Synchronizing External Equipment

A SPAN system allows you to synchronize with external equipment.

All SPAN-enabled receivers accept input pulses (events). Each event signal can be configured for positive or negative polarity. Time, or a solution (position, velocity, attitude), can be generated and output with each input pulse.

Configuring an Input Strobe

SPAN systems have several input strobes. The input strobes apply an accurate GNSS time to the rising, or falling, edge of an input pulse called an event. For each event, an accurate position, velocity or attitude solution is also available. Each input strobe is usually associated with a separate device, therefore different solution output lever arm offsets can be applied to each strobe.

Each input strobe can be configured using the EVENTINCONTROL command for the following parameters:

Polarity:
When polarity is set to positive, events trigger on the rising edge. When polarity is set to negative, events trigger on the falling edge.

Time Bias (t_bias):
A constant time bias in nanoseconds can be applied to each event pulse. Typically this is used to account for a transmission delay.

Time Guard (t_guard):
The time guard specifies the minimum number of milliseconds between pulses. This is used to coarsely filter the input pulses.

The time of the input pulses is available from the MARK1TIME, MARK2TIME, MARK3TIME and MARK4TIME log. The solution synchronous with the event pulses is available from the MARK1PVA, MARK2PVA, MARK3PVA and MARK4PVA log. The logs required for input strobes are:

LOG MARK1TIMEB ONNEW
Output time for every pulse received.

LOG MARK1PVAB ONNEW
Output time, position, velocity and attitude for every pulse received at the location specified by the SETINSTRANSLATION command and SETINSROTATION command.

The above example is for the MARK1 event input. The minimum detectable pulse duration must be greater than or equal to 1 microsecond.

The input signal levels are 3.3 V to 0 V. Signal voltages outside these bounds damage the receiver.