CiDRA GVF-100 Gas Volume Fraction Monitoring System - Manual (Page 82)

Copyright © 2006 CiDRA Corporation Page 10-8
20639-01 Rev 03
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SONARtrac TM Filters
The SONARtrac TM transmitter has 3 modes of signal output filtering.
These are ‘Damping’, ‘Noise Reduction’, and ‘Spike Filtering’,.
They are applied in that order. The filtering affects both the display on
the transmitter and the signal to the current, pulse, alarm and digital
outputs.
- ‘GVF Damping Filter’ is used to reduce the noise of a signal through
the use of a first order lag filter with a fixed time constant. The time
constant of the filter is set by the user.
State : Used to ‘Enable’ or ‘Disable’ this option.
Time Constant : User input range of values that can be applied are
0 – 600 seconds with 3 seconds as the factory default.
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
‘GVF Noise Filter’ should be used instead of the damping filter.
- ‘GVF Noise Filter’ is a filter that has been designed to provide 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 signal. Once the measurement begins to
ramp up or down, the filter will reduce the filter time constant to allow
the meter output to track the changes 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.
- ‘GVF 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 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 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