YHDC current sensor - the theory please

[flotulopex]

Hi All,

I'm resuming a project I started more than one year ago; it is about to use a YHDC current sensor.




For now, I have a 16F18446 carrying a 12 bits ADC that I hope sufficient just to put me on the track and avoid the usage of an external higher resolution ADC chip adding "difficulties".

The YHDC sensor I have on my bench is a 100A:50mA model.

I found a lot of these drawings like this one below but I can't make them work or better said, I don't know how to "read" their output.





Do I have to sample let's say a 30 to 50 times or so to grab an alternance, find out both zero-crossing values (or as close as possible) and then extract the higher value in between?

What is the correct way to do this?

Thanks for any explanation on this one

[Jerson]

If you are trying to read the magnitude of current flowing in the primary of the current transformer(CT), you would like to first amplify the AC output of CT using an op-amp. Then do a DC peak conversion on the output of the op-amp. Read this value. It will be proportional to the current flowing in the primary. The ADC on the PIC can now read this DC value in a poll.

[richard]

a simple digital peak detector will give a reasonable result,

eg
2v p-p input offset to approx 1.5v for a vcc of 3.3v for adc




[arduino ide serial plotter]
at a 200us sample rate


at 1000us sample rate , its still not bad

'****************************************************************'*  Name    : peak_detector_ADC_16F18446.pbp
'*  Author  : richard
'*  Notice  : 
'*          : All Rights Reserved
'*  Date    : 
'*  Version : 1.0
'*  Notes   :








 '====== PIC 16F18446 FUSES ========================================================================
  #CONFIG
    __config _CONFIG1, _FEXTOSC_OFF & _RSTOSC_HFINT32 & _CLKOUTEN_OFF & _CSWEN_ON & _FCMEN_ON
    __config _CONFIG2, _MCLRE_ON & _PWRTS_PWRT_64 & _LPBOREN_OFF & _BOREN_SBOREN & _BORV_LO & _ZCDDIS_OFF & _PPS1WAY_OFF & _STVREN_ON
    __config _CONFIG3, _WDTCPS_WDTCPS_31 & _WDTE_SWDTEN & _WDTCWS_WDTCWS_7 & _WDTCCS_LFINTOSC
    __config _CONFIG4, _BBSIZE_BB512 & _BBEN_OFF & _SAFEN_OFF & _WRTAPP_OFF & _WRTB_OFF & _WRTC_OFF & _WRTD_OFF & _WRTSAF_OFF & _LVP_OFF
    __config _CONFIG5, _CP_OFF
  #ENDCONFIG 


' ====== REGISTERS =================================================================================


    ANSELA  = % 00100000
    ANSELC  = % 00000000
    TRISC   = % 11101111
    ADCON0  = % 10000100 'ADC is ON, RIGHT justified result 


' ====== DEFINES ===================================================================================
    DEFINE OSC 32
    DEFINE ADC_BITS 12     'Number of bits in ADCIN result
    DEFINE HSER_TXSTA 24h ' Enable transmit, BRGH = 1
    DEFINE HSER_CLROERR 1 ' Clear overflow automatically
    'DEFINE HSER_SPBRG 138 ' 57600 Baud @ 32MHz, -0.08%
    DEFINE HSER_SPBRG 68  ' 115200 Baud @ 32MHz, 0.64%
    SP1BRGH = 0
    BAUDCON.3 = 1         ' Enable 16 bit baudrate generator
    pause 500
    RC3PPS = 15          ;tx            PORTC.3 
    RA0PPS = 15          ;tx            PORTA.0      ;PK3
    RC4PPS = 0           ;rx            unused
    LED    VAR LATC.4
    clear
    new_read     var word
    State        Var BYTE 'serial Bd (baud per second)
    peak         var word
    last         var word


' ====== setup PROGRAM =============================================================================
    led = 1
    ADCIN 5, last  
    pause 1000
    HSEROUT ["ready ",13,10]
    led = 0    
     ;707 -3670
' ====== MAIN PROGRAM =============================================================================
MAIN:
    ADCIN 5, new_read ' ADC 
    gosub getpeak
    HSerout ["ADC:",dEC new_read,",peak:",dEC peak,13,10]                    '    PLOTTER
    pauseus 200   ;   sample rate                         
GOTO MAIN


getpeak:
    if state==0 then    ;rising
       if   new_read < last  then
        state = 1;falling 
        peak =   last
       endif
    else        ;falling
       if   new_read > last   then 
        state = 0;rising 
        peak =   last
       endif
    ENDif
    last = new_read
return

[flotulopex]

Peak detector! That's it!

Thanks a lot for explaining and the code I can't wait to try when I'm back from office

Though, why do I always read about 3.3V measuring circuits and not 5V?

Also, a "peak detector" can be as simple as a resistor and a capacitor in parallel "smoothing" the output of the sensor, or like Jerson wrote, of the op-amp, right?

If "yes", how do I dimension them? Are trials and readouts on the scope the best way to go?

[richard]

why do I always read about 3.3V measuring circuits and not 5V?

my dev board has a 3.3v reg, otherwise can't see that it makes a difference

a "peak detector" can be as simple as a resistor and a capacitor in parallel "smoothing" the output of the sensor, or like Jerson wrote, of the op-amp, right?

not really , it needs a rectifier too. if the wave is not symmetrical the neg and pos peaks may be needed. plus it still needs adc code to read it in anyway

Are trials and readouts on the scope the best way to go?

almost essential, especially depending on the nature of the current being monitored,
if the current is not sinusoidal and/or varies rapidly then its going to need filtering and other compensation to get any sort of reasonable calibration