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Re: need u'r help

Started by Mariano Filippa February 27, 2004
Hi,

I don't know if I can help you with this. I guess that to calculate the
energy of the signal, you need to do some sort of FFT to decompose the
incoming signal into its fundamental frequencies. Then you can calculate the
energy content of it. You can check about this in any signal processing
book.

There is a nice link to a free e-book about signal processing. You might get
some info there : http://www.dspguide.com/

Regarding taking 230VAC to the AD, I suggest you to use a well designed
resistive (and capacitive) voltage divider, then isolate with a differential
isolator, such as Analog Devices AD210 or Agilent HPCL series or
HCNR200/201. I suggest good filtering and EMI protection. Filter the input
with a cut-off frequency less than half your sampling period.

You can also use a signal transformer if you input signal is only AC. Just
check the impedance, you don't want to use a low impedance with 230VAC.
Always try to use isolation. It is a pain in the neck to design a circuit
like this, but it is worse if you get 230VAC directly to the board. Do not
use wall transformers to step down the voltage. Generally, their magnetics
are really poor and they'll cause saturation. The output waveform will never
resemble the input.

Hope this helps,
Mariano

PS: By the way, I know my name is confusing. Mariano is a spanish male name.

----- Original Message -----
From: "noordspmot" <>
To: "Mariano Filippa" <>
Sent: Friday, February 27, 2004 1:04 AM
Subject: Re: need u'r help hello Madam,

i have been working on the dsp56805 board for a couple of weeks.
i have seen u answer many queries.so that's the reason iam posting
this query to u.

i have been asked to take the input to the adc as 230 v ac.and
calculate the energy content of the signal.

this input shall have 6 harmonics with it.

how do i calculate the energy consumed by each one (harmonics)of them.

i have read that the adc can take only 3.3v max,so we shall have to
scale it down to sample it.

pls ,help out.

thanks in advance,

bye,
Noor Khuteja

--- In , "Mariano Filippa" <mfilippa@f...>
wrote:
> I have never found the electrical specifications of 5680x family.
However, from what I've read, I assume that it also works with the
core voltage: 0V ~ 3.3V. There is an application note that might
help: DSP56800 ADC (AN1947/D).
>
> If needed to measure a sine wave, I would use either two methods:
> 1) reduce amplitude and add offset. Play around with the VREF pin
or do some sort of software calibration.
> 2) reduce amplitude and rectify (using a precision rectifier with
opamps)
>
> Check Motorola's application notes of Motor Control. They'll often
have to take a sinusoidal current feedback, add offset and isolate
from DSP. Take a look at page 29, application note MEMCOBUM/D.
>
> Hope this helps, and buena suerte
> Mariano
>
> ----- Original Message -----
> From: Oscar Javier Tadeo Jaramillo G
> To:
> Sent: Sunday, January 25, 2004 8:53 PM
> Subject: [motoroladsp] Electrical specifications for ADC > Greetings.
>
> I need work with the ADC module, sensing a senoidal wave, but i
don't know what is the max in voltage amplitude of the input for ADC.
>
> The ADC can work with negative and positive value in the input? > Thanks > Cordialmente,
>
> Oscar Javier Tadeo Jaramillo Galeano
> Nit: 98665185-4
> Telefono: 300-779-60-62 >
>
> --------------------------------
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If you want to measure the energy in an AC line you need to know the current
at the same time. You can measure the voltage but that's all you will be
measuring. If the current isn't in phase with the voltage you will not get
what you want.

Chris Pollard

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Do you need to measure the current? He is talking about measuring the energy
content of the signal, up to 6 harmonics. Here's the original question:

> i have been asked to take the input to the adc as 230 v ac.and
> calculate the energy content of the signal.
> this input shall have 6 harmonics with it.
> how do i calculate the energy consumed by each one (harmonics)of them

Don't you only need to measure the energy content of the voltage signal
regardeless the current you are taking? If you measure voltage and current,
then you are measuring power. Still, I'm not even 10% sure about this.

Mariano ----- Original Message -----
From: "C POLLARD" <>
To: <>; <>;
<>
Sent: Friday, February 27, 2004 5:42 PM
Subject: RE: [motoroladsp] Re: need u'r help If you want to measure the energy in an AC line you need to know the current
at the same time. You can measure the voltage but that's all you will be
measuring. If the current isn't in phase with the voltage you will not get
what you want.

Chris Pollard

_________________________________________________________________
Find and compare great deals on Broadband access at the MSN High-Speed
Marketplace. http://click.atdmt.com/AVE/go/onm00200360ave/direct/01/

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If it's AC - YES. You can have the voltage vary all over the place - but if
there is no current there is no energy.

Chris Pollard >From: "Mariano Filippa" <>
>To: <>, <>,"C POLLARD"
><>
>Subject: Re: [motoroladsp] Re: need u'r help
>Date: Fri, 27 Feb 2004 18:48:53 -0500
>
>Do you need to measure the current? He is talking about measuring the
>energy
>content of the signal, up to 6 harmonics. Here's the original question:
>

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