Absolute Best MultiMeter Test Leads - Very Low Resistance?

[2N3055]

Your 2-wire 4-wire test is interesting. Are your 2-leads compensated for in any way?

Those are special Fluke TL2X4W-PTII 2x4W test probes that are also 4W in compact form. It is not 2W setup

[tooki]

Yeah I understand all that, but I asked what they expect to gain by further improving the leads, i.e. beyond the already-superb Probe Master 8100 they already have?

I don't see an 8100 model, so I wanted to be clear that the pogo pin style was what he has.  If not, there is clear improvement to be had by going pogo.

As for further improvement, as I mentioned sometimes Kelvin sensing is impractical and the Fluke 2X4W system gives you the convenience of normal probes with much better performance, perhaps 100X better than a typical 2W setup. You can also get a probe set from Pomona the does something similar with almost any 4W-ohms meter.  I tried making my own, but was unable to source a decent tip end and the ProbeMaster SS tips don't work well enough.  If the OP has a compelling need to do low-resistance measurements with probes, than this is the way to go.

Your 2-wire 4-wire test is interesting. Are your 2-leads compensated for in any way? I ask because if they are not then we know something is perhaps off with your tests? Each test wire is expected to have more than 1.46mOhm per foot.

I did a little data searching, apply some physics. The best economical wire is likely gonna be silver plated copper wire. In kinda ideal circumstances such wire that is 12awg will give us approx 1.46mOhm per 30.48cm (1 foot). That's just for wire. Need to also account for junction points of different metals.


If your test leads are 1ft each and 12awg, we should expect to see your meter pick up a diff of ~3mOhm between 2-wire and the 4-wire test.
Your meter seems to only show a diff less than 1mOhm, displays closest 1mOhm (assumed to be from rounding), etc.

Another thing to note, 10.000 ohms vs 9.999 ohms can actually be way less than 1m Ohm depending of how the unit rounds off in order to paint the digital display.
Eg; if it rounds up at the 0.5 mark and down when under 0.5, a diff of just 0.0001 ohm (0.1m ohm) could mean a display diff of 10.000 vs 9.999 (1mOhm). That's a 10x differential between measured and displayed.

You missed the point — those aren’t standard two-wire probes. They’re special 4-wire kelvin probes that have kelvin connections right to the points, and then special custom 2-conductor banana plugs, so that that dual plug is actually 4 wires.

[Randy222]

Your 2-wire 4-wire test is interesting. Are your 2-leads compensated for in any way?

Those are special Fluke TL2X4W-PTII 2x4W test probes that are also 4W in compact form. It is not 2W setup

Are they just ungrounded-shielded 1-wire per probe?
That 1st pic shows just two single probes.

[2N3055]

Your 2-wire 4-wire test is interesting. Are your 2-leads compensated for in any way?

Those are special Fluke TL2X4W-PTII 2x4W test probes that are also 4W in compact form. It is not 2W setup

Are they just ungrounded-shielded 1-wire per probe?
That 1st pic shows just two single probes.

Just google Fluke TL2X4W-PTII

These are special 4W probes that work only with certain Fluke DMM

[Veteran68]

Silicone test leads BL21S2-T4SC Brymen

I have the ProbeMaster (both springy and normal) and Brymen. The ProbeMasters are certainly nicer, but the Brymen are not too bad either (esp. considering the price) - so the Brymen probes stay with the Brymen meter.

I have several sets of ProbeMasters (also both normal and springy) as well as a few extra sets of Brymen leads besides those that came with my Brymen meters. I love the PMs but they're a bit bulky to keep with smaller handheld DMMs so I keep them at my bench, and use the Brymen leads for portable use. Especially as replacements to the now-crappy TL75 leads that Fluke ships now. The Brymen leads are excellent, and an outstanding value at ~$10 a set.

I also have several sets of cheap Chinese leads that cost <$5 that are surprisingly good. Silicone (or at least very soft PVC, I haven't tried the melt test) wires and sharp gold-colored (plated? not sure) probes.

[Randy222]

You missed the point — those aren’t standard two-wire probes. They’re special 4-wire kelvin probes that have kelvin connections right to the points, and then special custom 2-conductor banana plugs, so that that dual plug is actually 4 wires.

Ahhh, so the current wire and the Vsense wires terminate somewhere in the probe downstream from probe tip? Doesn't that leave a little ohms between current path and Vsense points?
With the std 2-clamp 4-wire you are clamping current and Vsense at the same points.

[2N3055]

You missed the point — those aren’t standard two-wire probes. They’re special 4-wire kelvin probes that have kelvin connections right to the points, and then special custom 2-conductor banana plugs, so that that dual plug is actually 4 wires.

Ahhh, so the current wire and the Vsense wires terminate somewhere in the probe downstream from probe tip? Doesn't that leave a little ohms between current path and Vsense points?
With the std 2-clamp 4-wire you are clamping current and Vsense at the same points.

It does, but at very low resistance value that is below/ almost below what those meters can measure anyways...
Not perfect but superior to 2W setup but still simple to use...

[tooki]

You missed the point — those aren’t standard two-wire probes. They’re special 4-wire kelvin probes that have kelvin connections right to the points, and then special custom 2-conductor banana plugs, so that that dual plug is actually 4 wires.

Ahhh, so the current wire and the Vsense wires terminate somewhere in the probe downstream from probe tip? Doesn't that leave a little ohms between current path and Vsense points?

Correct.

With the std 2-clamp 4-wire you are clamping current and Vsense at the same points.

Yep, we know that.

[bdunham7]

Ahhh, so the current wire and the Vsense wires terminate somewhere in the probe downstream from probe tip? Doesn't that leave a little ohms between current path and Vsense points?
With the std 2-clamp 4-wire you are clamping current and Vsense at the same points.

The 'wires' are coaxial cables and the left set of input jacks on the meter are something they call "Split Jack" connectors.  It has what looks like a banana jack but there are two separate sides.  If you plug a standard banana plug into it, it simply bridges the two sides.  In the picture I've plugged in a set of the 2X4W test leads that have matching split plugs internally.  Yes, the both sides of the coax are soldered to the probe tips so you have a bit of resistance left at that end, but they use gold-plated CuBe for those tips and the residual resistance is less than one milliohm per tip measured at the sides, a tiny bit more if you are using the sharp point.

The whole setup has the advantage that you can use the meter normally on other ranges without changing the probes, in addition to getting good low resitance readings without using Kelvin clamps.

[Randy222]

Just google Fluke TL2X4W-PTII

These are special 4W probes that work only with certain Fluke DMM

I see them. (https://www.fluke.com/en-us/product/accessories/test-leads/tl2x4w-ptii/ds)
Those ports must have dual contact in each port? (as just read in the reply behind this one).

Given there's still a small current path outside of the Vsense on DUT side, let's say just 0.75" between tip and junction point in probe case, 0.75" of std copper wire of 18awg (probe tip dia), is gonna be around 0.406m-ohm each, x2 for 0.812m-ohm, which is enough to make a meter that reads to nearest 1m-ohm display non-accurate reading (assume using a 0.5 rounding scheme).

The 4-wire (two jack) setup that has just two probe tips, needs to have the tips fat and very short so that the ohms there adds into any rounding the meter will use, of which all efforts simply bring you back towards the 4W 4-probe configuration. Eg; actual is 1.0034 ohm, ideal is meter shows 1.003. Add in just 0.1m-ohm from probe tips, meter reads 1.0035 and then rounds up for display of 1.004. Yikes, the probes (super low additional ohms) makes the meter tell you the measured is 0.6m-ohm more than actual, vs 1.003 which is 0.4m-ohm below actual, yet from just the display diffs you see it as a 1m-ohm diff ! This appears to be what the pics have shown?

So I guess, why use a 4W 2-probe if the goal of any 4W is to remove any probe ohms from the readings? With the 1m-ohm resolution meter, the diplayed diff from error is near 1m-ohm, whereas the 4W 4-probe the displayed diff is from device resolution rounding.

[Randy222]

Silicone test leads BL21S2-T4SC Brymen

I have the ProbeMaster (both springy and normal) and Brymen. The ProbeMasters are certainly nicer, but the Brymen are not too bad either (esp. considering the price) - so the Brymen probes stay with the Brymen meter.

I have several sets of ProbeMasters (also both normal and springy) as well as a few extra sets of Brymen leads besides those that came with my Brymen meters. I love the PMs but they're a bit bulky to keep with smaller handheld DMMs so I keep them at my bench, and use the Brymen leads for portable use. Especially as replacements to the now-crappy TL75 leads that Fluke ships now. The Brymen leads are excellent, and an outstanding value at ~$10 a set.

I also have several sets of cheap Chinese leads that cost <$5 that are surprisingly good. Silicone (or at least very soft PVC, I haven't tried the melt test) wires and sharp gold-colored (plated? not sure) probes.

Any test leads for ohms, at least ones anyone can afford to buy, will be no better than silver plated copper wire that is soldered to termination using high silver solder.
For perhaps bench tests, practical use limitations seems to be near 1ft 12awg.

A meter that is tuned for best possible performance perhaps does not have panel jacks, but rather the wire is soldered directly to PCB to remove insertion/contact losses. 0.1m-ohm here, 0.1m-ohm there, it all adds up.

[tooki]

Given there's still a small current path outside of the Vsense on DUT side, let's say just 0.75" between tip and junction point in probe case, 0.75" of std copper wire of 18awg (probe tip dia), is gonna be around 0.406m-ohm each, x2 for 0.812m-ohm, which is enough to make a meter that reads to nearest 1m-ohm display non-accurate reading (assume using a 0.5 rounding scheme).

The probe tips are 2mm diameter, which is very close to 12AWG, not 18AWG.

12AWG copper has a resistance of approximately 0.00521 ohms per meter.
0.75” = 19.05mm = 0.01905m

So the resistance of one probe tip is 0.00521 x 0.01905 = 0.0000992505 ohms. That’s about 100μOhm, significantly less than the 406μOhm you calculated (which would be correct for 18AWG).

The 200μOhm probe resistance is an order of magnitude smaller than the accuracy spec of the best multimeter that can use these probes (8846A, 1.3mOhm maximum error for tightest spec), and two orders of magnitude smaller than the accuracy spec of the meter shown in the pictures (8m08A, 10mOhm maximum error for tightest spec). In both cases, calculated using the actual resistance and applicable range.

So I really don’t think this is a real problem.

[Randy222]

Given there's still a small current path outside of the Vsense on DUT side, let's say just 0.75" between tip and junction point in probe case, 0.75" of std copper wire of 18awg (probe tip dia), is gonna be around 0.406m-ohm each, x2 for 0.812m-ohm, which is enough to make a meter that reads to nearest 1m-ohm display non-accurate reading (assume using a 0.5 rounding scheme).

The probe tips are 2mm diameter, which is very close to 12AWG, not 18AWG.

12AWG copper has a resistance of approximately 0.00521 ohms per meter.
0.75” = 19.05mm = 0.01905m

So the resistance of one probe tip is 0.00521 x 0.01905 = 0.0000992505 ohms. That’s about 100μOhm, significantly less than the 406μOhm you calculated (which would be correct for 18AWG).

The 200μOhm probe resistance is an order of magnitude smaller than the accuracy spec of the best multimeter that can use these probes (8846A, 1.3mOhm maximum error for tightest spec), and two orders of magnitude smaller than the accuracy spec of the meter shown in the pictures (8m08A, 10mOhm maximum error for tightest spec). In both cases, calculated using the actual resistance and applicable range.

So I really don’t think this is a real problem.

Just checking my math. 0.75" 12AWG copper is approx 0.09674 m-ohm
x2 = 0.19348 m-ohm

So yeah, that's approx 5x below resolution of the display. However, the +0.2 m-ohm can still help trip rounding, which can look like a full 1 m-ohm diff on display.

Silver plated copper may improve things, but obviously oxidation plays a role. But since they can stick to each other I wonder if you can find copper plated silver to get between copper and silver-plated-copper.

[bdunham7]

So I really don’t think this is a real problem.

So yeah, that's approx 5x below resolution of the display. However, the +0.2 m-ohm can still help trip rounding, which can look like a full 1 m-ohm diff on display.

The 8808A 1-year spec would be 11 counts or 11mR, the 8846A would be 400 counts or 4.00mR (it has a 10R range in addition to the additional digit, along with a 5mA test current).  So while the effect of the probe tip resistance might be observable on the 8846A, it is pretty small compared to any reasonable expectations for the 8808A, which will typically wander around a few counts of 1mR each. With the 8846A using the ZERO (aka REL) function seems to be an improvement for looking at relative or near-zero resistances, but the overall effect is probably not much more than the best-case unexpanded uncertainty of the meter itself.  Also, thermal and contact voltages can cause variances greater than 1mR, even with Kelvin clips.  Gold-plated copper is the way to go IMO.

Here's a demonstration.  If I were trying to impress you with the 2X4W system, I'd just show the first photo!  But the reality is that microohms are hard to measure with small DC test currents. 

[Kleinstein]

The resistance if the probe is not the main quality point. The more tricky parts are contact resistance (as this is not that well reproducible) and the thermal EMF - so how much extra voltage is seen if one had touched the probes and made them warm a little. With poor probes one may get to the 100µV range this way. Part of the effect may also come from inside the meters, so it is not such an easy part to test.

Another point can be the quality of the isolation, when measuring high resistance (e.g.  100 M range). This would be less with a handheld meter, but could be a thing with a good bench meter.

[bdunham7]

With poor probes one may get to the 100µV range this way. Part of the effect may also come from inside the meters, so it is not such an easy part to test.

Yes, it's worth pointing out that the .00052 ohms of the probe tips as shown in the above photo represents 2.6 microvolts at a 5mA test current. 

[Randy222]

On that 8846, if you remove any REL setting and clamp the probes together at midpoint, what reading do you get?

[bdunham7]

On that 8846, if you remove any REL setting and clamp the probes together at midpoint, what reading do you get?

Between 1 and 3 milliohms, with a bit of variability depending on exactly how you hold them. 

[evmillan]

In case you want to measure very low resistances, for less than the price of two pairs of Fluke test leads you can buy the PeakTech 2705 Milliohmmeter.


https://www.peaktech.de/uk/PeakTech-P-2705-Digital-milliohmmeter-4-000-counts-400-mO-4-40-O/P-2705

It comes with 4-pin Kelvin test leads

[Randy222]

In case you want to measure very low resistances, for less than the price of two pairs of Fluke test leads you can buy the PeakTech 2705 Milliohmmeter.


https://www.peaktech.de/uk/PeakTech-P-2705-Digital-milliohmmeter-4-000-counts-400-mO-4-40-O/P-2705

It comes with 4-pin Kelvin test leads

Be nice to see what it measures when clamped to a 1inch section of solid 12awg copper wire.
Reviews of PeakTech here on EEVb are not that great.
Seems like PT brand is sold as Southwire in North America ?

[nytefog]

Lol, Jesus!  I was just looking for some suggestions on others opinions regarding the best quality test leads for 2-wire DMM resistance measurements.  I understand that a 4-wire/kelvin milliohm meter would be the best option for low resistance measure but unfortunately that’s not something I’m able to invest in at the moment.

So, if I’ve read correctly the Probe master Spring Loaded Micro-Tip Test Leads (8152) give better resistance reading than probe master 8100 series “softie” (8017s).

I’m mainly using them to take measurements of HVAC Inverter compress windings that have a low OEM specified Resistance range from 0.41- 0.72 ohms depending on the model.

Thanks

[bdunham7]

So, if I’ve read correctly the Probe master Spring Loaded Micro-Tip Test Leads (8152) give better resistance reading than probe master 8100 series “softie” (8017s).

I’m mainly using them to take measurements of HVAC Inverter compress windings that have a low OEM specified Resistance range from 0.41- 0.72 ohms depending on the model.

Yes, with proper technique you should be able to read those reasonably well using the 8152 or 8153 (which I have) and a Fluke 289 in Lo-Ohms mode.  The stainless steel versions would not do as well because the contact resistance changes depending on how far you stick those sharp tips into the solder joint, if that's where you're putting it.

[shapirus]

I understand that a 4-wire/kelvin milliohm meter would be the best option for low resistance measure but unfortunately that’s not something I’m able to invest in at the moment.

Are you sure?

Get a YR1035 with axial probes and alligator clamps. It's a cheap, but solid performer in the mOhm (and up to 200 Ohm) range with one caveat: it measures with 1 kHz AC, so results will be off when the measured part has a sufficiently high inductance. It can also measure internal resistance of batteries.

Trying to solve the inherent difficulties of 2-wire low resistance measurement by reducing the resistance of the probes is not going to yield a satisfying result anyway.

[Randy222]

Lol, Jesus!  I was just looking for some suggestions on others opinions regarding the best quality test leads for 2-wire DMM resistance measurements. I understand that a 4-wire/kelvin milliohm meter would be the best option for low resistance measure but unfortunately that’s not something I’m able to invest in at the moment.

So, if I’ve read correctly the Probe master Spring Loaded Micro-Tip Test Leads (8152) give better resistance reading than probe master 8100 series “softie” (8017s).

I’m mainly using them to take measurements of HVAC Inverter compress windings that have a low OEM specified Resistance range from 0.41- 0.72 ohms depending on the model.

Thanks

The best you can probably buy will be silver plated copper end-to-end (with maybe the tips and nanna plugs gold plated), with leads that are as short as you can use.
Your next option is just to find a reputable brand that can give you a real spec on how much ohms each lead really is, you then just use that # to offset your readings (which is just as good as 4W method).
Next can possibly be someone you know can spec the leads for you, use that # to offset meter readings.

Lastly, knowing the general properties of the leads (length, wire type, wire size, temp), you can use online claculator to drum up an approx ohmic value of the leads. You can even estimate nanna to tip, then add in tip ohms since tip is different size than lead wire.

And final lastly. You don't really need "the best low ohms" leads. You just need to know what you have.

[Veteran68]

Without going to exotic extremes and costs -- and you made it pretty clear you're doing this to avoid the cost of proper low-ohm gear -- you're going to be hard pressed to do better than ProbeMaster probes. Another advantage of PM is the ability to order them in a 24" length, shorter than most other meter leads. I hear they'll also do custom sizes, but not sure if they offer that for single quantity orders, or what it might add to the cost.