If the time duration of the sand timer is defined as when the first
grain of sand lands
on the bottom, until the last grain of sand lands on the pile of sand on
the bottom,
maybe an optical circuit may sense the passing and interruption with a
light beam.
Possibly the optical sensor mounted in the restricted center could sense
the
first grain starting to pass and when the last grain has passed.
That my change the definition, but it should be repeatable.
The acoustic approach has merit. I could then apply some DSP and more
test equipment.
Much easier than listening to the grass grow.
I personally like definitive starts and stops, to stay within my
attention span.
Stan, W1LE
Bob Camp wrote:
Hi
Even defining when the sand timer is "done" is not a real simple thing. Waiting for that very last particle to drop may not be the best approach.
Bob
On Mar 5, 2010, at 9:20 AM, Tom Holmes, N8ZM wrote:
tvb...
Not to kick sand in your face, but it seems that in order for your automated
turn-over device to work, as well as to accurately measure the time
intervals, you would need a means to determine when the sand quits flowing.
Possibly an accelerometer or microphone, with the added benefit of being
able to hear the close-in phase noise.
I admire your dedication to monitoring the hour long periods of the sand
timer so diligently. Truly a time-nut!
Regards,
Tom Holmes, N8ZM
Tipp City, OH
EM79xx
-----Original Message-----
From: [email protected] [mailto:[email protected]] On
Behalf Of Tom Van Baak
Sent: Friday, March 05, 2010 1:44 AM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] nubie querie
In the last slide you show a sand timer. Do you have accuracy data for
it?
Hi Brooke,
The past 3 hours the "one hour" timer measures 56:24,
56:19, and 56:30. That's at 67 F room temp. Somewhere
I have enough clean data to compute the ADEV; it's more
stable than accurate.
It also has a tempco (one day when my wife wasn't looking
I collected data inside the kitchen refrigerator, and oven).
I would guess it has very little dependence on barometric
pressure or humidity since all the sand is sealed inside the
blown glass bulb.
Eventually I will mechanically automate the hourly turn-over
and get 24x7 long-term data. If I also model the tempco it
may be possible to temperature compensate the rate error.
I don't know where the flicker floor will be. My prediction is
this hour-glass will gradually speed up as the glass or the
sand slowly wear over time.
/tvb
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