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Topic: Ohm meter accuracy (Read 3239 times)previous topic - next topic

zerocool5878

Dec 21, 2012, 06:38 am
I would like to build a circuit that measures resistance of a coil but I have a few questions.

First I am wondering how much resolution I will be able to achieve. I would like to get at least .1 resolution but .01 would be even better.

This project will also read the voltage as well. I currently have a voltage divider setup and i have it reading pretty accurately. I would like the resistance to refresh even as voltage is passing thru the coil so I assume the voltage divider is probably not going to work because anything else I tap into that circuit will change my resistance of the voltage divider. Could I somehow use a transistor maybe to oscillate the ground on and off of the voltage divider and store the value while the ground is now connected to other voltage divider?

Here is what I had in mind

+------4.7k---------4.7k---------GND
|
Analog  0 - Voltage

+------10k---------Coil------GND
|
Analog 1 - Resistance

Or maybe there is a better way to do this altogether

John_Smith

#1
Dec 21, 2012, 07:00 am
most coils are only a few ohms, so your 10k resistor is way too high.

Are you sure its resistance of the coil you want to measure and not its inductive reactance?  ( which is like resistance to AC signals, which depends on frequency )
45 years of editing projects with a knife and soldering iron, then I found Arduino !

zerocool5878

#2
Dec 21, 2012, 08:18 am

most coils are only a few ohms, so your 10k resistor is way too high.

Are you sure its resistance of the coil you want to measure and not its inductive reactance?  ( which is like resistance to AC signals, which depends on frequency )

Yes definitely resistance I need. The coil is made from nichrome wire and I need to read from 1 to 5ohms in .1 increments.

jackrae

#3
Dec 21, 2012, 09:27 am
See the attached for the basis of low resistance measurement.