User Manual
TRAX
Attitude & Heading Reference System (AHRS)
Table of Contents
1 COPYRIGHT & WARRANTY INFORMATION ................................................. 1
2 INTRODUCTION ......................................................................................... 2
3 SPECIFICATIONS ......................................................................................... 3
3.1 Characteristics & Requirements ........................................................... 3
3.2 Mechanical Drawings ............................................................................ 6
4 SET-UP ....................................................................................................... 8
4.1 Electrical Connections ........................................................................... 8
4.2 Installation Location .............................................................................. 9
4.2.1 Operate within the TRAX’s dynamic range .................................. 9
4.2.2 Locate away from changing magnetic fields ............................... 9
4.2.3 Mount in a physically stable location .......................................... 9
4.3 Mechanical Mounting ........................................................................... 9
4.3.1 Pitch and Roll Convention ............................................................ 9
4.3.2 Mounting Orientation ................................................................ 10
5 USER CALIBRATION .................................................................................. 12
5.1 Magnetic Calibration ........................................................................... 13
5.1.1 Full-Range Calibration ................................................................ 15
5.1.2 2D Calibration ............................................................................ 16
5.1.3 Limited-Tilt Calibration .............................................................. 17
5.1.4 Hard-Iron-Only Calibration ........................................................ 18
5.2 Accelerometer Calibration .................................................................. 18
5.2.1 Accel-Only Calibration................................................................ 19
5.2.2 Mag-and-Accel Calibration ........................................................ 20
6 OPERATION WITH TRAX STUDIO .............................................................. 21
6.1 Installation .......................................................................................... 21
6.2 TRAX Studio Header and Connecting to TRAX Studio ........................ 21
6.3 TRAX Studio Footer and Saving/Applying Settings ............................. 22
6.4 Configuration Tab ............................................................................... 23
6.4.1 General Settings ......................................................................... 24
6.4.2 Acquisition Settings .................................................................... 25
6.5 Calibration and the Calibration Tab .................................................... 26
6.5.1 Calibration Settings .................................................................... 27
6.5.2 Performing a Calibration ............................................................ 28
6.5.3 Calibration Results ..................................................................... 29
6.6 Test Tab ............................................................................................... 30
6.7 Log Data Tab ....................................................................................... 33
6.8 Graph Tab ............................................................................................ 34
6.9 System Log Tab ................................................................................... 35
PNI Sensor Corporation DOC#1016505 r06
TRAX User Manual Page i
7 OPERATION WITH PNI BINARY PROTOCOL ............................................... 36
7.1 Datagram Structure ............................................................................ 36
7.2 Parameter Formats ............................................................................. 37
7.2.1 Endianness ................................................................................. 37
7.2.2 Floating Point ............................................................................. 37
7.2.3 Signed Integer ............................................................................ 38
7.2.4 Unsigned Integer ........................................................................ 39
7.2.5 Boolean ...................................................................................... 39
7.3 Commands Overview .......................................................................... 40
7.4 Set-Up Commands .............................................................................. 41
7.4.1 Module Information ................................................................... 41
7.4.2 Module Configuration ................................................................ 41
7.4.3 Saving Settings ........................................................................... 46
7.5 Measurement Commands .................................................................. 46
7.5.1 Setting the Reference Magnetic Field Criteria ........................... 46
7.5.2 Data Acquisition Parameters ..................................................... 47
7.5.3 Data Components ...................................................................... 48
7.5.4 Making a Measurement ............................................................. 50
7.6 Calibration Commands........................................................................ 51
7.6.1 User Calibration Commands ...................................................... 51
7.6.2 Performing a User calibration .................................................... 53
7.6.3 Calibration Score ........................................................................ 53
7.6.4 Factory Calibration ..................................................................... 54
7.7 Compass Mode Commands ................................................................ 55
7.7.1 Switching Functional Mode ....................................................... 55
7.7.2 FIR Filters .................................................................................... 56
7.7.3 Power Down/Up ........................................................................ 58
PNI Sensor Corporation DOC#1016505 r06
TRAX User Manual Page ii
List of Figures
Figure 3-1: Typical Current Drawing During Application of External Power ......... 4
Figure 3-2: TRAX PCA Mechanical Drawing ........................................................... 6
Figure 3-3: Molex-to-Pigtail Cable Drawing, pn 12415 .......................................... 6
Figure 3-4: Molex-to-USB Cable Drawing, pn 13119 ............................................. 6
Figure 3-5: TRAX Enclosed Mechanical Drawing ................................................... 7
Figure 3-6: ODU-to-USB Cable Drawing, pn 13082 ................................................ 7
Figure 3-7: ODU-to-RS232 Cable Drawing, pn 13081 ............................................ 7
Figure 4-1: Positive & Negative Roll and Pitch Definition .................................... 10
Figure 4-2: TRAX Enclosed Mounting Orientations ............................................. 11
Figure 5-1: 12 Point Full-Range Calibration ......................................................... 15
Figure 5-2: Accelerometer Calibration Starting Orientations .............................. 20
Figure 7-1: Datagram Structure ........................................................................... 36
List of Tables
Table 3-1: Performance Specifications .................................................................. 3
Table 3-2: Absolute Maximum Ratings .................................................................. 4
Table 3-3: Electrical Requirements ........................................................................ 4
Table 3-4: I/O Characteristics ................................................................................. 5
Table 3-5: Environmental Requirements ............................................................... 5
Table 3-6: Mechanical Characteristics ................................................................... 5
Table 4-1: TRAX Pin Descriptions ........................................................................... 8
Table 5-1: Magnetic Calibration Mode Summary ................................................ 14
Table 5-2: 12 Point Full-Range Calibration Pattern ............................................. 16
Table 5-3: 12 Point 2D Calibration Pattern .......................................................... 17
Table 5-4: 12 Point Limited-Tilt Calibration Pattern ............................................ 17
Table 5-5: 6 Point Hard-Iron-Only Calibration Pattern ........................................ 18
Table 7-1: Port Configuration............................................................................... 36
Table 7-2: TRAX Command Set ............................................................................ 40
Table 7-3: Configuration Identifiers ..................................................................... 42
Table 7-4: Sample Points ...................................................................................... 44
Table 7-5: Component Identifiers ........................................................................ 48
Table 7-6: Recommended FIR Filter Tap Values .................................................. 56
PNI Sensor Corporation DOC#1016505 r06
TRAX User Manual Page iii
1 Copyright & Warranty Information
© Copyright PNI Sensor Corporation 2011. Revised March 2014.
All Rights Reserved. Reproduction, adaptation, or translation without prior written permission is prohibited, except
as allowed under copyright laws. For the most recent version of this manual, visit our website at www.pnicorp.com.
PNI Sensor Corporation
2331 Circadian Way
Santa Rosa, CA 95407, USA
Tel: (707) 566-2260
Fax: (707) 566-2261
Warranty and Limitation of Liability. PNI Sensor Corporation ("PNI") manufactures its TRAX products
(“Products”) from parts and components that are new or equivalent to new in performance. PNI warrants that each
Product to be delivered hereunder, if properly used, will, for one year following the date of shipment unless a
different warranty time period for such Product is specified: (i) in PNI’s Price List in effect at time of order
acceptance; or (ii) on PNI’s web site (www.pnicorp.com) at time of order acceptance, be free from defects in
material and workmanship and will operate in accordance with PNI’s published specifications and documentation
for the Product in effect at time of order. PNI will make no changes to the specifications or manufacturing processes
that affect form, fit, or function of the Product without written notice to the OEM, however, PNI may at any time,
without such notice, make minor changes to specifications or manufacturing processes that do not affect the form,
fit, or function of the Product. This warranty will be void if the Products’ serial number, or other identification
marks have been defaced, damaged, or removed. This warranty does not cover wear and tear due to normal use, or
damage to the Product as the result of improper usage, neglect of care, alteration, accident, or unauthorized repair.
THE ABOVE WARRANTY IS IN LIEU OF ANY OTHER WARRANTY, WHETHER EXPRESS, IMPLIED,
OR STATUTORY, INCLUDING, BUT NOT LIMITED TO, ANY WARRANTY OF MERCHANTABILITY,
FITNESS FOR ANY PARTICULAR PURPOSE, OR ANY WARRANTY OTHERWISE ARISING OUT OF
ANY PROPOSAL, SPECIFICATION, OR SAMPLE. PNI NEITHER ASSUMES NOR AUTHORIZES ANY
PERSON TO ASSUME FOR IT ANY OTHER LIABILITY.
If any Product furnished hereunder fails to conform to the above warranty, OEM’s sole and exclusive remedy and
PNI’s sole and exclusive liability will be, at PNI’s option, to repair, replace, or credit OEM’s account with an
amount equal to the price paid for any such Product which fails during the applicable warranty period provided that
(i) OEM promptly notifies PNI in writing that such Product is defective and furnishes an explanation of the
deficiency; (ii) such Product is returned to PNI’s service facility at OEM’s risk and expense; and (iii) PNI is satisfied
that claimed deficiencies exist and were not caused by accident, misuse, neglect, alteration, repair, improper
installation, or improper testing. If a Product is defective, transportation charges for the return of the Product to
OEM within the United States and Canada will be paid by PNI. For all other locations, the warranty excludes all
costs of shipping, customs clearance, and other related charges. PNI will have a reasonable time to make repairs or
to replace the Product or to credit OEM’s account. PNI warrants any such repaired or replacement Product to be
free from defects in material and workmanship on the same terms as the Product originally purchased.
Except for the breach of warranty remedies set forth herein, or for personal injury, PNI shall have no liability for any
indirect or speculative damages (including, but not limited to, consequential, incidental, punitive and special
damages) relating to the use of or inability to use this Product, whether arising out of contract, negligence, tort, or
under any warranty theory, or for infringement of any other party’s intellectual property rights, irrespective of
whether PNI had advance notice of the possibility of any such damages, including, but not limited to, loss of use,
revenue or profit. In no event shall PNI’s total liability for all claims regarding a Product exceed the price paid for
the Product. PNI neither assumes nor authorizes any person to assume for it any other liabilities.
Some states and provinces do not allow limitations on how long an implied warranty lasts or the exclusion or
limitation of incidental or consequential damages, so the above limitations or exclusions may not apply to you. This
warranty gives you specific legal rights and you may have other rights that vary by state or province.
PNI Sensor Corporation DOC#1016505 r06
TRAX User Manual Page 1
2 Introduction
Thank you for purchasing PNI Sensor Corporation’s TRAX attitude & heading reference system
(AHRS). The TRAX employs a proprietary Kalman filtering algorithm that intelligently fuses
PNI's patented Reference Magnetic Sensors with a 3-axis gyroscope and 3-axis accelerometer.
The result is an orientation device that provides accurate heading information under a wide
variety of conditions, including its ability to overcome errors normally caused by erratic motion
and/or changes in the local magnetic field. The advanced features of the TRAX make it ideal for
a variety of applications, including:
Unmanned Ground Vehicles (UGV) – Robots and Unmanned Conversions
Unmanned Underwater Vehicles (UUV) – Autonomous Gliders and ROV’s
We’re sure the TRAX will help you to achieve the greatest performance from your system.
Thank you for selecting the TRAX.
PNI Sensor Corporation DOC#1016505 r06
TRAX User Manual Page 2
Parameter
Value
AHRS
Mode
Heading
Accuracy2
2.0° rms
Resolution
0.1°
Attitude
Range
Pitch
± 90°
Roll
± 180°
Accuracy
2.0° rms
Resolution
0.01°
Compass
Mode
Heading
Static Accuracy3
0.3° rms
Resolution
0.1°
Repeatability
0.05° rms
Attitude
Range
Pitch
± 90°
Roll
± 180°
Static Accuracy
0.2° rms
Resolution
0.01°
Repeatability
0.05° rms
3 Specifications
3.1 Characteristics & Requirements
Table 3-1: Performance Specifications1
Footnotes:
1. Specifications are typical unless otherwise noted, and subject to change.
2. Assumes heading status is “1”. See Section 6.6 or Section 7.5.3 for a
discussion on heading status.
3. Assumes TRAX is motionless, the local magnetic field is clean relative to
user calibration, ≤65° of pitch, and after a Full-Range calibration has been
performed.
PNI Sensor Corporation DOC#1016505 r06
TRAX User Manual Page 3
Parameter
Minimum
Maximum
Units
Supply Voltage
-0.3
+10
VDC
Storage Temperature
-40
+85
°C
Parameter
Value
Supply Voltage
3.8 to 9 VDC
Communication Lines
High Level Input
2.4 V minimum
Low Level Input
0.6 V maximum
Output Voltage Swing
±5.2 V typ., ±5.0 V min.
Tx Output Resistance
300 Ω
Current Draw
AHRS Mode@ max.
sample rate
55 mA typical
Compass Mode @
max. sample rate
28 mA typical
During application of
external power
See Figure 3-1
Sleep Mode
0.5 mA typical
Table 3-2: Absolute Maximum Ratings
CAUTION:
Stresses beyond those listed above may cause permanent damage to the device.
These are stress ratings only. Operation of the device at these or other conditions
beyond those indicated in the operational sections of the specifications is not implied.
Table 3-3: Electrical Requirements
PNI Sensor Corporation DOC#1016505 r06
TRAX User Manual Page 4
Figure 3-1: Typical Current Drawing During Application of External Power
Parameter
Value
Communication Interface
RS232 UART & USB
Communication Protocol
PNI Binary
Communication Rate1
2400 to 921,600 baud
Maximum Data Output Rate
≈30 samples/sec
Parameter
Value
Operating Temperature1
-40C to +85C
Storage Temperature
-40C to +85C
Parameter
Value
Dimensions
(l x w x h)
TRAX Enclosed
6.4 x 5.9 x 2.3 cm
TRAX PCA
3.5 x 4.3 x 1.0 cm
Weight
TRAX Enclosed
75 gm
TRAX PCA
7 gm
Connector
TRAX Enclosed
7 pin ODU, pn K20L0C-P07LCC0-520S
TRAX PCA
9-pin Molex, pn 53780-0970
Table 3-4: I/O Characteristics
Footnote:
1. The TRAX can operate up to 921,600 baud, but native RS232 is limited to
115,200 baud.
Table 3-5: Environmental Requirements
Footnote:
1. To meet performance specifications across this range, recalibration will be
necessary as the temperature varies.
Table 3-6: Mechanical Characteristics
PNI Sensor Corporation DOC#1016505 r06
TRAX User Manual Page 5
3.2 Mechanical Drawings
Figure 3-2: TRAX PCA Mechanical Drawing
Figure 3-3: Molex-to-Pigtail Cable Drawing, pn 12415
Figure 3-4: Molex-to-USB Cable Drawing, pn 13119
PNI Sensor Corporation DOC#1016505 r06
TRAX User Manual Page 6
Figure 3-5: TRAX Enclosed Mechanical Drawing
Figure 3-6: ODU-to-USB Cable Drawing, pn 13082
Figure 3-7: ODU-to-RS232 Cable Drawing, pn 13081
PNI Sensor Corporation DOC#1016505 r06
TRAX User Manual Page 7
Pin #1
TRAX Enclosed
TRAX PCA
7 Pin ODU
Connector1
9 Pin Molex
Connector
Pigtailed Cable
Wire Color
1
USB D+
Ground
Black
2
RS232 +5 VDC
USB +5 VDC
Gray
3
RS232 Tx
Ground
Green
4
RS232 Rx
Not Connected
Orange
5
USB +5 VDC
USB D–
Violet
6
USB D– A
USB D+
Brown
7
Ground
RS232 Tx
Yellow
8 RS232 Rx
Blue 9
RS232 +5 VDC
Red
4 Set-Up
This section describes how to configure the TRAX in your host system. To install the TRAX
into your system, follow these steps:
Make electrical connections to the TRAX.
Evaluate the TRAX using the TRAX Studio program, or a binary terminal emulation
program, such as RealTerm or Tera Term, to ensure the TRAX is working properly.
Choose a mounting location.
Mechanically mount the TRAX in the host system.
Perform a user calibration.
4.1 Electrical Connections
The enclosed version of TRAX incorporates a 7 pin ODU connector, part number K20L0CP07LCC0-560S, which mates with ODU part S20L0C-T07MCC0-560S or equivalent. The
TRAX PCA incorporates a 9 pin Molex connector, part number 53780-0970, which mates
with Molex part 51146-0900 or equivalent. The pin-out for both is given below in Table 4-1.
Table 4-1: TRAX Pin Descriptions
Footnote:
1. For the TRAX Enclosed, pin #1 is the first pin to the left of the key, and
numbering runs counter-clockwise from pin #1, with pin #7 in the middle.
For the TRAX PCA, pin #1 is indicated on Figure 3-2.
After making the electrical connections, it is a good idea to perform some simple tests to
ensure the TRAX is working as expected. See Section 6 for how to operate the TRAX with
TRAX Studio or Section 7 for how to operate the TRAX using PNI’s binary protocol.
PNI Sensor Corporation DOC#1016505 r06
TRAX User Manual Page 8
4.2 Installation Location
The TRAX’s wide dynamic range and sophisticated algorithms allow it to operate in many
environments. For optimal performance however, you should mount the TRAX with the
following considerations in mind:
4.2.1 Operate within the TRAX’s dynamic range
The TRAX can be user calibrated to correct for static magnetic fields created by the host
system. However, each axis of the TRAX has a calibrated dynamic range of ±125 µT. If
the total field exceeds this value for any axis, the TRAX may not perform to
specification. When mounting the TRAX, consider the effect of any sources of magnetic
fields in the host environment that, when added to Earth’s field, may take the TRAX out
of its dynamic range. For example, large masses of ferrous metals such as transformers
and vehicle chassis, large electric currents, permanent magnets such as electric motors,
and so on.
4.2.2 Locate away from changing magnetic fields
While the TRAX can compensate for transient changes in the local magnetic field, it is
good design practice to keep the TRAX away from sources of local magnetic distortion
that knowingly will change with time; such as electrical equipment that will be turned on
and off, or ferrous bodies that will move.
4.2.3 Mount in a physically stable location
Choose a location that is isolated from persistent vibration or other dynamic motion. The
TRAX can provide accurate headings while experiencing intermittent dynamic motion,
such as vibration or quick heading changes. But if this is persistent the TRAX will have
difficulty holding an accurate heading over extended periods of time.
4.3 Mechanical Mounting
The TRAX is factory calibrated with respect to its mounting holes. It must be aligned within
the host system with respect to these mounting holes. Ensure any stand-offs or screws used
to mount the TRAX are non-magnetic. Refer to Section 3.2 for dimensions, hole locations,
and the reference frame orientation.
4.3.1 Pitch and Roll Convention
The TRAX utilizes Euler angles as the primary method for providing orientation data,
although quaternions outputs also are available. The Euler angles are the common
PNI Sensor Corporation DOC#1016505 r06
TRAX User Manual Page 9
method used for aircraft orientation, where the outputs are heading, pitch and roll. When
using Euler angles in aviation, roll is defined as the angle rotated around an axis through
the center of the fuselage, while pitch is rotation around an axis through the center of the
wings. These rotations are dependent on each other since the axes of rotation move with
the plane.
As shown in Figure 4-1, for the TRAX a positive pitch is when the front edge of the
board is rotated upward and a positive roll is when the right edge of the board is rotated
downward. The order of rotation is given as heading, pitch, and then roll.
Figure 4-1: Positive & Negative Roll and Pitch Definition
4.3.2 Mounting Orientation
The TRAX can be mounted in 16 different orientations, as shown for the enclosed
version of the TRAX in Figure 4-2. All reference points are based on the silk-screened
arrow on the cover of the enclosed version of the TRAX, or on top side of the TRAX
PCA board. The orientation should be programmed in the TRAX using the
Configuration Tab in TRAX Studio or using the kSetConfig command and the
kMountingRef setting in the PNI Protocol, as described in Section 7.4.2. The default
orientation is “STD 0°”.
PNI Sensor Corporation DOC#1016505 r06
TRAX User Manual Page 10
Figure 4-2: TRAX Enclosed Mounting Orientations
PNI Sensor Corporation DOC#1016505 r06
TRAX User Manual Page 11
5 User Calibration
The magnetic sensor in the TRAX is calibrated at PNI’s factory in a magnetically controlled
environment. However sources of magnetic distortion positioned near the TRAX in the user’s
system will distort Earth’s magnetic field and should be compensated for in the host system with
a user calibration. Examples of such sources include ferrous metals and alloys (ex. iron, nickel,
steel, etc.), batteries, audio speakers, current-carrying wires, and electric motors. Compensation
is accomplished by mounting the TRAX in the host system and performing a user calibration. It
is expected the sources of magnetic distortion remain fixed relative to the TRAX‘s position
within the host system. By performing a calibration, the TRAX identifies the local sources of
magnetic distortion and negates their effects from the overall reading to provide an accurate
heading.
As with the magnetic sensor, the accelerometer in the TRAX is calibrated at PNI’s factory. But
the accelerometer gradually changes over time, and the user either will need to periodically
perform a user accelerometer calibration or return the unit to PNI for recalibration. As a rule-ofthumb, the accelerometer should be recalibrated every 6 to 12 months. Unlike a magnetic
calibration, the accelerometer may be calibrated outside the host system. Accelerometer
calibration is more sensitive to noise or hand jitter than magnetic calibration, especially for
subsequent use at high tilt angles. Because of this, a stabilized fixture is suggested for
accelerometer calibration, although resting the unit against a stable surface often is sufficient.
Key Points:
Magnetic calibration:
o Requires incorporating the TRAX into the user’s host system such that the
magnetic components of the user’s system can be compensated for.
o Allows for 4 different methods of calibration. Full-Range Calibration provides
the highest heading accuracy, but requires ≥45° of pitch. 2D and Limited-Tilt
Calibration allow for good calibration when the range of allowable motion is
limited. Hard-Iron-Only Calibration updates the hard-iron compensation
coefficients with a relatively easy procedure.
Accelerometer calibration requires rotating the TRAX through a full sphere of coverage,
but it does not need to be incorporated in the user’s system during calibration.
If the TRAX will experience different states during operation, such as operating with a
nearby shutter sometimes closed and sometimes open, or operating over a broad
temperature range, then different sets of calibration coefficients can be saved for the
various states. Up to 8 magnetic calibration coefficient sets and 3 accelerometer
calibration coefficient sets can be saved.
PNI Sensor Corporation DOC#1016505 r06
TRAX User Manual Page 12
5.1 Magnetic Calibration
Two fundamental types of magnetic distortion exist: hard-iron and soft-iron. These are
discussed in the following paragraphs, plus a discussion on how temperature also affects
magnetic fields and other considerations. For more information on magnetic distortion and
calibration, see PNI’s white paper “Local Magnetic Distortion Effects on 3-Axis
Compassing” at PNI’s website (http://www.pnicorp.com/technology/papers).
Hard-Iron Effects
Hard-iron distortions are caused by permanent magnets and magnetized objects in
close proximity to the sensors. These distortions add or subtract a fixed component to
each axis of the magnetic field reading. Hard-iron distortions usually are unchanging
and in a constant location relative to the sensors, for all heading orientations.
Soft-Iron Effects
Magnetically “soft” materials effectively bend the magnetic field near them. These
materials have a high magnetic permeability, meaning they easily serve as a path for
magnetic field lines. Unlike hard-iron effects, soft-iron effects do not increase or
decrease the total field in the area. However, the effect of the soft-iron distortion
changes as the host system’s orientation changes. Because of this, it is more difficult
to compensate for soft-iron materials.
Temperature Effects
While the hard-iron and soft-iron distortion of a system may remain quite stable over
time, normally the distortion signature will change over temperature. As a general
rule, the hard-iron component will change 1% per 10°C temperature change. Exactly
how this affects heading depends on several factors, most notably the hard-iron
component of the system and the inclination, or dip angle.
Consider the example of a host system with a 100 µT hard-iron component. This is a
fairly large hard-iron component, but not completely uncommon. A 10°C
temperature change will alter the magnetic field by ~1 µT in the direction of the hardiron component. Around San Francisco, with an inclination of ~60°, this results in up
to a couple of degrees of heading change over 10°C.
Consequently, no matter how stable a compass is over temperature, it is wise to
recalibrate over temperature since the magnetic signature of the host system will
change over temperature. The TRAX helps accommodate this issue by allowing the
user to save up to 8 sets of magnetic calibration coefficient sets, so different
calibration coefficients can be generated and loaded at different temperatures.
PNI Sensor Corporation DOC#1016505 r06
TRAX User Manual Page 13
Calibration
Mode
Static Accuracy in
Compass Mode
Tilt Range
during Cal
Minimum
Recommended
# of Samples
Allowable
Range of #
of Samples
Full-Range
0.3° rms
>±45°
12
10 – 18
2D Calibration
<2°
<±5°
12
10 – 18
Limited-Tilt
<2° over 2x tilt range
±5° to ±45°
12
10 – 18
Hard-Iron-Only
Restores prior
accuracy
>±3°
6
4 - 18
Other Considerations
Unlike a compass, such as PNI’s TCM module, the TRAX is an AHRS and as such it
can compensate for transient changes in the local magnetic field. However, the
TRAX will work best if it is kept away from dynamic magnetic fields. For example,
if there is an electric motor is in the host system that will be turning on and off during
TRAX operation, then mount the TRAX far away from the motor such that the
motor’s state does not affect the heading when TRAX is in Compass Mode.
Alternatively, TRAX can store up to 8 different sets of magnetic calibration
coefficients, so in the case of the motor, generate and use one set of magnetic
calibration coefficients for when the motor is off and another set for when it is on.
The main objective of a magnetic user calibration is to compensate for hard-iron and softiron distortions to the magnetic field caused by components within the user’s host system.
To that end, the TRAX needs to be mounted within the host system and the entire host
system needs to be moved as a single unit during a user calibration. The TRAX allows the
user to perform a calibration only in a 2D plane or with limited tilt, but provides the greatest
accuracy if the user can rotate through 360° of heading and at least ±45°of tilt.
The following subsections provide instructions for performing a magnetic calibration of a
TRAX system. Several calibration mode options exist, as summarized in Table 5-1. To meet
the accuracy specification, the number of samples should be the “Minimum Recommended”
value, or greater. Calibration may be performed using TRAX Studio or using the PNI binary
protocol, and up to 8 sets of magnetic calibration coefficients may be saved. The
recommended calibration patterns described in the following sub-sections provide a good
distribution of sample points. Also, PNI recommends the location of the TRAX remain fairly
constant while only the orientation is changed.
Table 5-1: Magnetic Calibration Mode Summary
Before proceeding with a calibration, ensure the TRAX is properly installed in the host
system. The device should be installed as discussed in Section 4, and the software should be
PNI Sensor Corporation DOC#1016505 r06
TRAX User Manual Page 14
properly configured with respect to the mounting orientation, Endianness, north reference,
etc.
Section 6.5 outlines how to perform a calibration using TRAX Studio, while Section 7.6.2
provides a step-by-step example of how to perform a calibration using the PNI protocol.
5.1.1 Full-Range Calibration
A Full-Range Calibration is appropriate when the TRAX can be tilted ±45° or more. This
method compensates for hard and soft-iron effects in three dimensions, and allows for the
highest accuracy readings. The recommended 12 point calibration pattern is a series of 3
circles of evenly spaced points, as illustrated in Figure 5-1 and listed in Table 5-2. The
pitch used in the second and third circles of the calibration should at least match the
maximum and minimum pitch the device is expected to encounter in use.
Figure 5-1: 12 Point Full-Range Calibration
Note: While Figure 5-1 shows the location of the device changing, this is for illustration purposes and
it is best for the location of the device to remain constant while only the orientation is changed.
PNI Sensor Corporation DOC#1016505 r06
TRAX User Manual Page 15
Loading...