Signal Processing; Stacking; Filtering - Emerson Daniel 3415 Operation Manual

Measurement
4.2

Signal processing

The signal at the receiving transducer is amplified, digitized and processed digitally to
provide accurate transit time measurement.
A measure of the signal "quality" is the signal-to-noise ratio (SNR). The higher the SNR, the
better the signal. In general there are two types of noise: "white" noise and "colored" noise.
White noise is noise that occurs across the frequency spectrum and is asynchronous to the
transmitted signal. Colored noise is concentrated around a particular frequency and can be
synchronous with the transmitted signal. The meter provides two methods for improving
the received signal waveform SNR by reducing the noise energy: Stacking and Filtering.
When making changes to these parameters in dual-configuration meters such as the 3415,
3416, 3417, it is generally necessary to make the same changes in both transmitter heads
in order to maintain compatible transducer firing sequence durations. The meter will
generate an alarm if the two transmitter heads are not in synchronization which may be an
indication that they are not configured the same.
4.2.1

Stacking

Stacking is a method of firing a transducer multiple times and averaging the received
signals on a point-by-point basis. Stacking is effective on asynchronous noise such as is
typically seen with valve noise. This method is not useful for removing synchronous noise
and should not be used when there is a great deal of signal "jitter." Meters are configured
by default with a stack size of 1 (no stacking).
Care should be taken when turning on stacking and it is recommended to consult with
Daniel Customer Service if you are unsure of how stacking a signal can affect the meter's
operation. Refer to Technical Support under the Help menu of Daniel MeterLink for
contact information.
The number of consecutive times to fire each transducer is specified via the StackSize data
point. Available stack sizes are 1 (None), 2, 4, 8, and 16. A stack size of 1 selects no
stacking (i.e., stacking disabled). Stacking is only available when the standard update rate
is selected (see ).
4.2.2

Filtering

Filtering applies a bandpass filter that removes noise that is above and below the
transducer frequency. Filtering is effective on noise outside of the frequency passband of
the filter (e.g., filtering works on any noise outside of the passband of the filter).
Filtering is enabled/disabled via the Filter data point (TRUE=enable filtering, FALSE=disable
filtering). Meters are configured by default with filtering disabled. The minimum emission
rate for the gas meter is 2 milliseconds with the filter ON or OFF. We recommend the
default Filter setting, which is the OFF position.
Care should be taken when enabling/disabling filtering and it is recommended to consult
with Flow Lifecycle Services for Daniel products if you are unsure of how this change can
affect the meter's operation. Refer to Technical Support under the Help menu of Daniel
MeterLink
18
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for contact information.
3410 Series Gas Ultrasonic Flow meters