Milliohm Meter Kit from Ascel Electronic Review

[Martin72]

Of Course, they are differents to the last digit about +/- 1, but all in all I´m surprised in a positive way.
Next step will be a long time measurement as a "colleague" of mine suggest it.
( He is like me a administrator of our forum, at work a group leader of R&D in electronics)

That means mounting the shunts on a heatsink, measure their values for min. an hour at ambient temperature.
Then increase it to say plus 10 Degrees more and measure again.
Nevertheless, the possibility to adjust the current at every time is a benefit what precisely measurings concerns.

[Kleinstein]

With the low value shunts there is not that much resolution left. With 100 mOhms it is just 3 digits. So some small moderate time drift would likely no be visible. It would need a slightly larger resistor (e.g. 1 Ohms) to see drifting.

From the circuit design and pictures I would expect some drifting in the first 20 seconds or so after connecting the DUT: the reference resistors get quite some power and would thus show quite some self heating effect. 15 Ohms and some 1.25 V gives some 100 mW to the small resistor. This is within specs, not to damage the resistor, but the resistor would heat up considerably and thus show quite some change from the TC. I would expect something like 10 ppm/K * 100 K = 1000 ppm of resistor change as a reasonable order of magnitude.

The instrument could still meet the rather modest specs.

[Martin72]

Today I took a 1R21 metal film resistor (1%).
After say 10sec the displayed value is rockstable until I switched it off ( after 30min).
Damn, didn´t pay attention to the range, will repeat it on monday.

I would expect some drifting in the first 20 seconds or so after connecting the DUT

The drift is about 5..10sec.

[Martin72]

After long time searching for it, a distributor of isabellenhuette was so kind and send me a free sample of an PBV 1R0. 
With this one I´ll do "long time" measuring.
Because, with an "ordinary" metalfilm resistor 1R0, the values were instable, maybe due to the "high" current.
This one I can mount on a heatsink.
Measure results will be posted here when done.

[Martin72]

Today I did a 2 hours long measuring using the PBV 1R0.



Logging the values with the milliohm meter software



Two negative points about the software:

The time interval couldn´t be changed (always one second) and the output format is csv - but the content (value, range, time) is all in a single column 




So it takes a while to create a diagram (for me, I´m a totally noob in excel)….

At the end one positive thing:
The tolerance of the PBV resistor is 0.5% - And the measured values are always in this range - Nice...

[Kleinstein]

The photo show how not to connect the Kelvin probes:
There are 2 good ways:
1) Use only 2 of the contacts of the resistor and then the probes in both sides. This measures the 2 wire resistance of the shunt.
2) connect in a way that die current and voltage contacts go to different pins of the resistor. This measures the 4 wire resistance.

For the CVS file one can usually choose the separator character on importing to excel or similar. One may also have to choose the right decimal separator (. or ,).

[Martin72]

First I got the clips connected on the pins outside, but it was mechanical unstable so I put them like on the photo.
There was no difference between it what the values concerns but I could repeat the measure, trying to find a way for better fixing the clips on the pins.

For the CVS file one can usually choose the separator character on importing to excel or similar.

Ah, I remember - Thank You !

[HighVoltage]

Looks really stable.

Can you test it with stable 1 Ohm resistor?

I ordered one unit but it has not arrived.

[Martin72]

Hi,

Can you test it with stable 1 Ohm resistor?

This test was made with a Isabellenhuette PBV 1Ohm/ 0.5%  resistor.

[HighVoltage]

I was typing too fast ...

What I wanted to say is:

Can you make some longer measurements with true 4 wire connection from the Isabellenhütte resistor 4 wires to the instruments 4 wires, to see if there is any drift.

[Martin72]

Without kelvin clamps,  four wires directly on the pins soldered ?
Sure, why not...
On monday, I guess - Yesterday I took everything back to home.
Except the resistor...

Edit: Thinking about it, this is the better method, you can see any movement of the clamps as a disturbance due more or less contact on these little pins

[nctnico]

Looks really stable.

You can't say over such a short period. Better leave it on for a couple of days. You'll likely see it acts as a good thermometer.

[Martin72]

Better leave it on for a couple of days

That make sense, I´m also doing this at work (testing a resistor or something else for days) and everytime I got trouble with my boss because he thinks I´m too slow, what a stupid..

[Martin72]

Can you make some longer measurements with true 4 wire connection from the Isabellenhütte resistor 4 wires to the instruments 4 wires, to see if there is any drift.

Prepare the resistor today, measure follows in the next days, want to acclimate DUT und and tester to my room temperatures (at home, all tests before done at work).
Nevertheless I´ve test it for a short while at the evening without logging.
In the first ...say 2,3 minutes the measured value drifts a little bit before it becomes almost stable - but in every case it´s within the tolerance range of the resistor.
More to come in the next days.
Nice thing:
I wrote to Ascel, moaning about the "useless" csv export, they promptly doing an update and give me a link to this - nearly close to sunday midnight...
Of course, the next measuring will be with this version.

[andy3055]

Not bad 

A thing I´ve forgotten is this:

One of the screws for the lcd-display is close to another circuitpath, this could cause a short circuit when the screw is tighten too hard…

Martin,

You can use a fiber washer under that screw.

Where did you get that "holder" you are using to hold the PCB in place?

[Martin72]

Hi,

Thankyou for the hint, I´ve used a Isolation washer from work for this.

My pcb-holder I´ve bought from here:

Pollin Electronic

But also :

ELV Electronic

Amazon

Martin

[andy3055]

Martin,

Thanks for the links.

[Martin72]

You´re welcome.
For it´s price it´s really good.

[Martin72]

Of course, the next measuring will be with this version.

I´ve done an "one hour quickshot" today, with the resistor directly connected to the Ascel and using the new software.
Pro Thing:

Measuring the resistor in such manner will result in "rock-stable" values - in the whole hour I´ve done it, the value varies only about 100µOhm - Really nice.

Con Thing:

The updated software is still somekind of crap, when you export the logfile.
Now the values are departed in different columns - good.
But still you can´t create a diagram directly from it.

My conclusion:
For its price the Ascel milliohm-meter is a good choice.
The precision lies on your own hands when you calibrate/adjust the measuring currents.
This could be/is an advantage, when you want to measure everytime as precisely as possible - Just adjust the currents before.
The pots could be reached on the front without disassembling the unit.
Although you don´t need to do it - Ascel recommend to adjust the currents every half year, my adjustment is more than 2 months ago and still it measure pretty good.

What the logging concerns, they should/must work on it.
But to be honest, who really need this…
You grab your DUT and want to measure it here and now, after say a minute or half you got a stable result - And that is all you want.

Nevertheless I will keep this thread alive by posting eventually sw-updates their results.

[HighVoltage]

Today I received the kit and assembled it.
Worked right away and seems to be stable.
I just did not like the cheap and supplied 4mm posts and used a different kind.

Here is my first picture.
I am testing here a stable 2.2 Ohm resistor and the value shown sits at 2.200,5 Ohm in the 24 Ohm range.

[Martin72]

Looks good 

Today I did another measuring about two hours.
Stabilizing time is about 2 minutes from the start - but even in this time it´s already in the tolerance value of the resistor.

[andy3055]

Nice job!

[nctnico]

You really need to run this for a day (preferably even longer) with temperature variances. The way this device has been designed is not good and subjecting it to different temperatures will show that. Running it for 2 hours proves nothing at all from a metrology point of view.

[Martin72]

None test a resistor longer as a few seconds - If you know your device needs some warming up, you test a little bit longer, say a couple of minutes.
The Ascel needs some warming up as stated before and after this, the displayed value vary only in µOhms.

The used resistor got a tolerance band of 0.5%, 995 mOhm to 1.005 Ohm.
The Ascel measures 999.4 mOhm.
I think it´s trustworthy enough.

Sure I can take it back to work and do some climatic tests with it, but usual I´m testing at normal room temperature at home or at work, so how it will be measuring when ambient temperature is for example 40°C....for me it´s not important.
Nevertheless, if I get the chance for climatic tests, I´ll do it and post it here.

[nctnico]

None test a resistor longer as a few seconds - If you know your device needs some warming up, you test a little bit longer, say a couple of minutes.

You are missing my point: the Ascel milli-ohm meter is not constructed in a way that it will give you a guaranteed accurate reading after a year AND / OR when the temperature has changed. A properly constructed resistance meter (DMM) will be able to do that. It is all about making sure the reference is stable and cancelling aging / temperature effects. The Ascel meter has none of these (as others and me already pointed out). Doing a measurement over a day will show the effects of the temperature as an example.