Current transformer resolution

[gehan_s]

Hey all,

I need to measure an AC current of 0-6A rms using a CT. I have searched for CTs in the internet and found out that many of them go upto about 30A (some of them higher). If I use one of them (max 30A) will it reduce the resolution of the detected current ?

If so how can I increase the resolution ?(I am thinking of measuring atleast 50mA increments)

Also please tell me how to interface the CT to the PIC

thanks in advance !!!!!!!!!!!!!!!

 

[picgak]

connect CT to a precision rectifier using opamp and use a amplifying stage using opamp so that the maximum v is within 5v dc use a zenr for protecting the pic input

 

[Tahmid]

Use a load resistor at the output of the current transformer.

Here's one way you can interface the current transformer:

 

[madhusuthanan]

use a burdon resistor llel to CT. then you use precision rectifier signal, it's o/p range is max of 5v. then o/p given to the adc i/p of the pic microcontrller.

 

[klystron]

Use multiple primary turns (loop your load current wire multiple times through the CT). This will improve the CT resolution.

 

[babatundeawe]

Use a load resistor at the output of the current transformer.

Here's one way you can interface the current transformer:

tried making this circuit but i cudnt get the values stable on my display. when i measured the output i cudnt get a dc outptu except ac output can u or someone explain how to get dc output for interfacing with micro.

secondly the output is very low in the range of millivolt, i know i can amplify it but the output is still oscilating please help

 

[gehan_s]

Hi babatundeawe,

Well you are measuring a AC current. So it must vary with time. When you sample the voltage what you are getting is instantaneous values.

Regards

 

[babatundeawe]

thanks gehan. for ur resonse

please can you expantiate further especially how i can use the instantenous voltage to calculate the current and how can i use microcontroller adc to get these values

thankss

 

[picgak]

please can you expantiate further especially how i can use the instantenous voltage to calculate the current and how can i use microcontroller adc to get these values

thankss

the output of the CT can be bridge rectified and filtered for a stable reading

 

[babatundeawe]

the output of the CT can be bridge rectified and filtered for a stable reading

considering forward voltage of rectifying diode and the voltage output level (in mV)of CT's its difficult to rectify and get an output. i ve tried different precision rectifier found on this site but none is giving me a pure dc output. please what do u advice

 

[madhusuthanan]

hi,

the output of the CT should be precison rectifier & reading si read in microcontroller.

- - - Updated - - -

this is useful link in eada board

https://www.edaboard.com/threads/265127/