How to interface AC to ADC?

[chickyMeal]

ac adc

Hi all...

I have a 0 to 5V ADC which work well with my PIC microcontroller.
My problem is i need to measure a non sinusoidal AC voltage using the ADC.
Anyone can help me?

One more question... where should i place the ground reference for the AC? TQ!

 

[IanP]

adc for ac signal pic

The simplest way is to use a two-resistor voltage divider, reduce the AC voltage to 0-5V and impose 2.5V dc offset, so if the input AC voltage is 0V the ADC input "sees" 2.5V ..

Regards,
IanP

 

[nikhilele]

ac to dc interface

don't forget to use sample and hold ckt.

frequency of your signal is also important is should be atleat half of the sampling frequency.
"Nyquist "

 

[chickyMeal]

rms adc pic

let me rephrase my question a bit...

my input signal look like an square wave AC with a spike at the falling edge of each pulse..
the voltage (including the spike which i need to measure) is around +/-12V...

i'd have a 0 - 5V ADC with PIC...
how do i produce a rms voltage of the signal?

Thanks a lot!!

 

[flatulent]

measure ac voltage with adc

Not only do you have to use a resistive divider as stated above to reduce the peak to peak levels below the 5 V range of your converter, but you have to add a DC offset to the signal. This can be done by connecting the midpoint of the divider to the 5 V through another resistor. It is a simple matter of algebra to get two of the resistor values once you select the value of the third one.

 

[nikhilele]

interface ac signals to a microcontroller

i think spike have very high rise and fall time and they are of very short duration i am doubtfull that adc will able to have atleast two samples of spike u must use flash adc

and ofcourse all above accessories to limit level that adc can handle

 

[chickyMeal]

adc for ac

Is there anyway i can convert the ac to dc so that i can forget about the sampling frequency?

what if i use diode and capacitor to rectify the AC.. is that possible?

 

[nikhil_damle]

ac to adc

a simple way is to design a new adc forhigher resolution or if u want to mesure ac put it down to 5v ac using 6M resistance in circuit then u can connect it directlt to PIC inputs & pic will sample it for u

or connect the 5v ac to mic input of PC & using visual analyser8 s/w or matlab u can messure the signal & process it

 

[chickyMeal]

ac voltage measurement with adc

where do i place this 6M resistor?

 

[yousafzai]

precision high rms adc

first convert the AC to DC using an RMS to DC converter or using a conventional full wave rectifire. The using ur adc measure this value. Use a step down stage if required.

 

[chickyMeal]

measuring ac signal with adc

Thanx Guys.. I need some clarification though..
The AC that i'm going to measure is used for something else...
If i connect this to full wave rectifier and ADC, will this affect its operation?

 

[saurav_sdpl]

adc ac signal

To interface an AC signal to an ADc u need to first convert the same to DC level using a true rms to Dc converter IC or, a precision rectifier circuit.

For example if ur ac signal is 2 volt pk-pk

then its rms value in case of sine will be=.707V

An rms to Dc converter will output .707v DC signal which will be read by ADC.

RMS to DC converter IC=AD636,ad536,ad736 etc.

hope this might help u
saurav

 

[ashad]

adc output for ac signal

hi

for better results for AC signal measurment use AD736 ture RMS to DC converter