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ac current and voltage measurement using pic

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enamshah

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i want to measure 220V ac voltage and 5-15A current using pic.for this i have to convert the voltage to 5V using a transformer.I need help in choosing a suitable transformer and other components that may be required.
 

andre_teprom

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sahu

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i want to measure 220V ac voltage and 5-15A current using pic.for this i have to convert the voltage to 5V using a transformer.I need help in choosing a suitable transformer and other components that may be required.
i hope it...
 

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zeroskj1988

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i hope it...
i have problem in simular situation. can u help me?. i have measure 230v,50hz ac.i rectified ac with bridge,then use potential divider to dive to below 5v,(without using filter capacitor)then given to the 10bit adc pin of pic16f877a.i take sample on each 1ms(since for 50hz, period is 20ms,using timer 1) add then,average on 10 sample, multiply by form factor(1.1) then display.my problem is display value change between 208-230. i don't think it is because of supply variation
 

dv_sa559

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Could you explain which CT transformer you use ? also current to volt coefficient of that (for measure current)
May do you show your circuit in forum
 

zeroskj1988

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Could you explain which CT transformer you use ? also current to volt coefficient of that (for measure current)
May do you show your circuit in forum
i have problem(drift in value) in voltage, current.
voltage 100K,1k divider,
current 550ct
i have doubt relate to the filter capacitor, whether absense of it is reason for drift?
 

FvM

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You can calculate the uncertainty introduced by sampling a sine voltage at 1 ms intervals without synchronization to the input signal. In addition, you must expect harmonics and interferences to affect the measurement. Did you check the input waveform?

By using a bridge rectifier, the measurement circuit will have a floating ground or a safety transformer is needed.

A filter capacitor in parallel to the 1 k resistor should reduce the voltage variation.
 

zeroskj1988

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You can calculate the uncertainty introduced by sampling a sine voltage at 1 ms intervals without synchronization to the input signal. In addition, you must expect harmonics and interferences to affect the measurement. Did you check the input waveform?

By using a bridge rectifier, the measurement circuit will have a floating ground or a safety transformer is needed.

A filter capacitor in parallel to the 1 k resistor should reduce the voltage variation.
thank u for advice. i avoided capacitor because if i use capacitor then there is no meaning in sampling 10 for semicycle. by feeling that it will affect accurate measurement. i will try with capacitor. my circuit have common ground, i don't get the floating ground. i have this doubts because i am beginner to this can u suggest an alternative
 

arbj

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This could be one way to avoid a capacitor.

Start a timer, then start sampling the voltage as fast as possible, till the peak value is reached, this can be found when the sample values start to decrease, then stop the timer, record the time interval (in msec), now take the next sample after elapse of the time interval that was previously recorded.

The time interval represents the time taken for the voltage to reach peak value and this should be a constant, alternatively you continue sampling irrespective of the time interval.
 

FvM

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This could be one way to avoid a capacitor. (...)
Harmonics can still involve a considerable deviation from true voltage measurements. Personally, I would expect a sampled measurement (preferably of AC input rather than full-wave rectified voltage) for a RMS and PF or real power measurement. But a sampling intervall of 1 ms would be somewhat slow for this purpose.
 

andre_teprom

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