ET432 LCR Meter - Wild Results - Range Function?

[killingtime]

Hello,

I was attempting to take some transformer winding resistance readings with an East Tester ET432 LCR meter this evening, and was getting some very odd results.

This meter has a DCR function meaning no AC is used. This is necessary when measuring the winding resistance of an inductor as the reactance alters the measurement.

There's no series or parallel equivalent circuit in this mode, and no frequency setting. The only parameter you can alter is the RANGE, which cycles through 100Ω, 1KΩ, 10KΩ, 100KΩ and AUTO. AUTO normally gets it right, but on some occasions it gets it wrong and you have to manually pick a setting.

So far so good. It can't be that different to a multi-meter right? A DMM has different resistance ranges. You pick the one that gives the most precise reading. 3.001 KΩ and not 0.003 MΩ. Should be easy.

Cycling through the range options gives wildly different results.

For a 10KΩ 5% resistor in DCR mode after performing an open & short user calibration (2 wire):

100Ω - 921.6 KΩ
1KΩ  - 98.92 KΩ
10KΩ - 9.953 KΩ
100KΩ - -9.259 MΩ (minus!)
AUTO - 9.953 KΩ

I'd expect some loss of precision as you move around the ranges, but the above are at least an order of magnitude out. There's no warning it's out by such a margin either. You just have to know.

To confuse matters a bit more, the manual lists a bunch of 'ranges' for the DCR mode that are not available on the unit. Extract from the manual attached. Manual lists 0.4Ω, 40Ω, 400Ω, 4KΩ, 40KΩ, 400KΩ, 4MΩ, 10MΩ and 20MΩ.

So either:

1) The ranges in the manual never made it into the production model or,
2) They've just copied stuff from another manual (Keysight) or,
2) I've misunderstood how ranging works on an LCR meter.

Meter has the same issues on L or C ranges as well. Exact same options for RANGE. Changing measurement speed to slow doesn't improve matters either. Using 4 wire kelvin probes has little effect.

Do any of the Keysight_U1731C / U1732C / U1733C work the same way, or have the same issues? I wouldn't expect the values to be this far out. If anyone has a U17xxx Keysight LCR I'd be interested to know what you see when manually ranging.

Thanks.

[csuhi17]

If I understand the description correctly.
there is a physical range which is 100, 1k, 20k, 100k. It has to do with the resistors in it.

And there is what you shared from the description, the value that can be read from the display. for example, if you start adjusting a 0-220 ohm pot, you will see a change in resolution at 40 ohms. From 39.999 ohms to 40.00 ohms.
The accuracy associated with these has been described.

[killingtime]

>>The accuracy associated with these has been described.

It has been described in the manual, but it's not meeting those accuracy specs at all, apart from on one range, and you have to guess the range correctly, which makes the whole exercise a bit pointless. The whole point of a measuring device is to take the guess work out of it.

To be clear, a 10K resistor displays as 921.6K on the 100 Ohm range, and 98.92K on the 1K range, which isn't 0.x% + x digits is it? That's out by a factor of 9116% on the 100 Ohm range. That and the fact there isn't a 100 Ohm range in the manual, only 40 Ohms and 400 Ohms...

I wonder if the guy that wrote the manual actually had this unit in his hands to test with, or perhaps he just borrowed something else.

Edit:
Manual is here in case anyone else has this meter.

https://www.easttester-cn.com/uploads/ET430-HANDHELD-NEW-COMPACT-LCR-METER-USER-MANUAL.pdf

[Tycho_Brahe]

I have a slightly different model (ET431).   So, I used a 10K carbon film resistor 5%.   This thing has kelvin clips, so I just used those right off the bat.   I 'think' I got results similar to you.   Used DCR mode and got:

Range	Ohms Measured
100	908 K
1 K	98 K
10 K	9.848 K
100 K	negative 2.1 M
Auto	9.849 K

I guess I never noticed this before because I just rely on Auto.  Thank goodness Auto usually picks the magic range.   But what the heck?  I'm also wondering if I'm just using the thing incorrectly (I wouldn't be surprised as I really don't know my around this device yet). 

So you say it also happens when measuring capacitors and inductors (I didn't have time to test that tonight)?    Hey, so when you said on rare occasions the Auto setting gets it wrong and you have to resort to a manual range, how wrong was Auto?  Was it as crazy wrong as some of our numbers (like orders of magnitude and sometimes even crazy negative values)?

[killingtime]

... how wrong was Auto?

From the testing I've done, it depends on where the value you're measuring is compared to the nearest range. After the 10K I tried a 5.6K as it's half way between the 1K and 10K ranges. I got 5.6K and 7K on different ranges. The other values were out by a factor of at least 10.

If your DUT is near a range, one range reading will be accurate, and all the others will be out by a factor of 10 at least.... which is fine if you already know the value of your DUT, but if you don't then it's all guesswork. I'm thinking of smd capacitors and toroidal core inductors, both of which are usually unmarked.

In my case I was measuring the primary inductance of a 3KVA line transformer with the output unloaded (so just a large inductor). AUTO was giving me 0.7H which I thought was low, as transformers like this normally measure above 8 Henries (depends on the core type, number of windings and other things). The next range gave me the correct reading (9.9H).

If you're getting similar readings to me, then I didn't get the 'Friday afternoon model' and this is either just the way this meter has been designed, or it's how all LCR meters work.

If anyone has a different brand LCR hand held (Keysight or BK Precision) I'd be grateful if you would stick a 10K metal film on it and play with the range setting. That will tell us if it's worth spending about 3x for a different design.

Many thanks.

[Veteran68]

I'll try to remember to check with my Hantek 1833C tonight.

[csuhi17]

ET432 blue
I had time to test a few resistors.

In normal mode, when the frequency is not 0Hz.
Range: Auto <- All OK, writes the real value.
Range: 100;1k;10k;100k <- The value read rarely matches the value read in AUTO mode.
For example: 10k resistor tested at 1kHz frequency.
Auto: 9,974k
100: ~10,100k The value varies a bit
1k: 9.974k The value is stable
10k: 9.976k is also stable
100k: 18,641k Also stable
In DRC mode:
Auto: 9,979k
100: 9.520M changes by 0.4M Ohm
1k: 987.6k changes with 0.2k ohms
10k: 365.12k changes
100k: -60.00M changes

What I can't process:
4.99k resistance in DRC auto mode 4.980k
However
100: 4.760M
1k: 492.8k
10k: 1.4530M
100k: -71.80M
Range: auto mode measures well again.

Use only AUTO mode for DRC measurement!
For non-DRC measurements, use only in AUTO mode!

I don't know what causes it, but I don't think this phenomenon occurs with other brands of devices, at least I haven't read about it.

This meter has many bugs that the manufacturer has not fixed and probably will not.

[killingtime]

This meter has many bugs ....

The ones I have found so far;

1) In slow mode the meter can lock up. Keypad unresponsive. Power button unresponsive. You have to remove the bumper, unscrew the battery hatch and disconnect the battery to reboot. If you can wait 10 minutes after pressing the 'speed' button (seems to have a keypad buffer) it eventually jumps into 'medium' speed mode and things speed up. Press the speed button again to get into fast mode and you're back in business. Got this to repeat by just pressing buttons too quickly. Not had it lock up in fast mode. Thought this might be a dry solder joint initially but I can't find any on the PCB. I think it's a software issue.

2) The user calibration is either open or short, not both. Doesn't appear to be any way to do open and short at the same time. It only seems to remember the last calibration you did from my tests. If that was open, then short readings are out by quite a bit (they come back negative). If you cal on short then shorts read 0.000 but high values are then out. So it looks like you have to know which range the meter is going to use and calibrate accordingly. Doesn't help that in auto mode it doesn't tell you which range it selected. Guessing 100Ω and 1K use short cal, and 10K, 100k use open. Nothing in the manual about this.

3) After a user cal the meter sometimes jumps back into slow mode when moving between measurement types; LCR, DCR etc.

[csuhi17]

1) So far, it has not produced such an error for me.

2,) I didn't notice, it's true that you have to calibrate the open and closed states separately, but for me, if I do it in the order 1. closed 2. open, the resistance of the measuring cable remains 0 in DRC mode.
If I measure with an alternator, i.e. in non-DRC mode, 100-200mOhm remains, I think it might be a property of the measuring cable...
The factory Kelvin clip is not the best.

3) I don't have this error either.
In the case of calibration, if I calibrate in non-DRC mode, it lasts for 30 seconds and resets the frequency to 100Hz, all the others remain at the settings I left.
If I calibrate in DRC mode, it is done in about 4 seconds.
if I change the Range to another value, e.g.: 100k and calibrate one, it resets, i.e. it shows 0 Ohms, but when I change the Range to 10k and then back to 100k, it shows the wrong value again.

What I wrote as an error is the incorrect measurement of high-value resistors in non-DRC mode.
At 10kHz and 100kHz, it incorrectly measures high-value resistance.

There was another one that I thought was a bug, but it wasn't.
The RECord function does not work if the measured value has a negative sign.
I don't even understand :Đ

However, looking at the pictures, your version and mine are different.
I have the Blue, you have the yellow.
Things on the display look a little different to me.
It looks like this

https://www.aliexpress.com/item/1005004656845323.html

My Version : V1.00.2048.018

[killingtime]

My Version : V1.00.2053.019

[Tycho_Brahe]

I see you guys are posting your version numbers.  Does this mean we can update the firmware or we're just at the mercy of whenever we purchased the product?    I'm not finding any update files here:  https://www.easttester-cn.com/et430-handheld-new-compact-lcr-meter-product/

[Veteran68]

If anyone has a different brand LCR hand held (Keysight or BK Precision) I'd be grateful if you would stick a 10K metal film on it and play with the range setting. That will tell us if it's worth spending about 3x for a different design.

I'll try to remember to check with my Hantek 1833C tonight.

Results below in both 2W and 4W modes using the Hantek-supplied shorty croc leads and Kelvin clips with the slot connector. I recalibrated (open and short) between each probe type. Regardless of the manual range selected, the Hantek always displayed correctly as K ohms. The test frequency was at left 100Hz for these results, but I did try all the supported frequencies to see if it made a difference -- the reading didn't change between 100Hz and 10KHz, then creeped up ~10mOhm 10 Ohm between 40Khz and 100KHz. Overall, the 1833C tested as expected, with only the 100K manual range being significantly off. And nowhere near the cost of a Keysight or BK.

I also checked against my Agilent 34401A and Siglent SDM3065X 6.5 digit meters using the same ProbeMaster 8000 probes.

10K 1% Metal Film Resistor

Hantek 1833C - Croc leads 2W
AUTO 10.052K (stable)
10R 10.154K (moves)
100R 10.141K (moves)
1K 10.055K (stable)
10K 10.052K (stable)
100K 11.257K (stable)

Hantek 1833C - Kelvin leads 4W
AUTO 10.053K (stable)
10R 10.153K (moves)
100R 10.120K (moves)
1K 10.053K (stable)
10K 10.053K (stable)
100K 11.250K (stable)

Agilent 34401A - Probemaster 8000 2W
AUTO 010.0524K

Siglent SDM3065X - Probemaster 8000 2W
AUTO 10.05281K

EDIT: Corrected resistance creep value at high test frequencies

[killingtime]

Thanks for the test results Veteran68.

So it looks like it's just an EastTester thing then.

If you look at the official factory page for this model below, they seem quite happy to showcase the meter displaying negative capacitances. That should have been a warning that there's still some work to do on the firmware. Sigh.

https://www.aliexpress.com/item/1005004656845323.html

[Veteran68]

I'm generally not a fan of Hantek gear, but I have to say this 1833C LCR meter has been a pretty good one for my needs so far. I've been saying if I were buying another handheld I'd consider the Uni-T 622E or the Sanwa LCR700, but not really sure I'd need to.

I've been considering a step up to a bench LCR meter, but not one of the super expensive pro level ones. So that means the likes of the EastTester 44xx series and the RuoShui/Victor 40xx series in the $300-400 range. Based on what I've been hearing from EastTester reports lately, I'll probably steer clear of them. The RuoShui/Victor line looks like much the same hardware but seems to get better reviews, probably due to better QC and/or firmware.

Would love to have a Tonghui/Sourcetronic but can't justify spending that money for my hobby. It's not like a DMM that I'd use most every day.

[killingtime]

Pulled out another line transformer to see if it's just inductors that the meter doesn't like.

Hooked the Xfmr up to mains and measured the primary current with the secondary unloaded. 0.4A rms, which yields 1.95H using XL=2(pi)FL @245V AC rms 50Hz. Measured using a Watt meter and my DDM on the 10A range. Both agreed.

ET432 readings below. AUTO gave the wrong reading at 0.528H. That's out by a factor of 3 at least The ESR looks way out as well. I did a DCR measurement and got 2.3 Ohms which agrees with my Fluke DMM. The 10K range is closest at 1.6H, but that's still a big error.

Hmm.

[csuhi17]

Thanks, Then according to your measurements, this is one of my worst devices. I'll keep that in mind...
That way I won't fall in love

[Tycho_Brahe]

This is depressing.   I thought I had a decent brand/model picked out.   Oh well.   I think I still have until Feb 1 at the latest to start a return back to Amazon.   Wife bought me one for Christmas.

I emailed East Tester last night for their opinion, but haven't heard back (and may never, who knows).    I guess a Hantek could be in my future.   

[Randy222]

Hello,

I was attempting to take some transformer winding resistance readings with an East Tester ET432 LCR meter this evening, and was getting some very odd results.


Cycling through the range options gives wildly different results.

For a 10KΩ 5% resistor in DCR mode after performing an open & short user calibration (2 wire):

100Ω - 921.6 KΩ
1KΩ  - 98.92 KΩ
10KΩ - 9.953 KΩ
100KΩ - -9.259 MΩ (minus!)
AUTO - 9.953 KΩ

I'd expect some loss of precision as you move around the ranges, but the above are at least an order of magnitude out. There's no warning it's out by such a margin either. You just have to know.

To confuse matters a bit more, the manual lists a bunch of 'ranges' for the DCR mode that are not available on the unit. Extract from the manual attached. Manual lists 0.4Ω, 40Ω, 400Ω, 4KΩ, 40KΩ, 400KΩ, 4MΩ, 10MΩ and 20MΩ.

So either:

1) The ranges in the manual never made it into the production model or,
2) They've just copied stuff from another manual (Keysight) or,
2) I've misunderstood how ranging works on an LCR meter.

Meter has the same issues on L or C ranges as well. Exact same options for RANGE. Changing measurement speed to slow doesn't improve matters either. Using 4 wire kelvin probes has little effect.

Do any of the Keysight_U1731C / U1732C / U1733C work the same way, or have the same issues? I wouldn't expect the values to be this far out. If anyone has a U17xxx Keysight LCR I'd be interested to know what you see when manually ranging.

Thanks.

Did you scope it in DCR mode just to verify it's really DC ?

One of my old LCR meters says on the front "L C R", but R is really a Z mode, runs a fixed 1kHz. So that meter is 100% useless if I just want real component value.

I'm generally not a fan of Hantek gear, but I have to say this 1833C LCR meter has been a pretty good one for my needs so far. I've been saying if I were buying another handheld I'd consider the Uni-T 622E or the Sanwa LCR700, but not really sure I'd need to.

I've been considering a step up to a bench LCR meter, but not one of the super expensive pro level ones. So that means the likes of the EastTester 44xx series and the RuoShui/Victor 40xx series in the $300-400 range. Based on what I've been hearing from EastTester reports lately, I'll probably steer clear of them. The RuoShui/Victor line looks like much the same hardware but seems to get better reviews, probably due to better QC and/or firmware.

Would love to have a Tonghui/Sourcetronic but can't justify spending that money for my hobby. It's not like a DMM that I'd use most every day.

What FW version is your 1833C?

[Veteran68]

What FW version is your 1833C?

20210615AM
HW V1

[Randy222]

What FW version is your 1833C?

20210615AM
HW V1

I won't hijack this ET thread, but interesting, some are reporting a FW of "2023xxxxxxAM".
Thanks for noting it.

[Veteran68]

What FW version is your 1833C?

20210615AM
HW V1

I won't hijack this ET thread, but interesting, some are reporting a FW of "2023xxxxxxAM".
Thanks for noting it.

We can take the discussion over to the other thread, but I just looked and 20210615AM is still the latest version Hantek offers on their website. New units may be shipping with something newer -- isn't yours a brand new unit? What version is it?

[Randy222]

We can take the discussion over to the other thread, but I just looked and 20210615AM is still the latest version Hantek offers on their website. New units may be shipping with something newer -- isn't yours a brand new unit? What version is it?

I took this to the Hantek unlock thread.

[killingtime]

Did you scope it in DCR mode just to verify it's really DC ?

Good question. Hooked it up to a scope and switched it into DCR mode.

The unit outputs a square wave. Period 2 seconds, 1.16 pk-pk voltage. Minimum voltage is 234mV. I don't think this would cause an issue though.

In LCR mode it outputs a sine wave. The default 600mV reading on the ET432 display is RMS according to my scope measurements. See scope cursors.

Attached.

[Randy222]

0.5Hz 50% duty square, fo a Rdc measurement?

Just makes no sense to me. If the DUT is a large inductor then the hard rise and fall of sqaure wave "is" an issue.

Would really need to know how the meter runs the math to obtain Rdc from 0.5Hz 50%

[mawyatt]

This is often done to reduce thermal EMF effects.

Math is simple, Thermal EMF effects don't change with test voltage polarity reversal. So subtracting the negative test voltage from the positive test voltage yields twice the peak voltage value while eliminating the thermal EMF effects as they subtract out 

Best,

[killingtime]

This is depressing.   I thought I had a decent brand/model picked out....

Not so fast ...

I remember reading some posts on a guitar amp forum about valve output audio transformers. They love to measure them because the output inductance on the amp forms a low pass filter in the audio chain, and that affects the way it sounds. Conclusion was the level a transformer is driven at alters its electrical properties.

I was taught that as the AC voltage on an unloaded transformer primary (or inductor) increases for a given frequency, the core becomes more saturated with magnetic flux, and this affects the permeability of the core (assuming it's not air). As the permeability goes down, so does the inductance as the two are directly related. This means less reactance (Ohms) and the transformer will pull more current as you increase the driving voltage on the primary, even if the secondary is unloaded.

Spent last night searching the web for some charts on transformer\inductor driving voltage and inductance but couldn't find anything. This topic isn't discussed much, but it's important for LCR meters as you'll see. So I ran my own tests today.

Results and data attached.

I'm driving the original transformer (unloaded) with a variac, all the way from 300mV to 250V AC RMS. Recording the voltage and current using two DMMs. Reactance (XL) calculated using Ohms law as we know the current through the Xfmr and the voltage across it. Inductance then calculated using L = XL/2(pi)F.

The inductance starts off low and increases, peaks then decreases as the core starts to saturate. Did the same test again for an MOT I had lying around, as I know these saturate easily.

I don't know what's causing the low inductance at low voltages, but the figures don't lie.

I also ran 600mV AC RMS from the variac as this is used by the ET432 LCR meter (see post above), and got 0.68H. That's not too far off the 0.528H I got in AUTO on the LCR meter. A 22% difference, which sounds poor but when you look at the data I collected the inductance hits 7H @ 100V, so about 10x that.

What does all this mean? You need to drive an inductor or transformer at the voltage it will be used at to determine its actual inductance.

This brings LCR meters back into focus. They only output about a volt, so they're not going to tell us a whole lot unless the target circuit runs at that voltage as well. I'd hold off on that 1K bench LCR meter for now.

Incidentally, capacitors have a similar issue with voltage as well, but depends on the dielectric used. As you increase the bias voltage, the capacitance goes down, so you need to test them at working voltage.

[Randy222]

This is often done to reduce thermal EMF effects.

Best,

The tiny handheld, DC near 200mV, will run into a thermal EMF effect issue?
2nd, we know the meter cant do 200mv when measuring 1m-ohm, I just don't see how it can drum up 200A.

[mawyatt]

This is often done to reduce thermal EMF effects.

Best,

The tiny handheld, DC near 200mV, will run into a thermal EMF effect issue?
2nd, we know the meter cant do 200mv when measuring 1m-ohm, I just don't see how it can drum up 200A.

As said this is often done, whether this LCR meter does this we don't know, as we don't have one.

The lower the impedance measurement the more influence Thermal EMF has on the measurement. Thermal EMFs can easily produce many microvolts which for example measuring 1m-ohm with 10ma current (what our Hioki IM3536 can produce), that's only 10uV across the DUT, so a few microvolts due to Thermal EMF can introduce significant errors..

Obviously the LCR meter measuring 1m-ohm can't produce 200amps, what if you short the test leads!!!

Seems you need to study up on how these LCT LCR meters actually work, how measurements are made, and how these relate to the parameters displayed on these LCR meters.

Best,

[csuhi17]

Has anyone figured out how to properly calibrate this device?
That is, I mean the correct use of the CAL button.

[Phil1977]

Has anyone figured out how to properly calibrate this device?
That is, I mean the correct use of the CAL button.

I get the best results if I use the calibration function twice. Once with the short circuit bridge and once without.

I also have no idea why the instrument uses this square wave for the DCR measurement. I´ve never noticed these problems before I´ve read about them in this forum. So far my ET432 did and does a good job for characterizing caps and inductors over the frequency range. But the more I read about it the more difficult it gets to interprete its results 

[csuhi17]

Thanks,
I noticed the above-mentioned problems because I measure a component at multiple frequencies.
Also, before I start using an instrument, I make several test measurements. It's good to know when it's lying.

It is possible that I make a mistake during the measurement, or maybe my instrument is faulty.
As I can see there are many versions.

I understood my question to mean that if:
I use the kelvin clip, then I do the calibration with the kelvin clip.
I use the crocodile clip, then I do the calibration with the crocodile clip.
I insert the component to be measured directly into the two grooves, then I do the calibration with the added U plate?

Or

in any case, do I have to use it with the supplied U copper plate?

My measurements were very different from the tolerances in the manual.

I just ordered a UT622E because of its special price, when it arrives I will compare the two instruments and keep the more accurate one and pass on the other...

If the result is not correct due to my fault, and I measure something wrong, it will become clear whether it is my fault.

[Phil1977]

Please report about your findings - it´s always good to get experiences from other users.

I always do some plausability checks with my unit. I have a few high quality foil capacitors, air coils and metal film resistors that measure quite stable over the frequencies available at the ET432. As long as I get consistent results there, I can trust the instrument that it finds frequency dependent variations at other components or measurement setups. That´s what I need the LCR meter for and for this purpuse I think the device is performing quite well.

And regarding the calibration: Personally I always calibrate without test leads, using only the provided U-Plate. If I test then with leads, I expect the results to have an error due to the electric properties of the leads. If I need more precise results, I desolder the component and test it in the grooves, or I attach leads as short as possible.

But principally the way you describe (calibrate with the used test leads) should work too - at least at the lower frequencies. Especially at 100kHz the test leads can easily resonate, and then I think even the most expensive LCR meter can not be precise.

[mawyatt]

Has anyone figured out how to properly calibrate this device?
That is, I mean the correct use of the CAL button.

I get the best results if I use the calibration function twice. Once with the short circuit bridge and once without.

I also have no idea why the instrument uses this square wave for the DCR measurement. I´ve never noticed these problems before I´ve read about them in this forum. So far my ET432 did and does a good job for characterizing caps and inductors over the frequency range. But the more I read about it the more difficult it gets to interprete its results 

As an example to help understand the use of a precision squarewave to measure a low value resistor with an LCR meter in DCR mode.

Consider a DUT resistor of 10 milliohms (0.010 ohms) and the LCR meter produces a current of 10ma to measure the DUT in DCR with a unipolar drive. The test leads have a Copper to Nickel interface somewhere throughout the measurement "loop" that experiences a 1C temperature gradient across the connection. Then this produces a Thermal EMF of 10uV due to the Seebeck effect for CuNi of 10uV/C.

The LCR meter reads a voltage across it's inputs of 10ma * 0.010 ohms (DUT) + 10uV (Thermal EMF), or 110uV and computes the DUT value as 110uV/10ma, or 11 milliohms.

The LCR displayed the measurement as 11 milliohms, which has a 10% error due to Thermal EMF

Now the user switches the LCR meter to use a Bipolar Squarewave excitation current of 10ma peak. The meter subtracts the negative voltage readings from the positive voltage readings across the DUT resistor and averages the two readings.

So the meter reads for positive DUT voltage +10ma (positive excitation) * 0.010 ohms (DUT) + 10uV (Thermal EMF), or +110uV as before, then the excitation current polarity is switched (squarewave) and the meter repeats the DUT voltage reading of -10ma (negative excitation) * 0.010ohms (DUT) + 10uV (Thermal EMF) or -90uV.

Now the LCR meter subtracts the negative excitation reading from the positive reading and divides by two to average the readings as {-(-90uV) + (110uV)}/2, or 100uV.

The LCR displays the measurement as 100uV/10ma, or 10 milliohms without the Thermal EMF induced error

Please note the polarity of the Thermal EMF makes no difference in the final rendered LCR displayed measurement, nor the magnitude of such!! Multiple Thermal EMFs can occur throughout the measurement "loop" due to various conductor interfaces, but ideally their effects are neutralized by this technique. Also note the Thermal Induced error tends to become smaller as the LCR measurement voltage increases, either with higher DUT currents and/or higher resistance valued DUTs.

Edit: Should also add that with low resistance measurements the higher excitation DUT currents cause self heating due to I*I*R effects, and this alone produces Thermal Gradients across the DUT connections and other connections throughout the measurement "loop", and the Bipolar Squarewave Technique also helps with these self induced thermal effect measurement errors.

Anyway, hopes this helps and shows the value of using a Bipolar Squarewave DUT excitation for low DCR measurements. Believe most quality LCR meters offer this DCR mode, in addition to the typical fixed polarity DCR measurement mode.

Best,

[Phil1977]

Of course, for precision milliohm-meters this approach sounds good, but the ET432 is a low-end LCR-Bridge with an add-on-DCR-function. Yes it provides 4-wire-measurement, but beside this I do not see any special point that makes it better for that than a jellybean multimeter.

And on the other hand, in the case of my device it´s not even a bipolar squarewave but switching between around -0.2V and -1.0V. Of course, if you calculate the differential resistance over two voltages the thermal EMF will cancel out, but if your development target would really be to measure low resistances with low currents, then you should obviously use a bipolar wave as described by mawyatt.

Anyhow, there must be *some* reason it is designed that way, so thanks again for the explanation!