NEED HELP FOR CURRENT MEASUREMENT...

[BHARGAVSHANKHALPARA]

Hello everyone i need help in my project...

Actually i made one control circuit which control one 1HP motor. its working fine but i added one extra function which is over current protection. for current measurement i used current transformer. i used ATTINY88 microcontroller for whole project. i decide to use ADC of microcontroller for current measurement.

My current transformer ratings are as below...

Primary winding turns : 1 turn of 2 wire (17 SWG wire).
Primary Resistance : 0.01 ohm
Primary inductance : 3.72 uH

Secondary Winding Turns : 350 turn of 36 SWG Wire.
Secondary Resistance : 32 ohm
Secondary Inductance : 380 MH

after obtaining output from secondary i used signal conditioning circuit link attached below...

https://www.crmagnetics.com/Products/Assets/ProductPDFs/Precision%20Rectifier%20Circuit%20for%20CT%20Signal%20Conditioning.pdf

in above document i used burdan resistor R1=100 ohm, zener diodes of 5.1 volt, as mention in document R2 should be at least 10 times so R2= 10 * R1

R2=1K

also mention in doc that R2=R3 Should be equal so i used both R2=R3=1K.

For amplification i used R4=R5=22K.

Diode at output of each op amp i used 1N4148.

and at last FOR Filtering of output R=100 ohm and capacitor C=10uF.

When i test my microcontroller circuit in simulator for particular value of ADC its work fine but when i do it in real circuit at particular value of ADC circuit not give exceat response(of course i connect AVCC AND GND WITH VCC AND GROUND IN PRACTICAL CIRCUIT RESPECTIVELY). also another problem is that when i pass 5.5 amp current from primary i get some value after signal condition but when i double, mean connect 10 amp load there is minor change in value (in some points only). means CT is not giving LINEAR response...!!

i dont know whats going on...is there any problem in my value of signal conditioning circuit or any other thing is wrong...!!

please help me to solve my problem...!!

Thanks in advance...!!

[Psi]

I've seen this issue before (non linear CT output) but i was just playing around with current measurement for fun and didn't really care to investigate.
(Made up a system to measure the current of 50 power strips (multiboards) for a computer gaming LAN so we could display power stats per table)

I wasn't concerned with fixing the problem so i compensated for the non-linear response with a function inside the MCU.  I believe the reason for it, at least in my case, was non-ideal CT core material. 
I used some random cores i found and i'm pretty sure they saturated at high current which deformed the response. The response i got was pretty good up until 3A but started to ramp up after that and got really bad above 8A.

What core material are you using?

This is the raw response i got from the CT amp -> ADC input  (after software rectification and RMS conversion).


Response after software correction  (Corrected ADC value  vs CT current)


The CT circuit


CT core and sensor board