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Low-Ohm Meter Project.

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chemelec

Well-Known Member
I have recieved numerous Requests for a Low-Ohm Meter.
So here is what I came up with.
It will Accurately measure resistances between 0.001 to 1.999 Ohms, Assuming you Calibrate it Accurately.

**broken link removed**

ENJOY, Take care.....Gary
 
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You might want to investigate 4-lead milli/micro ohm meters.
 
You might want to investigate 4-lead milli/micro ohm meters.

With the Addition of an Op-Amp, I can Easly get this to measure Milli & Micro-Ohms.
But all my requests were for Milli-Ohms.
 
Great then...go for it. But one wonders how one will overcome the inherent contact resistance of the admittedly simpler two lead measurement even in the milliohm range. Perhaps Heisenberg was in error.
 
Hi Gary,

looks OK for me.

However to achieve 100mA output current the nominal value for the adjustment resistor is 62.5Ω.

Using a 56Ω fixed value resistor and a 25 turns pot at 10Ω adjustment will be easier.

Regards

Boncuk
 
Great then...go for it. But one wonders how one will overcome the inherent contact resistance of the admittedly simpler two lead measurement even in the milliohm range. Perhaps Heisenberg was in error.

If the test leads are not changed he can use the test lead resistance and take that into consideration.

Boncuk
 
Hi Boncuk,

That is true for fixed leads or traces. My impression was it was to be for multiple measurements. I guess I didn't see that being fixed was the application intended.
 
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Two wires or four wires?

Looking at the circuit diagram, a four wire connection is implied (to my way of thinking), but not clearly stated.

Looks like a nice simple device, it should do "exactly what it says on the tin".

JimB
 
Here is a four wire Milli/Micro-Ohmmeter as suggested by MAXIM.

I doubt that it's more accurate than the simple circuit introduced by chemelec.

Accuracy is ±2% if all resistors match the given values.

Board size is 67.3X62.9mm (2.64X2.5"). Batteries (holders) are located at the bottom.

Additionally it requires two batteries, 9V and 1.5V.

Boncuk
 

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Hi Gary

Nice little home brew DLRO for those who wish to build one. Considering the bang for the buck it gets things done in a reasonable fashion.

I have a question about the face plate. The current source is labeled 100 uA? That a mistake? Also as trivia I noticed in the image of the unit running one current lead seems inboard and one outboard on the resistor leads. Not any big deal but for actual use wouldn't the current source leads be outboard?

As to the use of Kelvin leads. While I agree that they would be nice to have, many sets, even cheap sets would cost well over what it cost to build the project. I figure all things considered that just a brief explenation of how to configure the leads is adequate.

Again, nice little project.

Ron
 
Hi Gary,

looks OK for me.

However to achieve 100mA output current the nominal value for the adjustment resistor is 62.5Ω.

Using a 56Ω fixed value resistor and a 25 turns pot at 10Ω adjustment will be easier.

Regards

Boncuk

For 100mA out on the LM317LZ, the Out to Adj resistance is 12.5 Ohms.

I Calibrated the Ouput Test Current with my "Sanua DMM, Model 9100E". (Has a 4 1/2 LED Display)
(On the 200 mA Range, It can read 199.99 mA.)

MRCecil, It is NOT 2 Leads, It is 4 Leads!
The Critical Part FOR ACCURACY, is the Placement of the DMM Leads. They MUST Be Exactially Placed as shown on the schematic.
 
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