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[SOLVED] Resistance of a thick wire using micro controllers

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prabhukaran3

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Hi guys,
Great evening to all.

I need to measure resistance of a wire(Thick wire-resistance ~0.1-10E).... Since its very low resistance I cant develop circuits with voltage divider network and ADC... I google a week before but most of results based on Op amp(Strictly they advised to do not use LM324). Is there any simplest way to measure low resistance... Any one having working circuit for this?
 

KlausST

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Hi,

The measurement range is 0.1 ohms up to 10 ohms?

Klaus
 

horace1

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Hi guys,
Great evening to all.

I need to measure resistance of a wire(Thick wire-resistance ~0.1-10E).... Since its very low resistance I cant develop circuits with voltage divider network and ADC... I google a week before but most of results based on Op amp(Strictly they advised to do not use LM324). Is there any simplest way to measure low resistance... Any one having working circuit for this?
have a look at Analogue Devices AD5933
https://www.analog.com/en/products/...hesis-modulators/ad5933.html#product-overview

it can be used to measure very low impedances
 

ads-ee

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have a look at Analogue Devices AD5933
it can be used to measure very low impedances

Very low?
Impedance measurement range from 1 kΩ to 10 MΩ
Capable of measuring of 100 Ω to 1 kΩ with additional circuitry
That's right off the overview page you linked.

I'd say a 100 ohm is a tad bit more resistance than the resistance of a thick wire.

- - - Updated - - -

Looks like you should try out the suggestions that were posted on physics.stackexchange: https://physics.stackexchange.com/questions/90338/how-to-measure-resistance-of-a-piece-of-wire

That bridge circuit brings back memories of measuring wire resistance in HS physics class.
 

Vbase

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You can use a digital circuit or uC to generate 0.5A pulse for 1ms you will get 5V on 10 ohm resistance.
Use sample and hold or uC to sample the reading.
If your supply has 1000uF cap it wont dip during the pulse.
 

SunnySkyguy

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The simple answer is found using a 4 wire kelvin bridge and pump enough current thru the resistance to get a measurable voltage in mV.

I did the same for a 100KA diffusion welder for Monel Steel tubes joined by a Zirconium shim. The giant copper electrodes rolled around the circumference inside and out with silver impregnated greased armatures and I measured the weld current on hollow copper arm that was 30cm thick feeding the roller electrode armature.

Using 2 terminals far from the source and termination avoids the gradient magnetic fields that raise impedance, so a true resistance in pico Ohms could be made.

So all you need are two wires orthogonal to the current inside coax with ferrite CM chokes in case of ripple and a good DMM and current source. Then Ohm's Law applies.
 

BradtheRad

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An NPN transistor will respond to different test resistances in the emitter leg. (I believe this is common base operation.)



The potentiometer was moved up and down a couple times. Output is almost 1/2 V when measuring a 1 ohm test device.

This circuit consumes just a few tens of mA from a single 1.5V source.

Response is non-linear. So a microcontroller is handy for interpreting the readings.
 

horace1

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Vbase

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I've noticed that several members from India use E for Ω , good replacement for the missing key in out keyboard.
 

Vbase

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Well, now you know that you don't have to tell that you have fat fingers, tell that you have an Indian finger.
 

hobbyckts

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Simple current source can be made to measure the range which you have specified
 

prabhukaran3

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Thanks to all....

I got datasheet of that wire strip... 50 ohms/km.20 degree temperatue.. I need to measure resistance of 1m wire(~0.05ohms).. Since its very low resistance no idea about what type of current source to give. If I select 5V(Lm7805) output terminals simply get shorthed.. Then where can measure the voltage across the wire?

If you can please draw circuit and explain how it can be measure. There is no chance for voltage drop.. If I am wrong, there may be very small amount of voltage drop occurs. By having ten bit ADC its not possible.. Right? 0.004v is the resolution of 10bit.....

Poor in calculation.....was with only digital part...

- - - Updated - - -

Hi BradtheRad...

The circuit you have attached in thread looks smal and easy to do... So I will try tommorrow and let you know if there any difficulties.. Thanks machieeee :laugh:
 

KlausST

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Hi,

You need a four wire measurement.
Two "force" wires with constant current. Maybe 1.0A.

Then if there us a 50mOhms wire, then you get a voltage drop of 50mV.
Use independent sense wires to a low offset opamp. Differential setup, gain 50.

This gives a value of 2.5V.

Feed it to an ADC input.

Klaus
 

hobbyckts

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You can try for the voltage to current converter using opamps.
 

SunnySkyguy

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Yes OA with CC and sine-wave injected in loop.. Does this make sense?

if you cannot measure signal on box, then no one can help.
 

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