PSN-L Email List Message

Subject: Re: Modified sound card and datalogging and geophones
From: BOB BARNS royb1@...........
Date: Fri, 22 Jul 2005 10:42:24 -0400

ChrisAtUpw@....... wrote:
> In a message dated 22/07/2005, royb1@........... writes:
>     Doug,
>        For a "ground-pinger": make a fitting to attach a bicycle pump to
>     the
>     screw cap on a large plastic (one liter?) soda-pop bottle.  Bury the
>     bottle down to the neck (or deeper) and pump until the bottle
>     fails.  (I
>     don't know how much pressure these things will stand.)
> Hi Bob,  
>     You could fit a car tyre type valve into the cap and use a foot 
> pump. I suspect that the bursting point will be quite temperature 
> sensitive. It might be OK to pump it up to 100 psi or more and then jab 
> the bottle with a knife on a long handle? 

    I agree that the bursting point would be temperature sensitive but I 
can't guess if that would be disabling.  The ground temperature at one 
location should be relatively constant for successive shots although 
different location would see different temperatures.
   A jab with a knife would probably result in a slower release of 
energy (than the bursting of a bottle) and hence a smaller peak pulse.

>        This scheme meets your criteria except the "multiple impact" and
>     possibly the "ping instead of thump" but it's hard to beat for cheap.
>        A glass bottle might be more ping-like but would leave a hazardous
>     residue. 
>     That would need an awful lot of pressure and flying glass is very 
> dangeous.

   I agree.

>        Another scheme:introduce a standard spark plug into a pop-bottle
>     just
>     below the neck.  Run two wires (thru a rubber stopper in the neck or a
>     screw cap) into the bottom of the bottle into an inch or so of
>     water.....
>     Umm? How about put 1/2" of water in the bottom, a couple of wires in 
> through the cap, add a teaspoonful of calcium carbide, shake and wait a 
> few minutes. Stand well clear and put a spark between the wires to fire 
> the gas mixture?
>     This sort of device is used in agricultural bird scarers and they 
> produce a bang which can be heard for a mile or so. It might well be 
> possible to adapt one for seismology?

   The carbide idea has some charm (I have a carbide cannon) but careful 
control of the acetylene-air ratio would be necessary to achieve a 
detonation.  Electrolysis of water automatically insures stoichiometry.

>     Alternatively, equip your self with some balloons, fill them with 
> acetylene + oxygen and apply a glowing fuse or cigarette? I 
> suggest setting the gas torch burning with the correct flame shape, wipe 
> out the flame and then fill the balloon? A local school kid did this 
> with one of the 3 ft weather balloons in is father's garage many years 
> ago. He removed all the nearby windows for about 100 yards.....

   Again, stoichiometry would require careful control of gas-air ratio. 
  Also, balloons are harder to bury than bottles.
I can see that a 3 ft balloon is a good choice for window removal.

>     Regards,
>     Chris Chapman
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