calculate the amplitude of sin signal ??

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gameelgamal

Joined: 14 Dec 2006
Posts: 89
Location: Egypt

28 Apr 2009 15:26 signal amplitude

Hi

How to calculate the amplitude of sin signal using microcontroller?

What I need is the algorithm which will be implemented in the microcontroller to compute the amplitude (or the RMS value) of the input signal...

thanx...

FvM

Joined: 22 Jan 2008
Posts: 5044
Helped: 752
Location: Bochum, Germany

29 Apr 2009 8:26 calculate amplitude

RMS can be calculated independant of the waveform type. It's exactly what it's named: RMS root of mean of squared signal. You may want to calculate an RMS of the AC signal by subtracting the DC value (or mean), the operation is equivalent to finding the standard deviation of a series of samples. You'll find the definition in the statistics section of a mathemical formulas collection.

smxx

Joined: 18 Aug 2005
Posts: 188
Helped: 8
Location: iran(ahwaz)

29 Apr 2009 10:04 amplitude of a signal

hi
Analog Divece ® have a special 8pin Ic for this purpose.
And for fully sine wave you can calculate this by two samples.
V1 : sample at t1 time
v2 :sampe at (t1+π/2)
V1=Vm sin(t1)
V2=Vm sin(t1+π/2)
Vm²=V1²+V2²
Vrms= Vm /√2

gameelgamal

Joined: 14 Dec 2006
Posts: 89
Location: Egypt

29 Apr 2009 12:07 amplitude of sin

smxx wrote:

And for fully sine wave you can calculate this by two samples.
V1 : sample at t1 time
v2 :sampe at (t1+π/2)
V1=Vm sin(t1)
V2=Vm sin(t1+π/2)
Vm²=V1²+V2²
Vrms= Vm /√2

Ok...
I'm going to implement this algorithm using a microcontroller, But I still find some difficulty. So please tell me if I'm wrong

First , at a random point of the program, I will perform an analog to digital conversion process to compute V1.

Secondly , after a certain time (say 1 ms), I will perform another ADC to compute V2.

Now I can compute V1 using the eqn: V1=Vm sin(t1)
But what is the value of (t1) ?? It should be equal zero, isn't ?

Also what do you mean by (n/2). Is it the delay time between the two conversions (1 ms in my case) or what??

thanx....

FvM

Joined: 22 Jan 2008
Posts: 5044
Helped: 752
Location: Bochum, Germany

29 Apr 2009 20:35 sin signal

n/2 must be equal to 1/4 period of the input frequency (90° phase shift), otherwise the nice algorithm doesn't work. Also V1, V2 must be DC-free.

gameelgamal

Joined: 14 Dec 2006
Posts: 89
Location: Egypt

30 Apr 2009 7:29 signal amplitude

FvM wrote:

n/2 must be equal to 1/4 period of the input frequency (90° phase shift), otherwise the nice algorithm doesn't work. Also V1, V2 must be DC-free.

So. in case of 50 Hz sin wave , n/2=5 ms. Right?

what do you mean by dc free?? you mean no DC offset added to it??

thanx..

shoaibali

Joined: 28 Jun 2007
Posts: 40
Helped: 3

30 Apr 2009 12:43 rms of sine wave with dc offset

Use microcontrollers adc to take n(100 would be fine) samples of the input sginal for one cycle of the sine wave and do the rms calculations for that. You will need to bias the sinusoidal signal if the adc low reference voltage is 0 volts.

For example, for 50Hz sinusoidal signal,
take 100 samples each 20ms/100 = 200us apart
This can be done using a timer and adc in the microcontroller

Regards

FvM

Joined: 22 Jan 2008
Posts: 5044
Helped: 752
Location: Bochum, Germany

30 Apr 2009 15:01 how to calculate amplitude of a signal

As said, you can calculate the AC voltage RMS without knowing the DC offset before (by using a standard deviation calculation method):

Code:

uRMS = √(1/n*∑u² - (1/n*∑u)²)

gameelgamal

Joined: 14 Dec 2006
Posts: 89
Location: Egypt

01 May 2009 12:25 calculating rms value of sine wave with dc offset

shoaibali wrote:

Should the 100 samples be in the one cycle, or it can be tooken over more than one cycle

trekkytekky

Joined: 04 Apr 2009
Posts: 77
Helped: 6
Location: Perth

02 May 2009 12:41 signal + amplitude

If you always know it will be a sinusoidal signal, then you also have the option of implementing a peak detector for maximum and minimum, the amplitude will be (max-min)/2 and multiplying by a constant 1/√2 for RMS

ie:
Amplitude = (max-min)/2
RMS = Amplitude/√2

Just another option.

shoaibali

Joined: 28 Jun 2007
Posts: 40
Helped: 3

05 May 2009 14:04 calculate amplitude discrete sine

gameelgamal wrote:

shoaibali wrote:

Should the 100 samples be in the one cycle, or it can be tooken over more than one cycle

The samples have to be in one cycle as you will be doing calculations over one cycle

Jack// ani

Joined: 02 Dec 2004
Posts: 484
Helped: 24

05 May 2009 17:08 how to calculate sine of an amplitude

Code:

#include <16F877A.h>
#device ADC=10
#include <math.h>
#fuses XT,NOWDT,NOPROTECT,NOLVP,NOBROWNOUT
#use delay(clock=4000000)
#use rs232(baud=9600,xmit=PIN_C6,rcv=PIN_C7)

void main()
{

int16 value, samples[29]; //Value is a 10bit data sample
int i;
float volts;
setup_port_a(ALL_ANALOG); // All the 8 channels are analog
setup_adc(ADC_CLOCK_INTERNAL); // Internal ADC Clock
set_adc_channel(0); // RA0/AN0(Pin2) is analog input channel

while(1)
{
for(i=0;i<=29;i++)
{
samples[i]=read_adc();
delay_us(666);
}

for(i=0;i<=29;i++)
{
samples[i]=samples[i]*samples[i]; // Sqaure
value=samples[i]+value; // Sum total
}

value = value/30; // Mean of 30 samples
value = sqrt(value); // Square root

volts=(float)value*0.0048828125; // 1024 discrete levels, 5/1024 = 0.0048828125
printf("Voltage is : %3.3f\n",volts);// Print upto 3 decimal places
delay_ms(500);
}
}

shoaibali

Joined: 28 Jun 2007
Posts: 40
Helped: 3

06 May 2009 11:12 amplitude signal

Jack// ani wrote:

Wrote a little code on CCS PIC, nothing fancy standard deviation with 30 samples at work as discussed by FvM.

Have run out of 16F877A, so couldn't burnt and tested it. Any comments, mistakes, improvements are always appreciated...

#include <16F877A.h>
#device ADC=10
#include <math.h>
#fuses XT,NOWDT,NOPROTECT,NOLVP,NOBROWNOUT
#use delay(clock=4000000)
#use rs232(baud=9600,xmit=PIN_C6,rcv=PIN_C7)

void main()
{

int16 value, samples[29]; //Value is a 10bit data sample
int i;
float volts;
setup_port_a(ALL_ANALOG); // All the 8 channels are analog
setup_adc(ADC_CLOCK_INTERNAL); // Internal ADC Clock
set_adc_channel(0); // RA0/AN0(Pin2) is analog input channel

while(1)
{
for(i=0;i<=29;i++)
{
samples[i]=read_adc();
delay_us(666);
}

//SQUARE OF SAMPLES
for(i=0;i<=29;i++)
{
samples[i]=samples[i]*samples[i]; // Sqaure
value=samples[i]+value; // Sum total
}

value = value/30; // Mean of 30 samples
value = sqrt(value); // Square root

volts=(float)value*0.0048828125; // 1024 discrete levels, 5/1024 = 0.0048828125
printf("Voltage is : %3.3f\n",volts);// Print upto 3 decimal places
delay_ms(500);
}
}

I would like to add a few things
1- I suggest initialize "vaue" variable to 0
2- Do following to get rid of dc level in the signal(for example if the signal has been biased)
a. DC_Average = sumOfSample/NoOfSamples
b. For each sample samples[i] = PositiveValueOf(samples[i] - DC_Average)
c. Do the rest as in //SQUARE OF SAMPLES

Regards

Jack// ani

Joined: 02 Dec 2004
Posts: 484
Helped: 24

06 May 2009 14:11 sin vrms

Hi shoaibali, Yeah the value=0 should be initialized to avoid any previous junk value.

Regarding DC_Average, its not necessary as samples will be taken over a complete cycle, so DC Average will be zero.

shoaibali

Joined: 28 Jun 2007
Posts: 40
Helped: 3

06 May 2009 17:16 rms of sine with dc offset

Jack// ani wrote:

Hi Jack
I was pointing to DC_Average in case the signal is biased to a dc level which most likey it will be if it is going to be sampled by mcu with positive reference only

smxx

Joined: 18 Aug 2005
Posts: 188
Helped: 8
Location: iran(ahwaz)

12 May 2009 4:57 sin find amplitude

HI gameelgamal
π/2 eq. 90 deg time shift .π is Pi coefficient (3.14)
I mean you nead two sample with 90deg shift time .
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FvM

Joined: 22 Jan 2008
Posts: 5044
Helped: 752
Location: Bochum, Germany

12 May 2009 6:21 calculating rms of sinusoidal signal

Unfortunately, the diagram (that can be imagined showing a sine waveform) has a phase shift near to pi rather than pi/2. It should be noticed, that the two samples method, you're referring to, is based on three prerequisitions:
1. The waveform is a sine (as illustrated by your diagram, this isn't obvious)
2. The samples have eaxctly pi/2 respectively 90° phase shift (see above)
3. The measured signal is DC-free. The above discussion is mostly about measurements with a DC offset.

smxx

Joined: 18 Aug 2005
Posts: 188
Helped: 8
Location: iran(ahwaz)

12 May 2009 9:21 how to calculate amplitude

Thank you FvM
in my 1st post I notify to fully sin wave
in last my post I mistake in showing Π/2 off sin wave only.
for sin wave with DC offset we can use as below by 3 sample (for fully sin wave with DC offset). for noisy sin wave we need more sample for digital filtering.
Be Happy and don't Worry.

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Last edited by smxx on 12 May 2009 9:24; edited 1 time in total

smxx

Joined: 18 Aug 2005
Posts: 188
Helped: 8
Location: iran(ahwaz)

13 May 2009 5:25 calculate amplitude of the signal from adc output

and by Fourier Transform we have all factors,but it's need more samples

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awaili

Joined: 18 Apr 2009
Posts: 7

15 May 2009 19:39 frequency of sine signal

sorry , but i'm looking for matlab code that can be used to calculate the amplitude and the frequency of sin signal...
if any one has any idea about it code you help me to write this code .....plz

thanks

Jack// ani

Joined: 02 Dec 2004
Posts: 484
Helped: 24

15 May 2009 21:08 how we can calcaulate the parameters of signals

awaili wrote:

Go though all the above posts, its carrying enough information to make those calculations. You've to do your homework though...

Petre Petrov

Joined: 05 Aug 2009
Posts: 51
Helped: 5
Location: Sofia

06 Aug 2009 8:49 rms dc offset calculate

gameelgamal “calculate the amplitude of sin signal ??”

Hello!
You could use one ADC to calculate all the parameters on the sinusoidal signal (SS) with or without displacement (DC offset).
You must take 4 samples per cycle of the SS (not necessarily at equal intervals, but you must know the intervals).
You should make a system with four equations using the formula below:

A = Am*sin(2*pi*Fss*t + phase) + DC

If you need parameters which are not in the formula above, you could apply the standard formulas in mathematics concerning sinusoidal signal.
I hope that is easy and useful for you.
BR

Prabakaran

Joined: 22 Jan 2007
Posts: 160
Helped: 5
Location: Chennai(India)

19 Aug 2009 16:02 calculate offset sinusoidal

Jack// ani wrote:
Wrote a little code on CCS PIC, nothing fancy standard deviation with 30 samples at work as discussed by FvM.

Have run out of 16F877A, so couldn't burnt and tested it. Any comments, mistakes, improvements are always appreciated...

#include <16F877A.h>
#device ADC=10
#include <math.h>
#fuses XT,NOWDT,NOPROTECT,NOLVP,NOBROWNOUT
#use delay(clock=4000000)
#use rs232(baud=9600,xmit=PIN_C6,rcv=PIN_C7)

void main()
{

int16 value, samples[29]; //Value is a 10bit data sample
int i;
float volts;
setup_port_a(ALL_ANALOG); // All the 8 channels are analog
setup_adc(ADC_CLOCK_INTERNAL); // Internal ADC Clock
set_adc_channel(0); // RA0/AN0(Pin2) is analog input channel

while(1)
{
for(i=0;i<=29;i++)
{
samples[i]=read_adc();
delay_us(666);
}

//SQUARE OF SAMPLES
for(i=0;i<=29;i++)
{
samples[i]=samples[i]*samples[i]; // Sqaure
value=samples[i]+value; // Sum total
}

value = value/30; // Mean of 30 samples
value = sqrt(value); // Square root

volts=(float)value*0.0048828125; // 1024 discrete levels, 5/1024 = 0.0048828125
printf("Voltage is : %3.3f\n",volts);// Print upto 3 decimal places
delay_ms(500);
}
}

I would like to add a few things
1- I suggest initialize "vaue" variable to 0
2- Do following to get rid of dc level in the signal(for example if the signal has been biased)
a. DC_Average = sumOfSample/NoOfSamples
b. For each sample samples[i] = PositiveValueOf(samples[i] - DC_Average)
c. Do the rest as in //SQUARE OF SAMPLES

Dear All

The above information is usefull to me . Can i have more details about the point(b)

Please say me in details what i should with DC Average and what would be the value.

Please say me in detail

And if i have a variable Frequency how could i sample the amplitude.

Waiting for u reply
Regards
Prabakaran