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How to measure milli ohm resistance?

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sztibi82

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Does have someone an idea how to measure milli ohm resistance?
If someone has a schematic for a miliohmmeter please post here.


It is possible to measure milliohm at 10kHz? while with frequency resistance change.

Thank you.
 

milliohm measurement

Hi,
I don't know what resistance you wanna measure ?
But I can tell you a Tip used to measure the resistance of winds in big Transformer.
Since V=R*I and R is very weak use a strong current and a Voltmeter to determine R.
 

measuring milliohms

sztibi82 said:
Does have someone an idea how to measure milli ohm resistance?
If someone has a schematic for a miliohmmeter please post here.


It is possible to measure milliohm at 10kHz? while with frequency resistance change.

Thank you.
Click to expand...
Whether you are aiming at impedance measurement? There are impedance bridges
and if it is pure resistance, there would be NO change with frequency.

4 wire Milli-Ohm meters with constant current source are generally used.
Sarma
 

how to measure milliohm

sztibi82, you should first try with bridge measurement. Search for low ohmic impedance measurement. There should be plenty of links
 

measure low resistance

Than you for the answeres.


The resistance of components change with frequency, while penetration depth is decreased, resistance increases.

I want to measure these resistances on several frequencies, to make a diagram.
 

how to measure milliohms

Hello,

I guess, when measuring AC "resistance" of a conductor, you are referring to the real part rather than impedance or apparent resistance? In this case, AC measurement must be taken vectorial to get real part (ohmic resistance including losses due to proximity effect) and imaginary (inductive resistance) separated.

Apart from necessary vectorial analysis, for a low ohmic measurement usage of separated source and sense connection to device under test, is even more recommended with AC, cause you get cable inductance as additional issue.

Basic measurement circuit would be similar to 4-terminal DC measurement: Sourcing a current to DUT and measuring the voltage at the terminals, additionally separating real and imaginary part by a synchrone demodulator synchronized from source, or doing the analysis in digital signal processing as with the Analog Devices AD5934 impedance converter IC.

Regards,
Frank
 

100 milliohm

The AD5934 works only above 100 ohms.
How can i reduce it to milliohms?
 

measure milliohms

sztibi82 said:
The resistance of components change with frequency, while penetration depth is decreased, resistance increases.

I want to measure these resistances on several frequencies, to make a diagram.
Click to expand...
So you want to determine the skin effect of your "components"?
Please specify what you understand by "components"!

What frequency range do you intend to use?
I gues good old HP 4285A LCR meter could do the job.
 

50 milliohm

Hello,

i did't want to particularly suggest AD5934 for a milliohmmeter but as a reference for a vectorial impedance meter. Basically you could supplement AD5934 with external amplifiers to extent the range. But for low impedance measurements, it should also utilize 4-terminal measurement, which would need a somewhat different circuit. For low impedance range, it could be meaningful to exchange voltage source by current source and current sense by voltage sense and invert the impedance value in postprocessing.

It's also true, that commercial LCR meters can do the job, some of them could be available from secondhand. But for the low resistance range, they have different specification, not all may be able to measure mΩ or µH accurately.

Regards,
Frank
 

impedance meter analog devices

I mean by components bus bars and coils.
 

ac milliohm circuits

Hello,

yes, I also imaged power electronic components when considering low impedance LCR (or LR in this case) instruments. I have been recently using a HP 4261A for such purposes, it has 1 mΩ range. Current Agilent replacement 4263B has almost similar data, execept for an additional higher measuring frequency of 100 kHz and a lot of extras.

4261A and larger 4262A user and service manuals are downloadable from agilent.com, including circuit diagrams. It may be however somewhat difficult to indentify the basic measuring circuit among the surrounding functions.

For professional purposes, I would try to get a HP4261A or 4262A from surplus or ebay. As I already said, it's no problem to design either a fully analog or "digital" vectorial impedance meter for low range. The basic measuring circuit can either be current source with voltage sense or voltage source with current sense. The said Analog Devices IC is using the latter principle, primary measuring succeptance, for low range the first is probably better.

The source has to be driven by a sine wave of suitable frequency, the sensed value has to be processed vectorial to separate real and imaginary impedance part. This is rather easy for sine wave, it can be done with a simple synchronous demodulator made from an OP and an analog switch.

Regards,
Frank
 

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