4-wire connections to reference resistors - Page 1
Forum section: electronics / general

author: leonerd
author_rank: Regular Contributor
timestamp: July 11, 2016, 03:46:24 pm
content: I'm planning to make myself a reference resistor; basically just putting a Vishay Z201 in a box with some banana sockets. E.g. this 10khttp://www.mouser.co.uk/Search/ProductDetail.aspx?R=Y145310K0000V9LI'm going to make two - a 100R and a 10k (because those are the values mouser has easily - I don't see a 10R or 1k). Less so for the 10k, but the 100R at least likely benefits from having 4-wire connections on it, so do two onto each leg in the case.I wonder - if I mount the resistor on stripboard, I can attach two sets of wires to it, one on each side. For minimising the error, should I "cross over" the force vs. sense flows? I.e. should I put the force on two diagonal corners and the sense out of the other two, or doesn't that matter?Relatedly, if I'm using a larger scale SMT resistor on a PCB (such as a 2010wide) and adding 4-wire sense support, should I pass the two flows in parallel, or cross them over?

author: TiN
author_rank: Super Contributor
timestamp: July 11, 2016, 03:54:32 pm
content: Just twist sense+/- together into one pair and current+/- into second pair, and you likely be okay to go for hobby needs. I'd recommend 4 wire connection for both values.Make sure you use fresh cleaned copper wires and copper terminals if you after good accuracy.

author: leonerd
author_rank: Regular Contributor
timestamp: July 11, 2016, 04:12:02 pm
content: Ah, just free mount it in air? That might be better actually, because looking at the data sheet, the pin spacing is 0.15" - who thinks that's a good idea?Won't fit in 0.1" stripboard. Well, *maybe* I could angle it diagonally; 0.15 is very nearly 0.141... but I don't like the idea of the stress.Speaking of - what would be best for physically mounting it within the case, if it's not mounted on stripboard which is then glued to the case? I don't know what I can sensibly do to the resistor without risking ruining its high precision.

author: TiN
author_rank: Super Contributor
timestamp: July 11, 2016, 04:18:28 pm
content: Have the suitable box, which allow air-tight seal (could be metal to provide more shielding).Mount good copper banana plugs on case securely, and then use copper wires (e.g. strands from CAT5 LAN cable work great) to do the wiring.There should be no tension to resistor legs or body. Good idea to drop in some humidity desiccant bags to dampen humidity effects (resistors in plastic package are not hermetic and subjected to humidity/resistance changes).Here is worklogon one of my resistance boxes I've build, but it's more specific to my needs with triaxial ports instead of banana. But idea is the same. I'd recommend also having separate box per resistor, so you can manage it easier.

author: kripton2035
author_rank: Super Contributor
timestamp: July 11, 2016, 06:16:05 pm
content: Quote from: TiN on July 11, 2016, 04:18:28 pmare the gloves necessary to handle these components ?? =)

author: Vgkid
author_rank: Super Contributor
timestamp: July 11, 2016, 06:51:01 pm
content: Quote from: kripton2035 on July 11, 2016, 06:16:05 pmShouldn't be, you still need to wash the flux off of the leads anyway. If you think about it, the average meter is specced to have less than 30pA of input bias current. That multiplied by 10k gives you .30uV. That is about the same voltage potential that you would have to deal with wrt thermal emf's. If we were talking about higher resistances, then leakage currents do reslly matter.

author: SeanB
author_rank: Super Contributor
timestamp: July 11, 2016, 07:11:40 pm
content: Gloves so skin debris and oil along with sweat salts do not contaminate the resistors or the connections. Causes leakage current to increase on high value resistors and also causes corrosion of the contacts so increasing residual resistance and noise on the lower values.

author: Vgkid
author_rank: Super Contributor
timestamp: July 11, 2016, 08:01:42 pm
content: Yep, a good cleaning with some strong ipa is all you need.

author: RobK_NL
author_rank: Frequent Contributor
timestamp: July 11, 2016, 08:24:28 pm
content: What is not there does not need to be cleaned away and cannot react with the cleaning agent to form some non-soluble residue.

author: zlymex
author_rank: Frequent Contributor
timestamp: July 12, 2016, 01:54:03 am
content: Quote from: leonerd on July 11, 2016, 04:12:02 pmSpeaking of precision, it can be mainly decompose to1. Long term stability. Hermetic sealed(instead of plastic sealed) is much better, with added benefit of not affected by humidity2. TCR. Z-foil or VHP101 is better than regular foils. It can be compensated to very small value if required(10 times to 100 times better, window TCR)3. Deviation to nominal value, not very big deal if you know the value.

author: TimFox
author_rank: Super Contributor
timestamp: July 13, 2016, 09:12:12 pm
content: I have had no problems with the 0.15" lead spacing into two diagonally-spaced holes (0.141" nominal) in 0.1" PTH breadboard PCBs.

author: leonerd
author_rank: Regular Contributor
timestamp: July 13, 2016, 10:16:23 pm
content: Quote from: zlymex on July 12, 2016, 01:54:03 amPeople have suggested using a hermetic sealed case to put it inside. I'm curious though - what do you do about the holes for the terminal sockets? Are there hermetically-sealed sockets available? Not much point getting a sealed case if I'm just going to drill 4 big holes in it anyway.Quote from: zlymex on July 12, 2016, 01:54:03 amYeah; these are indeed Z-foils; the Z201 range.Quote from: zlymex on July 12, 2016, 01:54:03 amMmm that's true; some sort of calibration and recording the value might be in order.

author: zlymex
author_rank: Frequent Contributor
timestamp: July 14, 2016, 02:50:59 am
content: Quote from: leonerd on July 13, 2016, 10:16:23 pmWhat I implied was to buy a ready made hermetic resistors such as VHP101, VHP202Z, VHP102Z or VHP203.Most of(if not all) the commercial standard resistors use hermetic resistors inside.If precision is not critical, then the 4-wire connection is not necessary for 10k after all in my opinion.