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Current transformer resolution

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gehan_s

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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

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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
 

madhusuthanan

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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

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

babatundeawe

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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

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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

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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

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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

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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

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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/thread265127.html
 

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