AVR-Chat

I am using two ADC's here (current and voltage monitoring). one ADC to measure voltage from 0-70. and another for current from 0-500 mA. For current monitoring, I used a current sense resistor and a precision op amp plus ADC. For the voltage monitoring, i used a voltage divider plus ADC. Sample rate is not critical. i dont mind reading it very slow. I just want to come up with acurate reading specially for the current.
   
  regards
  mago
   
  

Jim Wagner <jim_d_wagner@applelinks.net> wrote:
          doubly bad...

Your accuracvy in this situatioh will be dominated by the
voltage divider. You will have to pay a lot of money to get
0.1% resistors which is about what you would need to get
the accuracy contribution of the divider equal to the
accuracy of a 10 bit ADC with perfect reference mid-scale.

With a normal "good" reference, the full accuracy gets
worse.

How much "accuracy" do you need? 1% - 0.1% - 0.001%? 

And at what sample rate and bandwidth? What are the
processing and output requirments?

Jim

On Wed, 13 Jun 2007 21:20:27 -0400
Robert Adsett <subscriptions@aeolusdevelopment.com> wrote:
> At 06:04 PM 6/13/2007 -0700, mago Umandam wrote:
> >Yes, what i need ti accuray. Well, i opted higher
> resolution since the 
> >voltage im measuring is of high range 0-80 V. i assume
> higher resolution 
> >will give better accuracy.
> 
> Bad assumption. To get higher accuracy you need a lot
> more than higher 
> resolution. To get 16 bit accuracy you need to get your
> noise, sensor 
> accuracy, reference voltage and probably power supply
> stability to better 
> than 1 part in 65536. This is a non trivial exercise.
> 
> If you can define what you actually need a little better
> perhaps an easier 
> approach can be suggested. For instance do you really
> need to cover the 
> full 0-80 or perhaps a subrange? would a log scale work?
> 
> Robert
> 
> http://www.aeolusdevelopment.com/
> 
> From the Divided by a Common Language File (Edited to
> protect the guilty)
> ME - "I'd like to get Price and delivery for connector
> Part # XXXXX"
> Dist./Rep - "$X.XX Lead time 37 days"
> ME - "Anything we can do about lead time? 37 days seems
> a bit high."
> Dist./Rep - "that is the lead time given because our
> stock is live.... we 
> currently have stock."
> 

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