Design a New Precision LCR Tweezers with Much Lower Cost 【Shannon Tweezers ST42】

[ebastler]

I had not used my Shannon Tweezers for a few weeks, and now find that they no longer measure correctly. When I press two tips together, the displayed resistance is 9 to 10 kOhm (in Auto mode). The displayed value is fluctuating by several 100 Ohm, and depends mildly on the selected measurement frequency and voltage. When set to 10 kHz measurement frequency, approx. 7 nF is read instead.

I have done the SelfCal, Open and Short calibration from the Measure > Calibration menu, but the readings have not changed significantly. Is there anything else I can try?

[KungFuJosh]

I would check for a new firmware, and then manually do the calibration again.

[ebastler]

Thanks. New firmware was available and installed without issues, but unfortunately it did not fix the measurements.

I tried the "open" and "short" calibration again, and also resetting to factory calibration, without getting plausible measurement results. Also had a look inside, did not notice anything untowards, re-seated the FPC connector -- no change.

It looks to me like the tweezers are fried. But I am pretty sure they worked fine when I put them away a few weeks ago, and today all I tried was measuring some loose small caps (fresh out of their tape package). If one were to accidentally apply an external voltage or discharge a cap into the tweezers, what would the exected symptoms be?

[KungFuJosh]

Are you sure the tips are secured properly? If not, that could cause weird measurement issues.

If you applied voltage via a non-discharged cap or something, you could certainly fry the tweezers.

[ebastler]

Are you sure the tips are secured properly? If not, that could cause weird measurement issues.
If you applied voltage via a non-discharged cap or something, you could certainly fry the tweezers.

Yes, I double-checked that everything is tight, both outside and within the enclosure.

I am aware that it is possible to fry the tweezers by applying an external voltage. But, as mentioned, I am not aware of any mishap before I stored them for a few weeks. Hence it would be helpful if someone could describe the typical symptoms, or share other ways to diagnose -- I want to make sure it's not something else I am overlooking.

[KungFuJosh]

I would just email Shannon. I think you'll get a faster response that way.

[Traceless]

I got myself a pair of ST42, during some quick tests with the included calibration board I noticed some oddities with the unit, especially in dealing with small value MLCCs. I wonder if anyone else can confirm this or if this is an issue specific to my unit. The firmware version is 1.5.3.

1. Normally when measuring caps the secondary value shown is Rs, which makes sense, however once measuring values < 1nF the display shows switches to Rp instead.


2. The meter does not recognize small value caps in lower frequency modes. Particularly to measure a 10pF MLCC the measurement frequency needs to be at least 1 kHz, for 1pF at least 10 kHz is required.


3. The battery charge indicator is off. The unit charges quite quickly up to 100% however, when I unplug it, it almost immediately looses one bar. The problem disappears when I leave it charging for a while longer even after it shows 100% charge status.

[Kean]

I got myself a pair of ST42, during some quick tests with the included calibration board I noticed some oddities with the unit, especially in dealing with small value MLCCs. I wonder if anyone else can confirm this or if this is an issue specific to my unit. The firmware version is 1.5.3.

Congrats.  They are really useful, and better than all the other "low cost" ones that I've tried.

1. Normally when measuring caps the secondary value shown is Rs, which makes sense, however once measuring values < 1nF the display shows switches to Rp instead.
(Attachment Link) (Attachment Link) (Attachment Link)

This is quite normal operation for measuring low value capacitance.

From a Hioki document on using LCR meters https://www.hioki.com/sg-en/learning/usage/lcr-meters_2.html:

Generally speaking, series equivalent circuit mode is used when measuring low-impedance elements (with an impedance of approximately 100Ω or less) such as high-capacity capacitors and low inductances, while parallel equivalent circuit mode is used when measuring high-impedance elements (with an impedance of approximately 10 kΩ or greater) such as low-capacitance capacitors and high-inductances.

As with any test equipment, it is quite important to get an understanding of how the measurements are made.  LCR meters are somewhat trickier to understand than a DMM, so it is well worth reading up some of the documents that cover LCR theory of operation.  e.g. https://www.ietlabs.com/pdf/application_notes/030122%20IET%20LCR%20PRIMER%201st%20Edition.pdf

2. The meter does not recognize small value caps in lower frequency modes. Particularly to measure a 10pF MLCC the measurement frequency needs to be at least 1 kHz, for 1pF at least 10 kHz is required.
(Attachment Link) (Attachment Link) (Attachment Link)

Completely normal.  Measurement of low value capacitance requires a higher frequency, typically 1kHz or more.  Similarly measuring a high value capacitance will require a lower frequency.

A good discussion on this topic is here: https://www.eevblog.com/forum/beginners/lrc-meter-different-readings-at-different-frequencies-why/

3. The battery charge indicator is off. The unit charges quite quickly up to 100% however, when I unplug it, it almost immediately looses one bar. The problem disappears when I leave it charging for a while longer even after it shows 100% charge status.

Again, quite normal and although I don't recall seeing this myself on my ST42, I've certainly seen it in my own designs.  I expect that the battery capacity display is based on a simple voltage reading which is only a rough guide to remaining capacity.  As soon as you unplug the charging power the battery voltage will drop somewhat.  To get better battery capacity display you need a fuel gauge IC which adds cost and takes up space, and really would add little value overall.

[Traceless]

Thank you Kean,

I have no other "low cost" LCR meter at hand for comparison, but the ST42 seems pretty handy for measuring small SMD components, particularly when they are in circuit. Also thanks for the links to the Hioki and ietlabs documents. I just took a quick peak and will read them thoroughly during the holidays. Unfortunately the ST42 has a *very* bare-bones manual. It would be nice to have a more detailed reference of the devices capabilities for certain measurement conditions.

W.r.t. the meter displaying Rp instead of Rs I'm not so sure if that makes sense. The meter auto-detects that the DUT is a capacitor (if the proper frequency is selected), in this case I almost always want to know Rs not Rp. So I think it should keep Rs the default for caps unless manually configured otherwise.

I think an additional IC for battery level monitoring is probably not needed. Maybe the full-charge voltage level should be set a bit higher. Alternatively the firmware could wait for a fixed amount of time (maybe 30-60 minutes or so) at the "fully charged voltage level" before actually indicating full charge on the UI. Initially I suspected a faulty battery until I realized that the UI shows 100% quite while before the battery is actually fully charged.

[Kean]

Another good reference on the LCR measurements is the Agilent/Keysight Impedance Measurement Handbook, mentioned in the above linked thread.

The official download link is https://www.keysight.com/au/en/assets/7018-06840/application-notes/5950-3000.pdf but that will require you to provide an email address.  A Google search on the document number will find other download sources.

I don't have my Shannon Tweezers handy, but I am pretty sure the menu allows you to change measurement model from Auto, to Serial or Parallel.  The auto mode is recommended and you'll better understand why if you study the linked documents.

Do some back of the envelope calculations of the parts you are measuring at the measurement frequencies.  I am no expert but as I understand it, the parallel model is more appropriate unless you are measuring these low value capacitors at or near their SRF.  You wont be able to do that with the ST42, as your 10pF MLCC will have an SRF of about 2GHz.

My mind breaks thinking about this stuff, so I hope I got that right.

[battlecoder]

W.r.t. the meter displaying Rp instead of Rs I'm not so sure if that makes sense. The meter auto-detects that the DUT is a capacitor (if the proper frequency is selected), in this case I almost always want to know Rs not Rp. So I think it should keep Rs the default for caps unless manually configured otherwise.

As previously mentioned by Kean, you can set the instrument to do serial, parallel or auto measurements, BUT for smaller caps Rp in auto mode makes more sense. I do understand that "ESR" is what you are looking for, and that is a "series" value not "parallel", however, Does measuring ESR of low-value capacitors even make sense? I have seen many ESR meters (both commercial and DIY) that would only work with caps of > ~1uF. Even fully dedicated devices like the Peak ESR meters would have a lower limit in the order of several tenths of a uF, but not lower (e.g: Peak's Atlas ESR70 *GOLD* meter has a lower limit of 0.3uF). I would assume that this is because lower-value caps are normally ceramic (or at least not electrolytic) and inherently have an extremely low Rs but a higher Rp.

Let me quote a document I read at one point (Chroma System Solution's "Series & Parallel Impedance Parameters and Equivalent Circuits" Application Note)

Other cases where parallel measurements are preferred are when measuring very low values of capacitance, when making measurements on dielectric and magnetic materials, and, of course, when trying to determine the separate values of two components in parallel.

So I think it definitely makes sense that it switches to Rp for nF-range capacitors.

[ceut]

Hello everyone,
I'm looking for LCR Tweezers since some times ago.
I have posted a first message on the other topic here https://www.eevblog.com/forum/testgear/lcr-tweezers-test-and-analysis/msg5234478/#msg5234478
I found that the Russian version is very good, but seems to be impossible to buy one outside (english is inside the firmware).

Thanks to @Tautech , I discover this ST42 tweezers, and read full topic + looked at all review I found on Youtube.
It seems to be a great tool and I think I'll buy it !   

But, as I plan to use it also to check some low R value (current shunt resistor), I see that there is always a little drift on milliohms measurement.
So I don't know if this suggestion is still in development/optimization ?
https://www.eevblog.com/forum/testgear/design-a-new-precision-lcr-tweezers/msg4871915/?topicseen#msg4871915

Also, I saw some other suggestions I think that will be great additions to use it without looking always at the screen:
> Diode mode:
   - Short beep to tell good diode value
   - Double short beep for schottky
   - Continuous beep for dead diode
> Resistor mode:
  - continuity beep with low R value
 
Thank you ! 

Here is the original post:

Apologies if this has been covered previously (some quick searches in the thread didn't come up with anything similar), but would it be possible to add a REL/delta/NULL function for the resistance measurement?
I am trying to measure resistance in the milliOhms range and, even after doing a Short calibration, the tweezers are still displaying some 20 or so milliOhms with the probes shorted.
Thanks!

Hi giosif,

Thanks for your suggestion.

Yes, we have tried to make the short cal result in zero, but we did not have much motivation to finish this optimization.
Cause the 20milliOhms is the limitation of the tips contraction and ST42, and we have discussed one option is to use a "<30milliOhms" to replace the test result,
This way to show the result to users may be more reasonable.

Do you have many test cases that need a smaller range, which can be used for milliOhms measurement?
We are trying to design real four-wire measurement tips, but the user experience is not as good as the normal tips.

[Grandchuck]

Hello ceut.  You wrote: "But, as I plan to use it also to check some low R value (current shunt resistor)"  I don't think any tweezers are a good choice for this.

[ceut]

Hello ceut.  You wrote: "But, as I plan to use it also to check some low R value (current shunt resistor)"  I don't think any tweezers are a good choice for this.

Hello !
I think it could be possible if the delta/null/rel is added, because I use actually a modded lowcost kelvin tweezer on an YR1030 Internal Resistance Tester 
This meter is not bad, mesured Volt or Resistor values are very good, and works at 1kHz (I have not checked the output signal on DSO).
But it is impossible to NULL the value before checking a resistor, and this lowcost modded tweezer has about 5-7milliohms value, and a not super good smd contact.
I have used a USB cable with all the 4 wires until the tip, after checking how the original test leads works.
Also, the reading value is stable 

[ceut]

Hello everyone,
One question I have about the ST42:
- What is the max range of Capacitor mesurement ?
In the Delfom review, no problem and fast with a 10000uF: https://youtu.be/13cBzn5Svuk?t=1507
But in the specifications https://shannontweezers.top/docs/specifications/
4999uF (which is very very low for a LCR meter.)
Example: checking an audio capacitor of 22000uF would be ok with the ST42 ?

Also, some of you has got some news from Shannon as no new post since July ? 

Thanks 

[KungFuJosh]

Hello everyone,
One question I have about the ST42:
- What is the max range of Capacitor mesurement ?
In the Delfom review, no problem and fast with a 10000uF: https://youtu.be/13cBzn5Svuk?t=1507
But in the specifications https://shannontweezers.top/docs/specifications/
4999uF (which is very very low for a LCR meter.)
Example: checking an audio capacitor of 22000uF would be ok with the ST42 ?

Also, some of you has got some news from Shannon as no new post since July ? 

Thanks 

You can email Shannon directly for help.

I do audio stuff, but don't generally need to test above 2200µF. Even my bench LCR that costs 10 times as much as the ST42 considers 10mF and 100mF ranges in their lowest acceptable accuracy. You may be able to get acceptable results in those ranges, but the datasheet has to reference specific accuracy expectations.

This chart is for the ST2830 / ST2832 LCR meters:

[Shannon]

I had not used my Shannon Tweezers for a few weeks, and now find that they no longer measure correctly. When I press two tips together, the displayed resistance is 9 to 10 kOhm (in Auto mode). The displayed value is fluctuating by several 100 Ohm, and depends mildly on the selected measurement frequency and voltage. When set to 10 kHz measurement frequency, approx. 7 nF is read instead.

I have done the SelfCal, Open and Short calibration from the Measure > Calibration menu, but the readings have not changed significantly. Is there anything else I can try?

I did lose such important information.

When you encounter a problem and want to eliminate mismeasurements caused by calibration errors, you can select factory cal, which can erase the manually calibrated parameters and restore them to factory settings, and select auto mode, and do the test again.

and tell me your SN number by PM, I will check the production records of this ST42.

Sorry for the inconvenience, we try to make sure you have a good ST42, even though sometimes it will be a brand new one

[Shannon]

I would just email Shannon. I think you'll get a faster response that way.

I somewhat regret publishing our email address on the website, which resulted in too many spam emails. I thought this would only happen in China.

If you want to find me quickly, sometimes it is faster to send me a private message on this forum, because this website will send me an email reminder with very obvious characteristics. I can know at a glance that my friends are looking for me

[KungFuJosh]

I somewhat regret publishing our email address on the website, which resulted in too many spam emails. I thought this would only happen in China.

At least 90% of the business emails I receive are spam. It's awesome. 🙄

[ceut]

I would just email Shannon. I think you'll get a faster response that way.

I somewhat regret publishing our email address on the website, which resulted in too many spam emails. I thought this would only happen in China.

If you want to find me quickly, sometimes it is faster to send me a private message on this forum, because this website will send me an email reminder with very obvious characteristics. I can know at a glance that my friends are looking for me

I can completely confirm that 

And I have bought the ST42 today 

[shapirus]

Hmm, $180+ now? Just when I finally decided to order one...

[KungFuJosh]

Hmm, $180+ now? Just when I finally decided to order one...

Depends which version you get. The test board or leather case cost more. Still a good value anyway.

[shapirus]

Hmm, $180+ now? Just when I finally decided to order one...

Depends which version you get. The test board or leather case cost more. Still a good value anyway.

I mean the price increased like 70% in the last couple of weeks since I was last contemplating making an order. Then it started at about $100-ish (and the website still says $109 for the early birds), now the cheapest option is $168.

Meh.

[KungFuJosh]

I mean the price increased like 70% in the last couple of weeks since I was last contemplating making an order. Then it started at about $100-ish (and the website still says $109 for the early birds), now the cheapest option is $168.

Meh.

lol, you missed that boat. I was an early bird...2 years ago.

Production costs on everything went up...and what are you going to get that's better for the price? Or double the price?

[shapirus]

lol, you missed that boat. I was an early bird...2 years ago.

Production costs on everything went up...and what are you going to get that's better for the price? Or double the price?

I guess, I'm getting nothing, lol. At least until there's a sale or something.
I'm not saying it's expensive for what it is. Just regretting that I didn't get it when I thought of it. At its current price, it won't be as nice an addition to my set of tools as it would have been earlier.