Instruction manual

Photogrammtery & Event Marker Page A-1

Photogram-

Photogrammtery & Event Marker

Photogrammetry (Event Marking) Interfaces

When the event [P] option is installed, the sensor can measure and record event times with

high accuracy. In order to store an event time in the sensor's memory, a trigger signal

must be applied to the appropriate connector located on the panel of the sensor; in the

sensor, this connector is pin 9 of serial port B. The photogrammetry feature allows the

event time to be stored in memory and downloaded using the HOSE program, or output by

using the $PASHS,NME,TTT command.

At the rising or falling edge (selectable) of the trigger signal, the time is recorded in the

sensor's nonvolatile external memory. The recorded time can be read by the downloading

(HOSE) program at a later time. The trigger signal can be set to the falling edge using the

$PASHS,PHE command.

The measured time is accurate down to 1 microsecond. This is a GPS time (currently

UTC + 11 seconds) and is recorded as the number of seconds since the start of the GPS

week (00:00 a.m. Sunday). The HOSE program reads the time and converts it to day

number, hours, minutes, seconds, and fractional seconds up to 6 digits. With each event

time, the sensor also records the site name. One example of the record is:

TEXA 4 21:30:19:430964

The photogrammetry time measures the event time relative to the sensor's GPS time. It

measures only the first event during the period between 2 GPS epochs. Refer to Figure

A.1. This allows use of mechanical switches without concern for contact bounces.

The sensor stores only one event time per data collection period. If more than one event

time is measured within a data collection period, the sensor records only the first one.

Figure A.1: Photogrammetry Time Measurement