Chapter 3 SPAN Operation
OEM7 SPAN Installation and Operation User Manual v14
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3.6.2 Configuring the Software
Sensor objects are defined by using the
SETUPSENSOR
command. This command allows the Event_In and
Event_Out lines to be specified as well as some parameters for the outgoing and incoming signals.
After configuring a sensor using the
SETUPSENSOR
command, any other commands that affect the
selected event lines will disturb this functionality. For example, if MARK2 Out is selected for a sensor,
but later the
EVENTOUTCONTROL
command is sent, the
EVENTOUTCONTROL
command will
reconfigure the properties of the MARK2 line.
3.6.3 Using Timed Event Pulses
When sensors have been connected and configured, use the
TIMEDEVENTPULSE
command to queue events
on the system.
TIMEDEVENTPULSE
specifies the sensors that are affected, the GPS time for the desired
event (in weeks and seconds), and an event ID. You can queue 10 unprocessed events at a time. Any time input
specified via this command must occur at least 1 second after the command is entered.
The timing accuracy of the
TIMEDEVENTPULSE
output is 2 milliseconds.
3.6.4 Recording Incoming Sensor Events
After a
TIMEDEVENTPULSE
is sent, the system can be configured to accept an incoming pulse from the
sensor in order to produce a time and ID tagged inertial solution associated to that event. This is optional and use-
ful if a sensor provides a measurement TOV pulse. The produced log is a TAGGEDxMARKPVA where the 'x' is
the Event_In line associated with that sensor (via the
SETUPSENSOR
command).
For example, if the
SETUPSENSOR
command specifies SENSOR1 to use MARK1 in as the input event then a
TAGGEDMARK1PVA log will be produced when any pulses on that line are observed. In this case the
TAGGEDMARK1PVA log should be requested ONNEW to capture the data.
3.7 Distance Measurement Instrument
A Distance Measurement Instrument (DMI) can provide additional accuracy and reliability to a NovAtel SPAN
solution.
Typically, a DMI measures the distance traveled and represents the measurement using digital pulses. For a
land vehicle, where a DMI is also known as a wheel sensor, the pulses are referred to as wheel ticks. If the
pulses are accumulated and the size of the wheel known, a displacement of the wheel over time can be cal-
culated. The SPAN system takes in a DMI input and applies a displacement update to the GNSS+INS Kalman
filter in order to constrain the position error growth during GNSS outages. SPAN also automatically estimates
the size of the wheel to mitigate small changes in the size of the wheel due to hardware changes or envir-
onmental conditions.
A DMI with a higher accuracy will have more wheel ticks per revolution. For example, assume a wheel with a cir-
cumference of 2 meters and a DMI rated for 1000 ticks per revolution. The DMI will output 1000 pulses per com-
plete revolution of the wheel. The resulting precision will be 0.002 m/tick. Given the same wheel, but a DMI rated
for 10 ticks per revolution, the resulting precision will be 0.2 m/tick.
3.7.1 DMI Communication
Quadrature encoding is a widely used DMI data transmission method. Quadrature encoding uses two channels.
This method allows for the directionality of the DMI to be determined, resulting in a more stable DMI update to
the SPAN solution when compared to a single channel configuration. Quadrature encoding is supported on
NovAtel products using differential signal pairs per channel. The differential pair improves robustness in chal-
lenging electrical environments.
