Reading from Split core CT

[deepaktlives]

Dear All,

We are using the CT(attached in the image) for current measurement. The output of the CT is 50mA for 100A rating. I had attached our circuit to read from sensor also. We are using PIC18 series controller to convert and handle the analog values. I'm able to calibrate it to all equipment and getting a value similar to other measuring equipments like Clamp meter etc.. But when I tried connecting it to UPS, I found values 10times higher than other measuring equipments like Clamp meter.

Is there any specific reason that I was not able to read from UPS incoming and outgoing? Do I need to add anything to the attached circuit to handle the same

Thanks in advance
Deepak

 

[chuckey]

your attached circuit is meaningless as it does not label CT in O/P to opamp. . . Have you loaded the CT with a suitable resistor, normally 100 ohms?
Frank

 

[deepaktlives]

Sorry Chuckey,
I added without annotations. Please find the attached image now to differentiate CTs Input and output that leads to controller.

It would be grateful if you or anybody provides me a valid suggestion.

Thanks in advance

Deepak

 

[FvM]

C5/R15 will cause malfunction of the circuit. Negative halfwaves are clipped by the input protection diode of the ADC input.

The most simple solution is to omit the highpass, send the 2.5V centered AC signal to the ADC and process it in a suitable way. If you want to convert the AC current to a DC voltage in hardware, you need active rectifier circuits.

Depending on the CT specification (maximal load respectively output voltage), a bridge rectifier between CT output and burden resistor may be another option.

 

[chuckey]

C3,C7,C11... shown with their polarity round the wrong way? As FvM says the series capacitor gets rid of the 2.5V bias. :-(
Frank