DMI Connected to a PwrPak7

A DMI can be used with any SPAN enabled PwrPak7 receiver. This includes PwrPak7 receivers with an internal IMU (such as a PwrPak7D-E1) or PwrPak7 receivers with an external IMU.

When using a PwrPak7 with an external IMU, the DMI can be connected to the PwrPak7 or the IMU. If connecting the DMI to the IMU, refer to DMI Connected to an IMU.

The PwrPak7 can accept DMI data from only one DMI. If connecting the DMI to the PwrPak7, do not connect a second DMI to the external IMU.

Figure: DMI to PwrPak7 Setup shows an overview of a DMI connected to a PwrPak7.

DMI to PwrPak7 Setup

The DMI connections are A+, A-, B+, B- and GND for quadrature or A+, A- and GND for single channel.

DMI Data Collected on the PwrPak7

Typical DMI hardware generates wheel ticks constantly as the wheel rotates. The PwrPak7 interface is configured to accumulate wheel tick counts at a rate of 1 Hz.

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 a PwrPak7

The PwrPak7 DMI inputs are RS-422 differential inputs. Refer to Table: PwrPak7 Wheel Sensor Input Signal Levels for the required input voltages.

To connect a DMI:

  1. Connect the PwrPak7 All I/O Cable, or custom interface cable, to the HD26 COM PORT connector on the PwrPak7.

    For information about creating a custom interface cable, see PwrPak7 All I/O Cable.

  2. Connect the wheel sensor wires on the interface cable to the DMI.

    For a quadrature configuration, connect the DMI to the Wheel Sensor A+, Wheel Sensor A-, Wheel Sensor B+, Wheel Sensor B- and GND wires.
    For a single channel configuration, connect the DMI to the Wheel Sensor A, Wheel Sensor A- and GND wires.

  3. Connect an external power supply to the DMI.

    The power required for the DMI depends on the DMI used. Refer to the DMI user documents for more information.

Configure a DMI

  1. Send the following command to enable a DMI on the PwrPak7 wheel sensor inputs.

    DMICONFIG DMI1 ENABLE ENCLOSURE

  2. Send the following commands to log the DMI data.

    LOG DMICONFIGA ONCHANGED

    LOG RAWDMIA ONNEW

    LOG INSUPDATESTATUSA ONNEW

  3. Check the RAWDMI log to ensure the DMI is producing data.

  4. Check the INSUPDATESTATUS log to ensure the DMI is being used in the SPAN solution.

If there is no DMI data being produced or the DMI status is not USED, refer to DMI Troubleshooting.

For more information, see the DMICONFIG command, RAWDMI log and INSUPDATESTATUS log.