Reversing switch - Page 1
Forum section: electronics / general

author: lowimpedance
author_rank: Super Contributor
timestamp: April 01, 2016, 01:22:22 am
content: Okay a probably easy question for all you regular visitors to this section, but lets have some fun. Have a look at the pic's of this 'unloved' switch I found dumped in the junk store at work. Do you know its purpose ?. apart from being a switch(and yes I allready know).And it also needs quite a bit of restoration to reverse the state it was left in.

author: Vgkid
author_rank: Super Contributor
timestamp: April 01, 2016, 01:31:14 am
content: Looks like it is meant to switch in a 4-wire resistor.

author: SL4P
author_rank: Super Contributor
timestamp: April 01, 2016, 02:23:14 am
content: Beautiful... almost the definition of steampunk.Ebony, Bakelite and/or Brass

author: lowimpedance
author_rank: Super Contributor
timestamp: April 01, 2016, 03:46:30 am
content: Enough suspenseand of course every one who looked knew it was a reversing switch anyway!, which was made here in Australia by a company called .. J L William Instruments.see this short article on wiki. ;https://en.wikipedia.org/wiki/Les_William(well worth a quick look).And here is a pic of the top plate.I will try to restore this switch to full working condition again, unfortunately the wooden enclosure has vanished long ago.Quote from: SL4P on April 01, 2016, 02:23:14 amAll the electrical parts are actually copper and the brass appearance is most likely due to a lacquer (best guess!.).And I agree it is a thing of beauty and will be restored.

author: zlymex
author_rank: Frequent Contributor
timestamp: April 01, 2016, 08:53:24 am
content: Very nice. All made of pure copper isn't it?Do nano-voltmeter companies use pure copper instead of tellurium copper for their 'binding posts'?

author: manganin
author_rank: Regular Contributor
timestamp: April 01, 2016, 09:57:44 am
content: Quote from: lowimpedance on April 01, 2016, 01:22:22 amThat is a British design which I think was originally patented and manufactured by Tinsley.Many metrology instruments following the British tradition were also manufactured in other countries part of or in close connection with the Empire.Quote from: Vgkid on April 01, 2016, 01:31:14 amProbably used with standard cells. British standard resistors and bridges of that time were 2-wire.Quote from: zlymex on April 01, 2016, 08:53:24 amNo need for that. Tellurium is added to make the machining easier and faster, but fortunately it doesn't much affect the electrical properties.

author: manganin
author_rank: Regular Contributor
timestamp: April 01, 2016, 10:10:27 am
content: Quote from: lowimpedance on April 01, 2016, 03:46:30 amThe contact surfaces of these switches were usually made of silver. And spring copper alloy used for the multilayer brushes (copper alone would be way too soft).

author: zlymex
author_rank: Frequent Contributor
timestamp: April 01, 2016, 10:54:19 am
content: Quote from: manganin on April 01, 2016, 09:57:44 amBut it does affect the properties doesn't it? The requirements for nano-meter is very strict. Take 34420A for example, the input connectors 'are almost pure copper'(pp.271 manual), and certainly they are not gold-flashed. In the case of 3458A, they did say the terminal material is Gold-plated Tellurium Copper.Also, I just found out that they use pure copper terminals in their EM manometershttp://www.emelectronics.co.uk/n11.html

author: lowimpedance
author_rank: Super Contributor
timestamp: April 01, 2016, 12:08:27 pm
content: Quote from: manganin on April 01, 2016, 10:10:27 amYou are correct here the contacts do appear to be silver and the rotor does have multiple layers of copper to form the brush (might be able to see in the photo). The binding posts are copper.In the photos the top deck rotor has been removed, will post a nice closeup of that before I try to reassemble the whole unit.Must have a fish around the 'old junk' to see if any Tinsley or others are hiding in a 'corner', that show similar construction.

author: G0WZB
author_rank: Regular Contributor
timestamp: April 02, 2016, 05:56:34 pm
content: That is a thing of beauty

author: SeanB
author_rank: Super Contributor
timestamp: April 02, 2016, 06:02:09 pm
content: Wipers will be Beryllium copper, as the addition of a small amount of Be metal does a magic change to pure copper. It becomes hard, non ductile and behaves like spring steel, just with the low resistance of copper. Amazing in that you oly need a tiny ( less than 0.1%) addition to do this, and the most common use is as a flexible aneroid vessel, used in gauges as the bending element.Also used as a poison in railway brass centre rail, as the tiny amount is added as a disc in a press fit slug in the main wear area, so that if it is stolen as scrap this small amount of Be will render the whole batch of metal in the furnace to be unusable without further electrolytic refining, and also requiring the replacement of the entire refractory lining in the smelter from the contamination. In use the wear mark limit means the tiny disc will be rubbed away by the pantograph unit just before the limit is reached, removing this from the brass rod and spreading it in a thin coat on the ballast, where dilution renders it safe.

author: zlymex
author_rank: Frequent Contributor
timestamp: April 02, 2016, 11:05:09 pm
content: I find that amazing too that Beryllium does to copper. However, the specification of Fluke 5440A-7002 Low Thermal Test Lead Set is not very good at 'Less than 1.3 ?V per degree C when measured while engaged in a five-way binding post of Tellurium Copper Alloy145, half hard (John Fluke PN 637892 or equivalent)'. That is an indication to me of the influence of Beryllium, Tellurium or Gold to copper.

author: quarks
author_rank: Frequent Contributor
timestamp: April 03, 2016, 08:05:18 am
content: quite a while ago I searched for thermal emf infosand found copper to beryllium copper is around 5µV/Khttps://www.eevblog.com/forum/chat/help-wanted-low-and-high-ohm-measuremet/msg174908/#msg174908

author: zlymex
author_rank: Frequent Contributor
timestamp: April 03, 2016, 01:27:39 pm
content: Quote from: quarks on April 03, 2016, 08:05:18 amI have two of those Fluke 5440A-7002 Low Thermal Test Lead Set but seldom use them. Apart from suspicion of thermal EMF, they may come to loose by themselves and pop up from the binding posts.Also in that post, @robrenz referred 34420A "almost pure copper connections" as well but he "translated Tellurium copper", is that true? I though Agilent say that because pure copper has the best low thermal property but not Tellurium copper.

author: quarks
author_rank: Frequent Contributor
timestamp: April 03, 2016, 01:55:32 pm
content: Hello zlymex,about Tellurium, as discussed with and confirmed by robrenz, CuTe is only used because it is much easier to work with lathe/milling tools. The emf properties should be worse then pure copper. But because there is only very little Te in CuTe, it seems to be there is almost no difference. All you have to avoid/take care of is oxidation. Therefore I prefer gold plating (but without Nickel layer underneath).About the Fluke 7002 (4mm banana), they are the way to go, if you cannot use/connect the much better spade lug cables. I.e. on Fluke 5450A front connector is unfortunately 4mm banana only, which I do not like at all. Same is true for my R6581 and my 6.5 digit meters. Because of that, I have made several adapters, so I am able to use spade lugs.Byequarks

author: zlymex
author_rank: Frequent Contributor
timestamp: April 03, 2016, 03:53:20 pm
content: Quote from: quarks on April 03, 2016, 01:55:32 pmIt just because every nano-volt counts in a nano-voltmeter, you cannot choose materials other than pure copper no matter how hard they made. I had several dozens of pure copper binding posts custom made for this reason. I hate my 5450A and R6581 too. I'm going to take down/sell then.

author: quarks
author_rank: Frequent Contributor
timestamp: April 03, 2016, 04:08:21 pm
content: Quote from: zlymex on April 03, 2016, 03:53:20 pmif you really want to sell your R6581, please send me a PM with details, I am interseted to buy it

author: manganin
author_rank: Regular Contributor
timestamp: April 04, 2016, 11:38:56 am
content: Quote from: zlymex on April 01, 2016, 10:54:19 amWhen we talk about machined parts, "copper" is hardly ever just copper. The electrolyte copper is a good material for punching, but very slow and difficult to machine. And threaded parts like binding posts would wear out quite fast.According to my experience, protecting the connections from air currents (and everything else causing thermal gradients) is the most important thing. The copper alloy used and the possible gold plating come far behind.

author: lowimpedance
author_rank: Super Contributor
timestamp: April 05, 2016, 12:50:28 am
content: Hunting around for other switches I did find another one from the same manufacturer, so I could see exactly how it was put together (which has made it easier to reassemble all the bits correctly). Okay some pics side by side and re assembly complete, all bar the timber case.

author: lowimpedance
author_rank: Super Contributor
timestamp: April 05, 2016, 12:53:57 am
content: Quote from: manganin on April 04, 2016, 11:38:56 amI had to tweak the copper rotor brushes to make better contact on the stator and I found them to be quite soft and easliy 'manipulated'. here is a pic. of the rotor looking at the contact brush arrangement.

author: rx8pilot
author_rank: Super Contributor
timestamp: April 05, 2016, 01:32:51 am
content: I want that on my desk! Just to look at.

author: zlymex
author_rank: Frequent Contributor
timestamp: April 05, 2016, 05:46:33 am
content: @lowimpedance pieces of art

author: Vgkid
author_rank: Super Contributor
timestamp: April 05, 2016, 02:07:20 pm
content: That is a piece of art.