Chapter 3 SPAN Operation
OEM7 SPAN Installation and Operation User Manual v14
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Figure 31: DMI to IMU Setup
DMI Data Collected on IMU
Typical DMI hardware generates wheel ticks constantly as the wheel rotates. When a DMI is connected to the
IMU, the wheel ticks are accumulated in the IMU. The accumulated wheel ticks, along with the raw IMU data,
are sent the OEM7 receiver though the serial communication line.
DMI Update Logic
DMI data is available through the
RAWDMI
log. The
RAWDMI
log can be used for applying DMI updates in
post-processing.
The SPAN filter uses sequential
RAWDMI
logs to compute a distance traveled between update intervals (1 Hz).
This information is used to constrain free inertial drift during times of poor GNSS visibility. The filter also contains
a state for modeling the circumference of the wheel as it may change due to hardware changes or environmental
conditions.
Information about how the DMI updates are being used is available in the
INSUPDATESTATUS
log.
Connect the DMI to the IMU
All DMI compatible IMUs accept RS-422 differential signals from the DMI.
IMU-IGM-A1 and IMU-IGM-S1 accept TTL level input pulses from a DMI through the AUX connector.
The IMU-FSAS accepts signals from 2 V to 6 V.
To connect a DMI to the IMU:
1. Install the SPAN system using the instructions in
OEM7 Receiver Card Installation
on page 31 or
2. Connect the wheel sensor to the IMU.
