Re: Electrometer design? (fwd)

[Steven Roys <sroys@xxxxxxxx>]

---------- Forwarded message ----------
Date: Tue, 06 Jul 2004 16:02:58 -0700
From: Ed Phillips <evp@xxxxxxxxxxx>
To: High Voltage list <hvlist@xxxxxxxxxx>
Subject: Re: Electrometer design? (fwd)

"High Voltage list wrote:

> From: Malcolm Watts <m.j.watts@xxxxxxxxxxxx>

> I am currently examining a design which appeared in the July 1999
> Amateur Scientist section of Scientific American with a view to
> building several. The circuit is basically a transconductance amp
> which amplifies tiny currents which are then converted to a voltage,
> rectified and peak detected. I suggest having a look at that design
> and possibly throwing away the current set of electronics if it is
> too difficult to repair (I suspect it isn't ;)

This is a possibility. But I would like to keep the electronics,
that has a computer interface that can send the data through a
serial link for processing. The damage was caused by a bad design
combined with lack of attention of a student. At the back of
the instrument there are two pairs of identical connectors, one
for a voltage output to a meter, and another for a power supply.
If the power supply is connected to the wrong connector, the
device is immediately destroyed...

Antonio Carlos M. de Queiroz"

	Indeed a bad design but I've seen such things before.  As for the
destruction, it might not be as bad as you think.  Have you taken a
careful look at the remains?  I would suspect that the output circuit
would be fried but the damage might not go beyond that point very far
and might be repairable.  Of course, if high voltage got on the
collector supply for transistorized circuits or IC's things could be
much worse.

	Speaking of bad design and accidents waiting to happen, I once found a
couple of interesting items in a trash box outside a lab  at work
(Hughes Aircraft).  Both had a regular male 120 V AC connector (US
style).  The interesting part was the other ends.  In one case it was a
BNC connector and in the other it was an identical male AC connector!
Think of the mayhem either might have caused.  (Or maybe had, hence the
trash bin.)  I should mention that this stuff apparently came out of a
flight test airplane.

Ed