22
Smoothing
Section 4: Flow measurement
3410 Series Gas Ultrasonic Meters Operations Manual
January 2018
3-9000-777 Rev E
4.2.4
Smoothing
The Daniel 3410 Series Gas Ultrasonic Flow Meter applies a method for smoothing the output
(particularly the frequency output) by averaging times collected from past batch periods with
new times for the current batch period.
Smoothing can be applied in the following increments: 0 (i.e., smoothing is disabled), 20, 40,
60, or 80%.
For example, setting Smoothing to 20% means that of the samples used for the current update,
20% will be from previously collected samples and 80% will be from the newly collected
samples. Thus, if eight new samples are collected, then those eight samples along with the last
two previous samples would be used together for the current update period calculations.
Meters are configured by default for Smoothing of 0% (only new samples are used for the
Current Update
period).
4.3
Acquisition mode
Daniel 3410 Gas Ultrasonic Flow Meters have two modes of normal operation: Acquisition and
Measurement. The Acquisition mode is used to acquire the ultrasonic signals. This mode is
entered when power is applied to the meter. Once the ultrasonic signals are acquired, the
Measurement mode is entered and the flow velocity is measured. The meter remains in the
Measurement mode as long as at least one chord is operational.
If while in the Measurement mode all chords fail, then the meter re-enters the Acquisition
mode. If the
VelHold
data point is set to a value greater than zero, then, while in the Acquisition
mode, the meter holds the average weighted flow velocity to the last good value for up to the
VelHold
number of batches before setting the velocity to zero. The
VelHold
default value is 0.
The Acquisition mode uses the chords' "L" dimensions (
LA
…
LD
as appropriate to the meter type)
and the specified minimum and maximum sound velocities (
SSMin
and
SSMax
) determines the
signal search range. MinHoldTime and MaxHoldTime are also used to determine the signal
search range. The meter uses the more restrictive of SSMin/MaxHoldTime and SSMax/MinHold
time.
4.3.1
Re-acquisition
When fewer than MinChord (default 1) chords are good, then the meter re-enters the
Acquisition mode. If MinChord is set to the number of active chords, the meter will reacquire on
the first time a chord is failed for a batch.
Note that failed for a batch is different from hard failed. A chord fails for a batch when Pct-
Good[A1..D2] is less than MinPctGood.
Hard fails occur after AlarmDef number of batches in a row.
If the
VelHold
data point is set to a value greater than zero, then, while in the Acquisition mode,
the meter holds the average weighted flow velocity to the last good value for up to the
VelHold
number of batches before setting the velocity to zero. The
VelHold
default value is 0.0
