Help! Damaged resistor standards, WARNING: Graphic scenes inside - Page 1
Forum section: electronics / general

author: toastedcrumpets
author_rank: Regular Contributor
timestamp: February 14, 2019, 01:52:50 pm
content: !!!! Viewer discretion is advised !!!!I recently bought some resistance standards from Inverted18650's haul. While they were well packaged, no plan survives first contact with the UK post office. I think the package had been chucked around due to the dogged edges of the parcel. On opening the parcel, one resistor had somehow gotten out of its bubble wrap, then slid down the side of the packaging to come into contact with the outside surface. From there, the heathens at parcelforce did their wicked work....My first suspicion that something was wrong with the parcel was an oil patch on the outside of the parcel. The patch was not huge, so I think the damage was very close to delivery as not much oil had leaked.No avoiding it any longer. Onto the pictures....Overall, most of the standards are in good condition, except two.The 1 Ohm resistor had significant bending to the top terminals. The sealing ring at the top had also partially rotated and it was the source of the leaking oil. This has caused the label to soak off the resistor (and soak onto some other resistor labels).I proceeded to test all the resistors using my in-calibration DMM7510. Everything looks really good, with only a few ppm of drift from the values reported on the calibration labels (which themselves are nearly 40 years old). Very happy with their performance. Especially the 0.01 which I tested for several hours, it seems to be bang on. I'm getting some noise due to the lack of temperature control and poor quality connections but I will have an environmental chamber in a month or so with low thermal emf bindings to carry out some very careful testing.......Except for the 1 Ohm resistor. It turns out that bent terminal is causing several thousand ppm of change depending on if the terminals are wiggled. I tried wiggling the top terminal to see how loose it was, and it turned out to be very loose...sighOK, that's going to mess with the resistance! In the previous image you can also see some of the slight rotational bending of the 10k resistor's left binding post/arm. At least I now have nothing to lose in opening up the 1 Ohm resistor and checking the level of oil (and trying to figure out if/how to fix the binding post).I guess this is one good thing to come out of this disaster, I bet not many people are "brave" enough to take a look at the guts of a standard resistor. So I think its clear how the binding posts are removed. I'm intrigued by the use of double wiring to each of the binding posts....So, I have several questions/requests for help (1) does anyone know what kind of oil is in these? I would like to replace the oil in the 1 Ohm resistor if I attempt a repair (don't worry, I don't intend to open any of the others up). (2) Advice on how to replace the binding posts on the 1 Ohm resistor is needed. I think I'll never get the previous accuracy, but I'd still like to hear ideas on what could be done. I could try leaving the soldering in place, partially remove the binding post and either thread a center screw in to reconnect the two halves, or solder them together. I'll be honest, the idea of heating that huge binding post up enough to solder is making me get anxious as I couldn't sink enough heat from the coil below to stop it drifting, so I think mechanical solutions are the only way forward here.Finally, cleaning of the binding posts! I tried cleaning the broken 1 ohm binding post as it was already messed up, and IPA with a toothbrush seems to clear the green copper oxide off effectively. Am I a complete savage using this method? Is it safe to use on the other posts? I must be careful to stop the IPA attacking anything else on the resistor (like the label for a start).You should note thta I have access to quite a lot of scientific equipment in my job. I have access to a full chemical laboratory, mechanical workshop, and electronics labs, and I'm sufficiently senior enough to shuffle about in any of them. For example, I could CNC mill out a new top part of the binding post and possibly even electroplate it, or precipitate silver onto its surface(I'm guessing that's what I already have here?), but I'm not sure of the post's exact construction/composition, so perhaps repairing the original is a better idea than constructing a new top piece.Comments/suggestions welcome, but be nice. I didn't hurt this resistor deliberately....

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: February 14, 2019, 02:26:19 pm
content: Not sure about repairs, but wanted to mention that, if it hasn't been done already, the oil should be changed. It tends to go acidic and shift the values. I usually do two changes a few months apart, using good plain mineral oil. There are also some transformer oils that should be suitable.edit- I only do this with new-to-me resistors, then change every few years.

author: toastedcrumpets
author_rank: Regular Contributor
timestamp: February 14, 2019, 02:30:22 pm
content: Interesting. I was worried that removing/handling the resistor internals would mechanically stress the unit and may affect its value, but you're saying this is actually a "typical" maintenance proceedure?I could actually get some litmus paper and test the Ph of the current oil as an experiment as well as order some mineral oil. Do you do anything to remove the old oil, or just "wash" it out with the second replacement?

author: pigrew
author_rank: Frequent Contributor
timestamp: February 14, 2019, 02:36:59 pm
content: It should also be noted that the traditional method is to plate the terminal with mercury (after mixing it with sodium). See the Leeds & Northrup 4015 manual for details. The procedure seems scary to me.

author: toastedcrumpets
author_rank: Regular Contributor
timestamp: February 14, 2019, 03:06:01 pm
content: Wow, fascinatinghttps://doc.xdevs.com/docs/L%26N/L%26N_4015_4025_4035_4045_4020_4030_4040_4050.pdfMercury is sort of scary, and now i wished i handled these standards with a bit more care. I'll get some latex gloves for handling the terminal ends in future. I could carry out the renewal procedure described above in a fume cupboard, but I don't want to have any fresh mercury hanging around my office/lab when I'm using the standards.

author: langwadt
author_rank: Super Contributor
timestamp: February 14, 2019, 03:17:08 pm
content: Quote from: toastedcrumpets on February 14, 2019, 03:06:01 pmtouching metallic mercury isn't that dangers, inhaling the vapors are. organic compounds of mercury on the other hand can be stupidly dangerousand pass right though latex gloveshttps://en.wikipedia.org/wiki/Karen_Wetterhahn

author: ArthurDent
author_rank: Super Contributor
timestamp: February 14, 2019, 03:33:22 pm
content: Many years ago we would take a small amount of mercury and then place a small sliver of sodium on top and wait for the flash when they combined. This was done in a fume hood and probably today they have more stringent regulations. We would then use it to coat the ends of the resistor 'horns' and the surface of the metal support blocks that were in the oil bath.

author: SilverSolder
author_rank: Super Contributor
timestamp: February 14, 2019, 06:32:35 pm
content: Quote from: ArthurDent on February 14, 2019, 03:33:22 pmThe world is definitely much wimpier nowadays! (Probably a good thing)

author: Edwin G. Pettis
author_rank: Frequent Contributor
timestamp: February 14, 2019, 06:46:58 pm
content: The L&N 40xx series standards tend to have fairly high TCRs and are meant to be used in a temperature controlled oil bath. You do need to handle them gently and do not bump the resistor elements as Manganin is very sensitive. I use a high grade of mineral oil, food grade in mine and they should be oil changed periodically but usually not in months, the better oils will stay good for a few years if sealed well. You don't want to be handling the resistors frequently as that leads to higher chances of damaging them. The L&N .01 Ohm standard, 42xx series has a lower TCR than the 40xx series but is also meant to be used in an oil bath. The oil does not affect the resistor element so much but when it starts to degrade it increases the leakage resistance in parallel with the resistor, if the oil is really old it could begin to affect the resistance element by increasing acidity but I've rarely seen this in cal lab standards. The oil is clear when fresh and as it ages tends to get a yellowish hue to it, when it begins to change color it is definitely time to change it.Unfortunately the postal gorillas don't give a hang about what is in the package, frankly I think putting a fragile label on the package just invites some of these jokers to throw it around harder. It must be noted that such poor handling increases the cost of shipping, you have to put more packing around the contents to try to protect it better thereby making it heavier and increasing the shipping charges and insuring brings on another very expensive round of charges......ask me how I know (shipped an SR-104 for calibration, round trip was nearly $300 with insurance).

author: edpalmer42
author_rank: Super Contributor
timestamp: February 14, 2019, 07:17:03 pm
content: That one ohm resistor is basically scrap now so you've got nothing to lose. I'd unsolder the wires from the broken post and remove it from the cover so that it can be properly inspected and then decide what the next steps will be. Looking at the picture, I can't really tell what I'm looking at, but I suspect that the repair will involve soldering (maybe silver soldering?) or brazing - either will be done with a torch.I don't see any way that you could repair this without removing the post from the cover.Obviously, your calibration is useless now so the fact that the paper fell off is irrelevant.Ed

author: toastedcrumpets
author_rank: Regular Contributor
timestamp: February 14, 2019, 09:15:59 pm
content: Thanks for all the comments so far, and if anyone knows wire wound resistors it's you Pettis! I'll start looking for a good temperature controlled oil bath on eBay or going spare in the lab. My current plan was to repurpose an ex vaccine transport container I bought at auction, as it's highly insulated, electrically shielded, and has high control.What worries me with the mercury is that the final step is to wet the horns with elemental mercury, which may then evaporate.I agree with you ed, to sort the binding posts out I'm going to have to desolder it, then probably solder the two pieces back together.I'm more upset about the paper on the other resistors, the one ohm resistor is being restored more for fun than anything precise

author: Vgkid
author_rank: Super Contributor
timestamp: February 14, 2019, 09:33:53 pm
content: Here is a whole thread of standard resistor teardowns.https://www.eevblog.com/forum/metrology/teardown-standard-resistors/

author: Inverted18650
author_rank: Frequent Contributor
timestamp: February 16, 2019, 03:48:53 am
content: Quote from: Vgkid on February 14, 2019, 09:33:53 pmMan, had I known all this...

author: bitseeker
author_rank: Super Contributor
timestamp: February 16, 2019, 04:39:03 am
content: Quote from: toastedcrumpets on February 14, 2019, 01:52:50 pmSorry to see that they took quite a beating. But, as you said, it is cool getting to see how it's put together.Quote from: Vgkid on February 14, 2019, 09:33:53 pmThanks!

author: toastedcrumpets
author_rank: Regular Contributor
timestamp: February 17, 2019, 11:13:47 pm
content: Quote from: Vgkid on February 14, 2019, 09:33:53 pmWow, I stand corrected. I didn't see a teardown like the ones I have though. I'll keep this post updated with anything I do to the resistor in the end.

author: Mr. Scram
author_rank: Super Contributor
timestamp: February 17, 2019, 11:51:31 pm
content: I can't get over the amount of great test equipment destroyed by the postal services. What a bunch of bastards.

author: edpalmer42
author_rank: Super Contributor
timestamp: February 18, 2019, 08:25:13 pm
content: Hey toastedcrumpets,It occurred to me that if you really want that 1 ohm resistor to be repaired, maybe look at the other units and decide which one you're willing to sacrifice to get a good terminal. Maybe one that's off value, no labels, whatever. Swap the terminals, and then try to repair the sacrificial unit.Ed

author: martinr33
author_rank: Frequent Contributor
timestamp: February 24, 2019, 06:43:59 pm
content: Looking at the mercury reference in more detail, you only have to use mercury if you are using "mercury cups" as resistor connections. Seems that using the screw terminals is OK. I'd certainly recommend against using mercury, it is bad for anything biological in nature.The terminals clean up very nicely with a silver replacing polish. Something like a "silver dip".Patent description of mercury cup connection from 1904.https://books.google.com/books?id=Fg9LAQAAMAAJ&pg=PA2022&lpg=PA2022&dq=mercury+cup+connector&source=bl&ots=As3M7L-Q9e&sig=ACfU3U1oQkupqk_xKJmfdnKqDksrLZ8qCg&hl=en&sa=X&ved=2ahUKEwjN5tuAg9XgAhVLHjQIHWX5DaYQ6AEwB3oECAcQAQ#v=onepage&q=mercury%20cup%20connector&f=false

author: toastedcrumpets
author_rank: Regular Contributor
timestamp: February 25, 2019, 08:44:31 am
content: That's really good news. I'll be honest, after reading about organic forms of mercury I wasn't going to coat them in mercury and was actually looking at silver plating the terminals instead. Finding out there's a silver replacing polish is also highly interesting.I took a look at the silver-dip, but its chemical formula I think is contained in this patent:https://patentimages.storage.googleapis.com/fa/9b/02/9623172251faa8/US3468804.pdfThere's no silver in there, only thiourea, sulfuric acid, and a polyamine. I think this is the same formulation as Goddard's silver dip, as that has thiourea (and propan-2-ol) as listed on its MSDS sheet. So at least just looking for "silver dip" is a little dangerous.I found something that claims to be silver solution:https://www.amazon.co.uk/Silver-plating-solution-20-silver-plating/dp/B01ALCON0Y/ref=pd_day0_hl_201_20?_encoding=UTF8&pd_rd_i=B01ALCON0Y&pd_rd_r=1a820d63-38d9-11e9-96a8-df6022bfc235&pd_rd_w=dpXvt&pd_rd_wg=NXJDx&pf_rd_p=92d624bb-a334-423e-8722-8024dd09667f&pf_rd_r=PGG7B0Y0ZP6DBY10Q798&psc=1&refRID=PGG7B0Y0ZP6DBY10Q798And a silver anode:https://www.amazon.co.uk/Tifoo-Silver-Anode/dp/B078HVN2JZ/ref=sr_1_1?s=kitchen&ie=UTF8&qid=1551084207&sr=1-1&keywords=silver+anode+Tifooso I might explore electroplating the terminals.

author: bd139
author_rank: Super Contributor
timestamp: February 25, 2019, 09:25:09 am
content: Interesting thread. Never seen inside a standard resistor. Nothing like what I thought it might be.Delivery - not good though. Probably was this end. RM / PF are total clowns. I double box and tight back everything and use UPS usually.

author: SilverSolder
author_rank: Super Contributor
timestamp: February 25, 2019, 04:31:19 pm
content: LOL, that picture looks like it would have been hard to explain to the boss!

author: grizewald
author_rank: Frequent Contributor
timestamp: February 25, 2019, 08:31:50 pm
content: Quote from: Edwin G. Pettis on February 14, 2019, 06:46:58 pmIt's terrible to see such valuable standards damaged like this, but unfortunately, adding "Fragile" labels to parcels is completely pointless these days.The vast majority of parcels, regardless of carrier, are sorted by machine.The machines read the parcel labels with cameras and as the parcels travel down a conveyor, they are kicked off into appropriate bins depending on their destination. The video I've linked below will give you an idea. The problem here is that most carriers will sort all parcels at the same time - meaning that parcels weighing up to 35Kg will be on the same sorting routine as ones which weigh 500g. The local postal service here in Sweden has no sympathy for damaged parcels and state that any parcel must be able to withstand having another 35Kg parcel being dropped on it from two metres!The sorting machines don't read or recognise "Fragile" labels, so pack appropriately!edit: changed video to one which better shows what parcels have to withstand.

author: bd139
author_rank: Super Contributor
timestamp: February 25, 2019, 09:01:19 pm
content: That's not terrible really. It's when the gorillas get their hands on it.Typical training video:

author: grizewald
author_rank: Frequent Contributor
timestamp: February 25, 2019, 09:10:20 pm
content: Yeah, the machines in the video look fairly gentle, but there's the drop from the conveyor into a nearly 2 metre tall cage (just hope your parcel isn't the first into the cage), and then there's when the machine doesn't quite do what it's supposed to do...The speed of some of the belts means that things will (and do) get crushed, ripped and torn in true Ace Ventura style.Quite how you're supposed to make sure that any parcel can survive having 35Kg dropped on it from 2m is beyond me.

author: toastedcrumpets
author_rank: Regular Contributor
timestamp: February 26, 2019, 04:45:50 am
content: Wow, on the metrology forum I thought the resistor standards would be the popular part of this post but it turns out there's a lot of bad blood towards the post office (and their machines)!We're all looking for someone to blame BUT we all know that any kind of standard should only be handled by bearded engineers with tongues held at the right angle and wrapped in a nude virgin for transport.

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: February 26, 2019, 04:24:31 pm
content: We know exactly what happens to packages during shipment, so I assume we always package sufficiently well for the worst case conditions.

author: Mr. Scram
author_rank: Super Contributor
timestamp: February 27, 2019, 01:34:35 am
content: Quote from: Conrad Hoffman on February 26, 2019, 04:24:31 pmKnowing exactly what happens to packages sounds like an ancient curse.

author: KK6IL
author_rank: Regular Contributor
timestamp: September 13, 2020, 05:33:38 am
content: Guess my L&N 4040-B is due for an oil change. What's the procedure for opening these? the knurled ring seems quite resistant to turning, and attacking it with a pipe wrench seems like it might distort the metal causing more problems.Didn't know until today that it was oil filled or than the hole was a temperature well. Thanks, everyone.

author: chuckb
author_rank: Frequent Contributor
timestamp: September 13, 2020, 01:39:54 pm
content: I had some very old 4040s that needed an oil change. There was leakage resistance from the case to the resistor. The silver nut was a little corroded so I used two strap wrenches to start things turning. That's what they are made for. When they were open I cleaned things with Isopropyl, let them dry and put in new oil. I filled it 90% with oil so there would be some room for expansion.

author: jchw4
author_rank: Regular Contributor
timestamp: September 13, 2020, 03:01:09 pm
content: Oil filter wrench like this may help.

author: notfaded1
author_rank: Frequent Contributor
timestamp: September 13, 2020, 06:11:55 pm
content: Really neat getting to see the inside of one of these! Thanks! I think the oil filter wrench might be a good idea actually.Bill

author: HB9EVI
author_rank: Frequent Contributor
timestamp: September 13, 2020, 06:41:24 pm
content: another word of caution about the oilknowing the decade where these resistors originate from, it's not unlikely that the oil contains polychlorinated biphenyls (PCBs) which are most certainly contaminated (due to the manufacturing process) with any kind of polychlorinated dibenzofurans and dibenzodioxins.it's nothing but highly toxic waste which requires safe handling and disposal

author: bill_c
author_rank: Regular Contributor
timestamp: September 14, 2020, 05:39:38 am
content: Mineral oil will absorb some water from the surroundings (about 100ppm) so you may want to test the oil used for refilling and dry accordingly. A crackle test will tell you if it contains any water. 2 drops on a 160c surface, if it crackles then it has water.PLEASE USE FACE PROTECTIONand use some sort of shield to protect you from getting sprayed with hot oil.