Technical data

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
AcquisitionVelHold 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 meter operation mode is indicated by the IsAcqMode data point. When TRUE, the
meter is in the Acquisition mode; when FALSE, the meter is in the Measurement mode.
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) to
determine the signal search range.
3.3.1 Re-acquisition mode
Re-acquire transducer signals
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
PctGood[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
3.4 Chord average flow and sound velocity
measurements
At each batch update period, each firing path's transit time measurements are averaged.
The average (mean) value for each path is available via data points MeanTmA1 ...
MeanTmD2 (as appropriate for the meter type)
Note
The data point names often use a “short-hand” way of identifying the receiving transducer. The last
two characters identify the chord (A...D) and the transducer (1=upstream, 2=downstream). For
example, MeanTmA1 is the mean transit time for the chord A upstream transducer.
The difference between a chord's average upstream transit time and average downstream
transit time is the average delta time. The chord's average times and the chord “X” and “L”
dimensions are used to calculate the flow velocity and sound velocity measured by the
chord as shown in Equation 3-1 and Equation 3-2.
Flow measurement
18 Daniel 3810 Series Operations Manual