CiDRA SONARtrac HD VF-100 User Manual

Page 84

Page 10-9

20638-02 Rev 01

Care must be taken when choosing the time constant for the damping
filter as the response time for the reported measurement will increase
as the magnitude of the time constant is increased.

If the time response of the reported measurement is critical then the
‘VF Noise Filter’ should be used instead of the damping filter.

•

VF Noise Filter

A filter that provides both steady state noise attenuation and quick
transient response. Under steady state conditions the filter will use a
long time constant in order to attenuate noise on the flow signal.
Once the flow begins to ramp up or down, the filter will reduce the filter
time constant to allow the meter output to track the flow with a faster
response time.

‘State’ – used to ‘Enable’ or ‘Disable’ this option. Factory default
is ‘Disable’.

‘Magnitude’ – choices of ‘Low’ or ‘High’. The high setting differs
from the low setting with more damping in both the transient and
steady state condition.

•

VF Spike Filter

Provides spike suppression capability for normal operation as well as
for the ‘no flow’ condition.

While in the ‘no flow’ condition, this filter requires a user
programmable number of consecutive good flow readings to be
calculated prior to enabling the display and all outputs of the
transmitter. This is particularly useful in applications where spurious
signals are detected by the flow meter and are then reported on the
display and the transmitter outputs.

Once the meter is running and displaying flow 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 flow calculations of good
quality. These will manifest themselves as a positive or negative
spike of a magnitude much greater than the steady state flow
deviations. This filter will monitor the rate of change of the calculated
flow 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 velocity operational range
(typically 27ft/sec). If the rate of change is exceeded for three