Re: Problem with common leads in dual channel scopings?

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "June Heidlebaugh" <rheidlebaugh-at-desertgate-dot-com> 

Antionio. A scope requires high voltage to operate the deflection plates.
The vertical input has a high gain amplifier to change microvolt signals to
volts for deflection .If this is not grounded the scope will not display the
signal so the scope has many grounds throughout. Some of the new solid state
hand held scopes are isolated, but this is not a common condition.
----      Robert   H-
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Saturday, August 30, 2003 12:49 PM
Subject: Re: Problem with common leads in dual channel scopings?


 > Original poster: "Antonio Carlos M. de Queiroz" <acmq-at-compuland-dot-com.br>
 >
 > Tesla list wrote:
 >  >
 >  > Original poster: Harvey Norris <harvich-at-yahoo-dot-com>
 >
 >  > This brings me to a question of scope operation: can
 >  > anyone simply say why grounding is necessary?
 >
 > Oscilloscopes usually have the ground connection of all probes
 > connected to the metal case of the oscilloscope, and also to the
 > ground pin on the power plug. So, the ground probes can only be
 > connected to ground.
 > It is possible, for low-frequency measurements, to disconnect the
 > ground pin of the power plug using a suitable adaptor and then
 > float the ground connection of the oscilloscope. But the ground
 > connections of all the probes must be connected to the same
 > point, and the case must be insulated from the ground. Of course,
 > in a high-voltage (>30 V) measurement it's not a good idea to
 > touch the oscilloscope during the measurement, and in really
 > high voltage measurements (>500 V) the insulation of the power
 > transformer inside the oscilloscope, or of the power cable, may
 > fail, possibly leading to extensive destruction.
 >
 > Antonio Carlos M. de Queiroz
 >
 >