AC Datalogging Questions

Discussion in 'General Electronics Chat' started by DC_Kid, Feb 12, 2013.

  1. DC_Kid

    Thread Starter Distinguished Member

    Feb 25, 2008
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    so, i want to datalog my home AC (USA) voltage. i was looking at a cheap solution and i found this
    http://www.dataq.com/support/documentation/pdf/datasheets/di-155ds-usb-data-acquisition.pdf

    anyone see any issue if i use a tap (two 10k or 20k resistors in series) connecting tap to "+" of the DI-155 and the neutral (white) from home wiring to the "-" of the DI-155 channel? the DATA-Q tech guy wants to sell me a better way more expensive (~$1200) setup for what i want to do.

    cant a simple voltage tap work here? i can scale the capture accordingly (well, i am really only interested in seeing spikes and dips that fall outside the SLA of my power company), etc.

    thanks.
     
  2. bertus

    Administrator

    Apr 5, 2008
    15,648
    2,346
    Hello,

    In the datasheet of the device is given that there NO ISOLATION on the inputs.
    When you want to monitor the mains voltage, the device will carry the mains voltage.
    This is an unwanted situation. (and not allowed as written in the Terms of Service ).
    You could use a transformer for the input isolation.

    Bertus
     
  3. DC_Kid

    Thread Starter Distinguished Member

    Feb 25, 2008
    638
    9
    but would using a transformer dampen the spikes and dips due to inductive fields?

    i have lots of transformers.
     
  4. DC_Kid

    Thread Starter Distinguished Member

    Feb 25, 2008
    638
    9
    what about using a ~100uF capacitor on the voltage tap? would that suffice to give isolation?
     
  5. bertus

    Administrator

    Apr 5, 2008
    15,648
    2,346
    Hello,

    Capacitors will not be safe for isolation.
    They can break and make a short.

    Transformers will reduce the spikes and dips, depending on the type and size of the transformer.

    Bertus
     
  6. DC_Kid

    Thread Starter Distinguished Member

    Feb 25, 2008
    638
    9
    yeah, thats what i thought. ok, i ordered DI-155, will see what i can do. probably cant post my actual setup due to rules of the forum.

    you say cap can short. well, so can a transformer. it all depends on how good the component is.
     
  7. DC_Kid

    Thread Starter Distinguished Member

    Feb 25, 2008
    638
    9
    ok folks. here's what i have thus far using a dataq di-155
    this is through a wall-wart ac-ac. from measuring RMS of both sides the amplitude scaling factor is 29.07723 and is factored into the #'s below.

    sidebar - my curiosity was kickstarted when my APC battery UPS routinely tripped. the UPS had software that would record a generic reason why the UPS tripped, such as "voltage crossed threshold", etc. i then had power company put monitor on my house and they found some dips/spikes. they then switched the transformer to another phase hoping that would fix the issue, but i still have the issue. from what i know this seems to be ring wave issue, but i am not 100% sure on that because i dont know what a ring wave dip or spike looks like on the scope, etc. power company had made reference to old capacitor switching banks that could cause ring wave as they are switched in and out. the last report power company sent me was not satisfactory to me, and not knowing the details about their recording gear i took things into my own hands.

    i did three 24hr recordings at 5kHz. the 2nd one showed nothing odd, 1st and 3rd did (the 3rd one showed two events that were almost identical). my UPS thresholds are based on RMS values so i dont think these events tripped my UPS, and i didnt hear UPS trip. my goal is to capture an event while at the same time i hear UPS trip.

    time divisions are 0.0010sec/div

    1.png
    event at 2-25-13 07:40:49.2730(est)
    54.3v relative elapsed time 0.0000 sec
    10.5v relative elapsed time 0.0004 sec
    178.9v relative elapsed time 0.0012 sec
    135.9v relative elapsed time 0.0026 sec
    179.1v relative elapsed time 0.0034 sec

    2.png
    event at 2-27-13 07:34:23.9342(est)
    119.1v relative elapsed time 0.0000 sec
    53.6v relative elapsed time 0.0006 sec
    183.5v relative elapsed time 0.0026 sec

    the odd dips happen very fast, and the shape isnt exactly a good sin. so, can anyone offer insight as to what i am seeing here. i suspect the wall wart windings introduce some damping, so the dips are probably a tad bigger on the line. i also plan to measure line directly.
     
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  8. DC_Kid

    Thread Starter Distinguished Member

    Feb 25, 2008
    638
    9
    bump
    any ideas?
     
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