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

[Martin72]

I wonder if the shannon could do it better and if yes, why and how (didn´t read this thread so far, sorry).

Simply, Shannon never used the Mastech design to guide new product development. 

Instead focussing on what the marketplace leaders featureset and accuracy offered then bettering it.
AFAIK the only hiccup has been with a finer tip design he came up with that plainly wasn't robust enough for general purpose work.

Thanks tautech for the continued support from the very beginning 

But it answers nothing..

[dpenev]

The diode measurement seems to be broken in the latest version (not sure about the previous versions)

I have measured a diode in circuit with one pin connected only to 30K resistor.
I think this should be an easy case for diode measurements and with regular multimeter I measured it OK.
The tweezers in diode mode reports 0.47V in both directions.
In LED mode the tweezers reports 0.46V@0.18mA in forward direction and 3.08V@0.01mA in reverse which looks OK to me.
Please fix the diode measurements.

Does tweezers hardware support measuring in both forward and reverse directions in a single measurement?         

[KungFuJosh]

I love the tweezers, but I also don't trust them for diode measurement. I installed 18 diodes in 2 devices, and a bunch of them turned out to be bad, but tested fine with the tweezers.

[ebastler]

I love the tweezers, but I also don't trust them for diode measurement. I installed 18 diodes in 2 devices, and a bunch of them turned out to be bad, but tested fine with the tweezers.

In which respect were they bad? You can't expect a small battery-powered gadget to test for large reverse voltages or forward currents, and the ST42 does not claim to do such tests.

[Martin72]

Diode testfunction is in general not 100% safe because of the "low" testvoltage in nearly all cases.
Example given, if you have a defective 1N4148 diode which breakdown reverse voltage is 20V instead of 100V, your multimeter/ tweezer won´t find it.

[KungFuJosh]

Diode testfunction is in general not 100% safe because of the "low" testvoltage in nearly all cases.
Example given, if you have a defective 1N4148 diode which breakdown reverse voltage is 20V instead of 100V, your multimeter/ tweezer won´t find it.

That makes sense, but also proves that we shouldn't trust the tweezers alone for diode testing. I made a test rig with a DC source and a 100 ohm resistor to test the diodes after that. No surprise there wasn't any issue after that.

[dpenev]

I don't expect the tweezers to detect high voltage breakage of diodes. What I report looks like pure software issue to me.
Now I don't trust the tweezers for diodes at all.

In some cases for diodes the tweezers report the voltages in both directions which I think is good approach instead of rotating the tweezers. I think they have introduced software issues implementing this or I may be wrong , let's see what Shannon will comment.

[Shannon]

The diode measurement seems to be broken in the latest version (not sure about the previous versions)

The tweezers in diode mode reports 0.47V in both directions.
In LED mode the tweezers reports 0.46V@0.18mA in forward direction and 3.08V@0.01mA in reverse which looks OK to me.

Does tweezers hardware support measuring in both forward and reverse directions in a single measurement?       

Ay you said, ST42 support diode direction detection.

I'm curious about the circuit you test, it's a really abnormal phenomenon.
Could you try to test an independent diode, and observe the test result?
If you have a Shannon Test board, that would be easy.

BTW, you may need to pay some attention to the direction of the diode symbol, which is displayed on the screen.
The symbol is not just a "symbol", it has the direction information of the diode.


And there are four test result in diode mode: Forward, Backward, Short, N/A，
at the same time, some voltage information is displayed in these four modes, which could give the user more information to justify the DUT.

[Shannon]

I love the tweezers, but I also don't trust them for diode measurement. I installed 18 diodes in 2 devices, and a bunch of them turned out to be bad, but tested fine with the tweezers.

Hey KungFuJosh,

You know, our rule is, if you can point out the problem or the direction of improvement, and it is reasonable, then we can give you some gifts

So if you encounter this type of problem, please provide us with more details so that we can better optimize the tweezers.
And we can get together to analyze and learn the circuit, that would be interesting.

I think our diode measurements are the same as your experiment, by adding a resistor through a DC source to DUT, and observing the voltage drop.
So the remaining variables are, what V(A) is the DC Voltage(Current) source, what is the value of the series resistor, and is the voltage drop measurement accurate.
As ebastler mentioned, the multiple serial Diode measurement and diode breakdown voltage is an uncommon requirement, and easy to break the circuit on the board.

ST42 supports the detection of the diode direction, which will bring some troubles.
For example, if the diode is connected in parallel with a capacitor, it will be a headache problem. . .

Perhaps a purely unidirectional diode measurement, like a multimeter, is more appropriate for users.

[tautech]

I love the tweezers, but I also don't trust them for diode measurement. I installed 18 diodes in 2 devices, and a bunch of them turned out to be bad, but tested fine with the tweezers.

Hey KungFuJosh,

You know, our rule is, if you can point out the problem or the direction of improvement, and it is reasonable, then we can give you some gifts

So if you encounter this type of problem, please provide us with more details so that we can better optimize the tweezers.
And we can get together to analyze and learn the circuit, that would be interesting.

This ^^^^

Here we have a product developer only too willing to work with users to improve his product and this should be valued, highly valued !

Perhaps a purely unidirectional diode measurement, like a multimeter, is more appropriate for users.

Please NO !
Not needing to flip the tweezers to obtain diode forward direction information is valuable and time saving.

Instead ensure user instructions make it very clear how the product should be used and the symbols that could be displayed for the DUT and what they each mean.

[giosif]

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!

[dpenev]

OK I didn't realize that the diode icon rotates to show the correct diode direction.
So please disregard my previous complain.

My next issue with the diode measurements:
I have transformer and halfwave rectifier with 47uF capacitor at the output.
For DC this is equivalent with an diode and capacitor in parallels.
Normal multimiter shows me properly the forward diode voltage and OL in reverse direction.
Probably the tweezers can detect the capacitive current and based on the change to compensate for it?   

[tautech]

Even my old ST3 doesn't always get diodes correct and sometimes will show a good one as SHORT.

Testing any component 'in circuit' can give incorrect results just like a DMM will.
It's never easy......

[Shannon]

OK I didn't realize that the diode icon rotates to show the correct diode direction.
So please disregard my previous complain.

My next issue with the diode measurements:
I have transformer and halfwave rectifier with 47uF capacitor at the output.
For DC this is equivalent with an diode and capacitor in parallels.
Normal multimiter shows me properly the forward diode voltage and OL in reverse direction.
Probably the tweezers can detect the capacitive current and based on the change to compensate for it?   

Take it easy, all of the discussion is for a better understanding of ST42 or the DUT circuit, that's the way to make progress.

For the Diode paralleled with the cap, there is a trick method of ST42 for this test.
The issue is caused by the diode direction auto-detection feature,
we have to set a detection time, and during the detection time, if the constant DC current source of ST42 cannot charge the Cap fully,
there will be a wrong judgment.

So you can use LED mode to do the test, the reason is LED mode support unidirectional test only  ,
if you use the LED mode for the diode, the remaining issue is you may need to wait a few moments for the diode with a large cap.
The time is used to charge the cap fully.

We will try to make the value of the current source larger, which may make the test fast, but there are many limitations in design.

[indman]

Del

[Shannon]

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.

[Shannon]

Testing any component 'in circuit' can give incorrect results just like a DMM will.
It's never easy......

In-circuit testing of any components with parts connected in parallel is always associated with a very high probability of getting a big error in the results and disappointment with the tool.

Let's describe this phenomenon in another way,

The reality is that the tools are honest, they get a result according to the circuit theory and the actual DUT circuit,
it's just that the result is not what you expected.

During online measurement, in most cases, it is because we are not familiar enough with the circuit of online testing and the test principle of the tools,
such as ignoring the series-parallel relationship or parasitic parameters.

Instruments are real, circuits and components are real, and our goal is to understand these facts with this real information.

Hahaha, sounds like I'm making a philosophical excuse for the ST42's physical inaccuracies.

[indman]

Del

[dpenev]

For the Diode paralleled with the cap, there is a trick method of ST42 for this test.
The issue is caused by the diode direction auto-detection feature,
we have to set a detection time, and during the detection time, if the constant DC current source of ST42 cannot charge the Cap fully,
there will be a wrong judgment.

An idea:
Tweezers tries to pass certain current and measure voltages across. If the voltage gets exponentially changed you don't have to wait it to settle fully.
By a part of the exponential curve you can extrapolate assuming exponential curve with offset, amplitude and time constant and find out what will be final voltage.
This way you can find the diode direction quickly.
Also I don't think someone will complain if you put on a display "Capacitor - wait" as soon as you at the end provide useful measurement. 

   

[tautech]

During online measurement, in most cases, it is because we are not familiar enough with the circuit of online testing and the test principle of the tools, such as ignoring the series-parallel relationship or parasitic parameters.

There is such a wide variety of these parasitic parameters and connections that it is impossible to take into account all the nuances. You understand this only with experience, which sometimes comes too late. 

No, we should have all learnt about incorrect component measurements with DMM's and take that previous experience forward. Every tool has its limitations and with experience we get to know them.

When something does not measure as we expect we should immediately question the measurement type and the way we are doing it. Like: is the result different with the component removed from the circuit ?

I've not used ST42 but my considerable experience with ST3 is such when an incorrect measurement is displayed it is wise to check it again by selecting a dedicated measurement type and not always believing Auto mode.

That's why the dedicated measurement types are offered. 

[KungFuJosh]

ST42 supports the detection of the diode direction, which will bring some troubles.
For example, if the diode is connected in parallel with a capacitor, it will be a headache problem. . .

Perhaps a purely unidirectional diode measurement, like a multimeter, is more appropriate for users.

I think that's it. Since it autodetects the direction, it can't be connected backwards to test for faulty diodes. I would suggest having two options for diode, 1 that does and 1 that doesn't autodetect the direction. It's not essential to me though, I'm content using a different meter for diodes. I'm very happy with the tweezers otherwise.

My test was a 20VDC power source -> diode (in this case, bat86s) -> 100k resistor. Looking for low voltage drop across the resistor, with over 100mA = fail. The good ones were all tested under 11mA.

[electrolust]

I would suggest having two options for diode, 1 that does and 1 that doesn't autodetect the direction.

isn't that the existing LED mode?

[Shannon]

For the Diode paralleled with the cap, there is a trick method of ST42 for this test.
The issue is caused by the diode direction auto-detection feature,
we have to set a detection time, and during the detection time, if the constant DC current source of ST42 cannot charge the Cap fully,
there will be a wrong judgment.

An idea:
Tweezers tries to pass certain current and measure voltages across. If the voltage gets exponentially changed you don't have to wait it to settle fully.
By a part of the exponential curve you can extrapolate assuming exponential curve with offset, amplitude and time constant and find out what will be final voltage.
This way you can find the diode direction quickly.
Also I don't think someone will complain if you put on a display "Capacitor - wait" as soon as you at the end provide useful measurement. 

display "Capacitor - wait" is a good function, and we can have a try.
And if you try to use LED mode to test the diode paralleled with the cap, you can observe the voltage in real-time,
the voltage is increasing "linear" in the range, that's interesting as well.

ST42 uses a constant current source to do the diode test, so if we want to analyze the cap load, we can use the linearity increasing voltage to get the cap value.
But we still cannot get the diode forward voltage, until the cap is charged to the forward voltage(sorry for the bad use of fully charged in previous comments)

We have considered some fancy ways to do the test,
Such as if the voltage of the diode test is continuously increasing or decreasing, we can assume there is a cap or inductor paralleled with the diode.
So the circuit model will be more complicated, but we can still get a forward voltage.
and then ST42 can switch to L/C/R test mode, and get the paralleled cap or inductor value,
the last thing is to show the circuit model and the value to the user.

In other words, ST42 can detect Diode/L/C/R and their serial/parallel relationships in DIODE test mode(Maybe).
Is it too complicated for users?  sounds like this method is easy to go wrong

[Grandchuck]

In-circuit testing is always going to have potential pitfalls.  Trying to accomodate various possiblities might create more confusion.

[indman]

Del