Open Hardware Milliohm meter

[anishkgt]

Hi all,
Would anyone be knowing if this or is there a reliable milliohm meter like this ?
https://youtu.be/y9gWZH9k_BQ

One of his subscribers has the pcb designed https://oshpark.com/shared_projects/UWvehNO2



Www.Georgehobby.wordpress.com

Equipments: DSO104z, Hakko FX888D

[ogden]

Consider following: This meter is overcrowded with high-cost precision and low drift components, states 0.1% accuracy AND in the end of signal chain uses cheap "made in china" 0..2V panel meter having unknown drift and precision specs  For sure panel meter does not have 10ppm reference - then what's the point of using such in the current source?

[Kleinstein]

The mOhms meter from the video is really not the right way to do. Generally an Ohms meter should not rely on a good voltage reference. It is only one good quality reference resistor that is really needed to be stable.

I have seen a reasonable project, that uses the rather good differential input of an now relatively cheap SD ADC, controlled from a small µC. Not sure about protection of that circuit, so that an accidental applied voltage (e.g. 14 V battery) will not break everything.

[anishkgt]

Hmmm well bought it here for a second opinion. Thanks. Any recommendation for a decent one ? Or would the kelvin technique be the way to go.


Www.Georgehobby.wordpress.com

Equipments: DSO104z, Hakko FX888D

[Kleinstein]

A reasonable projekt for an DYI mOhms meter is this one:
http://circuitcellar.com/cc-blog/build-an-accurate-milliohm-meter/

I have not checked all the details and I don't like all the details, but at least the principle is OK.

[HKJ]

This here is also a good milliohm meter:

http://www.lygte-info.dk/review/InternalResistanceMeterYR1030%20UK.html

[anishkgt]

This here is also a good milliohm meter:

http://www.lygte-info.dk/review/InternalResistanceMeterYR1030%20UK.html

Page not found


Www.Georgehobby.wordpress.com

Equipments: DSO104z, Hakko FX888D

[HKJ]

This here is also a good milliohm meter:

http://www.lygte-info.dk/review/InternalResistanceMeterYR1030%20UK.html

Page not found

Links works perfectly, you must have some local blocking.

[anishkgt]

on the desktop linked worked. I was trying it on my phone via tap a talk.

So is a IR resistance basically an milliohm meter or can it be used as one ?

[HKJ]

So is a IR resistance basically an milliohm meter or can it be used as one ?

It is usual a milliohm meter that can accept a voltage at the same time. The resistance is measure with a 1000Hz AC signal, not a DC signal.
Some cheap milliohm meters, like those build into battery chargers, works a different way and cannot be used as a general milliohm meter.

[anishkgt]

Thanks, Still searching for an off the shelf and cheap one or a reliable circuit to built one with a decent accuracy. most of the seem to be 300+ USD The extech seems to be cheapest of them all. Are there anything specific that i should be looking for ?

[ogden]

A reasonable projekt for an DYI mOhms meter is this one:
http://circuitcellar.com/cc-blog/build-an-accurate-milliohm-meter/

Right. This is very close to what DIY milliohm-meter shall look-like. Obviously with proper kelvin wires. Circuit can be improved by conneting low-TC reference resistor not to 2nd ADC channel, but reference input. Thou, current source needed then, not necessarily precision one.

Such approach is widely used in thermocouple/RTD measurements (attached).  This comes from Analog Devices circuit note.

[Kleinstein]

Measuring at 1000 Hz is kind of tricky: it works in some cases, but even wire would resistors can be a problem. Measuring with AC is not that bad (as this allows for better amplification), but a low frequency (e.g. 10 Hz range) would be preferred. This would also allow to generate more current from a battery using a transformer.

Using 2 ADC input channels in the DIY solution is not that bad. It is a little slower and might suffer a little from current drift, but it eliminates ADC gain drift and allows for a low voltage for the reference resistor too. With something like a 10 or even 1 Ohms reference resistor to compare with, it is hard to get a suitable voltage without a high power resistor.

The main problem is not having much protection. Not sure how the readings are taken in the SW, but the HW at least allows for reversing the current and even working with a reduced current for slightly larger resistors.

[hugo]

A reasonable projekt for an DYI mOhms meter is this one:
http://circuitcellar.com/cc-blog/build-an-accurate-milliohm-meter/

I have not checked all the details and I don't like all the details, but at least the principle is OK.

It lacks input voltage protection and the current is way too high (80 ma) for tracing out shorts. 

[Damianos]

An idea to measure low value resistors is in AN-306: Synchronous System Measures µ?
With this method are eliminated disturbances such as thermal EMF, RFI, EMI etc. Also it does not use "huge" current, so the resistor is not heated. It is easier to implement it with a square, instead of sinusoidal, wave source. As mentioned by Kleinstein, it will be better to lower the frequency (increasing also the capacitances).

Edit: I just realized that the circuit proposed by Kleinstein uses the same method of synchronous demodulation.

[kripton2035]

http://kripton2035.free.fr/continuity-repos.html


or
http://kripton2035clone.free.fr/continuity-repos.html
if the above does not respond.