Re: Electrometer design (fwd)

[Steven Roys <sroys@xxxxxxxx>]

---------- Forwarded message ----------
Date: Fri, 09 Jul 2004 09:34:49 -0400
From: Charles Brush <cfbrush@xxxxxxx>
To: High Voltage list <hvlist@xxxxxxxxxx>
Subject: Re: Electrometer design (fwd)

>
>
>Could someone repost that NE-2 relaxation oscillator or tell me where I
>could find the posts.  Is this a static detector ??
>
>Thanks,
>
>Shaun Epp


Shaun,

The design is incredibly simple.  Basically you have a little NE2
lamp in parallel with a capacitor with one side attached to ground
and the other to an elevated and sharply pointed rod.  As the local
field increases current will flow through the circuit causing the cap
to charge and periodically discharge through the NE2 causing it to
blink.  The faster it blinks the stronger the field overhead.  I
tried this a few summers ago but I can't remember the cap value I
used (anyone have suggestions?).  It took a very close storm to get
it to work but it was pretty neat when it did.  Quite sobering really
considering what it was telling me about the field immediately
overhead.  Naturally you might not want to put the antenna up too
high since this is essentially a lightning rod and a direct strike
would not be good!  Mine was up just above the roofline of our house.

Another type of sensor just replaces the cap/NE2 with some type of
current meter allowing you to watch the current go up as the local
field intensifies.  I am setting up one of these with a Keithley
current meter and will let you know how it works when we get our next
storm.  A variation on this particular design uses a razor blade
coated with an ionizing radiation source to increase sensitivity.
There is a web page someplace about it if you do a search.

Yet another variation dates back to Ben Franklin and is knows as
"Franklin's Bells".  This consisted of two bells on insulated
supports with a metal clapper suspended between them.  One bell was
connected to a lightning rod above the house while the other was
connected to ground.  The rod would collect charge as storms
approached, the clapper would act as a charge transporter moving
charge from the charged bell to the grounded bell.  The faster the
ringing the stronger the overhead field.  Really a simple and
ingenious design, though once again a tad dangerous!

Zap!


Charles Brush