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Reference Manual
00809-0300-4750, Rev CA
March 2016
2.
Verify sensor is electrically connected to the process with process reference
electrode, grounding rings with grounding straps, or lining protector with
grounding straps.
3.
If possible, redirect chemical additions downstream of the magmeter.
4.
Verify process fluid conductivity is above 10 microsiemens/cm.
If the signal to noise ratio is less than 25 while operating in 37 Hz mode, proceed with the
following steps:
1.
Turn on the Digital Signal Processing (DSP) technology and follow the setup
procedure (see
Section 7: Digital Signal Processing
). This will minimize the level of
damping in the flow measurement and control loop while also stabilizing the
reading to minimize valve actuation.
2.
Increase damping to stabilize the signal (refer to
). This
will add response time to the control loop.
3.
Move to a Rosemount High-Signal flowmeter system. This flowmeter will deliver a
stable signal by increasing the amplitude of the flow signal by ten times to increase
the signal to noise ratio. For example if the signal to noise ratio (SNR) of a standard
magmeter is 5, the High-Signal would have a SNR of 50 in the same application.
The Rosemount High-Signal system is comprised of the 8707 sensor which has
modified coils and magnetics and the 8712H High-Signal transmitter.
Note
In applications where very high levels of noise are a concern, it is recommended that a
dual-calibrated Rosemount High-Signal 8707 sensor be used. These sensors can be
calibrated to run at lower coil drive current supplied by the standard Rosemount
transmitters, but can also be upgraded by changing to the 8712H High-Signal transmitter.
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. This type of noise can be mitigated by
switching to the 37 Hz coil drive frequency.
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. The type of noise can be mitigated by switching to the 37
Hz coil drive frequency and enabling the digital signal processing.
Содержание Rosemount 8750W
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