A simple circuit can provide disconnect at the peak of the ac waveform.

Ken Javor
Phone: (256) 650-5261



From: "doug...@gmail.com" <doug...@gmail.com>
Reply-To: "doug...@gmail.com" <doug...@gmail.com>
Date: Mon, 17 Oct 2022 13:08:17 -0600
To: <EMC-PSTC@LISTSERV.IEEE.ORG>
Subject: Re: [PSES] Assess risk of electric shock from charged capacitors

On the question of probe resistance, I always recommend 100:1 probes which
will have a negligible effect on overall timing.  Additionally, it may be
necessary to perform the test a number times to ensure the disconnect occurs
at the peak of the sine wave.  For me, experience has shown this may take up
to 10x attempts.

-Doug


Douglas E Powell
Laporte, Colorado USA
doug...@gmail.com
LinkedIn <https://www.linkedin.com/in/coloradocomplianceguy/>

(UTC -06:00) Mountain Time (US-MDT)




On Mon, Oct 17, 2022 at 11:32 AM Richard Nute <ri...@ieee.org> wrote:
>  
>  
> Hi Scott:
>  
> Many dual channel scopes (whether digital or analog) include an ³add² function
> for the two channels.  One channel must be inverted to measure the charged
> capacitance.
>  
> The resistance of the two probes must be accounted for in the capacitance
> discharge time.  (The same ­ for only one probe -- is true for the scheme
> using an isolating transformer.)
>  
> You should get the same results for both methods.
>  
> Best regards,
> Rich 
> IEEE Life Fellow
> IEEE Medal for Environmental and Safety Technologies
>  
>  
>  
> 
> From: Scott Xe <scott...@gmail.com>
> Sent: Monday, October 17, 2022 8:18 AM
> To: EMC-PSTC@LISTSERV.IEEE.ORG
> Subject: Re: [PSES] Assess risk of electric shock from charged capacitors
>  
> 
> In order to judge if there is no risk of electric shock from charged
> capacitors, it is required to measure the voltage across L and N of mains plug
> after the removal of power input.  To avoid grounding loop between test
> equipment and the unit under test, an isolating transformer is strongly
> recommended.  I have learnt another way by using Add Function and two hot
> probes of a dual channel DSO.  Can someone advise which way is more common in
> safety conformity test.  Especially the latter one, I have not tried it yet
> before and appreciate any notes I must take in the measurement.
> 
>  
> 
> Thanks and regards,
> 
>  
> 
> Scott
> -
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