X-ray images of precision resistors

[branadic]

Hi,

this thread is related to X-ray images of precision resistors.
All images are free to use by anyone License
First some G.R. 8G16D, a complete LTZ1000 set.
Construction: Evanohm supposed to be spot welded to Alloy180, Alloy 180 connected to copper leads ...

-branadic-

[branadic]

Next, some images of Burster resistors I got from Alexander B.

Type 1148 +-0.10% 50 Ohm
Type 1152 +-0.01% 247,038 Ohm
Type 1168 +-0.1% 1 Ohm
Type BP 2A 8/78 +-0.05% 3 kOhm

Construction: Manganin or Isaohm brazed? to copper leads

-branadic-

[branadic]

Here are images of UP805, also a complete LTZ1000 set.

Construction: Evanohm rod butt welded to copper, Evanohm wire CD welded to Evanohm rod

-branadic-

[ataradov]

Is there a specific reason they separate them into two sections?

[SeanB]

I would guess so they can wind them in 2 opposing directions, to minimise the inductance of the unit.

[Twenty4Pack]

I've wondered how these were constructed - absolutely fascinating - thank you very much for posting the images.

[ataradov]

I would guess so they can wind them in 2 opposing directions, to minimise the inductance of the unit.

Yes, this makes sense.

[branadic]

I would guess so they can wind them in 2 opposing directions, to minimise the inductance of the unit.

...One other 'myth' I'll pop while I'm at it, the misbelief that reverse winding the pi has a significant effect on overall inductance, it doesn't, measurements indicate that while there is a small reduction in overall inductance, it is not really that significant when it comes to AC signals.  The coupling between pi is quite loose and therefore has little cancelling effect because they are next to each other in series so the flux lines do not cancel significantly, not to mention that the Q of resistors is exceedingly low...

-branadic-

[ataradov]

Even if it has very little effect, why not do it? It is not like it will increase the price significantly.

[babysitter]

By a magic numeric procedure you split the number of turns that you would need otherwise in half, for faster processing and easier counting ! 

[glarsson]

The image 8G16D-12kR is an odd one. There are clearly not an equal number of turns on the two "coils".

[branadic]

By a magic numeric procedure you split the number of turns that you would need otherwise in half, for faster processing and easier counting ! 

My best guess is that this is done for symmetry reasons. They split the length of the wire into two equal halfs, both half of the bobbin are wound simultaniously starting from the middle of the wire.

-branadic-

[branadic]

The image 8G16D-12kR is an odd one. There are clearly not an equal number of turns on the two "coils".

As already mentioned in the T.C. thread this is because the 12k were fabricated by stripping some 18k resistors.

-branadic-

[Edwin G. Pettis]

To Branadic......thank you for quoting me but you forgot to give credit where credit is due.

The reverse pi winding myth has been around a very long time, mainly a marketing thing.  Actually, the real reason for multiple pi is for voltage ratings, the enamel coating on wire is quite thin by necessity, therefore using more than one pi reduces the voltage applied across each pi and reducing the likely hood of punch through of a pin hole in the enamel.

Bifilar winding is not commonly used in PWW resistors, it is not friendly to production, it is used in some special instances.

The unbalanced resistor from G.R. was much more likely a 24K unit, as one of the pi is practically empty leaving 12K, if it had been 18K, about half of the wire would have been left in the near empty pi as they would only have needed to remove 6K from it.


I'm with holding further comment on the Bursters at this time.

[741]

Hi

Nice, clear images 

Would it be possible to do this for chip ceramic capacitors? - I recall some feature on this forum about cracks in them. It would be interesting to see the plate layer stacking, but tricky to get a good picture, as they are such small devices.

PS - What is your equipment for taking these X-ray photos - Old CRT and real photographic film maybe?

[Magnificent Bastard]

Is there a specific reason they separate them into two sections?

There are 3 reasons that I can think of:

1) Multiple 'pi' sections reduces inter-winding capacitance.

2) Multiple 'pi' sections increases the ability of the resistor wire insulation to withstand higher voltages.

3) A slight reduction in inductance (assuming here that the wire is wound in opposite directions alternately between sections).

A bifilar winding would reduce the parasitic inductance, but would it would also maximize the inter-winding capacitance and would reduce the maximum withstand voltage of the resistor.

Within reason, the more 'pi' sections, the better; but the number of sections should always be evenly dividable by 2.

[Edwin G. Pettis]

The Burster resistors are solder terminated.  While I noticed Burster puts a top temperature of 85°C operating (at zero watts), they are really only rated to 60°C, wattage plus ambient, in short they're meant to be operated at room temperature, especially if running closer to rated power.  What happens to Manganin above 60°C?  The TCR increases rapidly and sustained temperatures above 60°C can cause permanent changes in TCR.

[branadic]

Would it be possible to do this for chip ceramic capacitors? - I recall some feature on this forum about cracks in them. It would be interesting to see the plate layer stacking, but tricky to get a good picture, as they are such small devices.

In principle yes, as the voxel size is <10µm. But I currently won't make images of chip capacitors, as I think there is enough material shown on the web.

What is your equipment for taking these X-ray photos

It's a HMXST 160, X-TEK Systems Ltd., Tring, Herts, UK.

-branadic-

[Conrad Hoffman]

I like manganin because I think it's easier for a DIY person to get a decent result with it. Not as good as the 800 alloys, but there are many pitfalls there. There's lots of NBS/NIST history on the use of manganin. Or, if you don't like resistors, apparently it makes a dandy explosive blast sensor. On the reverse winding thing, I've made measurements and agree the benefit on inductance is minimal at best. There are way better geometries for low inductance, but probably not suited to minimal size and sensible production methods. Something (IMO) really interesting is you can buy inexpensive "non-inductive" power resistors for audio use that have two paralleled concentric ribbon windings. They seem fine on the surface, but interact in such a way as to dramatically increase THD at high frequencies. Not sure, but I think one of the windings acts as a metallic core for the other and saturates or goes non-linear somehow. Love the X-rays. I had heard a story that somebody (the military?) X-rayed some Julie resistors and rejected them for having contamination.

[branadic]

Obviously kWeld is a good solution to butt weld and spot weld, if some additional effort is put into it:

https://www.keenlab.de/index.php/portfolio-item/kweld/



-branadic-

[MisterDiodes]

That weld looks like it's only barely done...I know it's just a first attempt, but have you tried pulling that wire off?  Does the wire or the weld break first?  If the wire pops off then that was not a join at all.

Looking at the weld from the top is only a very small part of the story - You really have no idea unto you slice that joint open and look for the actual weld penetration and metal grain structure at the join zone...  It all gets a -lot- trickier with resistance wire.

[branadic]

This weld isn't made by me, as you might already expected. And you can be sure that if this would have been made by me, that I would have already performed a pull test to measure the force nessecary to lift the wire off as well as an analysis under the microscope of the weld interface itself. And I wouldn't have used a steel rod nor a copper wire.

-branadic-

[babysitter]

Clearly a case of Hahn*********ism ?

[branadic]

Clearly a case of Hahn*********ism ?

No, scientific acting

[Edwin G. Pettis]

I knew the photo was from the keenlab.de website since I went there out of curiousity, as I've said in the past, you cannot CD weld two dissimilar metals together and get it right.  I am talking large differences in tensile strength for one thing.  That copper wire is merely stuck (mashed) on there because of the heat and weld pressure, it will come off without too much effort.  Looking at the interface between the copper and iron will show the lack of a true weld.  That photo is a rather poor choice for showing their welding capabilities.  Their CD welders are probably just fine for welding similar metals like any other CD welder.

This is nothing new, all of this trial and error happened decades ago when dental braces came into being and they needed a welder to do the work.  CD welding was tried on Evanohm >70 years ago with I don't know how many different combinations of metals trying to match it to standard copper leads, at one time, even stainless steel was used plated with copper...ugh.  Sure it welded but made terrible resistors.  All of the 'successful' (to one degree or another) interfaces between Evanohm and copper leads has been in production for decades, you're just repeating history if you're trying to interface Evanohm and copper leads again, nothing new to find here.