X-ray images of precision resistors - Page 1
Forum section: electronics / general

author: branadic
author_rank: Super Contributor
timestamp: February 05, 2018, 06:29:59 pm
content: Hi,this thread is related to X-ray images of precision resistors.All images are free to use by anyoneLicenseFirst some G.R. 8G16D, a complete LTZ1000 set.Construction: Evanohm supposed to be spot welded to Alloy180, Alloy 180 connected to copper leads ...-branadic-

author: branadic
author_rank: Super Contributor
timestamp: February 05, 2018, 06:32:19 pm
content: Next, some images of Burster resistors I got from Alexander B.Type 1148 +-0.10% 50 OhmType 1152 +-0.01% 247,038 OhmType 1168 +-0.1% 1 OhmType BP 2A 8/78 +-0.05% 3 kOhmConstruction: Manganin or Isaohmbrazed?to copper leads-branadic-

author: branadic
author_rank: Super Contributor
timestamp: February 05, 2018, 06:37:57 pm
content: 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-

author: ataradov
author_rank: Super Contributor
timestamp: February 05, 2018, 07:09:46 pm
content: Is there a specific reason they separate them into two sections?

author: SeanB
author_rank: Super Contributor
timestamp: February 05, 2018, 08:39:58 pm
content: I would guess so they can wind them in 2 opposing directions, to minimise the inductance of the unit.

author: Twenty4Pack
author_rank: Contributor
timestamp: February 05, 2018, 08:51:53 pm
content: I've wondered how these were constructed - absolutely fascinating - thank you very much for posting the images.

author: ataradov
author_rank: Super Contributor
timestamp: February 05, 2018, 08:53:09 pm
content: Quote from: SeanB on February 05, 2018, 08:39:58 pmYes, this makes sense.

author: branadic
author_rank: Super Contributor
timestamp: February 05, 2018, 09:05:35 pm
content: Quote from: SeanB on February 05, 2018, 08:39:58 pm...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-

author: ataradov
author_rank: Super Contributor
timestamp: February 05, 2018, 09:07:38 pm
content: Even if it has very little effect, why not do it? It is not like it will increase the price significantly.

author: babysitter
author_rank: Frequent Contributor
timestamp: February 05, 2018, 09:15:27 pm
content: By a magic numeric procedure you split the number of turns that you would need otherwise in half, for faster processing and easier counting !

author: glarsson
author_rank: Frequent Contributor
timestamp: February 05, 2018, 09:23:39 pm
content: The image 8G16D-12kR is an odd one. There are clearly not an equal number of turns on the two "coils".

author: branadic
author_rank: Super Contributor
timestamp: February 05, 2018, 09:27:27 pm
content: Quote from: babysitter on February 05, 2018, 09:15:27 pmMy 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-

author: branadic
author_rank: Super Contributor
timestamp: February 05, 2018, 09:29:29 pm
content: Quote from: glarsson on February 05, 2018, 09:23:39 pmAs already mentioned in the T.C. thread this is because the 12k were fabricated by stripping some 18k resistors.-branadic-

author: Edwin G. Pettis
author_rank: Frequent Contributor
timestamp: February 06, 2018, 01:23:55 am
content: 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.

author: 741
author_rank: Frequent Contributor
timestamp: February 06, 2018, 10:37:42 pm
content: HiNice, clear imagesWould 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?

author: Magnificent Bastard
author_rank: Regular Contributor
timestamp: February 06, 2018, 11:10:47 pm
content: Quote from: ataradov on February 05, 2018, 07:09:46 pmThere 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.

author: Edwin G. Pettis
author_rank: Frequent Contributor
timestamp: February 07, 2018, 12:16:51 am
content: 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.

author: branadic
author_rank: Super Contributor
timestamp: February 07, 2018, 02:00:09 pm
content: QuoteIn 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.QuoteIt's a HMXST 160, X-TEK Systems Ltd., Tring, Herts, UK.-branadic-

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: February 07, 2018, 04:54:01 pm
content: 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.

author: branadic
author_rank: Super Contributor
timestamp: February 08, 2018, 06:33:32 pm
content: 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-

author: MisterDiodes
author_rank: Frequent Contributor
timestamp: February 09, 2018, 05:49:33 pm
content: 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.

author: branadic
author_rank: Super Contributor
timestamp: February 09, 2018, 06:24:05 pm
content: 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-

author: babysitter
author_rank: Frequent Contributor
timestamp: February 09, 2018, 08:26:51 pm
content: Clearly a case of Hahn*********ism ?

author: branadic
author_rank: Super Contributor
timestamp: February 09, 2018, 08:57:46 pm
content: Quote from: babysitter on February 09, 2018, 08:26:51 pmNo, scientific acting

author: Edwin G. Pettis
author_rank: Frequent Contributor
timestamp: February 09, 2018, 11:03:34 pm
content: 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.

author: Magnificent Bastard
author_rank: Regular Contributor
timestamp: February 09, 2018, 11:18:59 pm
content: All you need to attach the AWG#16 Evanohm "plug" to the AWG#20 copper wire is a DIY version of one of these:http://www.percussionwelder.com/I contacted the engineer that designed the machine. He said that it is DC, not AC or RF. So, reverse engineering what they are doing on their website should not be too difficult; here is a video introduction to the technology (and there also is a video playlist on this machine):There is a mechanical device that positions the 2 wires together, with a lever that first moves them apart, then back together but with a small solenoid that "slams" the wires together at just the right moment. The videos do not explain the process exactly right; I think they are hiding the details on purpose (they want to sell you a welder, not tell you how to build one). If you are going to weld Evanohm to copper, a plasma-arc is absolutely essential-- nothing else gets hot enough to properly join the materials. If this were a continuous process, then it would be called "TIG" [Tungsten Inert Gas] welding, but it is a pulse of a measured amount of energy; not a continuous arc, and there is no tungsten electrode (the 2 wires are the work pieces and also act as the electrodes); also there is a mechanical percussion that TIG does not have. That said, much of the information on TIG welding dissimilar materials applies here also.Imagine that you have a power supply that puts put a high voltage at very low current (a large resistor in series). When the 2 wires are touching, this current flows between the wires. When you pull the two wires apart a short distance, an electric arc forms; but because the current is very low (say, 10mA to 100mA) it really doesn't heat either of the wires very much; it is more of a "pilot arc" to keep the gas in between the wires (either air or an inert gas like Argon) at a low impedance. Now, lets say the wires are about 2mm apart at this time, with this pilot arc happening. If we have a large capacitor charged to a high voltage, and then suddenly (through a solid-state switch like an SCR) connect that capacitor to the two wires, there will be a powerful arc formed, and because of the very high current, the arc temperature can exceed 8000K. Probably, the negative arc voltage should be connected to the Evanohm wire, with the positive lead connected to the copper wire. This plasma-arc melts the ends of both wires, and at the right moment, the wires are moved back together mechanically, and simultaneously slammed together with the solenoid. This entire process happens in 0.5ms to 2ms (depending on the requirements). The switch between the capacitor and the arc is a high voltage high current SCR (which also prevents back-feeding the pilot current into the capacitor until the switch is turned on). The energy in the capacitor is0.5*C*V^2, so you control the energy both by controlling what voltage you charge the capacitor to, and the value of the capacitor(s) for the discharge. The voltage for the pilot arc is simply a high (isolated) voltage (say 100V) going through a high-wattage resistor. The SCR should be rated to 400V at very high amperage. The capacitors should be multiple polypropylene film type, on the order of 100uF (but I haven't tried this or done the math; that may be too much or too little capacitance). You can make a switched arrangement that will parallel 1-10 capacitors to get more range out of the setup. If you are always welding #20 copper wire to #16 Evanohm wire, then the capacitor value and charge voltage can be fixed. The capacitor charge current needs to be shut off before firing the SCR so that the SCR will eventually turn off. Once the SCR turns off, the charger can then be reconnected to the capacitor (using some kind of relay). There needs to be some kind of SCR driver that can provide a fast pulse to the gate of the SCR, and a solenoid driver too. All of this could be controlled by an Arduino or something similar. Oh; and because copper wire oxidizes rapidly at high temperatures, there needs to be an Argon tank, regulator, and solenoid valve that controls the shielding gas at the weld point. The gas is only on just before the weld, and then is shut off just after the weld, so one canister of gas can be used to make many thousands of lead sets. The video does not show using a shielding gas; if you don't use the Argon shielding gas, then the copper will oxidize, and it will still have a mechanically good weld, but it will have a lot of copper oxide in the weld which will create a high thermal EMF connection (which would be very bad).The price for one of these welders is > US$10000 (and that's just for the butt-welder), so it must be a DIY project.

author: MisterDiodes
author_rank: Frequent Contributor
timestamp: February 10, 2018, 12:07:26 am
content: ...None of which really applies to maintaining a precision low TC joint in resistance wire. You don't want to "slam" anything together or create noise-inducing ridged heat affected zones around the weld. The alloy distribution in the resistance wire must be remain absolutely undisturbed if you're building a precision resistor - otherwise the apparent total TC and noise from one weld can be many times higher than the rest of the resistor.A much more delicate & controlled weld process is involved if you want to maintain low TC.

author: Edwin G. Pettis
author_rank: Frequent Contributor
timestamp: February 10, 2018, 01:40:58 am
content: To reply #25,Yes, a percussion welder is what has been used for decades to make the lead assemblies, light bulbs, vacuum tubes and a host of other things that use dissimilar metals. In concept, the percussion welder is relatively 'simple' but in actual use, things get rapidly complicated. Technically, if you bought one of these setups, you could eventually make rough lead assemblies, quite expensive but it would work. There are mechanical parameters which must be observed precisely if you intend on making lead assemblies for precision wire wound resistors. Sloppy results isn't going to work very well in practice, ask me how I know.The main reason most resistor manufacturers buy their lead assemblies from a company that makes them by the millions for lots of various customers, is the cost of the precision welding and handling equipment to make these assemblies in larger quantities, that is over $20,000 minimum and you need operators who can set them up properly to produce lead assemblies to spec. and that doesn't always happen, even well experienced manufacturers can have problems with consistency. Of all the resistor houses I am familiar with, none of them make their lead assemblies in house.There is a heck of a lot of details that goes into making a PWW resistor that requires knowledge and experience to execute properly, when you're trying to make resistors with TCR <<10 PPM/°C, the details and execution are exceedingly important. I'm not trying to discourage anybody from experimenting but if you're going at it with the idea of making your own LTZ resistors, forget it, at the very least it will be way more expensive and the results will be disappointing with inconsistency bugging you all the way. I'm talking from a position of history and knowledge of the resistor industry, you are simply repeating what has been tried and done before.Experiment with alloys and materials that are friendly to experimenters and have fun seeing what you can produce, you just might be able to produce a bit less than 10 PPM/°C with Manganin or Cupron without trying to acquire much more expensive welding equipment and frustration. You can buy a lot of PWW resistors for the cost of a welder even if it is DIY (don't forget your time should be worth something).

author: Magnificent Bastard
author_rank: Regular Contributor
timestamp: February 10, 2018, 02:44:03 am
content: @Edwin:Well, since nobody in the resistor industry is willing to teach us how to properly build a PWW resistor, then we have to figure this all out on our own. It might take some time, but there are many of us working on this, and most of the engineers on this forum are intelligent; so if we simply put our minds together, we can develop a process that is inexpensive and friendly to hobbyists to build a few PWW resistors ourselves. I don't think anyone on this forum (other than yourself) wants to be in the resistor business; but it is very satisfying (and more rapid) to do things ourselves. Also, we can try things that the main stream resistor houses would not want to do, because of lack of volume production.Yes, we know it will be difficult, and reallyscarrrrrryto build our own resistor leads, and to make our own bobbins, and to wind our own resistors. We will get it wrong; (a lot!); but that's OK as long as we don't make the same mistake twice. If we never try, then it is certain that we will never know how to do it. By sharing our experience and knowledge in this forum, the learning process can accelerate exponentially. We will get there; you will see! Thank you for sharing the knowledge that you have (even if you do appear to hold some information back for business reasons).

author: branadic
author_rank: Super Contributor
timestamp: August 07, 2018, 06:01:35 pm
content: Managed to make some further x-ray images of resistors.-branadic-Some additional comments: So what is all that Ultraohm Plus myth about?InThe last half-century: Wirewound resistors Part oneandThe last half-century: Wirewound resistors Part twowe can read about the history of resistors and the position Edwin G. Pettis is claiming for Ultraohm Plus resistors.In theUltraohm Plus "datasheet"we can read the following:QuotePlease feel free to judge the construction of the different resistors yourself, how the wire is attached to the leads and how strain relief is realized by the x-ray images given above. E.g. 8G16D shown above and the construction explained in their datasheet uses strain relief and what looks like a proper weld.Use the search function of the forum to read about reliability of Ultraohm Plus resistors and experience of forum members with them too. Once the resistors left the factory the manufacturer can't guaranty for anything and it is known that the welded joins tend to break when bending the leads due to missing strain relief.InGroup buy: LTZ1000 precision resistor setwe can find the following quote:QuoteHere is the full text for completeness:QuoteAs proven by Nikolai Beev in "Measurement of Excess Noise in Thin Film and Metal Foil Resistor Networks" but also measurement results provided by himherewith the following image being share with the forum:some resistor networks including LT5400 exhibit extremly low 1/f noise <-60 dB or even <-70 dB, while at the same time they provide extremely good t.c. tracking. There is the myth that precision wirewound don't exhibit 1/f noise. While this can be true in principle for some special treated resistors, this isn't true in general. There are many contributors to 1/f or excess noise, such as impurities in the wire, cracks/strain in the wire from winding, noise from joining the resistive wire to the leads, ...Most of the myth that wirewound resistors exhibt no excess noise is coming from a time when measurement capabilities were limited and excess noise was measured as defined by MIL-STD-202-308. With modern test equipment, capable of measuring very low signal levels over a long period of time one is able to spot even very small noise indices. Stay tuned for results that are coming soon.