Electronics > Metrology

Looking for instrument to measure 1.0 Ohm to <10ppm

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alligatorblues:
I'm searching for an instrument to measure 1.0 Ohm to <10ppm.. Anyone know of one offhand, for less than \$2,000.

mzzj:
Your requirements are off by about a decade. You probably have to choose between 100ppm and 20000 usd.

tggzzz:

--- Quote from: alligatorblues on August 17, 2023, 05:59:04 am ---I'm searching for an instrument to measure 1.0 Ohm to <10ppm.

--- End quote ---

So you think purchasing such an instrument will solve your problem.

But what is your problem?

This smells like an XY-problem situation.

Alex Nikitin:
As already noted, not enough information. What kind of resistors, what conditions? If you need to measure only one value - 1 Ohm with, say,  +/- 1% distribution with 10ppm accuracy, it should be possible with a reasonably simple bridge setup and one good quality reference 1 Ohm resistor, say Fluke 742-1 or an equivalent (only the reference with calibration data will happily eat your budget, I suspect). Whichever way you measure 1 Ohm, there will be some limits, including the maximum allowable power dissipation on the DUT - more current will give you a better sensitivity but the DUT will heat up and unless it has an exceptionally low tempco you can kiss goodbye your 10ppm accuracy. A low current will be better in this respect but the required voltage sensitivity will limit the accuracy again. For example, 1A current will give you 1uV/ppm sensitivity but 1W dissipation which is far too much (Fluke 742-1 spec is 0.5A max current) . 10mA resolves the problem with the power dissipation as it drops to only 0.1mW but the voltage change for 1ppm is almost immeasurable 10nV. 100mA looks like a reasonable compromise with 10mW dissipation which will spoil things a bit but hopefully not too much for a reasonable size resistor, with a low (2-5 ppm/C) tempco (not 0603 size though). 0.1uV/ppm sensitivity also possible to deal with, taking a good care of thermal voltages (reverse polarity switch on the bridge supply etc.). Good quality 4 way connection is required as is a quiet room with a stable temperature  ;) .

In short - 100ppm accuracy is do-able with a calibrated reference and a good meter, 10ppm from 1 Ohm is not easy at all.

Cheers

Alex

thermistor-guy:

--- Quote from: Alex Nikitin on August 17, 2023, 10:50:24 pm ---... 100mA looks like a reasonable compromise with 10mW dissipation which will spoil things a bit but hopefully not too much for a reasonable size resistor, with a low (2-5 ppm/C) tempco (not 0603 size though). 0.1uV/ppm sensitivity also possible to deal with, taking a good care of thermal voltages (reverse polarity switch on the bridge supply etc.). Good quality 4 way connection is required as is a quiet room with a stable temperature  ;) .

In short - 100ppm accuracy is do-able with a calibrated reference and a good meter, 10ppm from 1 Ohm is not easy at all.

Cheers

Alex

--- End quote ---

This would be a great DIY project - measuring nominal 1 ohm resistors with as low an uncertainty as possible, subject to
some affordable limit on build cost.

I have a self-balancing double Kelvin bridge on my DIY project list, but will take more than a year before I can get to it.

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