9-dial resistance ratio instrument VERI - Page 1
Forum section: electronics / general

author: Overspeed
author_rank: Frequent Contributor
timestamp: February 03, 2025, 06:45:24 am
content: Helloa quite old ( 1966) but interesting article on A Versatile Ratio Instrument for the High RatioComparison of Voltage or Resistance ( VERI)RegardsOS

author: Overspeed
author_rank: Frequent Contributor
timestamp: February 05, 2025, 07:05:47 am
content: Helloan interesting design used a tetra junction sphericalRegardsOS

author: Kleinstein
author_rank: Super Contributor
timestamp: February 05, 2025, 09:05:30 am
content: Looks like a really old style tetra junction. Not sure if it really helps, but it looks expensive to manufacture. The more modern version with disc of triangle and center looks a lot easier to produce.

author: Overspeed
author_rank: Frequent Contributor
timestamp: February 05, 2025, 01:11:45 pm
content: Quote from: Kleinstein on February 05, 2025, 09:05:30 amHelloI agree that look as old style , close to sci-fi movie in BW from the 50's but the circuit itself seems to work quite wellI use triangle shape cut in 2 mm copper sheet , improvement will be to success to crimp rather to solder but that request more machining / forming work .RegardsOS

author: donlisms
author_rank: Frequent Contributor
timestamp: February 09, 2025, 10:56:55 am
content: The sphere-with-posts is the original tetrajunction design used at NBS, where I would not expect them to cut corners in complexity or cost. It would indeed be much harder to make than the ESI versions of cut-and-tuned plates. The ESI patent talks quite a bit about the simplifications, and the goal of making it easy and inexpensive to manufacture. U.S. Patent 3,252,091, Four Terminal Junction for Electrical Measurements and Method of Making the Same, Merle L Morgan, 1961 -- a few years after Hamon, and five years before VERI.The curious thing about the VERI is that I've never seen any other significant references to it actually being used (and I've read a lot of NBS historical documents). I wonder if it was a complex solution to problems that people didn't really have, because of other adequate ways to make those measurements. But it is an interesting device.

author: Overspeed
author_rank: Frequent Contributor
timestamp: February 09, 2025, 11:43:01 am
content: Quote from: donlisms on February 09, 2025, 10:56:55 amHelloThanks for the detailin the 50/60's some machining was difficult now with 5 or more CNC lathe that a dreamcould be be interesting to compare side by sideI draw a CAD and send to my usual ''affordable'' Chinese CNC shop to received a quote , try to made them with a minimum of soldering .RegardsOS

author: guenthert
author_rank: Frequent Contributor
timestamp: February 09, 2025, 03:45:44 pm
content: "The transresistances of the junctions used in the described instruments are less than 10 - 8 Ω."Assuming they were able to detect with confidence voltages as little as 0.1μV, they had to pump a whopping 10A though it in order to make the above claim. I can't see that working well for the flat tetrajunction ESR deployed.

author: Overspeed
author_rank: Frequent Contributor
timestamp: February 10, 2025, 03:23:02 pm
content: HelloSorry but I think that a connector and not a resistor ? all tetra junction have very low resistance up to supposed ''zero Ohm''RegardsOS

author: Kleinstein
author_rank: Super Contributor
timestamp: February 10, 2025, 05:58:06 pm
content: The residual 4 wire resistance is what descibes the quality of the tetra junctions. Ideally this is zero, but if not perfectly symmetric there will be some nOhms of residual trans-resistance. To really measure very low one may have to get to below 100 nV in the resolution and do polarity reversals or similar, so separate from thermal EMF. Ideally one is at the measurement limits - so definitely not easy to test. Not all the junction may need to be really high end and good enough could be more moderate. It would be only the junctions used with low resistance / high current that really need to be good. These junctions would also be strong enough to carry a high current.

author: Overspeed
author_rank: Frequent Contributor
timestamp: February 10, 2025, 07:04:20 pm
content: Quote from: Kleinstein on February 10, 2025, 05:58:06 pmHelloI agree , when the circuit use low resistor up to ultralow resistor value the resistor value of the tetra junction itself is a concern and even a real concern.Playing with ultra low resistors values is a trip in another planetRegardsOS

author: Vgkid
author_rank: Super Contributor
timestamp: February 10, 2025, 10:16:33 pm
content: This is what the VERI is based on:https://www.eevblog.com/forum/metrology/ln-4393-universal-ratio-set/Unfortunately I have an early version of the 4393 URS. I have a crude manual further down on the page.