Multimeter probes

[Gauss163]

That explains it, it is not the most precise way to measure low ohmic values.

What do you mean by "it", the probe-shorting method, the LoZ, the spec's on that meter's range. or something else?

 

[dragosios]

That explains it, it is not the most precise way to measure low ohmic values.

That is true, but i expect it to be more precise than an order of magnitude.

 

[HKJ]

That is true, but i expect it to be more precise than an order of magnitude.

I have used that method sometimes and often seen silly results. Now I either use a power supply with constant current or a 4 terminal meter.
When the results are way off I believe that the reason is oxidized probes. Variations can also be due to zero offset in the meter and thermoelectric effects.

 

[Gauss163]

I have used that method sometimes and often seen silly results [...]

I've used it often and I don't recall ever seeing results off by 10x or more. On quality DMM's they are usually very close. Hopefully dragosios will do further tests to narrow down the culprit.

 

[dragosios]

Found a pair of older Fluke probes, maybe TL71. They show 0.080 ohms, using the same method.
The rest of the probes i have are of a modular design, wires separated from probes themselves, i guess this will add some resistance. I will test them one by one when i can (1 year old son here, he likes colorfull wires and probes and tries to eat them, not good).
Tried to measure the TL175 probes touching between them at different points, the minimum is 0.401ohms somewhere around the indent of the tip.
Also, looking at what @HKJ posted, my probes look different, the marking "Fluke TL175" is on an yellow insert together (i mean not separate, both on same yellow insert) on each probe, not like HKJ's Fluke embedded in the probe body and TL175 on a separate grey insert.

 

[alpg88]

do flukes and amprobes come with good probes??? mine are damaged a bit (burned insulation from touching hot iron) and need to be replaced soon, so should i get same oem probes or look for something better?

 

[dragosios]

In my opinion, they are decent to good probes.
But i would not by them. There are many choices from Probe Master, Pomona, SKS-Hirschmann and even Brymen. I saw on ebay gold-coated Brymen probes with silicone wire for around 18USD.

 

[alpg88]

thanks, will look for those brands, now that i know what to look for,

 

[Gauss163]

Found a pair of older Fluke probes, maybe TL71. They show 0.080 ohms, using the same method [...] Tried to measure the TL175 probes touching between them at different points, the minimum is 0.401ohms somewhere around the indent of the tip [...]

That settles it - the problem is the "TL175" probes. In this eevblog thread cyr reports that his TL175 measure 31.5 mOhm/lead, so at 7x that your probe(s) have issues. If they are genuine, then possibly one lead is bad (narrow down the culprit by testing with one TL175 and one TL171). Also try wiggling the plug and bending them near the strain reliefs while measuring. It could be a bad internal connection, or loose 4mm plug, etc.

 

[dragosios]

And the results: red TL71+black TL175=0.51 ohm, black TL171+red TL175=0.26 ohm.
At first sight, black TL175 is the worse of the two, but the red one is not too good either.
Moving the strain relief part of the probes i got the the minimum of 0.065 ohm, but the culprit seems to be the black one. There is no visible damage on outside.
I need some time to prepare a constant current source and all that precise stuff, but will be done eventually. Will post updates then.

 

[HKJ]

And the results: red TL71+black TL175=0.51 ohm, black TL171+red TL175=0.26 ohm.
At first sight, black TL175 is the worse of the two, but the red one is not too good either.
Moving the strain relief part of the probes i got the the minimum of 0.065 ohm, but the culprit seems to be the black one. There is no visible damage on outside.
I need some time to prepare a constant current source and all that precise stuff, but will be done eventually. Will post updates then.

Then you will probably get some very different results, if you check my multimeter reviews I seldom find probes with more than 0.1ohm (100mOhm) resistance (Defect cables excepted).
With good probes it is possible to use REL and measure something below 1ohm, but that do not include the probes them self.

A good stable constant current source of 1A (or 10A)* is the easiest way to measure mOhm, even my four terminal (fairly expensive) bench meters are fiddly when measuring mOhm.

*My lab power supplies can easily do that with two digits (or more) precision.

 

[Gauss163]

[...] There are many choices from Probe Master, Pomona, SKS-Hirschmann and even Brymen. I saw on ebay gold-coated Brymen probes with silicone wire for around 18USD.

Those eBay Brymen PP-BM10A probes with screw-on banana shrouds are sold by Frankie from 99cent-hobbies (he used to source many items from Asian markets for eevblog members). They seem to be well-received there, e,g, see here.

 

[HKJ]

Those eBay Brymen PP-BM10A probes with screw-on banana shrouds are sold by Frankie from 99cent-hobbies (he used to source many items from Asian markets for eevblog members). They seem to be well-received there, e,g, see here.

99cent is not Frankie anymore, he left Hong Kong. The stuff sold still looks to be good.

 

[Gauss163]

99cent is not Frankie anymore, he left Hong Kong. The stuff sold still looks to be good.

Yes, but it's the same eBay account (18 years old) and same stuff, and still 100% positive feedback since he left, so I wouldn't worry about who he has running the business now.

 

[HKJ]

Yes, but it's the same eBay account (18 years old) and same stuff, and still 100% positive feedback since he left, so I wouldn't worry about who he has running the business now.

As Frankie explained when he left, it is his brother and he do not have the same technical knowledge.

 

[Gauss163]

As Frankie explained when he left, it is his brother and he do not have the same technical knowledge.

But no one recommend the eBay seller as a source of "technical knowledge". Many trustworthy sellers have very limited technical knowledge, e.g. this is true of most all sellers of Li-ion cells, and most all sellers (and many manufacturers) of Li-ion chargers.

 

[HKJ]

But no one recommend the eBay seller as a source of "technical knowledge". Many trustworthy sellers have very limited technical knowledge, e.g. this is true of most all sellers of Li-ion cells, and most all sellers (and many manufacturers) of Li-ion chargers.

One reason for the good quality products was that he did know what he was selling.