Michael
Can you tell us the expected maximum and minimum time duration you
want to measure and the measurement resolution you require? At
present we are just guessing, especially re the latter.
DaveB, NZ
----- Original Message -----
From: "Michael Baker" <[email protected]>
To: <[email protected]>
Sent: Tuesday, November 02, 2010 1:03 PM
Subject: [time-nuts] A real world project need for timing accuracy...
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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