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Your DC magnetic tracker
will operate as specified
for many years to come, provided
you take a few straightforward
steps to minimize metallic
distortion (inaccurate measurements)
and environmental noise (jittery
data).
Some steps are as simple
as changing your measurement
rate, adjusting filters, or
not mounting the transmitter
/ sensors on metallic platforms.
Others may require the use
of our metal detector software
utility or of our Environmental
Analyzer.
How
to Minimize Metallic Distortion
Generally, there are three
ways to avoid metallic distortion:
- Use a DC magnetic tracker
- Change tracker measurement
rate
- Move away from the metal
object
DC Tracker
By choosing a DC
magnetic tracker from Ascension,
you have made the best decision
for great tracking performance
in real world environments.
Ascension transmitters emit
a series of steady DC fields
that do not
continuously generate eddy
currents in nearby metals.
This enables them to operate
accurately in workspaces full
of common conductive metals,
such as aluminum, non-magnetic
stainless steel (300 series),
zinc, nickel, bronze, tin
and brass.
AC trackers, on the other
hand, continuously generate
eddy currents in nearby conductive
metals. Eddy currents are
the phenomenon that badly
distorts measurements in trackers
that emit AC electromagnetic
fields, such as Polhemus'
FasTrak, IsoTrak, Patriot
and Liberty trackers.
Gernerally, DC trackers are
5 times less susceptible to
conductive-metal distortion
than AC trackers. This means
that the accuracy of an AC
tracker in real world application
in which conductive metals
are present will be 5 times
worse than specified on paper.
In one recent test, a 12-inch
plate of non-magnetic steel
was introduced to the workspace
of an AC and a DC tracker.
The metal produced errors
of 100 degrees and 5 inches
in the AC tracker. No discernable
errors were detected in the
DC tracker.
DC trackers typically perform
as specified in all kinds
of environments. Although
affected, DC trackers are
less susceptible to errors
caused by the presence of
ferrous metals, such as iron
and carbon steel.
Change Tracker Measurement
Rate
DC trackers nominally track
sensor motion at 86-105 measurements
per second. At this rate,
the tracker will not see low
conductive, low permeability
metals such as 300 series
stainless steel or nickel.
In the presence of highly
conductive metals, such as
aluminum, you can reduce metal
errors to zero simply by decreasing
the DC tracker measurement
rate. Experimenting with measurement
rates will let you choose
the right rate for your application.
Watch out for carbon
steel and iron!
Changing the measurement
rate will not have a positive
effect when in the presence
of low conductive, high permeable
metals such as carbon steel.
In this workspace, the best
approach is to move away from
its distorting effects. See
below.
Tools to Visualize Metallic
Hot Spots
Ascension's Environmental
Analyzer
is a valuable tool to
alert you to the presence
of distorting metal. You
can use it to graphically
display metallic hot spots
in your workspace so you
can adjust parameters
or re-locate transmitter/sensors.
Environmental Analyzer |
It's simple to use and available
to qualified customers simply
by contacting your sales manager
at the following e-mail address:
productsales@ascension-tech.com
How
to Minimize Noise Interference
NEW
Noise-Reduction
Software, Noise
X, Automatically
Detects Optimal Operating
Frequency for your Tracking
Environment
Ascension now offers
a powerful new software
program that will run
your tracker in a mode
that measures any interfering
noise in the environment
and determines the best
tracker measurement
rate to reduce jitter
in measurements. This
noise reduction program
is available for all
Ascension RS232 and
ISA trackers: Flock
of Birds, miniBIRD,
Nest of Birds, pcBIRD
and MotionStar Wired.
»
Click
here to download
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If you detect jitter in tracker
measurements, you may be operating
in a workspace in which noise
in the 60Hz bandwidth is present.
One way of dealing with this
noise is to change tracker
filter settings. These settings
are adjustable to let you
control the type and amount
of filtering to be applied
to your measurements.
If you need to reduce noise
to a minimum, consider employing
our default filters: a wide
band notch AC filter and an
adaptive DC filter. These
filters will squelch noise
but should be employed carefully.
Over application will add
lag to tracker outputs, which
may or may not be accaptable
to you. Another good optioin
that does not adversely affect
lag is to employ a narrow
AC notch filter. See your
User's Manual for more information
about changing filter settings
to reduce tracker noise.
You can also use the Environmental
Analyzer to
scan your workspace for high
amounts of electronic noise
that might interfere with
tracker measurements. In addition
to scanning for noise, the
Analyzer will recommend
the best frequency to run
your tracker. Customers report
dramatic improvements in data
quality in noisy environments
simply by adjusting to the
measurement recommended by
the Analyzer.
For more information about
using the Analyzer
to limit noise in your measurements,
contact:
productsales@ascension-tech.com
If you are not fully satisfied
with the performance of your
tracker please contact our
Technical
Support Group:
Telephone: 802-893-6657, Extensions
19 & 14
E-mail: techsupport@ascension-tech.com
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