Shunt resistor issue

[LukaszRed]

There is a video how do we measure it using Cropico below:
{...snip!...}

OK.  The CURRENT from the Cropico needs to be attached to the big copper tabs.  These are known as the "Force" terminals.  Let's say the 4 binding posts on the Cropico are numbered 1..4 from the top to the bottom.  1 & 2 are red, and 3 & 4 are black.  In this setup, 1 & 4 need to be connected to the giant copper tabs on your shunt.  2 & 3 need to be connected to the small "sense" terminals on your shunt.  The "Sense" terminals are the small tabs just either side of the manganin resistor.  You can make your own leads to do this.  The Cropico is pushing about 10A to make this measurement, so the value of the shunt will be different from what it would read at 100A, but that is irrelevant until you buy (or build) a set of cables that will properly connect to the shunt.  The wires that connect to the big copper tabs need to be pretty "beefy" (large).  The wires that connect to the small "sense" terminals can be any size wire that is easy to work with.

In the video, and in your photos, I don't see where the high-current connects to the big copper tab on the left side.  Can you show a picture of how this shunt is mounted in the final product?

The thing is that it is Cropico unit which applies potential and current exactly in the clamping spot. It means if we clamp it down to pins it will apply 10A in the pins position (3-3). If we apply it as you describe big copper tabs (5-5) then readings are different but we are not sure why. Current still flows through the resistor and shouldn't we get similar readings?

[altaic]

There is a video how do we measure it using Cropico below:
{...snip!...}

OK.  The CURRENT from the Cropico needs to be attached to the big copper tabs.  These are known as the "Force" terminals.  Let's say the 4 binding posts on the Cropico are numbered 1..4 from the top to the bottom.  1 & 2 are red, and 3 & 4 are black.  In this setup, 1 & 4 need to be connected to the giant copper tabs on your shunt.  2 & 3 need to be connected to the small "sense" terminals on your shunt.  The "Sense" terminals are the small tabs just either side of the manganin resistor.  You can make your own leads to do this.  The Cropico is pushing about 10A to make this measurement, so the value of the shunt will be different from what it would read at 100A, but that is irrelevant until you buy (or build) a set of cables that will properly connect to the shunt.  The wires that connect to the big copper tabs need to be pretty "beefy" (large).  The wires that connect to the small "sense" terminals can be any size wire that is easy to work with.

In the video, and in your photos, I don't see where the high-current connects to the big copper tab on the left side.  Can you show a picture of how this shunt is mounted in the final product?

The thing is that it is Cropico unit which applies potential and current exactly in the clamping spot. It means if we clamp it down to pins it will apply 10A in the pins position (3-3). If we apply it as you describe big copper tabs (5-5) then readings are different but we are not sure why. Current still flows through the resistor and shouldn't we get similar readings?

Please read https://en.wikipedia.org/wiki/Four-terminal_sensing. You're not measuring resistance; you're measuring the minute voltage drop across something you're flowing masses of current through, and deducing what the resistance of the thing is given the known current. Force terminals flow the massive current (big chunky ends, #5). Sense terminals measure the minute voltage drop (little tabs with resistance boosting holes #1-4).

[StillTrying]

Yesterday, I was going to post.  "I'm shocked after watching the video, it'll be interesting to see what happens next". Today - I'll stick by that for now!
           

[HighVoltage]

It seems to me, that the OP is not listening to what we have to say.
It also seems that there is a fundamental lack of understanding the very basics.
You probably need to have some local electrical engineer showing you step by step of how to do it.
 
Your sense terminals need to be at a very different spot than your force terminals.
You can NOT use the standard clips of the Cropico, that will NOT work at all.
 

[LukaszRed]

Hello,
To avoid confusion I just want to tell that we know how to measure the shunt resistance in the proper way. The question we would like to have an answer for is:

Why the results on pins using cropico unit are so different from results in 1-1 position? I know that all of you will say that "you should not measure it that way!" "I am shocked how you measure it!" etc. But this is not the answer that actually helps, because we already know that it is not the right way to do such test. We are not familiar with the knowledge behind it because we are not electricians and we don't understand why the readings on the pins are much different than in other spots of the component. What is causing that fluctuation of resistance?

We have also prepared quick report for you guys, to calm down some of the voices. We are just looking for the answers 

** Forgot to mention in the report. We used fluke multimeter to measure voltage drop. http://www.fluke.com/fluke/uken/digital-multimeters/fluke-45.htm?pid=56082

[zlymex]

To represent graphically/intuitively, I draw isopotential lines or equal potential lines.
Any point in a line has the same potential.
The voltage drop(hence the resistance) of any two points is equal to the number of lines in between(times the step if precise).
The shape and distance of these lines vary very much with the actual materials, often very difficult to calculate especially the shape is irregular, but can be measured by a probe pen.

The principle of the drawing is: current likes the shortest path(least resistance path).
I draw these lines very rough, but somethings are certain such as:
 - the resistance of 1-1 is smaller than 2-2
 - the resistance of 2-2 is smaller than 3-3
 - the resistance of 3-3 is nearly equal to 4-4 (there must be a measurement error if not)

Edit: the last three lines should be:
 - the voltage drop of 1-1 is smaller than 2-2
 - the voltage drop of 2-2 is smaller than 3-3
 - the voltage drop of 3-3 is nearly equal to 4-4 (there must be a measurement error if not)

[Alex Nikitin]

- the resistance of 3-3 is nearly equal to 4-4 (there must be a measurement error if not)

The resistance of each "pin" is about 25uOhm, together - 50uOhm. As simple as this.

Cheers

Alex

[zlymex]

- the resistance of 3-3 is nearly equal to 4-4 (there must be a measurement error if not)

The resistance of each "pin" is about 25uOhm, together - 50uOhm. As simple as this.

Cheers

Alex

Oh yes, I should say 'voltage drop' in place of 'resistance'.

[Gyro]

@LukaszRed:  Please look at the picture of the DO7Plus Manual page that you posted in Reply #31. Look at the picture, then note the...

"HINT: It is important to connect the I (current) leads outside the U (potential) leads"

You need to do that... Do what the manual says if you want to get accurate readings.

I notice from your picture of your probes that the leads are plugged in with 4mm plugs. Unplug these and buy some small individual clips so that you can make the measurement properly as the manual tells you to do!



Edit: Or if there are enough of you, then just hold the 4mm plugs on the correct points on the shunt... I leads at points 5 and U leads at points 4. It really isn't difficult to do the correct thing.

[The Soulman]

OP is nearly there, just need to connect the four wires coming from your tester to the terminals of the shunt resistor in the same way as in the end product.
I'd suggest the current carrying terminals be the numbers 5, and the sense terminals the numbers 4, then you should get repeatable readings.

The tester is actually a two part device: a current source that lets a known current flow from one current terminal thru (in this case) the shunt to the second current terminal, and a voltmeter on the two sense terminals to measure the voltage drop across the shunt.
Using ohms law (done inside your tester) resistance=voltage/current we get the value of the shunt resistor in ohms, then grind or mill the material and retest and repeat till you get the desired value, by taking away material you can only go up in resistance, once to high... make a new one.

Now the shunt has a known value the customer can let a unknown current flow thru the shunt (again using terminals 5) and measure the resulting voltage drop with a voltmeter (again connected to terminals 4), now he can use ohms law in a different way: current=voltage/resistance.
Resulting in a customer who knows how much current there is flowing thru his motor/device/apparatus.

In a nutt shell, that is how it works.

There are a few pitfalls still, but keep posting and people will help you out.

[The Soulman]

Not for the OP to worry about, just to get some brainwaves flowing and to get the feet of the ground... 

"HINT: It is important to connect the I (current) leads outside the U (potential) leads"

Now imagine a straight bare copper wire of 10 meters long with a end to end resistance of 30 Ohms and we have a connection terminal on each end called A and a set of connections spaced 1 meter apart somewhere along the line called B.
Now if we force 1 amp of current from A to A we get a total voltage drop of 30 volts across the wire and at our measurement terminals B We measure
3 volts, all is well.
If we put the same 1 amp of current thru terminals B and measure voltage at A, we´d measure 3 volts  the same.

And what if we swap one A terminal for one B terminal, 3 volts again.... 

[StillTrying]

Right...

All my posts are carefully considered believe it or not, shocked was/is the right word.

You keep asking why the resistance at 1-1 is different from 2-2/3-3 for some reason, it doesn't matter what it is at 1-1, you can make it anything you want because the lugs are not measuring there. But..

The only way to measure resistance is to force a known steady current between 2 carefully selected points and then measure how much force(voltage) was needed to do it. The more force(voltage) that was needed the higher the resistance is.

When you force this known steady current though 1-1 or 2-2 the current does not flow like this. shunt1.jpg

If you could see the current flowing between 2 points on a surface it would look more like this. shunt2.jpg

Most of the current total flows directly through the middle line between the 2 points, but there are smaller currents taking longer curved paths, each side of the center line, and even smaller currents flowing all over the place. If you need a very accurate measurement, then all these smaller currents add up to quite a few % of the total current.

Drawing these currents on your shunts would look vaguely like this. shunt3.jpg

Right away, hopefully, you can see that some of the lower parts of the 1-1's current paths are missing - cut off, by the cutout, compared with 2-2. So when you come to force the steady known current between 1-1 it takes a bit more force(voltage) to get it to flow though the paths which are still there. And of course this bit of more force means 1-1 has a bit more resistance.

Here's one you prepared earlier. shuntg.jpg

If you moved points 1-1 down towards the bottom edge even slightly, then more of 1-1's current paths would be missing, and show up as more resistance. If you moved points 1-1 up a bit it would give 1-1 more current paths and less resistance, you'll get a different resistance nearly every time.

The 4 wire measurement bit to avoid all these errors has already been done.. and done, so just do it for now.

All this won't be 100%, but close enough for me!

[LukaszRed]

@up StillTrying
Thanks! This is sort of answer that puts more light into some corners. So what you are trying to say that the current density affects the resistance? We agree with that and we did a simulation of that phenomenon and we can confirm that resistance readings change across the shunt.
So it looks like when we measure the resistance with cropico we are applying the 10A current to the pins which potentially makes the current density relatively high across the measuring path. That's why we are getting high resistance results. Of course ideally we want to apply the current on the component ends to provide that current flow and only voltage leads to the pins.

If I am getting this right I think we are nearly there.

[Alex Nikitin]

So it looks like when we measure the resistance with cropico we are applying the 10A current to the pins which potentially makes the current density relatively high across the measuring path. That's why we are getting high resistance results.

When you measure the resistance with Cropico on the pins you add the resistance of the pins to the measured value. A simple estimate is that each pin has about 25-30uOhm resistance, hence +50uOhm reading.

Cheers

Alex