# CT measuring circuit with PIC

1. ## CT measuring circuit with PIC

Dear all,

I am using external CT to measure Current parameter. I am using PIC16F1938 to measure analog . Now here i am looking for circuit and calculation involved to get proper current rating.https://www.promelec.ru/pdf/AC-1030_Jun-06.pdf

Min Current : 0.8A
max Current :30A
Primary Current 30A nom., 75A max
Turns Ratio 1000:1

I have 10 bit resolution ADC.
Kindly suggest me the circuit how we can choose the value. I got article with Arduino . https://www.instructables.com/id/Sim...-Energy-Meter/

Let me know best circuit to be achieve better accuracy. Some forum recommend to use amplifier circuit . Let me know which is best

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2. ## Re: CT measuring circuit with PIC

The circuit suggested in the article looks just fine for the Talema CTs. There's also a calculation of burden resistor values.

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3. ## Re: CT measuring circuit with PIC

I have taken sample example here. In general if external circuit used which is recommended design & what are calculation involved here.

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4. ## Re: CT measuring circuit with PIC

Hi,

Go step by step:
First the requirements:
Min Current : 0.8A
max Current :30A
Primary Current 30A nom., 75A max
This is just half the information of the current.
What counts is the maximum peak-to-peak current you want be able to measure.
A single value like "75A max" diesn't say much in an AC system. It can be 75ARMS sine, or it can be 75Ap, or it can be 75App, or something else.
Example:
For a pure sinewave with 30 A RMS, you get a peak of 30A x 1.414 = 42.4V. For peak-to-peak this is 84.8A.
Mind, that you can't expect the current to be pure sine shap, thus you need to extend the range.
Also mind, that many devices have higher inrush current, thus you need to extend the range.
How much? It depends on your load.. and on your requirements. You are free to allow short time overload of your current measurement system. The desicion is yours.

I have 10 bit resolution ADC.
This is no useful information for calculating the circuit.
The (only) value that counts is the decodable ADC input voltage range (peak to peak).

Please show your own effort. Draw a sketch, show your calculations, show what you have understood so far, show what you did not understand.
Don't expect us to do the whole job for you.

Klaus

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