Continue to Site

Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

Impedance Calculation

Status
Not open for further replies.

mrblueblue1234

Junior Member level 1
Joined
May 28, 2019
Messages
16
Helped
0
Reputation
0
Reaction score
1
Trophy points
3
Activity points
200
In the attached image I am showing a voltage divider with the values of 50M (fixed) , 4.7k (fixed) and an unknown impedance Z.

Is it possible to calculate the value Z only using Vin, 50M and the 4.7k without using Vout directly?

I am looking for a simplified equation for Z that doesn't explicitly need Vout.

For this same application I saw a formula that didn't include Vout here so I was curious on the details.

Thank you for your thoughts.

Impedance.PNG
 

Vout is a percentage of Vin. The formula is:

(4700 + Z)
divided by
(50M + 4700 + Z)

To find Z, make the above formula equal to your desired percentage, then solve for Z algebraically.
 

Hi,

Using Brad's formula works for pure ohmic values.

But for true impedances (and this is how I understand your question) you need graphic (vector) solution.
I assume even with the value of Vout it is not possible to calculate Z as an unknown impedance.
(Combination of R L C, or R C, or R L, or L C)

Klaus

Added:
Maybe with:
* Vin, sinewave, known amplitude, known frequency
* Vout, amplitude, phase shift
* and the knwledge it is no R LC impedance
...you may be able to calculate Z
 

Thanks for the posts everyone. A follow-up to what BradtheRad posted.

My follow-up question is that if Vout is a percentage of Vin how do I know what this percentage is? Do you mean the transfer function, i.e. Vout / Vin ?


For example, if I capture some data for Vin and Vout should the ratio of Vout/Vin always been the same?

This is a simple case but I was not make sure I am following you.

divider_2R.png


table_data.png


In this case the ratio would be Vout/Vin that is ~0.091


If one of the resistors was changed I should be able to solve for this because I know the ratio and the other resistor value. Right?

Thanks.
 

Hi,

Now it's a completely different situation:
* only two resistors
* no complex impedance

You now have a simple resistive voltage divider.
The formula can be found million times in the internet.

Klaus
 

Status
Not open for further replies.

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Back
Top