20
Signal processing
Section 4: Flow measurement
3410 Series Gas Ultrasonic Meters Operations Manual
January 2018
3-9000-777 Rev E
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.
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
Section 4.2.3
).
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
Daniel Customer Service 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 for contact information.
