PNI FieldForce Trax - Manual (Page 29)

PNI Sensor Corporation DOC#1016505 r06
TRAX User Manual Page 25
Declination
The declination represents the heading difference between magnetic north and true
north, and needs to be entered if “True” is selected as the “North Reference”.
Declination varies primarily with location, although it also gradually changes over
time (years) for a given location. To find the declination for where the TRAX will be
used, go to http://www.ngdc.noaa.gov/geomagmodels/Declination.jsp .
Filter Taps
When operating the TRAX in Compass Mode, the TRAX will use a finite impulse
response (FIR) filter to effectively provide a stable heading reading. When operating
in AHRS Mode a completely different filtering method is used and the number of FIR
Taps is not relevant.
The number of taps (or samples) represents the amount of filtering to be performed.
Either 0, 4, 8, 16, or 32 taps may be selected, with zero taps representing no filtering.
Note that selecting a larger number of taps can significantly slow the time for the
initial sample reading and, if “Flush Filters” is selected, the rate at which data is
output. The default setting is 32.
The FIR filtering operates on a first-in, first-out (FIFO) basis. For example, with FIR
Taps set to 32, once the initial 32 samples are taken the next sample (#33) is included
in the filtering and the initial sample (#1) is dropped from the filtering.
Flush Filter
The Flush Filter setting is only relevant when in Compass Mode, as it affects how the
FIR filters are implemented. Flushing the FIR filter clears all the filter values so it is
necessary to fully repopulate the filter before a good reading can be given. For
example, if 32 FIR taps is set, then 32 new samples must be taken to provide a good
reading. It is particularly prudent to flush the filter if the Sampling Delay is set to a
non-zero value as this will purge old data. Note that flushing the filters increases the
delay until data is output, with the length of the delay being directly correlated to the
number of FIR taps. The default is not to Flush Filters.
6.4.2 Acquisition Settings
Acquisition Mode
When operating in Continuous Acquisition Mode, the TRAX continuously outputs
data to the host system. The rate is set by the Sample Delay. When operating in
Polled Mode, TRAX Studio simulates a host system and polls the TRAX for a single
measurement; but TRAX Studio makes this request at a fixed rate which is set by the
Polling Delay. In both cases data is continuously output, but in Continuous