Yeah you got it.
Sometimes curcuit run on dual polarity supplys. For example an LM741 OpAmp
needs a +9V and -9V to work. This can be done by connecting two 9V batteries
in series. The un connected +ve teminal is now +9V the -ve is -9V, and the
connection between the 2 batts is ground or 0V.
-9 GND +9
If u put the black wire of your meter on the GND point you should read -9
and +9 when you put the red wire on the other points.
I think Gunther mean just dont put your shield on the -ve end.
When just running on 1 batt the -ve terminal is really 0V or GND, like u
Grounding sometimes works better if u connect to a large metal object (eg
the chassis of a robot)
but this can also bring in other problems if you are not careful.
>From: hihihi <hihihi@...>
>Subject: Re: [k8000] Electrical interference
>Date: Fri, 12 Mar 2004 14:15:26 +0100
>On Wednesday 21 January 2004 21:49, Gunther COPPENS wrote:
> > Gents, Ladies,
> > Any shielding of a shielded cable MUST be connected to EARTH-terminal
> > NOT the minus of the voltage source.
> > Otherwise shielding does not take place and interference passes the
> > (mostly) aluminium shielding.
>This one is still bugging me.
>A long time ago i played around with building audio circuits.
>I did not ground these to the real earth.
>I connected the shielding to the minus or 0 in case of a +X volt/ zero/ -X
>volt power supply.
>The result was no interference like noise or the 50 hertz buzz..
>So, to at least a certain level, you do not need to ground to real earth to
>make shielding work.
>Part of the role of real earth, as i understand it, is safety.
>Take a washing machine.
>It has to be grounded for safety.
>Suppose the mains wire comes lose inside the machine.
>And touches the casing of the washingmachine.
>When a human then touches a ungrounded casing he gets a shock.
>But because the casing is grounded the current goes trough the easier
>the ground connection.
>And not, or less through the human.
>Or something like this..
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