Smart SMD tester MS8911.

[DaneLaw]

There are mainly 3 new models.. atleast i the budget category.. sub 50$

Zoyi MD1, Fnirsi ST1 & QPLINK S1.

MD1 and ST1.. are very similar while QPLINK S1 do differ quite a lot, with more digits (tolerances) alongside more voltage & frequency ranges, and it's able to measure live voltage up around 16v (if I recall correct) and the build is quite a step up' but also more than double the cost at 47$ (incl. EU25%VAT and shipping) than the likes of Zoyi & Fnirsi.

These 3.

Yes. the MD1. will do 0.0 mOhm by shorting the tips..

how steady you gonna land 0.0mOhm is difficult to quantify from a brief test, by just holding it with your fingers.
Here is an example, but its an older FW1.7 not FW1.8 or newer.

[iet]

Please explain a few more points.
Is the calibration of the tweezers in the C,R mode carried out with shorted and open probes?
Is the calibration value remembered by the tweezers?
What you show in the video, is it before or after calibration?
What does the tweezers show with shorted probes before and after calibration, when you hold the tweezers in the normal, working position.
What is the minimum resistance shown by the tweezers in the continuity mode?
What voltage drop does the tweezers show when checking Schottky diodes of the 1N5817-19 type at a measuring voltage of 0.6 V?

[iet]

Recently, the contact of the tips of the MS8911 tweezers has become poor, in fact, metal surfaces are in contact. This affects the measurements. I made new tips from a polished brass plate. Now everything is fine.

[DaneLaw]

Please explain a few more points.
Is the calibration of the tweezers in the C,R mode carried out with shorted and open probes?
Is the calibration value remembered by the tweezers?
What you show in the video, is it before or after calibration?
What does the tweezers show with shorted probes before and after calibration, when you hold the tweezers in the normal, working position.
What is the minimum resistance shown by the tweezers in the continuity mode?
What voltage drop does the tweezers show when checking Schottky diodes of the 1N5817-19 type at a measuring voltage of 0.6 V?

All the calibration aspects, I haven't looked into..its still vanilla.
I recall I updated the fw, at one time shortly after I got it.
In continuity 0.6v = 0.4 Ohm and 0.3v its 0.7 to 0.8 Ohm..
As highlighted in the other ST1 vs MD1 compare thread, the refresh & response rates vary drastically depending on what frequency you have it in..
in 10K instant display readings while 100Hz it takes around ½ sec before you get the reading and 1K are in between.. the beeping is instant.
1N5819 0.6v = 0.38/0.39v and 0.3v = 0.22v.  [MD1 FW1.7 1K] while Fnirsi ST-1 FW1.5 and same 1N5819 0.6v = 0.50/0.51v and 0.3v = 0.29v.

Havent checked the QPLINK LCR 1S (V1.1.0).. which do has some more features & more counts. seems to be a 10.000 count in most of the modes.
it will also do 120Hz & 100k Hz, alongside a 0.1v test mode, while in Diode-mode it also displays R and Z values..

[iet]

All the calibration aspects, I haven't looked into..its still vanilla.

Yes, there is little information about the calibration. Although it can be assumed that it is somewhat similar to ST1.
Your video has +0.4 mOhms. And the video with ANENG GN702 shows an accurate measurement of a 2.3 mOhms resistor for 3 seconds. Either they specially selected a well-tuned copy or it is not an exact copy. Maybe someone will clarify the situation over time.
In general, I think that instability in the milliohm range can be improved. Perhaps, after all, you can try other op-amps or R, C elements. At the same time, everyone understands that this tweezers circuit corresponds to a price of $ 25-30.
Now regarding the measurement of diodes. In the video with the ANENG GN702 tweezers, there is a measurement of a diode at a voltage of 0.6 V. The voltage drop is 0.3 V. I asked you to measure the voltage drop on the Schottky diodes. According to the datasheet, they have +/- 0.2 V.
So something doesn't add up here. Either some changes were made to ANENG, or this is a diode with a voltage drop of 0.1 V.
I have already written about this mode before. The ST1 tweezers have a sine signal, but it should be DC like the Pro1 Plus. Therefore, it does not measure the voltage drop of the diodes quite correctly. It is necessary to make this mode like multimeters, with a fixed DC voltage. Otherwise, switching the measuring voltage will mislead the user even more.
Most likely, nothing more will happen in these versions of the tweezers. But there is a multimeter for this.
Continuity mode. 0.5 Ohms can be reduced to at least 0.1 like in multimeters. And even better, to 10 mOhms.
You have QPLINK 1S tweezers. You said that it is a little better. I looked at it closely, but there is some mistrust.
The main thing is that the information I am interested in is missing. The video shows normal measurements. There are no measurements in the milliohm, picofarad and nanohenry ranges. There are no measurements at a frequency of 100 kHz. The developer needed to show why he needed a frequency of 100 kHz. And voltage measurement is an additional option, like D in ST1.
It is better to make the measuring voltage 0.1, 0.6, 1 V.
Perhaps you can clarify the situation, it would be very interesting and useful.
Thanks for the information.

[iet]

It is not known when the necessary changes will be made to the operation of the ST1 tweezers, so I made myself a table of voltage drops on diodes. I made measurements with two tweezers, ST1 and Pro1 Plus.

[iet]

This is how I solved the problem with checking diodes for myself. I shortened the table a bit. What are the advantages?
Quick check.
Convenient when checking SMD diodes.
Possibility to sort by Vf.
No need to use a multimeter.
During the initial check, you don't need to waste time searching for datasheets.

[iet]

The ST1 manual has an addition in the diode mode concerning continuity. The previous manual does not have this.
Continuity: In diode mode, a resistance measurement of less than 50 Ohm triggers continuity.
In fact, it works like this, but. The ST1 tweezers overestimate the resistance value by 10 Ohm. It measures 40 Ohm as 50 Ohm. That is, it actually beeps at a resistance of 40 Ohm. I checked it with a multimeter. Everything is fine there, the sound signal is triggered at a resistance of 50 Ohm. FNIRSI engineers need to correct this. And at the same time stabilize the lower limit for resistance.

[iet]

Managed to significantly improve stability in the milliohms range.
Disassembled the tweezers. Washed the board from flux. Used brass bolts. Now in the working position, within a second, the readings are set to 0.0 mOhms. Zeroing is no longer necessary. Drift is only 0.1 mOhms. This is the maximum that can be achieved in this tweezers.

[DaneLaw]

Managed to significantly improve stability in the milliohms range.
Disassembled the tweezers. Washed the board from flux. Used brass bolts. Now in the working position, within a second, the readings are set to 0.0 mOhms. Zeroing is no longer necessary. Drift is only 0.1 mOhms. This is the maximum that can be achieved in this tweezers.

If you wanna give other users an indication of milliohm "stability" then still pictures leave some to be desired, when trying to relate to possible gains (differences).
Instead maybe record a small video that shows what stability you are experiencing around 0.0mOhm, as  I exampled above on the MD1, as getting the Fnirsi ST1 to show 0.0mOhm, I reckon any ST1 would do that out of the box, at least for a brief moment, but it fluctuates a lot not least under pressure, as that single connection point seemed flawed, fingescrews or not..

My ST1 unit.. will gladly show 0.0mOhm but it's far from stabilized around those minute milliohm-values and also less than what I experienced on MD1 (GN702) but also worth noting MD1/GN702 got a lot wider tips than the original incl. on ST1 [straight / bend tipcombo], and likely from changing those to a wider custom version, as you seem to have done' I would estimate to make the biggest impact on Fnirsi ST1 and miliohm stability.

[iet]

My ST1 unit.. will gladly show 0.0mOhm but it's far from stabilized around those minute milliohm-values and also less than what I experienced on MD1 (GN702) but also worth noting MD1/GN702 got a lot wider tips than the original incl. on ST1 [straight / bend tipcombo], and likely from changing those to a wider custom version, as you seem to have done' I would estimate to make the biggest impact on Fnirsi ST1 and miliohm stability.

Let's try to understand some things regarding calibration and zeroing. The Pro1 Plus tweezers store the calibration result in memory. The ST1 tweezers have a general calibration in resistance mode, which is stored in memory. But it does not have this calibration before precise measurements, that is, calibration with closed and open probes with memorization. That is why zeroing was invented. This is good, but the zeroing result is used for a one-time measurement, the next measurement will require a new zeroing. All this turns into an unnecessary routine and a waste of time. That is why I first came up with a device for zeroing and used it for some time. Naturally, I wanted to do zeroing in the normal, working position of the hand and by closing the tips. That is why I made other tips that are more resistant to abrasion and have a slightly larger contact area. In addition, I completely accidentally found two brass bolts, which, oddly enough, further improved the quality and stability of measurements. Thus, I managed to eliminate the need for constant zeroing. The photo clearly shows the difference in results with shorted brass tips when using original and brass bolts.

[DaneLaw]

Managed to significantly improve stability in the milliohms range.

I Try again...

A brief video. would go a long way, to show that "improved stability" you mentioned you have obtained, as "stills" do jack in that regard.

[iet]

A brief video. would go a long way, to show that "improved stability" you mentioned you have obtained, as "stills" do jack in that regard.

It's not time to shoot a video yet. Not all things have been used to stabilize zero. Now we can prepare for some experiments with the tweezers circuit. The next step may be to replace the op-amp and related components. Maybe you've already tried something? If so, please share the information.
Yes, and how is the calibration of your MD1 tweezers? Any interesting information?
What can you say about the calibration of the QPLINK 1S? Does it have a calibration with closed and open probes before measuring?

[iet]

There is another very cool calibration method - automatic. This was done by the engineers of the MASTECH MS8911 tweezers. It does not have a calibration mode. All measurements are carried out quickly and accurately in automatic mode, according to the specification. No unnecessary movements and time wasted. The only condition is good contact of the tips with each other, as well as with the measured component. If the engineers of the FNIRSI ST1 tweezers managed to do this, it would be just great.