Yer thanks Shawn, but my question is regarding sensing AC voltage, not
current.  Did you misread this, or am I missing something?

I have looked at many options for sensing AC current, including the hall
effect sensor approach as used by these Allegro chips.  In the end, I
decided for the power levels I am measuring (up to about 50A AC, or approx.
12kW), the easiest solution was using a 50:5 CT, with a TVS diode and burden
resistor on the secondary output of the CT.  This works great for monitoring
average AC current.  Thanks to those on this list just recently for their
advice concerning this.

Rgs
Ian.

> -----Original Message-----
> From: pic microcontroller discussion list
> [mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Shawn Wilton
> Sent: Thursday, 15 April 2004 1:51 am
> To: PICLIST@MITVMA.MIT.EDU
> Subject: Re: [EE:] AC Voltage measurement
>
>
> Yeah, go to Allegromicro.com and pick up some of their current sensing
> chips.
>
>
> Shawn Wilton
> Junior in CpE
> MicroBiologist
>
> Phone: (503) 881-2707
> Email: shawn@black9.net
>
> http://black9.net
>
>
> Ian McLean wrote:
> > Hi all,
> >
> > Could someone point me somewhere or give some advice on
> monitoring 240VAC
> > 50Hz mains voltage using PIC A/D.
> >
> > The reason I wish to do this is to display the output of a
> variac on an LCD
> > panel.
> >
> > Immediate methods that come to mind are:
> > a) Step down the mains with a step down transformer,
> rectify the output,
> > filter, and resistive voltage divider.
> > b) Leave the step down transformer out of the equation, and
> use higher
> > voltage rated filter caps, and a bigger resistor divider.
> >
> > Both the above methods could empoy a level of PIC
> protection by using an
> > op-amp configured as a voltage follower with no gain to
> clip the output to
> > the AD 5V rail limit.  I figure both methods should give a
> reasonably enough
> > linear output.
> >
> > I can see problems with both of these methods however,
> particularly in
> > regards to ground rail impedance caused by the high voltage
> divider, esp. in
> > option(b), and causing major headaches for the low voltage
> ground reference
> > side for the digital electronics.  Can anyone suggest a better way ?
> >
> > Hmmm.  Maybe I should have just stuck with the simple
> moving iron meters ;)
> >
> > Regards,
> > Ian
> >
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