mesuring AC current,powerfactor

[r.madhav]

power factor + adc+asm

i need an help to find AC current and power factor using microcontroller

 

[meysam_abbasinia]

an939 power meter

you can use one resistor and convert current to voltage and send it to ADC also you need one diff. amp. with opamp(LM358).

 

[bobcat1]

squarewave current power factor measuring

Hi

Use ANALOG DEVICE ADE7753 IC for reading and calculating AC RMS voltage and Current and do simple calculation using the microcontroller

All the best

Bobi

 

[FvM]

measure square wave current

AD7753 or similar is the perfect and high accurate solution. A less accurate measurement can be performed by an internal ADC uP, calculating the values from current and voltage samples. With suitable scaling, it may be good for percent accuracy. Some programming skill and understanding of fundamental electrical theory is required, however.

 

[r.madhav]

mesuring of current

thank,s to every one for the reply

can i give ac voltage (430v) directly to an internal adc of microcontroller(mega8)
and how to give current wave to measure current and powerfactor
plz kindly help me to develop the software

 

[FvM]

Generally you need to preprocess input current and voltage. The ADC input voltage range is 0 to 5 V (for a 5 volt supply). So the AC voltage has to be divided and shifted by an offset voltage to achieve a bipolar range. The current can be sensed by a current transformer or a shunt, it's output voltage has to be amplified to the ADC range.

 

[aq_mishu]

fine, how the pf??

 

[umery2k75]

For measuring PF, you need to convert current wave form into square wave and voltage waveform into square wave also, then you could use XOR gate to get the difference between them or you can run your microcontroller to watch for voltage or current wave which will come first, then run the timer until you achieve the other waveform. For example, if voltage is leading, then first square wave will be of voltage after a little while, you will get current square wave. Both of these outputs will be inputed through two different pins of controller. You have run the internal timer to wait for the other wave form to come. When you get the other wave form. You then have the time factor and by doing simple calculation, you can calculate PF and you could also turn on/off line voltage capacitor for compensation.

 

[FvM]

For measuring PF, you need to convert current wave form into square wave and voltage waveform into square wave also.

Yes and no. This way you get a simplified power factor measurement, valid for sinusoidal current waveforms only. With any power electronic equipment, the waveform is most likely distorted and you get incorrect results.

The said AD7753 and similar parts give waveform-independant measurements of real power, apparent power and power factor by calculating the values exactly as per definition. The operations can be performed also by an µP, but at a limited sample rate, due to ADC speed restrictions and time consuming arithmetics.

P.S.: An application note from Microchip describing a µC based power meter (sourcecode also available)
https://ww1.microchip.com/downloads/en/AppNotes/00939a.pdf
https://ww1.microchip.com/downloads/en/AppNotes/AN939.zip
https://ww1.microchip.com/downloads/en/AppNotes/AN939_CALIBRATION.zip

 

[aq_mishu]

well, i need a device that will give me the measurement of AC voltage, AC current, AC power (Watt), PF, AC frequency and temperature+humidity. For this, I'll use sht7x for temp and humid. Next is the voltages, amps, power, pf... can somebody tell me a description of it? I want to show the data in an lcd and the measurement is in realtime. my AC line is a 220V 50Hz, current can be max 10amps.

 

[r.madhav]

hello , we can give ac 230v directly to an adc pin in microcontroller. i had that program in assembly lang for mega8 but iam not able to analyse it. in this code they are measuring only voltage with respective neutral, if u want that code i will farward.... plz help me to write the code in c lang ..

 

[FvM]

we can give ac 230v directly to an adc pin in microcontroller

Not directly, not without a voltage divider and shifting the input range for a bipolar signal.

 

[umery2k75]

Doing so, will cook up your IC.

 

[r.madhav]

yes, they are giving voltage through a resistor but when i measured with an multimeter on the adc pin it is showning about 220v ac..

my manager is not allowing me to convert AC in to DC for sensing..

 

[marabdul]

For measuring PF, you need to convert current wave form into square wave and voltage waveform into square wave also, then you could use XOR gate to get the difference between them or you can run your microcontroller to watch for voltage or current wave which will come first, then run the timer until you achieve the other waveform. For example, if voltage is leading, then first square wave will be of voltage after a little while, you will get current square wave. Both of these outputs will be inputed through two different pins of controller. You have run the internal timer to wait for the other wave form to come. When you get the other wave form. You then have the time factor and by doing simple calculation, you can calculate PF and you could also turn on/off line voltage capacitor for compensation.

First of all Thanks for the info can you help me realise the sourcecode for this job? the
approach is ok for my final year project and i have a month to present.
Thanks

 

[chennaiups@gmail.com]

Generally you need to preprocess input current and voltage. The ADC input voltage range is 0 to 5 V (for a 5 volt supply). So the AC voltage has to be divided and shifted by an offset voltage to achieve a bipolar range. The current can be sensed by a current transformer or a shunt, it's output voltage has to be amplified to the ADC range.

I understand your hardware quote. Please explain the software idea (flow chart). Every one is expecting in this forums.
Thanks
kitcha

 

[chennaiups@gmail.com]

Generally you need to preprocess input current and voltage. The ADC input voltage range is 0 to 5 V (for a 5 volt supply). So the AC voltage has to be divided and shifted by an offset voltage to achieve a bipolar range. The current can be sensed by a current transformer or a shunt, it's output voltage has to be amplified to the ADC range.

Dear FvM sir
I understand your hardware idea of quote. Please explain the software idea (flow chart & algorithms). Every one is expecting in this forums.
Thanks
kitcha

 

[Booleano]

Hi,

give a look to EM773 from NXP - it's a cortex-m0 based device

there is also a reference design, very useful.

NXP Semiconductors - ICs [Design Examples - EM773 Energy Metering IC]

Regards
B.