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Installation
Orientation
The connector face of the unit must point in the forward direction. The "Fore" antenna is placed ½
meter ahead of the "Aft" Antenna on a line parallel to the axis of the vehicle. The DMS drawing,
with wire call outs, is located in Figure 3.
Mounting
Although a mounting plate is provided for a flat surface mount, the unit may also be adhesively
mounted at any of its surfaces. If high shock loads are expected (greater than 10G or repeated
shocks greater than 5G), appropriate shock mounting should be used to prevent damage. Vibration
isolation should be used if operation in 2.5G or greater vibration environments is expected.
GPS Antenna Mounting
The GPS antennas have magnetic mounts with two M 2.6 mounting holes and need an unobstructed
view of the sky to receive signals from GPS satellites. Both Antennas need a minimum 6" x 6"
ground plane. Nothing between or around the antennas can be higher than these ground planes.
Antenna spacing is directly related to the GPS heading accuracy. The antennas must be placed
within 1 cm of the spacing selected to maintain accuracy. The "Fore" antenna is placed ahead of
the "Aft" Antenna on a line parallel to the axis of the vehicle. This sensor allows antenna spacing
(in millimeters) from 0.3m up to 5m (See Appendix A). The larger the spacing, the more accurate
the GPS heading output will be. Unfortunately, with larger spacing values there is also an increased
risk of signal reflections between GPS antennas that can degrade accuracy.
Please Note: Adjustable antenna spacing was implemented for DMS-SGP02 sensors Rev I and
later. Earlier models require a fixed value for spacing that is set at the factory.
GPS Antenna Spacing (meters)
0.5m
1.0m
2.0m
5.0m
Environment
Avoid mounting sites that are subject to significant temperature changes over the duration of the
test. Temperature variation will induce noticeable rate sensor bias drift, which will result in
degraded attitude accuracy.
Power / Connectors
This unit has an internal regulator to allow operation over a wide voltage input range. Best
operation is obtained at either 12 or 24 VDC, although operation is fully satisfactory down to 10
VDC and up to 30 VDC. Power draw of the unit is about 4.9 Watts. Internal capacitors are
provided to remove a reasonable level of power line noise, however, capacitors should be added for
long power line wiring or if noise is induced from other loads on the circuit. The DMS power
system is isolated from the DMS signal system. The mating connector for the Power/Analog
Output Connector is a 25 Pin female D-Sub.
Watson Industries, Inc.
GPS Heading: Accuracy: Static
0.5° rms
0.25° rms
0.13° rms
0.07° rms
Figure 1 Antenna Spacing
4
DMS-SGP02 Rev K 03/22/2018
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