drgeoff wrote: ↑
Tue May 08, 2018 8:02 am
You don't appear to be fully understanding the discussion.
1. There is no
fix required for R1.
2. You show no figures with R2 absent nor any attempt to confirm the actual value of the input resistance of the ADC channels.
1. I did read that r1 may not need a fix and have done the calculation with and without it. Without the fix resulted in more accurate results.
2. But now I know what I need to do: confirm the results of input resistance of ADC. But according to davidcoton that number is irrelevant anyway. This may be some of my confusion.
If I know the values of v1, v2, r1 and r2, shouldn't I be able to calculate the values of rL in this circuit?
I would like to verify the resistance of the ADC channel, however, I don't know how to do that. I will contact AB electronics and see what they suggest.
And just to clarify, you say the board has 16.8k resistance in parallel, but because the vout on the board is between 10k and 6.8k, wouldn't the correction number I want to use 10k instead of 16.8k?
davidcoton wrote:I haven't checked the source (no time, have to go to work) but that equation gives a negative resistance. Unlikely.
Here is how I came up with that formula and it seems to work:
https://www.khanacademy.org/science/ele ... ge-divider
v2 = v1*(R2/(R2+R1))
solved for R2 instead of v1 and this is the equation:
r2 = (-v1*r1)/(v1-v2)
Which results in a positive r2.
Thank you both for all of your input and knowledge. You have been an enormous help in understanding this.