 is generally inadequate for
measuring fl ow reliably, so generally the minimum setting
for Low Signal Cutoff is 5. A good practice is to set the Low
Signal Cutoff at approximately 60-70% of actual measured
maximum signal strength.
NOTE: The factory default “Low Signal Cutoff ” is 5.
If the measured signal strength is lower than the Low Signal
Cutoff setting, a “Signal Strength too Low” highlighted in
red will become visible in the text area to the left in the Data
Display screen until the measured signal strength becomes
greater than the cutoff value.
Signal strength indication below 2 is considered to be no
signal at all. Verify that the pipe is full of liquid, the pipe size
and liquid parameters are entered correctly, and that the
transducers have been mounted accurately. Highly aerated
liquids will also cause low signal strength conditions.
Substitute Flow is a value that the analog outputs and the
fl ow rate display will indicate when an error condition in the
fl ow meter occurs. The typical setting for this entry is a value
that will make the instrument display zero fl ow during an
error condition.
Substitute Flow is set as a percentage between Min Flow and
Max Flow. In a unidirectional system, this value is typically
set to zero to indicate zero fl ow while in an error condition.
In a bidirectional system, the percentage can be set such that
zero is displayed in an error condition. To calculate where
to set the Substitute Flow value in a bidirectional system,
perform the following operation:
100
100 -
-
u Maximum Flow
Substitute Flow
Maximum Flow Minimum Flow
Entry of data in the Basic and Flow tabs is all that is required
to provide fl ow measurement functions to the fl ow meter.
If the user is not going to utilize input/output functions,
click on the Download button to transfer the confi guration
to the TFXL instrument. When the confi guration has been
completely downloaded, turn the power to the meter off and
then on again to guarantee the changes take eff ect.
FILTERING TAB
The Filtering tab contains several fi lter settings for the TFXL
fl ow meter. These fi lters can be adjusted to match response
times and data “smoothing” performance to a particular
application.
Download Cancel File Open... File Save...
System Configuration
Display Basic Flow Filtering Output Security
%
Flow Filter (Damping): % 80 Time Domain Filter: 8
Advanced Filter Settings:
Flow Filter Hystersis: 5
psec Flow Filter Min Hystersis: 303
Bad Data Rejection: 3
Flow Filter Sensitivity: 3
Factory Defaults
FIGURE 4.5 - FILTERING TAB
Time Domain Filter (range 1-256) adjusts the number
of raw data sets (the wave forms viewed on the software
Diagnostics Screen) that are averaged together. Increasing
this value will provide greater damping of the data and slow
the response time of the fl ow meter. Conversely, lowering
this value will decrease the response time of the meter to
changes in fl ow/energy rate. This fi lter is not adaptive, it is
operational to the value set at all times.
NOTE: The TFXL completes a measurement in approximately
350-400 mS. The exact time is pipe size dependent.
Flow Filter (Damping) establishes a maximum adaptive
fi lter value. Under stable fl ow conditions (fl ow that varies less
than the Flow Filter Hysteresis entry), this adaptive fi lter
will increase the number of successive fl ow readings that are
averaged together up to this maximum value. If fl ow changes
outside of the Flow Filter Hysteresis window, the fi lter
adapts by decreasing the number of averaged readings and
allows the meter to react faster.
The damping value is increased to increase stability of the
fl ow rate readings. Damping values are decreased to allow
the fl ow meter to react faster to changing fl ow rates. The
factory settings are suitable for most installations. Increasing
this value tends to provide smoother steady-state fl ow read-
ings and outputs.
Flow Filter Hysteresis creates a window around the average
fl ow measurement reading allowing small variations in
fl ow without changing the damping value. If the fl ow varies
within that hysteresis window, greater display damping
will occur up to the maximum values set by the Flow Filter
(Damping) entry. The fi lter also establishes a fl ow rate
window where measurements outside of the window