Velocity Edge DualX Service Manual download pdf (Page 210)

184 Signal processing

Section 6: Meter operation Reference, Installation, and Operations Manual

August 2014 3-9000-743 Rev U

6.1.2 Signal processing

The signal at the receiving transducer is digitized and digital signal processing techniques are

used to provide accurate transit time measurement.

A measure of the signal “goodness” is the signal-to-noise ratio (SNR). The higher the SNR, the

better the signal. In general there are two types of noise: asynchronous “white” noise and

synchronous “colored” noise. Asynchronous noise is noise that occurs across the frequency

spectrum. Synchronous noise is concentrated around a particular frequency. The meter

provides two methods for improving the received signal waveform SNR by reducing the noise

energy: Stacking and Filtering.

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

2. Care should be taken when turning off stacking and it is recommended to consult with Daniel

Customer Service if you are unsure of how stacking a signal can effect 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 6.1.3 below).

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 for filtering disabled. Care should be taken when turning on filtering and it is

recommended to consult with Daniel Customer Service if you are unsure of how filtering a signal

can effect the meter's operation. Refer to Technical Support under the Help menu of Daniel

MeterLink for contact information.

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Velocity Edge DualX Service Manual Page 210