AC power measurement

Discussion in 'The Projects Forum' started by electrophile, Apr 26, 2016.

  1. electrophile

    Thread Starter Member

    Aug 30, 2013
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    I'm trying to understand and tweak this smartplug reference design from TI. I'm stumped on the Metrology Analog Filters section on page 1. What I do not understand is why is there a 0R resistor on the Neutral line and why is this line grounded?

    Also since the shunt method is inherently unsafe, can I simply replace the shunt with the primary of the current transformer? In the attached schematic the current source and the terminating resistor essentially mimic the secondary of a current transformer. If I can replace the shunt, can I simply do away with the instrumentation amp in the reference schematic and simply put the attached bit in and feed the signal to the MCU?
     
  2. electrophile

    Thread Starter Member

    Aug 30, 2013
    100
    1
    Anybody?
     
  3. wayneh

    Expert

    Sep 9, 2010
    12,100
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    Maybe if you explained what your goal is? Random messing around inside a commercial product isn't a compelling project to invest time into.

    The neutral line-in establishes ground for the circuit. The neutral out is allowed to be a wee bit higher due to RSHUNT1. As to why the designer bothered to draw in a zero-ohms resistor (I see at least one other one), your guess is as good as mine.
     
  4. nsaspook

    AAC Fanatic!

    Aug 27, 2009
    2,907
    2,166
    I've seen zero-ohms resistors used as single layer board jumpers, a piece of wire.
     
  5. electrophile

    Thread Starter Member

    Aug 30, 2013
    100
    1
    Here is an AC mains power measurement schematic that I tweaked from one of TI's smartplug designs. This simulates well in LTSpice and I was hoping you could give feedback on this. What improvements could be made, what could be eliminated etc. There is no user interaction anywhere here and hence no isolation.

    The first section across the voltage source is the voltage measurement bit. The resistor divider step the voltage down and then through filters its offset by 0.7V. The current measurement is about the same except here the voltage is measured across a shunt resistor. The maximum current measured is 15A and the max voltage measured is 240V AC. I thought about using the ACS712 for current measurement (and I'm still in two minds) but it bumps up the cost and I have not read good feedback about working with the chip.
     
  6. electrophile

    Thread Starter Member

    Aug 30, 2013
    100
    1
    I was trying to build a AC power measurement unit and was referring to this design. I've posted the design for feedback here.

    MOD NOTE: The linked thread has been integrated into this one. The only post in that thread is now the post directly preceding this one.
     
    Last edited by a moderator: Apr 28, 2016
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