Help me to solve problem related to current measurement using current transformer

[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...

**broken link removed**

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...!!

 

[barry]

Start at the beginning; forget about the microprocessor for starters. Then measure some points in your circuit. What's the voltage across that 100 ohm resistor? What does the signal out of the first opamp look like? (And I don't understand the point of that diode in the second opamp). How much ripple are you seeing on the output?

 

[BHARGAVSHANKHALPARA]

i measure direct AC voltage across burdan resistor of 100 ohm and take reading which is as below...

Reading at BURDAN RESISTOR

AT LOAD 5.5 AMP = 0.858 VOLT (AC)
AT LOAD 8.3 AMP = 0.936 VOLT (AC)
AT LOAD 1.0 AMP = 0.216 VOLT (AC)

OUTPUT AFTER FIRST OP-AMP (RECTIFIED)

FOR 5.5 AMP = 0.772 VOLT (DC)
FOR 8.3 AMP = 0.808 VOLT (DC)
FOR 1.0 AMP = 0.195 VOLT (DC)

i have no oscilloscope so i cant see nature of output signal but it looks steady in my multimeter reading...

Thank you.

 

[barry]

Well, obviously you've got something wrong. When your current changes from 5.5 to 8.3, a factor of 1.5, your voltage only changes by a factor of 1.5.

Is your 100 ohm too small such that it's loading the transformer? It sure looks like it. With 5.5 amps, you should get 157mA in the secondary-->1.57 volts across 100 ohms.