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AC Voltmeter [wattmeter] — Parallax Forums

AC Voltmeter [wattmeter]

ArchiverArchiver Posts: 46,084
edited 2000-07-28 20:14 in General Discussion
Craig, do yourself a favor and go to http://www.analog.com
and look at the AD7750 product to frequency converter
data sheet. [noparse][[/noparse]PDF format download 16 pages].

This IC is cheap and was made specifically to be used in
electronic watt meters [noparse][[/noparse]small error over large current
range]. It handles power factor issues and gives a
pulse output proportionate to _real_ power in the
circuit. This pulse can be measured by the Basic Stamp!

Accurate power measurement with odd waveforms is not
trivial. A multiplier is required usually.

A simple analog circuit which accomplishes multiplication
is to vary pulse width with current and the pulse height
with voltage and then integrate the pulse output with
a capacitor and you'll get a reading of current x voltage
for one phase quadrant. In simple terms you can switch
the voltage you are trying to multiply with a pulse
width determined from the current - just a CMOS switch
can do this.

Another way this is done is with Hall effect devices
[noparse][[/noparse]OHIO Semitronics] where a magnetic field proportional
to voltage is put across a hall effect linear sensor
having a signal proportional to current running through it.

This gives a signal proportional to VxI out continuously.
[noparse][[/noparse]These are somewhat bulky and expensive modules].

Good luck...

________________________________________________________________
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Comments

  • ArchiverArchiver Posts: 46,084
    edited 2000-07-28 14:16
    Great Idea. Good Input.

    Gary

    Original Message
    From: "s premena" <premzee@j...>
    To: <basicstamps@egroups.com>
    Sent: Thursday, July 27, 2000 7:34 PM
    Subject: [noparse][[/noparse]basicstamps] Re: AC Voltmeter [noparse][[/noparse]wattmeter]


    > Craig, do yourself a favor and go to http://www.analog.com
    > and look at the AD7750 product to frequency converter
    > data sheet. [noparse][[/noparse]PDF format download 16 pages].
    >
    > This IC is cheap and was made specifically to be used in
    > electronic watt meters [noparse][[/noparse]small error over large current
    > range]. It handles power factor issues and gives a
    > pulse output proportionate to _real_ power in the
    > circuit. This pulse can be measured by the Basic Stamp!
    >
    > Accurate power measurement with odd waveforms is not
    > trivial. A multiplier is required usually.
    >
    > A simple analog circuit which accomplishes multiplication
    > is to vary pulse width with current and the pulse height
    > with voltage and then integrate the pulse output with
    > a capacitor and you'll get a reading of current x voltage
    > for one phase quadrant. In simple terms you can switch
    > the voltage you are trying to multiply with a pulse
    > width determined from the current - just a CMOS switch
    > can do this.
    >
    > Another way this is done is with Hall effect devices
    > [noparse][[/noparse]OHIO Semitronics] where a magnetic field proportional
    > to voltage is put across a hall effect linear sensor
    > having a signal proportional to current running through it.
    >
    > This gives a signal proportional to VxI out continuously.
    > [noparse][[/noparse]These are somewhat bulky and expensive modules].
    >
    > Good luck...
    >
    > ________________________________________________________________
    > YOU'RE PAYING TOO MUCH FOR THE INTERNET!
    > Juno now offers FREE Internet Access!
    > Try it today - there's no risk! For your FREE software, visit:
    > http://dl.www.juno.com/get/tagj.
    >
    >
    >
  • ArchiverArchiver Posts: 46,084
    edited 2000-07-28 20:14
    Yes, I agree. Iam looking into that device now. Looks promising. Thanks!

    Original Message
    From: G. Shearer [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=eD1o6ULfGXPgibxOC-Y-W1Yo0dcH6W1o7RjW7uj_lO1Z-qqevwL5cu-tUOHvfq8wShst9inpC2qamItRmDuESA]g.shearer@v...[/url
    Sent: Friday, July 28, 2000 9:16 AM
    To: basicstamps@egroups.com
    Subject: Re: [noparse][[/noparse]basicstamps] Re: AC Voltmeter [noparse][[/noparse]wattmeter]


    Great Idea. Good Input.

    Gary

    Original Message
    From: "s premena" <premzee@j...>
    To: <basicstamps@egroups.com>
    Sent: Thursday, July 27, 2000 7:34 PM
    Subject: [noparse][[/noparse]basicstamps] Re: AC Voltmeter [noparse][[/noparse]wattmeter]


    > Craig, do yourself a favor and go to http://www.analog.com
    > and look at the AD7750 product to frequency converter
    > data sheet. [noparse][[/noparse]PDF format download 16 pages].
    >
    > This IC is cheap and was made specifically to be used in
    > electronic watt meters [noparse][[/noparse]small error over large current
    > range]. It handles power factor issues and gives a
    > pulse output proportionate to _real_ power in the
    > circuit. This pulse can be measured by the Basic Stamp!
    >
    > Accurate power measurement with odd waveforms is not
    > trivial. A multiplier is required usually.
    >
    > A simple analog circuit which accomplishes multiplication
    > is to vary pulse width with current and the pulse height
    > with voltage and then integrate the pulse output with
    > a capacitor and you'll get a reading of current x voltage
    > for one phase quadrant. In simple terms you can switch
    > the voltage you are trying to multiply with a pulse
    > width determined from the current - just a CMOS switch
    > can do this.
    >
    > Another way this is done is with Hall effect devices
    > [noparse][[/noparse]OHIO Semitronics] where a magnetic field proportional
    > to voltage is put across a hall effect linear sensor
    > having a signal proportional to current running through it.
    >
    > This gives a signal proportional to VxI out continuously.
    > [noparse][[/noparse]These are somewhat bulky and expensive modules].
    >
    > Good luck...
    >
    > ________________________________________________________________
    > YOU'RE PAYING TOO MUCH FOR THE INTERNET!
    > Juno now offers FREE Internet Access!
    > Try it today - there's no risk! For your FREE software, visit:
    > http://dl.www.juno.com/get/tagj.
    >
    >
    >
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