IM-P505-02-US
Issue 1
53
UTM20 Series Ultrasonic Transit-time Flowmeters
For example, if the average flow rate is 100 gpm and the Hysteresis is set to 10%, a filter window
of 90 to 110 gpm is established Successive flow measurements that reside within that window are
recorded and averaged in accordance with the Damping setting Flow readings outside of the window
are rejected or accepted in accordance with the
Bad Data Rejection setting Filter settings for this example:
Filter Method
Adaptive
Damping
40 seconds
Sensitivity
60%
Hysteresis
10%
Bad Data Rejection
3
Fig. 47 Hysteresis window
Bad Data Rejection (Range 0 to 10 Samples; Default: 3)
The Bad Data Rejection setting is related to the number of successive readings that must be measured
outside of a the Hysteresis value before the flow meter considers the new flow value valid In this
example, a Hysteresis setting of 10% produces a ± 10% band centered on the current valid flow rate
of 100 gpm
The Bad Data Rejection setting is the number of successive samples that must be outside of the
Hysteresis window before the flow meter considers the change in flow as real Larger values are
entered into the Bad Data Rejection window when measuring liquids that contain gas bubbles, as the
gas bubbles tend to disturb the ultrasonic signals and cause more extraneous flow readings to occur
Larger Bad Data Rejection values tend to make the flow meter less responsive to rapid changes in
actual flow rate
In Figure 41 , flow data falls outside the flow Hysteresis window but does not reach the minimum time
specified in the Bad Data Rejection window When data appears that is outside the Hysteresis band
and shorter than the Bad Data Rejection window time, the data is rejected
150
110
100
90
50
0
Flow Within
Hysteresis Limit
±10% Hysteresis
Limit
Flow