Where to buy 4 point probe  - Page 1
Forum section: electronics / testgear

author: Gibson486
author_rank: Frequent Contributor
timestamp: October 24, 2020, 01:09:05 pm
content: Any know a places where I can search for one? I did a Google search and only found 1. It was cheaper than expected, but it would be nice to see other options priced without having to deal with sales people.

author: dzseki
author_rank: Frequent Contributor
timestamp: October 24, 2020, 02:05:31 pm
content: 4 point probe as for sheet/bulk resistance measurement?The de facto standard is the Jandel probe, but it requires deep pocket... Signatone is a much simplier construction.Other than that you can build your own: it is just a matter of precise drilling skills and a few pogo pins.

author: Gibson486
author_rank: Frequent Contributor
timestamp: October 27, 2020, 02:14:08 pm
content: Yeah, for sheet resistance. I was thinking about building my own, but I am not the best at the machine shop when it comes to drilling...I am actually surprised there is not that many brands that make this. This must not be a huge market for this....

author: HKJ
author_rank: Super Contributor
timestamp: October 27, 2020, 02:43:45 pm
content: Quote from: Gibson486 on October 27, 2020, 02:14:08 pmIf it is just four pogo pins with fairly precise placement, a 3D printer is the tool, you do not need a machine shop. There are free 3D design tools available that is easy to use (One example ishttps://www.tinkercad.com/)

author: Gibson486
author_rank: Frequent Contributor
timestamp: October 27, 2020, 09:15:13 pm
content: Just got a quote for one...almost $18k....I think half of that cost goes towards the Keithly meter.... may have to build my own...

author: Gibson486
author_rank: Frequent Contributor
timestamp: October 27, 2020, 09:37:11 pm
content: Basically, I just make a current source (+, - on the outer leads), then the inner leads are where I measure?

author: Gibson486
author_rank: Frequent Contributor
timestamp: October 27, 2020, 09:40:50 pm
content: Quote from: HKJ on October 27, 2020, 02:43:45 pmGood idea! I may try that....

author: dzseki
author_rank: Frequent Contributor
timestamp: October 28, 2020, 06:36:21 am
content: Jandel probes are quite precise puppies, they employ jewel busings/bearings, precisey machined tip radius and tip distances, they give a certiciation for each probes, with the actual pin distance. The difference is in the order of few um-s from the ideal! indeed, if you aim accurate measurements the mechanical properties of the probe becomes also very important...Signatone probes (that I know of) are much-much simplier, I would dare to say even "primitive" compared to Jandel's, therefore I expect them to be much cheaper as well.KLA-Tencor is a major player in the industrial 4PP measurement scenery, in older times they rolled their own probes, but as far as I know they also movedl to customized Jandel probes.Search the internet for "ASTM-F84" or "SEMI MF84-0307" this is the standard way of performing 4PP measurements.Practically using a real current source on the outer pins can often cause problems, especially if the pin contacts are uncertain, rapid jumps in the voltage (to keep the current constant) often have adverse effects eg. welding the pins. Instead a constant voltage source is a better approach where you monitor the current flowing.You can build your own 4PP measuring circuit surprisingly cheap, even on an Arduino shieldFor non standard sample shapes the so called "Van der Pauw" method can also be used but it is rather time consuming to faithfully perform...

author: paulbt
author_rank: Regular Contributor
timestamp: October 28, 2020, 06:55:29 pm
content: Hi!If you mostly need to measure through-hole components or wires, you can search for "380465 EXTECH" or "GTL-108A GW INSTEK" which will cost you roughly 70 EUR. There are a few topics on this forum where many others are discussed, just search for "kelvin probes".But if you mostly need to measure SMD components like shunts, you will probably need your probes to be more pointy/sharper/needle-like. I made ones myself and they work great. Please click and expand the picture below. If you are interested, I can explain to you how I made them.

author: dzseki
author_rank: Frequent Contributor
timestamp: October 28, 2020, 09:59:46 pm
content: Quote from: paulbt on October 28, 2020, 06:55:29 pmSheet resistance is the "measure" of eg. a thin film's resistance on a large area. Think of a transparent windscreen heater, not exactly like measuring resistance with four wires.

author: paulbt
author_rank: Regular Contributor
timestamp: October 28, 2020, 10:18:48 pm
content: @dzsekiI can't understand what are you trying to say, in my reply I did not mention anything about "sheet resistance". Anyways, OP (Gibson486) did not told us for what purpose is he going to use kelvin probes. I just gave him 2 practical examples that maybe will help him choose the right type (buy or build). So far I have only used kelvin probes for measuring motor windings resistance, wire length resistance and low value resistors/shunts. I did not imagined it can be used for something else...

author: dzseki
author_rank: Frequent Contributor
timestamp: October 28, 2020, 10:41:50 pm
content: Quote from: paulbt on October 28, 2020, 10:18:48 pmIn fact he said he wants to measure sheet resistance:https://www.eevblog.com/forum/testgear/where-to-buy-4-point-probe/msg3298364/#msg3298364The math behind the Kelvin probe and a 4 point probe is substantially different, and to highlight this, a measurement performed by a Kelvin probe givesOhm, while sheet resistance have dimension ofOhmsquare.

author: paulbt
author_rank: Regular Contributor
timestamp: October 29, 2020, 07:01:47 am
content: @dzsekiSorry, my bad, I did not noticed that message (I guess too many consecutive replies from him tricked my eyes). At least I was not too much offtopic with my first reply and I hope my answer and photo will enlighten someone else. I don't know anything about sheet resistance measurement, so I'm out of this discussion.Have a nice day !