Sub ohm resistance measurement.

[Buk]

Is there any simple way to measure resistances less than 1Ω to 2 or 3 digits of accuracy using a cheap multimeter?

 

[ronsimpson]

No, ..... maybe.
Do you have a way to measure (and make) current? Put current through the resistor and measure the voltage drop.
You will need to measure current (1A) and voltage (1V) at the same time.

 

[Nigel Goodwin]

Yes, put a constant current through it, and measure the voltage drop across the resistor - usually done with a four wire probe, but easy to do with separate wires. Ensure the meter connections are actually on the resistor, in order to eliminate the resistance of the wires carrying the constant current.

You simply choose the current (and can switch it for different ranges) based on the required resistance range, and the FSD of your meter. You can also use an opamp to increase the sensitivity of your meter.

 

[Musicmanager]

Some members will remember Chemelec - Gary, who passed away, seems like a few months ago, but I bet it's a couple of years .. .. he was a great bloke !

He showed me this and I had intended to build it but not yet got around to it; Knowing Gary's designs I'm sure it will work well .. .. .

MM

 

[audioguru]

I agree that Gary was a nice guy and provided us with many of his excellent circuits.

 

[danadak]

Build an Accurate Milliohm Meter - Circuit Cellar

A milliohm meter is a handy benchtop tool for measuring small electrical resistance values. In this article, Mark Driedger details how to build a microcontroller-based milliohm meter that accurately measures DC resistance from 10 mΩ to 10 kΩ. I built an Arduino-based milliohm meter that...

circuitcellar.com

Milliohm Meter Version 1.5

A milliohm meter is a very handy piece of test equipment. Most hand-held multimeters cannot measure low resistances and bench meters that can, are usually quite expensive. [barbouri] has shared det…

hackaday.com

Possibilities.


Regards, Dana.

 

[Pommie]

Some members will remember Chemelec - Gary, who passed away, seems like a few months ago, but I bet it's a couple of years .. .. he was a great bloke !

Agree completely and was surprised when I discovered that his site is still available. http://chemelec.com/

Someone should make a copy of this before it disappears.

Mike.
Edit, seems it was Nov 7th 2019. Over two years ago.

 

[Nigel Goodwin]

Some members will remember Chemelec - Gary, who passed away, seems like a few months ago, but I bet it's a couple of years .. .. he was a great bloke !

He showed me this and I had intended to build it but not yet got around to it; Knowing Gary's designs I'm sure it will work well .. .. .

View attachment 135202

MM

A friend of mine designed and built one the other year, very similar to that - he'd been wanting to built one for many years, but couldn't find a reasonably priced four point probe, then he discovered cheap parts from China

I was going to built one for work, but then I just ordered a complete meter from China.

 

[Musicmanager]

I agree that Gary was a nice guy and provided us with many of his excellent circuits.

OMG !

Somebody call the Police .. .. .. AG's agreeing with me !

 

[Buk]

Build an Accurate Milliohm Meter - Circuit Cellar

A milliohm meter is a handy benchtop tool for measuring small electrical resistance values. In this article, Mark Driedger details how to build a microcontroller-based milliohm meter that accurately measures DC resistance from 10 mΩ to 10 kΩ. I built an Arduino-based milliohm meter that...

circuitcellar.com

Milliohm Meter Version 1.5

A milliohm meter is a very handy piece of test equipment. Most hand-held multimeters cannot measure low resistances and bench meters that can, are usually quite expensive. [barbouri] has shared det…

hackaday.com

Possibilities.


Regards, Dana.

Thanks.

Any thoughts on the comparative efficacy of this one?

 

[rjenkinsgb]

For info and depending on the accuracy you need, the Peak ESR70 meter reads low value resistance to two decimal places, eg. 10 mOhm increments - and it's a very useful device for checking capacitors, the main reason I got one.

Peak Atlas ESR Gold ESR Plus model ESR70 | Peak Electronic Design Limited

 

[Nigel Goodwin]

For info and depending on the accuracy you need, the Peak ESR70 meter reads low value resistance to two decimal places, eg. 10 mOhm increments - and it's a very useful device for checking capacitors, the main reason I got one.

Peak Atlas ESR Gold ESR Plus model ESR70 | Peak Electronic Design Limited

And are made not far from me, in fact I visit a friend on the same Industrial Estate as Peak are - we sub-contract work to my friend.

The Peak instruments are also PIC based, but pretty expensive, I have two of them - where my friend has the full range, given to him for evaluation purposes as he's very near to them.

I actually have an ESR70 (old version) but there's no mention of using them as a low resistance meter, only for ESR - as it uses 100KHz for it's readings it's accuracy as a resistance meter would be suspect (such as trying to read wirewound resistors). Great little instruments though.

 

[Buk]

Peak ESR70 meter

Looks like a great device; just more pennies than I can justify for something that might get used twice a year.

 

[Nigel Goodwin]

Looks like a great device; just more pennies than I can justify for something that might get used twice a year.

If you're repairing switch-mode PSU's (in TV's, set-top boxes etc.) then you use them multiple times per day for checking ESR of the electrolytics - otherwise you're unlikely to use it as much as twice a year, I've not used mine once in the three years or so since I stopped TV etc. repairs.

As I mentioned above, it's not designed for resistance measurements.

 

[rjenkinsgb]

As I mentioned above, it's not designed for resistance measurements.

According to the label, the present version explicitly is?

 

[Nigel Goodwin]

According to the label, the present version explicitly is?

View attachment 135260

I see that's the Plus, not just the ESR70 - does it work OK then on wirewound resistors?, I'm presuming it still tests at 100KHz?.

 

[rjenkinsgb]

does it work OK then on wirewound resistors?

Interesting point!

I don't have a large selection of low value wirewounds, but I've found three:
0.22 10% = 0.28
1R0, no tolerance = 1.34
1R5 10% = 1.82

As a comparison, a one ohm metal film 1% reads 1.00

It does appear to read somewhat high on wirerwounds.

 

[Nigel Goodwin]

Interesting point!

I don't have a large selection of low value wirewounds, but I've found three:
0.22 10% = 0.28
1R0, no tolerance = 1.34
1R5 10% = 1.82

As a comparison, a one ohm metal film 1% reads 1.00

It does appear to read somewhat high on wirerwounds.

Surprising on the 0.22 ohm, as when you look at them there's VERY few windings, so presumably not much inductance?.

However, it's always been suggested that you don't use wirewounds for emitter resistors or zobel networks in high quality audio amplifiers, because of their inductive nature.

 

[ChrisP58]

Even carbon and metal film resistors can be inductive. At least the axial through hole types.

They're usually made by depositing a continuous film on the alumina core. Then a spiral is cut into the film to make up the actual resistance.

https://www.eeweb.com/overview-of-the-film-type-resistors/