Current Sensing with the CT1248

[Bjtpower]

Dear Friends

i am planning to develop a isolated current Sensing Methods for AC Current sensing.

I have one CT1248 (1:1500) and recommended Burden is 84ohm

Now if i want to amplify the same signal and give it to the Controller Pin.

What will be the Probable circuit..??

I have used earlier AD620 for amplification but its not the good selections as it is Differential Amplifier and full voltage swings to 2.2V when we apply 3.3V supply at its terminals

i want to have full access of 3.3V which we can give it to the Controller.



Regards
Marx

 

[KlausST]

Hi,

I usually recommend to just bias the CT secondary to ADC_range/2 then feed it to the ADC input.
It is the most flexible and simple (hardware) solution.

But without knowing about currents and frequencies and without knowing WHAT you want to measure (true RMS, fake RMS, rectified average....) and other parameters .... it's about impossible to give a recommendation.

Klaus

 

[FvM]

If the CT doesn't provide 3 Vpp swing with sufficient linearity, you'll need a rail-to-rail amplifier. I don't see a particularly advantage of instrumentation amplifier for this function. Transimpedance amplifier configuration achieves lowest CT linearity error.

 

[mtwieg]

Seconding the transimpedance amp suggestion. Just make sure the opamp will maintain low distortion while handling the full secondary current of the CT. But you will need additional circuitry to bias the output's common mode voltage.

 

[FvM]

Just make sure the opamp will maintain low distortion while handling the full secondary current of the CT.

Forgot to mention that it's only useful for CTs with low mA secondary current. CT1248 has 10 A rated primary current (9.5 mA secondary peak current, so it falls in this category). Regular burden and single ended voltage amplifier would work too, of course.

 

[Bjtpower]

Forgot to mention that it's only useful for CTs with low mA secondary current. CT1248 has 10 A rated primary current (9.5 mA secondary peak current, so it falls in this category). Regular burden and single ended voltage amplifier would work too, of course.

How 9.5mA..??

My Calculations are here
Voltage drop across secondary Burden:1/1500=0.66mA (When passing 1 amp through primary)

Recommended Value for Burden resistor=94Ω
Voltage Drop across Burden resistor=94x0.66mA=62.4mV (Between IN+/IN- Pins)

check for attached



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Hi,

I usually recommend to just bias the CT secondary to ADC_range/2 then feed it to the ADC input.
It is the most flexible and simple (hardware) solution.

Klaus

Hi Klaus..

How we can Bias without op-amp..??

I never used the circuits like this..

 

[FvM]

How 9.5mA..??

Rated current is 10 A rms, so 6.7 mA rms or 9.5 mA peak for sine current waveform.

 

[KlausST]

Hi,

How we can Bias without op-amp..??

--> two resistors as voltage divider...

Klaus

 

[Bjtpower]

But i want to connect it to the controller..

Are you elaborating that reference generated by the Voltage divider should mix with the ac voltage getting across the Diodes or 2 RESISTORS..??

pls post schematics if its easy to show you

 

[KlausST]

Hi,

diodes???



Klaus