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Event Marker Interface

What Event Latch trigger rates are supported by the Event Latch Interface?

The Event Latch Interface module will support triggering rates of up to one frame/ pulse per second.

Why do we need to use the Event Latch Interface?

The event pulse output by many cameras and other aerial survey sensors does not have sufficient power to trigger the GPS event latch circuitry. The even latch interface conditions and amplifies the pulse so that it can be successfully integrated with the GPS receiver. It eliminates the requirement of 3-6V DC with 50 Ohm load input impedance.

What sensors or devices have been tested with the Event Latch Interface?

Leica RC-30 cameras have been successfully tested with this module.

How do I use the Event Latch Interface?

Connect the LEMO connector to the EVT MKR/CAN connector located at the back panel of your SF-2050M GPS Receiver. Input is through a female BNC connector, where the center pin is the signal and outer shell is ground.

I used the Event Latch Interface, how do I obtain my Event positions?

Logging the 0xB4 binary message at a rate of “On Trigger” will output a message containing the time mark of when the trigger occurred. The position in the B1 records on both sides of the event must be interpolated by post mission software to obtain the exact position of the event NavCom’s StarPac is available for such a purpose.

How is the event latch interface powered?

The event latch interface is powered from the GPS receiver. There is no input or need to power it from an external source.

Does the event latch trigger on the rising or falling edge of the pulse?

The event latch triggers on the falling edge of the pulse. However, use of the Event Latch Interface will condition the pulse appropriately, so is able to accept either rising or falling edge configurations (a.k.a. active high or active low).

What is the minimum pulse width and voltage level required by the event latch interface?

The minimum pulse width is 10usec with input voltage logic high 4-5.5V DC and logic low 0-0.4V DC with minimum 4mA sink current.

What is the minimum pulse width and voltage level that must be output by a device for connection to the GPS receiver without using the event latch interface?

This information is also in the SF-3050 User Guide, and downloadable from NavCom’s web site. The minimum pulse width is 100nsec with input voltage 3-6V DC for high and 0 to 1.2V DC for low.

The time of an event is recorded to what precision?

The precision time of an event is 1µsec, but hardware delays (12µsec) are also associated with this precision, accumulating to a total system delay of ~13µsec. The precision will be incumbent upon the velocities experienced, but typically cancel out due to the consistency of the total delay.