Lower voltage for resistance measurement for FLuke 289

[tonycstech]

I have fluke 289.
measuring 1.8v buck converter based circuit gives me incorrect resistance compared to other meters.
It gives me ohms instead of kohms.
This is because fluke 289 uses 2v to measure resistance and if you change the range, it will jump to 5v.
This is a big problem for me. Is there a way to change it to lets say 1v like a normal multimeter uses ?
Even 0.5v.
How am i suppose to measure 1.8v low resistance circuit pushing 2v or even 5v through it ? It screws up the reading.

Basically i need it to use about 1v in 500ohm range and 0.5v above, which i think is what every other meter uses more or less but clearly not 5v

Thanks !

[TimFox]

Make your own circuit with a low-voltage cell (1.5 V or so) and a three-resistor "T" circuit that has an open-circuit voltage of <0.5 V.
Measure the voltage with no load and with load connected, using your voltmeter.
The rest is algebra.

[tonycstech]

yea simplest solution ever.
very helpful

[TimFox]

You want the third resistor (that connects to the device under test) to be roughly the same resistance or higher than the expected resistance of the device for a good result.

[Fungus]

If the resistance changes with voltage then it's not really resistance.

[TimFox]

Yes:  that would be a non-ohmic device, many of which exist, especially in complex circuits.

[tonycstech]

If the resistance changes with voltage then it's not really resistance.

No, it would be a charging capacitor.

[tonycstech]

You want the third resistor (that connects to the device under test) to be roughly the same resistance or higher than the expected resistance of the device for a good result.

I cannot measure resistance under load.
I mean i can but i do not want to power the device before knowing the resistance.
This is madness.

[TimFox]

You want the third resistor (that connects to the device under test) to be roughly the same resistance or higher than the expected resistance of the device for a good result.

I cannot measure resistance under load.
I mean i can but i do not want to power the device before knowing the resistance.
This is madness.

What were you planning to do if you had a DMM whose output voltage was < 1 V?
By "under load", I meant connecting the battery/resistors circuit to either nothing ("no-load") or your device under test, where "loaded" meant with respect to the external network.

[J-R]

This thread is madness...

Use a power supply set for the voltage you think you desire, then use your DMM to measure the voltage drop and calculate resistance.  Ohm's law assumes ideal components, as does your DMM when in resistance mode.

[TimFox]

It is not "madness", it is "ill-posed".

[bdunham7]

How am i suppose to measure 1.8v low resistance circuit pushing 2v or even 5v through it ? It screws up the reading.

Basically i need it to use about 1v in 500ohm range and 0.5v above, which i think is what every other meter uses more or less but clearly not 5v

The F289 has a full-scale voltage of about 0.5V up to the 500k range.  Its open-circuit voltage is higher, about 5V.  There's nothing unusual about this, other meters may have more or less current or voltage in various resistance functions.  The Lo-Ohms function is different and you wouldn't want to use it for your application.

If you think the open-circuit voltage is causing some component to start (and stay) conducting when you initially connect the meter, then you could temporarily put a resistor across the test leads of the same value as the range you are using.  So you'd manually set the range to 5k, put a 5k resistor across the test leads, connect the meter and then remove the extra resistor.  As long as the resistance of your DUT is under 5k, it will not exposed to more than 0.5V this way. 

Another way would be to just use the next-higher range with a resistor equal to that range without disconnecting it.  So use the 50k range and a 50k resistor and you'll have no more than a 10% error--and one you can calculate--when you measure your DUT.  This would be handy if the first method doesn't work or you have no idea what your DUT resistance actually is.

[tonycstech]

so basically i need cheap junk multimeter to do precision work and the top leading brand is not good enough ?
Thats all i am getting out of this.

[BeBuLamar]

The Fluke is resistance measurement sends out a constant current not voltage. The curent changes with the ranges.

[TimFox]

Constant current into load, and measuring voltage across the load, is a normal method to measure resistance, and it is meaningful for an actual resistor.
Practical current sources have a maximum "compliance voltage", which is what you will find with no load across the source (just like how I told you to run my three-resistor circuit).
I have a laboratory current source with accurate current and adjustable compliance, but I don't think you need something that complicated.  Keithley 225  https://accusrc.com/uploads/datasheets/4106_225.pdf
What do you intend to measure on your device under test?  A complex circuit with semiconductors is not a resistor, but you can certainly look for a short circuit (for example).

[tonycstech]

I dont have any problems with any cheap chinese multimeters to measure resistance on a complete semiconductors circuit, any of them
But there is one particular that throws the reading off significantly which makes be believe there is a problem.
So if i cannot trust FLUKE for giving me expected reading while chinese junk does, i have no point to continue with this conversation because solutions are rather absurd.
Anything from starting from adding resistors all the way to making my own multimeter.
What is the point to pay premium for Fluke then ? Absolutely no point at this point.

[J-R]

Spot on, that junk 289 is broken, better dump it: https://www.eevblog.com/forum/buysellwanted/

[TimFox]

Different instruments connected to a given non-linear circuit will give different answers for the ratio V/I, if I is different for the two meters.  Why would your cheap meter give the better or more accurate value for an ill-defined parameter?  Not every object between two terminals is an Ohmic resistor.

[tonycstech]

its not broken. I've seen bench meters do same thing, giving me weird readings.
Only cheap chinese meters or smaller cheaper meters can measure it correctly.

[tonycstech]

Why would your cheap meter give the better or more accurate value for an ill-defined parameter?  Not every object between two terminals is an Ohmic resistor.

I dont know why. All i know is: there are hundreds if not thousands of people who use hundreds of different multimeters and they all report same values as my cheap junk.
Yet Fluke reports completely different value, much lower.
To me this sounds like a FLUKE problem than the circuit.

[Helix70]

Quality meters do not "push voltage" to measure resistance, they apply a specific current, and the voltage (compliance voltage) adjusts according to the circuit it is connected to. Perhaps your understanding of how a multimeter works is the issue here. A quick google might help you.

[TimFox]

Why would your cheap meter give the better or more accurate value for an ill-defined parameter?  Not every object between two terminals is an Ohmic resistor.

I dont know why. All i know is: there are hundreds if not thousands of people who use hundreds of different multimeters and they all report same values as my cheap junk.
Yet Fluke reports completely different value, much lower.
To me this sounds like a FLUKE problem than the circuit.

Perhaps it is your misunderstanding?

[Fungus]

Only cheap chinese meters or smaller cheaper meters can measure it correctly.

So use those instead...   

[tonycstech]

Only cheap chinese meters or smaller cheaper meters can measure it correctly.

So use those instead...   

i do. I just wanted something professional with live graph view and true RMS.
I guess FLUKE is a really a fluke/accident and not a multimeter.

[Helix70]

When used incorrectly, any multimeter reading is a fluke.