Replacing The Manufacture’s Jumper Bar

[DonR]

In your post above, you stated that meter is great.

It's OK for general hobbyist work but making such extreme measurements requires specialist equipment. The cheapest new meter I know of that can get to 1 milliohm is a DER DE5000 LCR meter (which is also good at measuring capacitors for ESR although not the most robust handheld meter). It sells for about $50 on eBay.

 

[Speedskater]

In your post above, you stated that meter is great.

Yep, it's a great low budget meter! I use them all the time. But they are not suited to this task. Heck, there are lots of tasks that are outside the range of the yellow DT830B meter.
* * * * * * * * * * *
My 6 & ½ digit, 4 terminal Keithley Model 2000 Multimeter (available used for under $1000) has a resolution of 100 micro Ohms. That might be enough.

 

[antcollinet]

OK - lets do some simple maths:

R = ρL/A

Where
R = resistance,
ρ = resistivity of the material
A = cross sectional area of the conductor.
L=length of the conductor.

Some resistivity figures, taken from : https://www.rfcafe.com/references/electrical/resistivity.htm

Material

Material	Resistivity, ρ @ 20 °C (Ω·m)
Copper	1.72E-8
Brass	3.00E-8
Silver	1.59E-8
Steel	46.0E-8

Lets say a jumper bar is 1cm wide, 3cm long and 1mm thick.

Cross sectional area is 1cmx0.1cm / 10000 (to get it in m^2) = 0.00001m^2
Length in m = 3/100 = 0.003

So resistance of the jumper bar in the different materials is ρ*0.003/0.00002

Gives:

Material	Resistivity	area (m)	length (m)	resistance (mΩ)
Copper	1.72E-08	0.00001	0.03	0.052
Brass	3.00E-08	0.00001	0.03	0.090
Silver	1.59E-08	0.00001	0.03	0.048
Steel	4.60E-07	0.00001	0.03	1.380

As you can see, the difference between copper and brass is from 0.05mΩ to 0.09mΩ

Even if the jumper was stamped from steel, with more than 20x the resistivity, it is only going to be 1.38mΩ

For a wire jumper to have the same cross sectional area, you'd have to be using 7awg. Even if the jumper were only 0.5mm thick, you'd still be talking about 10awg.

I put it to you all, that the resistance of jumpers - copper or brass, are not a problem. Any issues with your measurements are either with the measurement kit, or getting a sufficiently low resistance contact.

 

[Deleted member 48726]

Hmm, when using the 200u setting on the metal jumpers, I get a reading of 0.00.

You should set the DMM to OHM and not use the probes but install the jumper bars on the speaker terminal clamps. or somethings similar that has the same area of contact than the terminal screws.

They are completely capable of conducting enough current to make your speakers burn down. You've been questioning this before-->

What cables do you use in your systems?

But the difference after installing the wire jumpers is not imagination. How do you know that?

www.audiosciencereview.com

Also a comparison. Below is a 40 A fuse. Look at the filament..

 

[MAB]

@MarcT you need two things to make such low resistance measurements.
You need a specialized measurement setup that allows for the lead resistance to not factor into the resistance measurement. The leads on a 2-wire Ohmmeter will be much higher resistance than the device you are testing, in this case a little piece of copper with very low resistance. Please read chapter 3.3.1 of the Low Level Measurement Handbook:

https://download.tek.com/document/LowLevelHandbook_7Ed.pdf

You also need a ammeter that supports four-wire measurements and can measure on the order of tens of uA, like the example @Speedskater gave.

Actually, you need two other things:
A solid background in measurements since you are starting out with a difficult measurement that you don't seem to fully understand.
A reason to do this measurement. Transport in metals is a studied subject... think of Ohm, Kirchhoff, Sommerfeld, Drude, et. al. The actual conductivities of metals has been studied, and tabulated across temperature. The calculation that @antcollinet provided is really accurate, and you are not likely to push the boundaries of physics with a fancy ammeter. And none of this is relevant to audio, you could use steel nails as jumpers and not affect the response of your speakers in an audible fashion.

 

[Speedskater]

For others with two reasonable meters (but not a 4 terminal Low-Ohm meter) and some skill & experience.
a DIY measurement set-up. scroll far down the page.

BETATRONICS&reg, Electrical photos, communication, Long Cable, High Baud Rate, RS-232, fast, I232, vendor, supplier, manufacturer, industrial

Electrical photos.

www.beta-a2.com

 

[egellings]

@MarcT you need two things to make such low resistance measurements.
You need a specialized measurement setup that allows for the lead resistance to not factor into the resistance measurement. The leads on a 2-wire Ohmmeter will be much higher resistance than the device you are testing, in this case a little piece of copper with very low resistance. Please read chapter 3.3.1 of the Low Level Measurement Handbook:

https://download.tek.com/document/LowLevelHandbook_7Ed.pdf

You also need a ammeter that supports four-wire measurements and can measure on the order of tens of uA, like the example @Speedskater gave.

Actually, you need two other things:
A solid background in measurements since you are starting out with a difficult measurement that you don't seem to fully understand.
A reason to do this measurement. Transport in metals is a studied subject... think of Ohm, Kirchhoff, Sommerfeld, Drude, et. al. The actual conductivities of metals has been studied, and tabulated across temperature. The calculation that @antcollinet provided is really accurate, and you are not likely to push the boundaries of physics with a fancy ammeter. And none of this is relevant to audio, you could use steel nails as jumpers and not affect the response of your speakers in an audible fashion.

Low resistance measurements require a 4-wire, also called Kelvin connection. Two of the wires supply the test current from a constant current source, and the other two measure the voltage drop across the DUT. Since the voltage sense wires carry micro- to nanoscopic current, there's essentially no voltage drop and hence no or negligible measurement error due to resistance in the cabling leading to the meter. It's also important to connect the two leads on each end of the DUT to two separate spots on the conductor leading to the DUT. That way, contact-to-the-DUT resistance is also eliminated as a source of measurement error. (DUT is Device Under Test.) With very low resistances in the milliohm region, rather large tests currents may be needed to develop a readable voltage across the DUT.

 

[MAB]

Low resistance measurements require a 4-wire, also called Kelvin connection. Two of the wires supply the test current from a constant current source, and the other two measure the voltage drop across the DUT. Since the voltage sense wires carry micro- to nanoscopic current. there's essentially no voltage drop and hence no or negligible measurement error due to resistance in the cabling leading to the meter. It's also important to connect the two leads on each end of the DUT to two separate spots on the conductor leading to the DUT. That way, contact-to-the-DUT resistance is also eliminated as a source of measurement error.

Yeah, that's what I said and linked in that Keithley/Tektronix document.

I just figured out how to create a QR code that links to the section on low resistance measurements:

 

[egellings]

Yeah, that's what I said and linked in that Keithley/Tektronix document.

I just figured out how to create a QR code that links to the section on low resistance measurements:
View attachment 329862

Keithley is an excellent source of measurement information. I have used their model 2400 SourceMeter(TM) in automated test systems I have configured at work. What a universally useful instrument that is!

 

[Salt]

Yeah, that's what I said and linked in that Keithley/Tektronix document.

I just figured out how to create a QR code that links to the section on low resistance measurements:
View attachment 329862

Is @Doodski trapped in this now forever

 

[antcollinet]

@MAB had it right upthread.

There is absolutely no point discussing how to measure this. We KNOW what the reistance will be of metal conductors of particular dimensions.

For pretty much all jumper bars of copper or brass this is going to be of the order of 1mΩ - or less.

The contact resistance between the connectors and the bar will probably be more significant - and this will be the case whether using jumper bars or wire conductors (of 10awg or bigger).

 

[Doodski]

Is @Doodski trapped in this now forever

Trapped for all time ad infinitum!

 

[Salt]

But with the *magical metal in the wrist* You will escape.

 

[Deleted member 48726]

@MAB had it right upthread.

There is absolutely no point discussing how to measure this. We KNOW what the reistance will be of metal conductors of particular dimensions.

For pretty much all jumper bars of copper or brass this is going to be of the order of 1mΩ - or less.

The contact resistance between the connectors and the bar will probably be more significant - and this will be the case whether using jumper bars or wire conductors (of 10awg or bigger).

I imagine how impossible it would be if all electrical sizing wouldn't move on as long as the team of measurement haven't finished measuring from a-b on the specific cable runs..

This is passé. Other people have done the work before us.

Now I will go measure if the wheels on my bicycle are perfect circles and I will document it with my carpenter ruler..

 

[antcollinet]

I imagine how impossible it would be if all electrical sizing wouldn't move on as long as the team of measurement haven't finished measuring from a-b on the specific cable runs..

This is passé. Other people have done the work before us.

Now I will go measure if the wheels on my bicycle are perfect circles and I will document it with my carpenter ruler..

I'm going to go and meausre if my stove top gets hot enough to boil water using a medical rectal thermometer.

I refuse to believe that water boiling on my stove renders this measurement pointless.

(Oblig anti poes law emoji --> )

 

[IPunchCholla]

Since I’m the one who told him to measure…

My learning is strongly tied to kinetics. While I can do the math, physically doing something often makes it far more real in my mind. I mean I just built a balanced driver because that’s how I learn. I have no need of it.

As an educator, many of my students learn this way. There is a reason in medicine lectures are followed by see one, do one, teach one. It helps reinforce for everyone while helping various different learning styles.

Anyway, you can put up the equations and show the steps to solving them and I’ll get it but I won’t feel I really know it until I can see or feel the ways the variables interact.

 

[DonR]

If you don't have the proper tools, measurement at these levels will only yield an incomplete picture and may make someone draw incorrect conclusions.

 

[antcollinet]

Since I’m the one who told him to measure…

My learning is strongly tied to kinetics. While I can do the math, physically doing something often makes it far more real in my mind. I mean I just built a balanced driver because that’s how I learn. I have no need of it.

As an educator, many of my students learn this way. There is a reason in medicine lectures are followed by see one, do one, teach one. It helps reinforce for everyone while helping various different learning styles.

Anyway, you can put up the equations and show the steps to solving them and I’ll get it but I won’t feel I really know it until I can see or feel the ways the variables interact.

I get it - that is how I learn also - normally by screwing up.

But in this case the measurment is non trivial - especially for someone with close to zero engineering knowhow.

 

[fpitas]

Also a comparison. Below is a 40 A fuse. Look at the filament..

Well sure, but that's why you need audiophile fuses with big conductors

 

[DonR]

Well sure, but that's why you need audiophile fuses with big conductors

Night and day.