[time-nuts] A real world project need for timing accuracy...

Robert Atkinson robert8rpi at yahoo.co.uk
Tue Nov 2 03:36:30 EDT 2010


Hi Michael,
I have a couple of Trimble Palisade receivers (replaced by the Accutime). These have a timestamp input. you could use a pair, one at each end with the timestamp trigger connected to the skyscreen. log the data locally (PIC or what ever) and then post process the time stamps. I''ll have to check the resolution of the Palisade. You could do something similar with a simple GPS, external TIC and logger.
 
Robert. G8RPI

--- On Tue, 2/11/10, Michael Baker <mpb45 at clanbaker.org> wrote:


From: Michael Baker <mpb45 at clanbaker.org>
Subject: [time-nuts] A real world project need for timing accuracy...
To: time-nuts at febo.com
Date: Tuesday, 2 November, 2010, 0:03


   Timenutters--
   I appreciate the feedback for implementing my
   ballistic field measurement project but I think
   there is some misunderstanding of what the goal is.
   For instance, it is not practical to find 800 meters
   of coax and trench it in out to the downrange target.
   This system needs to be relatively portable so it
   can be set up at any given shooting range.
   I need to determine: A) down-range velocity of the
   still super-sonic projectile, B) time of flight and
   C) shot-group size.
   Measuring down-range shot-group size with an array of
   ultrasonic sensors is pretty straightforward. I can
   do all the computation with a $6 microprocessor and
   send the X/Y coordinates back to the laptop at the
   shooting bench with a simple RF link.  Down-range
   velocity is easily determined with a set of sky-screens
   and the results also sent back via an RF link.
   Time-of-flight is much more problematic to determine
   but the plan is to determine the elapsed time between
   the moment the projectile passes over the muzzle skyscreen
   and the moment of passing over the downrange skyscreen.
   This means syncing the 10 MHz clocks at both ends together.
   I guess the crux of my question to the time-nuts gang
   is what is the easiest (cheapest!!) way to do this.
   For a number of years I have been using an ultrasonic
   shot-group size measurement system made by Oehler
   Research.  It can resolve individual shot placement
   to within 1 cm.  Some less expensive systems that
   use fewer sensors can only resolve to +/- 2 cm. The
   Oehler Research system also determines time of flight.
   The problem is that these systems all use a cable
   to connect back to the equipment at the shooting bench.
   I am trying to find a way to synchronize/coordinate
   a downrange 10 MHz clock to the "master" 10 MHz system
   clock at the shooting bench without spending hundreds
   of $$ doing it.  It is not too big a problem to process
   all of the signals from the downrange skyscreens and the
   ultrasonic shot-group sensors and telemeter the results
   back to the shooting bench.
   However, time-of-flight info (via an RF link requires
   that I sync the 10MHz clocks at both ends together.
   Use of GPS receivers seems to be the most likely way
   to do this but how do I keep the cost and complexity
   down?
   Thanks in advance for any feedback on the matter!
   Mike Baker
   ---------------------
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