CiDRA SONARtrac HD GVF-100 - Manual (Page 90)

Copyright © 2006 CiDRA Corporation Page 10-12
20675-02 Rev 01
particularly useful in applications where spurious signals are detected
by the meter and are then reported on the display and the transmitter
outputs.
Once the meter is running and displaying values, this filter will provide
two other forms of spike suppression. The first is for spurious
dropouts due to poor quality readings. The filter will hold the last good
value until a user programmable number of consecutive bad readings
have been accumulated. This user programmable number is the
same number as described above for the ‘no flow’ condition. When
the number of consecutive bad readings is exceeded, the output will
blank (-----) and the 4-20mA output will be set to the ‘Out Of Range’
state. The second is for spurious in-range calculations of good
quality. These will manifest themselves as a positive or negative
spike of a magnitude much greater than the steady state deviations.
This filter will monitor the rate of change of the calculated value for a
number of consecutive readings. If a single reading exceeds the
desired rate of change, the transmitter will hold the last value. The
rate of change limit is a user programmable value entered in units of
percent of total transmitter flow rate or gas volume fraction. If the rate
of change is exceeded for three consecutive readings, the filter will be
reset and the calculated value will be displayed.
- State : Used to ‘Enable’ or ‘Disable’ the Spike Filter.
- Length : Defines the number of consecutive measured points that
must be within the reading-to-reading variation range defined by the
‘Percent’ or ‘Delta’ parameter in the filter setup.
- Delta or Percent: Defines the reading-to-reading variation limit.
This is in units of percent of transmitter operating range.
Therefore, Reading-to-Reading Variation (RV) is the device Maximum
Measurable Value (MaxMV) in ft/sec minus the device Minimum
Measurable Value (MinMV) in ft/sec times the percent of the
Measurable Range ‘Percent’ (‘Delta’) (MR) input by the user to be
used for the filter; or:
RV = [(MaxMV – MinMV) * MR]
For example, in a device with an SOS MaxMV of 5000 fps and SOS
MinMV of 50 fps and a %MR of 10%, reading variations greater than
495 fps will be rejected.
RV = [(5000 – 50) * 0.10] = 495 fps
Therefore, measured points that have measurement variations greater
than 495 fps will not be displayed or outputted until the number of
consecutive readings that do not vary by more than RV is greater than
that set by ‘Length’.