Adding Timed Sensor Triggers

Use the EVENT IN and EVENT OUT connections to attach up to three sensor devices to an OEM7 receiver and then trigger the sensors based upon GPS time.

In this context a 'sensor' is any external device. The 'sensor' reference in the receiver is an object consisting of an Event_In and Event_Out pair of system strobes all linked by a sensor identifier.

You can send multiple trigger events marked with a user-specified ID and a GPS time to trigger the sensor. At the requested trigger time, the receiver outputs a user-specified pulse to the sensor and waits for a response pulse to indicate a sensor measurement (i.e. camera exposure). When this response is received, the SPAN system outputs a log with the inertial position/velocity/attitude and the ID of the event.

Configuring the Hardware

A sensor's trigger input is connected to a valid Event_Out and the sensor’s response output is connected to a valid Event_In. Three sensor slots are available for use, but may be limited to less depending on the hardware platform used.

Valid Event Inputs and Outputs for Timed Sensor Triggers

Valid Event Outputs	Valid Event Inputs
MARK1	MARK1
MARK2	MARK2
MARK3	MARK3
MARK4	MARK4

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.

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.

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 useful 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.