Other than TE porn, what the heck is this? - Page 1
Forum section: electronics / testgear

author: HalFoster
author_rank: Frequent Contributor
timestamp: June 15, 2019, 09:41:23 pm
content: Picked this up recently - looked interesting and no one else was interested. Opened it up and... nerdgasm.

author: Kjelt
author_rank: Super Contributor
timestamp: June 15, 2019, 09:47:13 pm
content: The most elaborate potentiometer I have ever seen

author: Bud
author_rank: Super Contributor
timestamp: June 15, 2019, 10:07:29 pm
content: Holy crap, whatever it is, it is awesome!

author: HalFoster
author_rank: Frequent Contributor
timestamp: June 15, 2019, 10:28:19 pm
content: Itlookslike a potentiometer... Itsaysthat it is a potentiometer... But is doesn'tdoanything a potentiometer is supposed to do. I mean, it looks to be pristine inside, but I can't find any combination of terminals that works like I would think. Of course, most of the dials appear to be in the sub-ohm range but still... Going to take it back apart and measure and trace I guess. A sticker that was on it said that it came from a college physics department - I'll try to find them and contact to see if I can find out more. My Google-fu hasn't been up to the task on the part number so far.Hal

author: 0culus
author_rank: Super Contributor
timestamp: June 15, 2019, 10:34:19 pm
content: https://web.pa.msu.edu/people/edmunds/scratch/potentiometer_and_bridge_notes.txtMight be useful. In any case, the person who runs the page might know more.

author: BillB
author_rank: Unknown
timestamp: June 15, 2019, 10:35:25 pm
content: Wow, that's some wiring job!

author: windsmurf
author_rank: Frequent Contributor
timestamp: June 15, 2019, 10:43:05 pm
content: Quote from: BillB on June 15, 2019, 10:35:25 pmYah its a work of art!Lot of hits googling "Rubicon Potentiometer"

author: Peabody
author_rank: Super Contributor
timestamp: June 15, 2019, 10:47:17 pm
content: Porn indeed. In the same class visually as the Harrison chronometers at Greenwich.

author: HalFoster
author_rank: Frequent Contributor
timestamp: June 15, 2019, 11:31:15 pm
content: https://www.antiqueradios.com/forums/viewtopic.php?f=8&t=346630Looking like probably meant to be one leg of a Wheatstone bridge. I emailed the physics dept that originally had it, so possible some Operating Manual love there if I'm lucky. Huh... if I'm that lucky, need to buy lotto tickets.Think I'm going to have a nice Plexiglas case made and put it in that. You just know that will look awesome on the shelf.Hal

author: edpalmer42
author_rank: Super Contributor
timestamp: June 15, 2019, 11:32:59 pm
content: Okay, I think this is mostly right.....The terminals from left to right:EMF = the voltage you want to measure. Yes, that's what this is for.1.0 =Input? Output?Shield = GroundGA = Galvanometer - the meter you use to measure the output. You null the meter by adjusting the other dials and then read the voltage off of the dials.G.D.R. =S.C. = Standard Cell - a Weston standard cell which is a very stable voltage reference. The small dial in the top right is set to the precise voltage of the cell in use. This is how you calibrate everything. Notice the very limited range on that dial!6V 3V BA+ = Battery - looks like a common positive lead with either of two voltages depending on what you need for a good indication on the meter. I think that you'd normally use 3V if possible to help keep down internal power dissipation in the precision resistors.This unit has more controls than a typical potentiometer. I have no idea what they would be for.Ed

author: Bud
author_rank: Super Contributor
timestamp: June 15, 2019, 11:48:48 pm
content: po·ten·ti·om·e·ter/pəˌten(t)SHēˈämədər/noun1.an instrument for measuring an electromotive force by balancing it against the potential difference produced by passing a known current through a known variable resistance

author: Mr. Scram
author_rank: Super Contributor
timestamp: June 15, 2019, 11:55:06 pm
content: Is there a name for this type of "wiring". I'd almost call them busbars.

author: HalFoster
author_rank: Frequent Contributor
timestamp: June 16, 2019, 12:04:00 am
content: Ed:"This unit has more controls than a typical potentiometer. I have no idea what they would be for."It also occurred to me that oh, maybe, possibly, an extra label or ten really would not be out of place.Hal

author: HalFoster
author_rank: Frequent Contributor
timestamp: June 16, 2019, 12:05:53 am
content: Mr. Scram:I'm sure there is, but i just call them impressive as h#!!.Hal

author: tautech
author_rank: Super Contributor
timestamp: June 16, 2019, 12:28:39 am
content: Quote from: Mr. Scram on June 15, 2019, 11:55:06 pmPoint to point.Done beautifully of course.Dads valve Tripletone 5W stereo amp was beautifully wired like this.

author: Mr. Scram
author_rank: Super Contributor
timestamp: June 16, 2019, 01:02:27 am
content: Quote from: tautech on June 16, 2019, 12:28:39 amCalling it point to point doesn't seem to do it justice. They're closer to bars than wires.

author: GerryR
author_rank: Frequent Contributor
timestamp: June 16, 2019, 01:04:11 am
content: Looks like Honeywell's rendition of a Kelvin-Varley Voltage divider. Fluke made a 720A version used for calibration purposes. Extremely accurate. I may be off base but the stacked coils look like accurately wound resistors. Just a guess.

author: schmitt trigger
author_rank: Super Contributor
timestamp: June 16, 2019, 01:52:01 am
content: 👀I am confident that, had the electronics magazines had a Playboy-style centerfold spread with photos like these, they would still be in business.

author: Arjunan M R
author_rank: Regular Contributor
timestamp: June 16, 2019, 02:18:32 am
content: Thumbs up to the design engineers

author: Arjunan M R
author_rank: Regular Contributor
timestamp: June 16, 2019, 02:20:15 am
content: Quote from: Arjunan M R on June 16, 2019, 02:18:32 amWhy is that image small(when i posted)

author: tautech
author_rank: Super Contributor
timestamp: June 16, 2019, 03:41:02 am
content: Quote from: Arjunan M R on June 16, 2019, 02:20:15 amDunno but let's investigate......For this I copied the thumbnail URL and inserted it between IMG (Image) flags.You've done something different......Quote this post and examine the differences in syntax.

author: Arjunan M R
author_rank: Regular Contributor
timestamp: June 16, 2019, 04:11:31 am
content: I clicked on copy link address.I needed to click on copy image address.

author: Arjunan M R
author_rank: Regular Contributor
timestamp: June 16, 2019, 04:13:31 am
content: Nice wiring.

author: shakalnokturn
author_rank: Super Contributor
timestamp: June 16, 2019, 08:13:24 am
content: Stiff copper and clunky mechanics it must be a "nerdgasmatron".

author: Gandalf_Sr
author_rank: Super Contributor
timestamp: June 16, 2019, 01:07:10 pm
content: It says 'potentiometer' on it but it's really a device for calibrating mercury torsion field UFO drive systems.

author: Cnoob
author_rank: Regular Contributor
timestamp: June 16, 2019, 01:13:05 pm
content: Something that should be in a see through box.

author: Fungus
author_rank: Super Contributor
timestamp: June 16, 2019, 01:32:07 pm
content: I don't often say "wow!", but ... "Wow!".I hope you aren't thinking of putting the lid back on.

author: tinhead
author_rank: Super Contributor
timestamp: June 16, 2019, 04:40:40 pm
content: very nice one, here description ->https://www.muffwiggler.com/forum/viewtopic.php?t=154572&sid=fe3b4669c6e5af37261d46adbba42628

author: ArthurDent
author_rank: Super Contributor
timestamp: June 16, 2019, 06:35:04 pm
content: If you worked in a standards lab around 50 years ago you would be familiar with this type of measurement equipment. Today with DMMs like the HP3458A you can get far, far greater accuracy and it is far less complicated. These 'potentiometers' worked over a fairly limited range of EMF unless you used an external 'volt box', which was a matching multiplier that allowed you to measure up to 750 volts.Here is a couple of photos I just took of my Leeds & Northrup K-3 potentiometer which was more or less the standard for quality back then. There is a copy of the first page of instructions that will give you some idea of the connections. The galvanometer would generally be a lightbeam galvanometer that is diagrammed below. The sensitivity was increased by making the distance from the mirror to the scale greater and might be around 3 feet. Seeing this was just used as a null indicator it wasn't too critical.

author: edpalmer42
author_rank: Super Contributor
timestamp: June 16, 2019, 07:29:07 pm
content: One thing that hasn't been mentioned about these devices is the fact that even though they might use a meter that draws microamps, their input impedance is infinite! Since you null the meter to take the reading, no current is flowing.The same trick can be useful today. Even if your DMM has an input resistance of a gigaohm or more, that only applies on the lower one or two voltage ranges. At higher voltages, you're probably still looking at the standard 10 megaohm input resistance. Using a potentiometric measurement technique allows you to get infinite input impedance at any voltage. Of course, normal rules of sanity still apply!So, don't use this trick to measure hundreds or thousands of volts without knowing EXACTLY what you're doing!https://www.eevblog.com/forum/blog/eevblog-584-what-effect-does-your-multimeter-input-impedance-have/Ed

author: coromonadalix
author_rank: Super Contributor
timestamp: June 17, 2019, 10:18:33 am
content: This is a beauty, look at the bent wires, should have taken lot of time doing this, keep it pristine

author: Fungus
author_rank: Super Contributor
timestamp: June 17, 2019, 12:44:26 pm
content: How did they even get the wires so straight?

author: Mr. Scram
author_rank: Super Contributor
timestamp: June 17, 2019, 12:45:42 pm
content: Quote from: edpalmer42 on June 16, 2019, 07:29:07 pmThat could be useful for measuring Weston cells.

author: Kjelt
author_rank: Super Contributor
timestamp: June 17, 2019, 05:05:51 pm
content: Quote from: Fungus on June 17, 2019, 12:44:26 pmA mold, for production items with solid wire that was common back in the day.For prototyping you bent it with flat nose pliers.

author: edpalmer42
author_rank: Super Contributor
timestamp: June 17, 2019, 05:11:19 pm
content: Quote from: Mr. Scram on June 17, 2019, 12:45:42 pmYes, back when this equipment was in use, this was the way to measure them. Today, many of the high impedance ( > 1 G ) meters would be able to measure 1.x volts in high impedance mode without the added complexity. However, if you only have 10 Megaohm meters, this method is still useful.Ed

author: donlisms
author_rank: Frequent Contributor
timestamp: October 23, 2021, 03:06:29 am
content: I got it! And... I got it!When Hal offered this on eBay with those beautiful pictures, I had to step up and answer the call. That was a while ago; it's been waiting for its chance on the bench, so I pulled it off the shelf and started poking.Like Hal, I couldn't find any combinations of connections and ins and outs that seemed to do anything, and opening it up and looking just made me appreciate how much it was going to be to reverse engineer it and draw the schematic -- no ten minute job, this! But with this thread and snippets from other places, it started to come together; finally getting to square one!I used a 3v supply as the battery, and a nice stable Power Designs Precision 2005A as the standard cell on the "S.C." terminals, connected my HP 34401A Galvanometer, and put about half a volt on the E.M.F. terminals to be measured.Set the galvanometer sensitivity buttons in the lower left to "3", which is momentary but also has a locking position with a little twist of the knob, indicated by the line across the top of the button. Nice touch. The "R" here is "reverse", i.e., flip the direction on the null meter. (This was all clarified through Arthur's helpful reference to some Leeds&Northrup information.)Now... set the upper right dial to 1.0181 to match my standard cell, and then flip the upper left switch to "S.C." to send the balance to the galvanometer. The upper row of three pots are used to "standardize" (I think you say...) and I dialed them around, coarse medium fine, until the null meter said "about zero," with some noise crossing zero down in the microvolt range. Ready!Flip the upper left mode switch to "E.M.F." and use the lower three resistors to get a null. The first has a range of 0 to 1.5 in 0.1v units, the second is 0 to 0.09 in 0.01v units, and then the big dial, which is wonderful and has a wonderful loud wire-wound tactile thing happening. It is has graduations at 0.00005v, and estimates are pretty easy between them, so we're approaching five digits of resolution.My first reading was good to four digits, and was out a bit on the fifth digit. I don't know what errors were in my cheap and quick setup, besides the obvious noise. I haven't done any calibration or investigation yet, I don't know what the 1.0 or I.O connection is for, or the "EMF 1.O" switch setting is for, or what some of the other switches or connections are, but at least I feel like I'm in the building, ready to ask useful questions! It really is beautiful inside. It's a lot bigger than I thought -- close to 11x20 inches, double my initial impression. But the components and design are so very well thought out and carefully made, the rotary switches loaded with resistors and little thermal compensator coils, the clever leaf switches (e.g. 4PDT), the wiring, the no-doubt hand-wound resistors... it's really gorgeous.I'm hoping to dig into it a little more, figure out the other controls, and take a stab at checking calibration and such. It deserves it. But I have to put that on a list... sigh.

author: HalFoster
author_rank: Frequent Contributor
timestamp: October 27, 2021, 07:12:19 pm
content: Glad you are enjoying it - really haven't had any free "stuff" time between Covid and then (currently) moving. Still going to send you a list of stuff when I can get to it.Hal

author: yo0
author_rank: Regular Contributor
timestamp: October 27, 2021, 09:36:58 pm
content: deleted, sorrybest regardsPio

author: TimFox
author_rank: Super Contributor
timestamp: October 27, 2021, 09:39:11 pm
content: Around 1968 to 1973, we used L&N potentiometers to measure temperature with thermocouples in teaching labs, using standard tables of thermocouple emus.