Author Topic: Voltcraft LCR 300 micro review  (Read 12680 times)

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Offline grumpydoc

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Voltcraft LCR 300 micro review
« on: June 13, 2014, 11:00:09 pm »
I finally bought an LCR meter  - specifically the Voltcraft LCR 300 from Rapid



It's a ES51919/ES51920 based design with several re-badged versions as shown below although, as far as I am aware only the Voltcraft one is available in the UK.

So, I've been playing with it for all of half an hour - here are my initial impressions.

In the box:
Voltcraft LCR 300.
Manual, in German  >:( fortunately there's an English one online.
Set of Kelvin leads
Short ground lead thing
Shorting widget for cal
Insulating widget for cal
Carry case

The good:
4 wire measurement with guard
100Hz - 100kHz measurement frequencies
0.3% best accuracy
Dual display with D/Q/series(ESR) or parallel resistance for caps and inductors.
Defaults to auto mode which senses L/C/R
0.01pF resolution at 10kHz and 100kHz
1nH resolution at 100kHz
1milliohm resolution on AC resistance

The so-so
Readings not always quite stable enough to believe the 0.3% best accuracy. Maybe better with the Kelvin clips.
Rather chunky case; doesn't feel right in the hand somehow.
Back light from one side only - noticeably uneven although bright enough.
No USB link despite the tantalisingly labelled button.
Only 10milli-ohm resolution on DC ohms and 20Mohm max range
Stand a bit flimsy and skates around the desk a bit too easily.
Had to download manual, see "in the box"
No manual ranging for values.

The awful:
The buttons are totally crap and feel horrible - especially the "Func" button which looks as though it should rock but doesn't and sticks in the case, needing to be retrieved with a fingernail.
The built-in contacts - you really have to look at them when inserting component leads to get in-between the two contacts rather than slipping above or below and only hitting one. It is also next to impossible to get the supplied shorting link (or O/C "link") inserted between the clips as it is too think.

I'll try to do a fuller review when I've been using it for a while as well as a tear down - maybe in a couple of weeks. In the meantime I'll update this post as I use it or discover more information.

« Last Edit: June 15, 2014, 04:08:48 pm by grumpydoc »
 

Offline robrenz

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Re: Voltcraft LCR 300 micro review
« Reply #1 on: June 14, 2014, 12:35:15 am »
Like the DE-5000 you may get 1m Ohm resolution by measuring resistance as Rs instead of using DC resistance mode. That also cancels thermal emf issues because of the AC excitation instead of DC excitation.
« Last Edit: June 14, 2014, 12:36:49 am by robrenz »
 

Offline grumpydoc

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Re: Voltcraft LCR 300 micro review
« Reply #2 on: June 14, 2014, 08:50:58 am »
Quote
Like the DE-5000 you may get 1m Ohm resolution by measuring resistance as Rs instead of using DC resistance mode. That also cancels thermal emf issues because of the AC excitation instead of DC excitation.
Yes, you do - I've added it into "the good"

I'm sure AC resistance measurements would be more useful at 50Hz, 60Hz and 440Hz though.
 

Offline Hydrawerk

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Re: Voltcraft LCR 300 micro review
« Reply #3 on: June 14, 2014, 05:29:27 pm »
This is another Cyrustek based LCR meter, like my CEM DT-9935. This Velleman instrument is sold under many different brands. I wonder who is the original manufacturer. On my CEM DT-9935 there is excellent backlight, but no external power supply and no true 4-wire kelvin probes.
Amazing machines. https://www.youtube.com/user/denha (It is not me...)
 

Offline Bored@Work

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Re: Voltcraft LCR 300 micro review
« Reply #4 on: June 14, 2014, 06:47:51 pm »
I wonder who is the original manufacturer.

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Offline kripton2035

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Re: Voltcraft LCR 300 micro review
« Reply #5 on: June 14, 2014, 07:14:49 pm »
and who is the original maker of all these cyrustek based lcr meters ?

Offline robrenz

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Re: Voltcraft LCR 300 micro review
« Reply #6 on: June 14, 2014, 07:22:24 pm »
Quote
Like the DE-5000 you may get 1m Ohm resolution by measuring resistance as Rs instead of using DC resistance mode. That also cancels thermal emf issues because of the AC excitation instead of DC excitation.
Yes, you do - I've added it into "the good"

I'm sure AC resistance measurements would be more useful at 50Hz, 60Hz and 440Hz though.

The readings will be the same as offset compensated Ohms of a DC driven ohmmeter. Its not really AC resistance, its resistance measured with a technique that uses AC excitation in the measuring process.

You will also notice that if you measure a large wire wound power resistor and force the meter to measure the inductance of it  you can then read the ESR on the secondary display and it will match the Rs resistance value.

Offline The Electrician

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Re: Voltcraft LCR 300 micro review
« Reply #7 on: June 14, 2014, 10:22:22 pm »
The readings will be the same as offset compensated Ohms of a DC driven ohmmeter. Its not really AC resistance, its resistance measured with a technique that uses AC excitation in the measuring process.

Why is this not AC resistance?  How else would one measure AC resistance?
 

Offline robrenz

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Re: Voltcraft LCR 300 micro review
« Reply #8 on: June 15, 2014, 02:05:44 am »
The readings will be the same as offset compensated Ohms of a DC driven ohmmeter. Its not really AC resistance, its resistance measured with a technique that uses AC excitation in the measuring process.

Why is this not AC resistance?  How else would one measure AC resistance?

Remember I am machinist not an EE but I think of AC resistance as "impedance" being the sum of resistance, capacitive reactance and inductive reactance. AFAIK the DE-5000 in Rs mode is equivalent to DC resistance. It is not the sum of reactances and DC resistance.  I was simply trying to convey to grumpydoc that thinking these resistance readings were somehow AC specific was not correct and would be the same readings as obtained with a DMM except more accurate in the very low ohms and milli Ohms because the AC method of obtaining the readings effectively eliminates thermal EMF issues.

Offline johansen

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Re: Voltcraft LCR 300 micro review
« Reply #9 on: June 15, 2014, 02:19:02 am »
i would be interested in a meter like the above that measures inductance and Q and all that at much higher frequencies like 100Khz or 500Khz.

parasitic capacitance and skin effect are no longer negligible, as they usually are at 1Khz
 

Offline JackOfVA

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Re: Voltcraft LCR 300 micro review
« Reply #10 on: June 15, 2014, 02:22:10 am »
The readings will be the same as offset compensated Ohms of a DC driven ohmmeter. Its not really AC resistance, its resistance measured with a technique that uses AC excitation in the measuring process.

Why is this not AC resistance?  How else would one measure AC resistance?

Remember I am machinist not an EE but I think of AC resistance as "impedance" being the sum of resistance, capacitive reactance and inductive reactance. AFAIK the DE-5000 in Rs mode is equivalent to DC resistance. It is not the sum of reactances and DC resistance.  I was simply trying to convey to grumpydoc that thinking these resistance readings were somehow AC specific was not correct and would be the same readings as obtained with a DMM except more accurate in the very low ohms and milli Ohms because the AC method of obtaining the readings effectively eliminates thermal EMF issues.

The problem being that resistance, i.e., the R component of R+jX, can change with frequency, even at surprisingly low frequencies, for a variety of reasons. For example, even an air core inductor will show change due to skin effect and proximity effect, as the current distribution changes with frequency and hence the resistance. (You can think of this as the conductor changing shape if a visualization aid is needed. Not quite right, but close.) . If the inductor has a magnetic core, then core losses will appear as resistance when measured with AC excitation. It takes energy to move around the B-H curve and flip the magnetic domains and that energy must come from the excitation and hence will appear as a loss element.

Depending on the inductor value, core material, physical size, etc., the changes may be immaterial at 60 Hz or 1 KHz or maybe not.

And, keep in mind that there are no 'pure inductors' as all have some form of distributed capacitance. Hence the inductor is really an RLC network, not an RL network. As the measurement frequency approaches the RLC self-resonant point you will see changes in the measured inductance and resistance due to circuit resonance. At the extreme, if the measurement frequency matches the self-resonant frequency the inductor will measure 0 inductance and a resistance equal to the 'true' resistance in the absence of distributed capacitance multiplied by the component Q. There are ways of determining the distributed capacitance which may then be backed out of the measurement data to yield a 'true' inductance and 'true' AC resistance. 

HP had a decent explanation of this in the 4342A Q-meter manual. It's on line and can be found with a quick search. Or, the older Boonton 260A Q-meter manual as well. And, there's a great wealth of useful discussion in the old Boonton Notebook publications. http://www.hparchive.com/Boonton.htm


 

Offline The Electrician

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Re: Voltcraft LCR 300 micro review
« Reply #11 on: June 15, 2014, 04:42:12 am »
The readings will be the same as offset compensated Ohms of a DC driven ohmmeter. Its not really AC resistance, its resistance measured with a technique that uses AC excitation in the measuring process.

Why is this not AC resistance?  How else would one measure AC resistance?

Remember I am machinist not an EE but I think of AC resistance as "impedance" being the sum of resistance, capacitive reactance and inductive reactance. AFAIK the DE-5000 in Rs mode is equivalent to DC resistance. It is not the sum of reactances and DC resistance.  I was simply trying to convey to grumpydoc that thinking these resistance readings were somehow AC specific was not correct and would be the same readings as obtained with a DMM except more accurate in the very low ohms and milli Ohms because the AC method of obtaining the readings effectively eliminates thermal EMF issues.

Let me clarify a few points.  I posted a long thread a few days ago that attempts to explain about impedance:

https://www.eevblog.com/forum/projects/impedance-lcr-esr-meters/

As I explained there, impedance is the total "opposition" to the flow of AC electricity.  It is indicated as an expression Z = R + jX, where the R and X quantities are values at a single frequency.  They probably have different values at other frequencies, although the R quantity may be constant over a range of (usually low) frequencies for some objects being measured (such as a short piece of wire).

The real part of the impedance is represented by R, and that is the part that dissipates energy.  It is the part tells you how much heat is generated when a current passes through the impedance.  That is just what resistance does with DC currents, and so the R part of impedance is the AC resistance, because it also gets warm when an AC current passes through it.  Its value may be nearly constant with frequency up to maybe a few megahertz, if it's a good quality resistor, designed not to vary with frequency.  If the impedance measured is something other than a short piece of wire, or a good resistor, perhaps a winding on a small power transformer, for example, the value of this AC resistance will be different when measured with different frequencies.  The general variable R is called Rs or Rp on LCR meters, such as the DE-5000, according to whether it was measured in series equivalent mode or parallel equivalent mode.

The DE-5000 can't directly measure Z or X (as in Z = R + jX), but it does directly measure R (Rs or Rp).  It can be used to determine Z and X with a little math.  For example, I measured the primary of a small 60 Hz power transformer with the impedance analyzer at 1 kHz with an excitation level of .6 volts (to try to imitate the DE-5000).  Here's the result:



This shows the impedance Z, the phase angle theta, the real part of the impedance Rs and the reactance X.

The DE-5000 measurement of this transformer winding was measured two ways.  First, as an inductance Ls; this measurement mode can also give the phase angle.  Second, as Rs; this gives directly the real part of the impedance, which is the AC resistance.  The results are Rs is 1.99 ohms, and theta is 70.4 degrees.

The impedance is obtained by dividing Rs by the cosine of the phase angle, Z = 1.99k/Cos(70.4) = 5.932k ohms.  The impedance analyzer gave 5.857k ohms, and an angle theta of 71.141 degrees.  The agreement with the DE-5000 is good.

The Rs resistance readings given on the DE-5000 are indeed AC specific, although as I have explained, if you're measuring a good quality resistor or a short piece of wire, not wound around a core, the measurements will probably be constant over the 100 Hz to 100 kHz frequency range of the DE-5000; this constancy could lead a person to think that the Rs measurement is not AC specific, but this is not true for all things you might measure.  For many measurements on other items, Rs will vary with frequency.

But you are quite right that because the Rs measurement uses an AC stimulus, the thermal voltages are cancelled out.  I often use the AC measurement capability of the impedance analyzer to get low milliohm measurements of items I know have relatively constant Rs with frequency.  And, even some things that do vary with frequency can be measured with AC stimulus and obtain nearly the same value that a DC measurement would give IF the measurement frequency is low enough.

The ESR of a capacitor is the AC resistance of the capacitor at the frequency of measurement.  The ESR measurement of a capacitor does not include the reactance if the measurement is made properly with sine wave stimulus (as the DE-5000 does), but, on the other hand, the dissipation factor D does involve both Rs (the AC resistance) and X (the reactance).
« Last Edit: June 15, 2014, 04:52:02 pm by The Electrician »
 

Offline grumpydoc

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Re: Voltcraft LCR 300 micro review
« Reply #12 on: June 15, 2014, 09:43:02 am »
Quote
I was simply trying to convey to grumpydoc that thinking these resistance readings were somehow AC specific was not correct and would be the same readings as obtained with a DMM except more accurate in the very low ohms and milli Ohms because the AC method of obtaining the readings effectively eliminates thermal EMF issues.
Measuring a resistor, yes it should provide the same reading as a DMM but I agree using an AC current source would avoid thermal EMF.

I had thought that the value displayed for a cap or inductor would be the impedance at the test frequency - after looking again (and watching Dave's Mastech LCR review) I see that it's just another way of displaying the series/parallel resistance with one more digit of precision.



 

Offline robrenz

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Re: Voltcraft LCR 300 micro review
« Reply #13 on: June 15, 2014, 03:31:07 pm »
@ JackOfVA and The Electrician

Thanks for the resources and excellent explanations. Fortunately I could follow them and I agree with all your corrections to my imprecise statements.  Thanks again for all the work you put into those responses and the friendly helpful attitude. :-+

Offline The Electrician

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Re: Voltcraft LCR 300 micro review
« Reply #14 on: June 15, 2014, 04:45:53 pm »
i would be interested in a meter like the above that measures inductance and Q and all that at much higher frequencies like 100Khz or 500Khz.

parasitic capacitance and skin effect are no longer negligible, as they usually are at 1Khz

The above meter can measure at 100 kHz.  All the meters based on the Cyrustek chip can do 100 kHz, AFAIK.  But to get above 100 kHz at a reasonable price, you have to look for Chinese bench meters, and even then you don't get them for $100 like you can the DE-5000.

Here are some examples:

http://www.ebay.com/itm/Bench-LCR-Meter-200KHz-Inductance-Capacitance-RZDQ-Test-Component-Sort-JK2816C-/301208339835?pt=LH_DefaultDomain_0&hash=item46216a857b

http://www.ebay.com/itm/Digital-Comparator-Component-Parameter-Test-Bench-Top-LCR-Meter-TH2816B-A-/291165303277?pt=LH_DefaultDomain_0&hash=item43cacdf1ed

http://www.ebay.com/itm/Hi-precision-0-05-Digital-LCR-Meter-10Hz-300KHz-Comparator-TFT-LCD-USB-AT2818-/271515089610?pt=LH_DefaultDomain_0&hash=item3f378f7aca

http://www.ebay.com/itm/Hi-accuracy-0-01-LCR-Meter-20Hz-1MHz-Transformer-Test-DC-Bias-Source-TFTLCD-USB-/301215454189?pt=LH_DefaultDomain_0&hash=item4621d713ed

I notice that the last one has been made to look like the Agilent E4980 which costs over $15000, and in fact there is a direct comparison, feature for feature, at the bottom of the page.  I suspect they're going to sell a lot of those.
 


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