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'ac measurement circuit'
1999\02\09@095003 by WIL REEDER

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The circuit posted this AM or last PM with the fuse in the ground line is
dangerous. If the fuse blows or is removed, the whole circuit beyond the
fuse, yes, even the line marked ground, is HOT! Fuse needs to be in the
line ahead of the diode. Be careful!

Wil Reeder
spam_OUTteachtechTakeThisOuTspambc.sympatico.ca
Vancouver,Canada 0x33
solar,wind,tide, TEG  renewable energy

1999\02\09@095602 by Andres Tarzia

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Thanks for the tip!

Andres Tarzia
Technology Consultant, SMART S.A.
e-mail: .....atarziaKILLspamspam@spam@smart.com.ar

-----Original Message-----
From: WIL REEDER [teachtechspamKILLspamBC.SYMPATICO.CA]
Sent: Tuesday, February 09, 1999 11:51
To: .....PICLISTKILLspamspam.....MITVMA.MIT.EDU
Subject: ac measurement circuit


The circuit posted this AM or last PM with the fuse in the ground line is
dangerous. If the fuse blows or is removed, the whole circuit beyond the
fuse, yes, even the line marked ground, is HOT! Fuse needs to be in the
line ahead of the diode. Be careful!

Wil Reeder
EraseMEteachtechspam_OUTspamTakeThisOuTbc.sympatico.ca
Vancouver,Canada 0x33
solar,wind,tide, TEG  renewable energy

1999\02\09@101240 by Nuno Pedrosa

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Hi! You said:

WIL REEDER wrote:
> The circuit posted this AM or last PM with the fuse in the ground line is
> dangerous. If the fuse blows or is removed, the whole circuit beyond the
> fuse, yes, even the line marked ground, is HOT! Fuse needs to be in the
> line ahead of the diode. Be careful!

I think you're talking about this circuit:
      o---|>|-----/\/\/\/\-----*----------*----------*-------o
         Diode       R1        |          |          |
                               \          |          |
                               /          | +        |
    115V AC                 R2 \     C1 =====   C2 =====     To PIC
                               /          |          |
                               \          |          |
         Fuse        R3        |          |          |
      o----~------/\/\/\/\-----*----------*----------*-------o GND

> Where the resistors are in the order (not EXACTLY equal to) of: R1=R3=5M and
> R2=400K. So we will get a voltage drop of aprox 4.5V on R2 with an input
> voltage of 115V (full 5V with 130V input).

Could you explain where the fuse should be placed to make it safe, and
why?

Thank you,
Nuno.

--
----  ~~~~~~~  -------  Nuno Filipe Freitas Pedrosa
--  ~~~~     ~~  -----  SIEMENS S.A. Portugal       TEL: +351 1 4242454
-  ~~~~       ~~  ----  Nuno.Pedrosaspamspam_OUToen.siemens.de
-  ~~~~       ~~  ----  "MSWindows - Best run on a SlideShow"
=======================================================================

1999\02\09@214033 by Mike Keitz

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On Tue, 9 Feb 1999 15:00:54 +0000 Nuno Pedrosa
<@spam@Nuno.PedrosaKILLspamspamOEN.SIEMENS.DE> writes:

>I think you're talking about this circuit:
>       o---|>|-----/\/\/\/\-----*----------*----------*-------o
>          Diode       R1        |          |          |
>                                \          |          |
>                                /          | +        |
>     115V AC                 R2 \     C1 =====   C2 =====     To PIC
>                                /          |          |
>                                \          |          |
>          Fuse        R3        |          |          |
>       o----~------/\/\/\/\-----*----------*----------*-------o GND

>Could you explain where the fuse should be placed to make it safe, and
>why?

The circuit is pretty much "safe" as it is.  Assuming that the 5M
resistors R1 and R3 don't fail, they will limit potential shock currents
to a very small amount.

But it won't work very well because any leakage from the circuit ground
to line ground will reduce the apparent value of R3 (or R1), causing an
inaccurate reading.  This circuit really isn't suitable to use.

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