Dynasonics DXN Portable Ultrasonic Measurement System - Manual (Page 58)

Low Flow Limit [Low Flow Cut-off] – (Value)
A Low Flow Limit entry is provided to allow very low flow rates (that can be present when pumps are off and valves are closed)
to be displayed as zero flow. Typical values to enter are between 1.0% and 5.0% of the flow range between Min Flow Limit and
Max Flow Limit.
The Low Flow Limit can also be thought of as the minimum flow rate that the meter will give reliable readings.
Filter Page
Site Name 0.00 GPM
03/28/2012
13:24
Meter Display Adv Cal System Site Log I/O
Totalizer Energy Limit Flow Filter
Filter Method
Hysteresis (%)
Sensitivity (%)
Damping (sec) (Hz)
10.0
80
1.0
Simple
Figure 74: Filter Settings
Filter Method
The DXN can be set for several levels of signal filtering. They are:
• None imposes no filtering on the signal from the transducers.
• Simple with Rejection uses Damping and Bad Data Rejection to filter the flow data.
• Adaptive filtering allows the DXN’s software routines to alter the filtering depending on how variable the signal
from the transducers is. This filter used a combination of Damping, Bad Data Rejection, Sensitivity, and Hysteresis to
modify the flow input data.
Damping (Numeric Time Value) [Range 0…100 Seconds]
Damping is the approximate amount of time the filtering routines use to attain a 99% stable rate value. Generally the higher
the damping value the more stable the rate readings are but at the expense of response time.
Sensitivity (Numeric Value in %) [Range 0…100]
The sensitivity adjustment determines how fast the adaptive filtering will respond to a change in rate. Increasing the
sensitivity has the effect of decreasing the filtering allowing the display to respond to rate changes more rapidly.
Hysteresis (Numeric Value in %) [Range 0…25]
Creates a window around the average flow measurement reading defining the limits in which the automatic damping
increases will occur. If the rate varies within the hysteresis window, greater damping will occur up to the maximum values set
by the flow filter Damping entry. The filter also establishes a flow rate window where measurements outside of the window
are captured by the Bad Data (Rejection) Window. The value is entered as a percentage of actual flow rate.
For example a Hysteresis setting of 5% allows the flow to vary ± 5% from the currently established flow rate without
automatically decreasing the value of the Damping.
DXN Portable Ultrasonic Measurement System
Page 58 February 2013