4 wire kelvin resistance measurement tutorial
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- Опубліковано 5 жов 2024
- How to use the 4 wire (Kelvin) resistance measurement technique to measure tiny resistances (in the milliohm range) using only a cheap multimeter!
Webpage: www.afrotechmod...
I started with Arduino about 2 years ago. Now I make my own dc lab bench power supply’s. Robot arms. The famous eggduino for Easter. I think you get it. I’ve become absolutely fascinated with electronics and building them. I have used your video’s throughout my journey. They are very helpful. They deal with components and situations I come in contact with on a day to day basis’. Thank you very much for taking the time to talk to use newbies and in a way I ,and many others can understand . If you could dive into , and explain how to use, some of these lower end oscilloscopes new people like myself are forced to buy due to financial constraints. I’d greatly appreciate it.
Once again. A large thank you for all you’ve done.
Thanks for making this modest-seeming video. It's laudably clear and concise, compared to a number of other overly elaborate efforts attempting to cover this same territory. Well done!
This is one of the most useful electronics tutorials I have ever seen!
@Imran Davis no problem :D
Finally made me understand what our shop micro-ohmmeter is for after not being able to "get it." Thanks
Thank you for an outstanding presentation explaining 4-Wire low resistance measurement! Knowing sub-Ohm Resistance is an OK theoretical exercise, but I am using this presentation as a reference for explaining practical results when in-line Resistances occur in vintage automotive electrical systems.
i've made a constant current source using an opamp an a mosfet built into a bench supply i made, it has 6 presets which connects different shunt resistors so i get different current ranges
i've made it so it has 100uA 1mA 2mA 10,20 and 40 mA, handy for testing LEDs, zeners up to about 15 volts (or high voltage diodes) and 4 wire resistance measurements
Thank you for making this! I adore your videos, they are practical and easy to understand and yet I find them handy for my electronics hobby! Your teaching style is perfect and your humor makes it even better! Thanks and I hope you keep making these! (ps your site is AWESOME!)
imho , the best electronics tutorials on youtube..
i'm your fan!!!
I always learn a lot by watching your awesome videos! Thank you for putting them on UA-cam.
8 resistors of 10Ω/0.5W/1% connected in parallel will give you a decent 1.25Ω/4W equivalent, which is perfect for this application.
You can convert a constant voltage source into a constant current source with a transistor and a resistor. The resistor goes on the base and draws a negligible current, avoiding power resister and regulator.
You could be the best teacher EVER!
Thanks a lot! I needed to test IR in my Brushless Outrunner Motor, and Now I can do it pretty easily. I just bought LM317 on ebay!
@dealio82 Nope, the power supply is capable of running loads of 10amps, the fuse is to protect the PSU from the input current, not the output =)
Just when I needed it, thanks!
Thank you a lot for this outstanding explanation on this subject. Found it very useful.
Yeah ! Dont Stop. Is this the method to measure a coil or a solenoid? Or motor coils?
Why doesn't the resistance of the wire matter when measuring voltage? Should you get voltage drop as well and basically have the same error from the wire resistance?
Why don't multimeters implement resistance measuring this way?
Thanks for the video!
did you figure it out?
Couldn't you use a pot together with the LM317 instead of fixed resistors to tune it to 1A with the multimeter?
battery holder springs have like 60 mOhm. If you insert battery in a parallel pack in reverse, its not the battery that will smoke, but those springs. They cannot handle 5A.
@Serostern Liquid nitrogen doesn't stay cool forever, so I need to measure the resistance of the coil once it warms up, so I know how much longer I can make it run before shutdown is necessary : ]
You just earned another subscriber.
I'm not really into electronics at all, but I might actually try this. I need to know the exact resistances of the liquid nitrogen cooled fullerene superconductor electromagnets in my deuterium-deuterium fusion reactor : P.
You can use an incandescent flashlight bulb and a single "D" size battery as your current source. It won't be exactly 1 amp, so you will have to measure the current then use some math on your voltage measurement but it is a very cheap solution.
Al sacar el cable del tester cambió la resistencia, y por lo tanto, cambió la intensidad
OMG! Welcome back!
what if the DUT can take no more than 10mA, wouldn't that make your voltage measurement inaccurate?
Thanks for the response!
Ok, so i gonne google it. Sounds like an interesting idea.
Been a while. Illuminating as usual though. Or should that be electric / electrifying?
Really nice explanation. Thanks.
cool video!
but could you explain how this current limitation actually works inside the power supply ?
what circuit is inside it, to do that?
I was wondering the same question?
*!
I don't know how exactly current limiting works in power supplies. But a basic current limiting technique is the BJT foldback circuit. What you do is put a sense resistor across Base and Emitter of a BJT and size it so that the drop across the resistor is 0.7V when you hit your set current limit. At this point, the BJT turns on and output voltage drops to insignificant value like 0.1 to 0.3V, this limits the power dissipation. Just google Foldback circuit for details.
good stuff. Thanks for taking the time to explain.
I don't think i can use this method to measure the internal resistance of a car battery, can i? the battery will have its own voltage unlike a piece of wire or anything else tested in this video. Any info on the topic would be much appreciated
well you'd do basically the same thing. firstly, figure out the voltage at zero load. next, put some load on it and measure the load's current and the new voltage. calculate the voltage drop and divide it by the current to get the internal resistance.
And if you don't have a variable power supply, how can you do it? you need 2 multimeters,one in series to measure amps,and another one to measure voltage, and then use ohms law, V=RI.
Using this method on thinner wires can cause them to heat and that would mess up your measurements
Wheatstone bridge may be a lot more complicated but better
smart guy!! Outstanding description! Thanks so much..
@dealio82 Oh.
You needa power supply where you can adjust the amperage, the computer PSU always gives its max.
Does it matter whether I used AC excitation source or DC excitation source? If yes which one will be good as per your suggestion if I want to measure very low resistance? Please give you suggestion.
Another great video. Thanks...
if you put 1amp through a coil, doesn't it get too hot and changes its ohmian resistance so that dont measure the resistance that interests you but the resistance of the coils temperature at 1 amp?
what should i use for a power supply using the second method?
if i use figure 1 from this website with 3 AA batteries what resistor should i use? what ohm and what watt. and what gauge speaker wire should i use?
diyaudioprojects.blogspot.com/2008/11/simple-low-resistance-measurement.html?showComment=1522613613163#c7552392211450068627
Such a good video! Thank you!
AWESOME. Now do a video on death rays XD
At 3:02 did you connect the resistor to the test leads? Parallel or series? Cause whenever I turn the knob of current limiter on my bench supply it jumps back to voltage control...
@Afrotechmods is that + or - 10%, or 5% ?
yes
THANK YOU THANK YOU THANK YOU!!!!
Without the lm317 or any other Ic regulator, it won't be constant current. Right? I have that same power supply, but every time I across the current thru a resistor, the current flow will vary the consumption in the amperimeter based on value ohm resistance, so drop voltage. But an Ic like lm317 it will give constant current no matter watt resistance value I use. Right? I don't get it at all yet.
Was just searching for an explanation on this method of measurement and was suddenly hit by the word „coilgun“ in the first 20s as if you would already know why I came here😅😳
so if i want to measure the resistance of a steel rail, which power source is suitable?
Awesome, thank you so much
Very Nice
As easy as that!!
Thank you
The explanation doesn't sound logical to me. How can a constant current source be possible? I thought that the current depends on the sourevoltage and the resistance, because I=U/R.
If the current should be constant the sourcevoltage would have to be variable and thats not the case, or is it?
Could someone please explain that to me?
@Afrotechmods Yeah you should keep up :D
Great one, thanks !
Thanks for sharing.
@Serostern My power supply is made of a computer PSU so every time i connect the 12V output to a relay or an inductor it will shut down. Is there any way to prevent it from shutting down
Cool video
Hi. I need a low resistance tester or megger circuit diagram for graphite to voltage-current diagram on Pspice. Do you help me ?
Cool tutorial
Thank you :)
4 x 5R1(5.1Ω) 5W ceramic resistors, wired in parallel... should get pretty close to 1A with LM317(1A limit= warm), (LM338 rated for 5A=not warm)... FWIW...
For 12VDC situation: 120Ω 5W (ceramic 'J" series) resistor, in series, should get you in the ballpark of 100mA (0.1A)... do the math.
Won't that blow a fuse in your power supply
Awesome. Thank you.
can I use an precision resistor
i take a transformer, an electrolytic capacitor and a diode bridge. or a car battery charger.
NEED MORE
Doesn't running a whole amp through a wire make it very hot?
Good question! It depends on the gauge (diameter) of the wire. 1A is fine for anything but extremely thin wire.
Afrotechmods I guess it comes down to getting a feel for what works and what doesn't without having to calculate everything all the time -- in a word "experience." I've very much enjoyed your vids and learned a lot. You're a very good presenter. I now need to spend time at the bench making mistakes and learning the hard way!
thx for explaining :D
Hey thanks, man.
@yellowmetalcyborg The resistace of a LN2 superconductor?
0.
That's the entire damn point of a superconductor xD
so nice..
sir if the wire so thin ,then how it will handle one amps
A wire with very little resistance isn't necessarily that thin. Actually the thinner the wire, the greater the resistance
More vids. Please!!!
damn :-o its EXACTLY what i need :-o THANK YOU !!!!!!!!!!!!!!!!!!!!!
THANKSSSSS
Damn this is hard!
Funny.. I'm watching this video in an effort to measure the resistance of the commutators installed in the L-3 Brashear KTM mount (deathray) you show at the very end of the video.. Bizarre.
isn't that a short at 3:21?
+danh le Constant current is applied at the PSU
cool
@dealio82 THX Man for your tips
kkk
:O