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Reference Manual
00809-0100-4444, Rev AC
Section 7: Digital Signal Processing
January 2015
Digital Signal Processing
7.3 Process noise profiles
1/f noise
This type of noise has higher amplitudes at lower frequencies, but generally degrades over
increasing frequencies. Potential sources of 1/f noise include chemical mixing and slurry flow
particles rubbing against the electrodes.
Spike noise
This type of noise generally results in a high amplitude signal at specific frequencies which can
vary depending on the source of the noise. Common sources of spike noise include chemical
injections directly upstream of the flowmeter, hydraulic pumps, and slurry flows with low
concentrations of particles in the stream. The particles bounce off of the electrode generating a
“spike” in the electrode signal. An example of this type of flow stream would be a recycle flow in
a paper mill.
White noise
This type of noise results in a high amplitude signal that is relatively constant over the frequency
range. Common sources of white noise include chemical reactions or mixing that occurs as the
fluid passes through the flowmeter and high concentration slurry flows where the particulates
are constantly passing over the electrode head. An example of this type of flow stream would be
a basis weight stream in a paper mill.
7.4 High process noise diagnostic
The transmitter continuously monitors signal amplitudes over a wide range of frequencies. For
the high process noise diagnostic, the transmitter specifically looks at the signal amplitude at
frequencies of 2.5 Hz, 7.5 Hz, 32.5 Hz, and 42.5 Hz. The transmitter uses the values from 2.5
and 7.5 Hz and calculates an average noise level. This average is compared to the amplitude of
the signal at 5 Hz. If the signal amplitude is not 25 times greater than the noise level, and the coil
drive frequency is set at 5 Hz, the high process noise diagnostic will trip indicating that the flow
Failure to follow safe installation and servicing guidelines could result in death or
serious injury.
Installation should be performed by qualified personnel only.
Do not perform any service other than those contained in this manual.
Process leaks may result in death or serious injury.
The electrode compartment may contain line pressure; it must be depressurized
before the cover is removed.
High voltage that may be present on leads could cause electrical shock.
Avoid contact with leads and terminals.