Working Prototype of a Kelvin (4-Wire) Milliohm Meter

RE: Working Prototype of a Kelvin (4-Wire) Milliohm Meter

jdceletronica — Wed, 05 Apr 2023 02:09:12 GMT

muito interesante , mais ten algun amigo que ja feis con arduino nano e que tenha todos os componentes aky no brasil ?

RE: Working Prototype of a Kelvin (4-Wire) Milliohm Meter

kltm — Thu, 18 Jun 2020 14:11:27 GMT

Very interested in this. I’ve been looking for a circuit to build myself a resistivity meter for archaeology and I guess this uses the same principal. I’m pretty much an amateur, but I have built electronic circuits from kits in the past.

RE: Working Prototype of a Kelvin (4-Wire) Milliohm Meter

fmilburn — Thu, 26 Mar 2020 22:10:24 GMT

Hi [mention:b0bc65b9ecdc4307bd967592f00e340a:e9ed411860ed4f2ba0265705b8793d05]

I still have this on my list to fix the issue around stability at the lowest range and to add auto-range. Below is a new architecture sketched out and I would appreciate your opinion:

[View:/resized-image/__size/620x457/__key/commentfiles/f7d226abd59f475c9d224a79e3f0ec07-f21a80d7-dfd8-486f-8fbc-f54c303f90e9/1526.contentimage_5F00_189107.png:620:457]

The current source design is the same but there is only a single 10 mA source
The instrument has 4 ranges: x1, x10, x100, and x1000
A microcontroller (I successfully did some tests with a MSP432 with 16 bit resolution at one point) reads the voltages
x1 is just a differential reading across the DUT
x10 uses a differential Op Amp similar to the current design
x100 and x1000 are achieved with amplification in stages as shown in the sketch. Oops. Left the feedback off the last stage.
Trimmers not shown would be used to calibrate the stages

The microcontroller would autorange by searching for the highest reading that isn't saturated.

The advantages would seem to be:

relatively simple design
large range and autoranging with no switches

What do you think? Would the added stages of amplification add too much noise and would it add or possibly decrease stability issues?

RE: Working Prototype of a Kelvin (4-Wire) Milliohm Meter

shabaz — Wed, 02 Jan 2019 05:24:20 GMT

Hi Frank,

I recorded details and a video here!

Building Frank's Milliohm Meter

RE: Working Prototype of a Kelvin (4-Wire) Milliohm Meter

shabaz — Mon, 12 Nov 2018 16:49:51 GMT

Hi Frank,

I'm looking forward to building this milliohmeter hopefully in a week with your PCB. Regarding the overload circuit, there is a pin compatible comparator LMV7271MF LMV7271MF that may work in place of the op amp, so I'll try that and report back. For the enclosure, I am going with this one: Bopla 26085000Bopla 26085000 , it was low-cost. It's quite small though, so the banana sockets may be on the back (i.e. just the panel meter and buttons on the front).

[View:/resized-image/__size/265x181/__key/commentfiles/f7d226abd59f475c9d224a79e3f0ec07-f21a80d7-dfd8-486f-8fbc-f54c303f90e9/0268.contentimage_5F00_189106.jpg:265:181]

For the LDO, I'm using the pin-compatible LP3985IM5-4.7LP3985IM5-4.7 since it is available in the UK Farnell store.

For the power and range buttons, I've ordered some push-button latching ones, which are awkward (need square hole and are not panel mount so will need gluing) but take up less space on the tiny front panel that I have to work with!

RE: Working Prototype of a Kelvin (4-Wire) Milliohm Meter

genebren — Sat, 10 Nov 2018 23:49:49 GMT

You MilliOhm meter is working very nicely. Great video showing the operation and the accuracies that you are achieving.

Well done!

Gene

RE: Working Prototype of a Kelvin (4-Wire) Milliohm Meter

shabaz — Sat, 10 Nov 2018 17:30:22 GMT

Hi Frank,

Great video demo, it is nice to see it functioning! And it's really good to see the dual ranges.. it makes the project cover a really good range up to 40 ohms (by the way there's a typo in the blog, it says "40 milliohms" in the features list but you mean 40 ohms).

I looked around for other milliohmmeter circuits online, and many of them result in quite high amounts of current through the DUT (which is fine if required, but for some electronics components measurement it causes drift), so that's another differentiator that should be on the features list : ) as well as the ultra-low cost..

I'm excited to build this too hopefully within the next few weeks.