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Hot!Read Sinusoidal Current Cycle by Cycle:

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karan123
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2021/02/21 20:02:40 (permalink)
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Read Sinusoidal Current Cycle by Cycle:

Hello,

How to read current ( Sin ) Cycle by Cycle with MCU (PIC18F4520) ADC of variable Inductive load ?
Voltage lead/lag from Current.

--
Karan
#1

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    Bob White
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    Re: Read Sinusoidal Current Cycle by Cycle: 2021/02/21 20:48:19 (permalink)
    +1 (1)
    Your question is vague and ambiguous.  What are you really asking?

    About possible current sensors?

    Algorithms to process the output of an A2D converter to compute the RMS current?

    Something else?
    #2
    karan123
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    Re: Read Sinusoidal Current Cycle by Cycle: 2021/02/21 21:01:59 (permalink)
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    Your question is vague and ambiguous.  What are you really asking?

    I have to measure AC Current of Inductive load without External A2D Converter.


    About possible current sensors?
    Rogowiski Coil.

    Algorithms to process the output of an A2D converter to compute the RMS current?
    Yes, With Internal ADC of PIC But cycle by cycle
    RMS or Average Current.


    Something else?
    See above

    Thanks.
    #3
    PStechPaul
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    Re: Read Sinusoidal Current Cycle by Cycle: 2021/02/21 21:32:18 (permalink)
    +2 (2)
    This was extensively discussed in your previous thread several months ago.
     
    https://www.microchip.com/forums/m1148151.aspx
     
    You will need an integrator with the Rogowski coil.

     
    #4
    karan123
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    Re: Read Sinusoidal Current Cycle by Cycle: 2021/02/21 21:50:27 (permalink)
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    PStechPaul
    This was extensively discussed in your previous thread several months ago. https://www.microchip.com/forums/m1148151.aspx You will need an integrator with the Rogowski coil.


    Yes,
    Thanks ..As you said ,there is (in Software) No need of taking Zero Crossing of Current ,Zero Crossing ofLine Voltage will used to read cycle by cycle for measurement of Current.
    Is this vaild for Inductive Load?
    Where Voltage lead with current.

    The suggestion in that thread, I am not getting Appropriate results

    Thanks for your concern.

    --
    Karan
    #5
    ric
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    Re: Read Sinusoidal Current Cycle by Cycle: 2021/02/21 22:03:05 (permalink)
    +2 (2)
    karan123
     I am not getting Appropriate results

    Could you be any less helpful in your replies?
    What on earth does "not getting Appropriate results" actually mean?
     

    I also post at: PicForum
    Links to useful PIC information: http://picforum.ric323.co...opic.php?f=59&t=15
    NEW USERS: Posting images, links and code - workaround for restrictions.
    To get a useful answer, always state which PIC you are using!
    #6
    PStechPaul
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    Re: Read Sinusoidal Current Cycle by Cycle: 2021/02/21 22:18:30 (permalink)
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    If you are only reading current, the load does not matter. But if it is distorted, you should use a true RMS method. Just take 40 readings at a 2 kHz sampling rate (500 uSec/sample) which will measure a single cycle. Square each reading, total all 40, and take square root. Result is true RMS of one cycle. It may be better to start reading at a zero crossing, but not necessary.

     
    #7
    karan123
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    Re: Read Sinusoidal Current Cycle by Cycle: 2021/02/21 22:24:48 (permalink)
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    ric
    karan123
    I am not getting Appropriate results

    Could you be any less helpful in your replies?What on earth does "not getting Appropriate results" actually mean? 

    Ok .. I mean to say that Current (Load) is significantly delay ( in milliseconds ) ZCD voltage in
    case Inductive load.Then how to measure cycle by cycle.

    --
    Karan
    #8
    karan123
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    Re: Read Sinusoidal Current Cycle by Cycle: 2021/02/21 22:32:27 (permalink)
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    PStechPaul
    If you are only reading current, the load does not matter. But if it is distorted, you should use a true RMS method. Just take 40 readings at a 2 kHz sampling rate (500 uSec/sample) which will measure a single cycle. Square each reading, total all 40, and take square root. Result is true RMS of one cycle. It may be better to start reading at a zero crossing, but not necessary.


    Ok..

    Waveform is stable sin wave without any distortion.

    If current wave is shifted from (ZCD) voltage ,how the measurement could be accurate cycle by cycle.

    --
    Karan
    post edited by karan123 - 2021/02/21 22:36:59
    #9
    karan123
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    Re: Read Sinusoidal Current Cycle by Cycle: 2021/02/21 22:33:34 (permalink)
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    PStechPaul
    It may be better to start reading at a zero crossing, but not necessary.


    Ok..

    Waveform is stable sin wave without any distortion.
    If current wave is shifted from (ZCD) voltage ,how the measurement could be accurate cycle by cycle.

    --
    Karan
    post edited by karan123 - 2021/02/21 22:36:41
    #10
    PStechPaul
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    Re: Read Sinusoidal Current Cycle by Cycle: 2021/02/21 22:50:09 (permalink)
    +1 (1)
    If you take samples over a period of time equal to that of a single cycle, it does not matter where the sampling starts. If you really want to, you can just detect a ZC of the current waveform.

     
    #11
    karan123
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    Re: Read Sinusoidal Current Cycle by Cycle: 2021/02/21 22:54:46 (permalink)
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    Ok... Thanks .

    I will modify hardware accordingly to detect zero crossing of current.
    Actually I have to measure one cycle and control other (Next) cycle for CC.

    --
    Karan
    #12
    davea
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    Re: Read Sinusoidal Current Cycle by Cycle: 2021/02/21 23:11:39 (permalink)
    +1 (1)
    Actually I have to measure one cycle and control other (Next) cycle for CC.

    what exactly are you trying to do..
    measure power factor 
    power factor correction
    does CC mean constant current
    #13
    karan123
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    Re: Read Sinusoidal Current Cycle by Cycle: 2021/02/21 23:16:34 (permalink)
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    Yes, CC means Constant But cycle by cycle.
    I have to meaure current (one) from thyristors and control on other (next) cycle to make and so on
    to make Constant current source.

    Not for Power Factor.
    #14
    davea
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    Re: Read Sinusoidal Current Cycle by Cycle: 2021/02/21 23:41:29 (permalink)
    +1 (1)
    at what current 
    is the output AC or DC
    #15
    PStechPaul
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    Re: Read Sinusoidal Current Cycle by Cycle: 2021/02/21 23:53:57 (permalink)
    +1 (1)
    First, provide code that successfully builds and runs and properly reads the output current. Once that is working well, add the code to adjust firing angle for the SCR controller.

     
    #16
    karan123
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    Re: Read Sinusoidal Current Cycle by Cycle: 2021/02/22 00:12:21 (permalink)
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    davea
    at what current is the output AC or DC

    AC
    #17
    PStechPaul
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    Re: Read Sinusoidal Current Cycle by Cycle: 2021/02/22 00:34:07 (permalink)
    +1 (1)
    If the current control is a dual SCR with phase firing, the waveform will have a sharp transition which will cause current measurement error because of the sampling frequency. With 10 samples per half-cycle, the RMS measurement can have error in the order of 10%. Faster sampling can improve this, and possibly a series inductor might smooth the sharp transition and improve accuracy.

     
    #18
    karan123
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    Re: Read Sinusoidal Current Cycle by Cycle: 2021/02/22 03:33:09 (permalink)
    +1 (1)
    PStechPaul
    If the current control is a dual SCR with phase firing, the waveform will have a sharp transition which will cause current measurement error because of the sampling frequency. With 10 samples per half-cycle, the RMS measurement can have error in the order of 10%. Faster sampling can improve this, and possibly a series inductor might smooth the sharp transition and improve accuracy.


    I will send waveform after some time.
    #19
    TS9
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    Re: Read Sinusoidal Current Cycle by Cycle: 2021/02/26 10:05:14 (permalink)
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    What Intergrator circuit you have used ?
    post edited by TS9 - 2021/02/26 10:17:51
    #20
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