LCR meter feature terminology and buying advice - Page 1
Forum section: electronics / testgear

author: Esquared
author_rank: Contributor
timestamp: September 08, 2021, 06:22:07 am
content: Hello, I'm looking to buy an LCR meter; I am specifically interested in measuring inductance. I was looking at different models and I notice on some meters they say they have a "Resistance mode" and a "Direct Current Resistance mode". This is confusing to me because that implies that "Resistance mode" is really AC impedance which is definitely different from resistance. I got really confused by a BK precision meter which in its manual states that it has "AC resistance", "Direct Current resistance", and "Impedance"! I've seen several meters from different companies have this weird terminology in their feature list so I began to doubt that it was a typo/marketeering.As far as buying an LCR goes I'm looking for a handheld unit that costs less than $400 USD before tax. I have a few models below that I am considering, but since I am unfamiliar with this type of meter I honestly don't know what is out there and what is a deal or not. Ideally Whatever model I buy can perform measurements at least at a max frequency of 1kHz although more is better. A good interface and product support will go a long way too. Measurement tolerance I don't have a target for as I am going to use this to characterize some large solenoids that have no documentation so I wouldn't know if it is really wrong anyways! Just reasonably accurate across the meter's range and repeatable. If you have experience with any of the listed models please let me know if you like them or not! Cheers!Keysight U1731Chttps://www.keysight.com/us/en/product/U1731C/handheld-lcr-meter-100-hz-120-hz-1-khz.html#ResourcesBK Precision 879Bhttps://www.bkprecision.com/products/component-testers/879B-40000-count-dual-display-handheld-lcr-meter-with-esr.htmlUNI-T UT622Ahttps://instruments.uni-trend.com/list_85/1002.htmlExTech LCR200http://www.extech.com/products/LCR200Amprobe LCR55Ahttps://www.amprobe.com/product/lcr55a/Amprobe 37XR-Ahttps://www.digikey.com/en/products/detail/amprobe/37XR-A/1534460?s=N4IgjCBcpmAMVQGMoDMCGAbAzgUwDQgD2UA2iACwBMcVsIAuoQA4AuUIAyqwE4CWAOwDmIAL6EAtAA5EIFJAw4CxMiADscAKyNRuoA

author: David Hess
author_rank: Super Contributor
timestamp: September 08, 2021, 11:12:57 am
content: Add the DE-5000 to your list. They can be had for not much more than $100.

author: fishwhispers
author_rank: Contributor
timestamp: September 08, 2021, 12:14:40 pm
content: I bought a BK Precision 880 recently and I’ve been really happy with it so far. It’s pretty easy to use, decent build quality, the calibration is really quick, has a 100kHz mode, and it ships with both 4-wire alligator clips and 4-wire tweezers, which I believe are optional extras for the Keysight handhelds. (I could be wrong about that.)https://www.tequipment.net/BK/880/LCR-Meters/If all you want to do is identify components I might be a bit overkill to spend that much on an LCR meter, but it should still be in your price range through that link.

author: mawyatt
author_rank: Super Contributor
timestamp: September 08, 2021, 12:44:58 pm
content: Don't have any experience with the handhelds but your question about Resistance and DC- Resistance or DCR is the Resistance is an AC measurement like used for L and C measurements, while the DCR is measured with a DC source like your DMMs utilize. On our bench top LCR meter the Resistance mode give various parameters like R+-jX or R and Q, while DCR mode gives just R. On the Inductance mode you can select L Series or L Parallel modes which provide L and R series or parallel respectively and also Q.Best,

author: fishwhispers
author_rank: Contributor
timestamp: September 08, 2021, 01:35:47 pm
content: As I understand it, an LCR meter only measures impedance. It does this by sending an AC signal through a component and then measures the magnitude and phase shift. While impedance is a complex number, some handhelds will only display the “real” part, leaving the imaginary part… to the imagination I guess. The meter can model this impedance as the product of three ideal components, an inductor L, a capacitor C and a resistor R. These ideal components can be modeled as in “series” or in “parallel” and you will want to choose which model based on the component under test to get the most accurate reading. That is the difference between R and Z. You will get a different value for R depending on if you are modeling things as in series or parallel, but your Z value will stay the same.I sure hope I got that right.

author: TimFox
author_rank: Super Contributor
timestamp: September 08, 2021, 01:41:51 pm
content: A typical LCR meter measures the "real" (in-phase) and "imaginary" (quadrature) components of the voltage across the DUT (compared with the AC current applied to the DUT), or vice-versa.From this, with corrections obtained from measurements with the device open-circuit and short-circuited, the usual parameters can be computed, including magnitude (impedance), phase, resistance, and reactance.From those, the series or parallel inductance, capacitance, resistance, and admittance can be computed, knowing the frequency.

author: Grandchuck
author_rank: Super Contributor
timestamp: September 08, 2021, 02:21:50 pm
content: Since you are interested in inductors, check this out:https://www.nist.gov/system/files/documents/calibrations/WaltripProceedings.pdfI have the Keysight LCR meter and like it.

author: TimFox
author_rank: Super Contributor
timestamp: September 08, 2021, 03:31:06 pm
content: To clarify my earlier post, where I was referring specifically to the DE-5000 (which uses the same basic technology as the older General Radio "Digibridges").The AC applied to the DUT is from a voltage generator through a current-limiting resistance.The current through the DUT is measured through a virtual ground at the "low" terminal.The voltage across the DUT is measured with a differential voltage sense.Those four nodes are applied preferably to the DUT with a 4-terminal Kelvin connection.The 90 degree phase difference in the phase-sensitive voltmeters is critical, and done by digital synthesis of the reference voltages in the generator circuit.With accurate 90 degree phase offsets, a reference reactance (e.g., capacitor) is not needed, and only precision resistors (cheaper) are needed to get accurate ranges in the current sense.

author: Esquared
author_rank: Contributor
timestamp: September 08, 2021, 08:52:45 pm
content: Okay so essentially the way they use the termsResistance = AC Resistance = Only the real part of impedanceDCR = ResistanceImpedance = Impedance (real+imaginary components)Gotcha glad that was cleared up! I don't really need DCR as I already have 2 good DMMs but I was curious on what it meant as models that had DCR tended to have a significant price increase. Actual impedance is nice, however.Thanks for the tip about the DE-5000 I will take a look at that one too.

author: TimFox
author_rank: Super Contributor
timestamp: September 08, 2021, 09:06:20 pm
content: I’m happy with my DE-5000. Note the following:As with other LCR meters of this type, neither end of the DUT should be grounded, since the low end is the current sense. Since the DE-5000 is battery operated, I often float it on a plastic box when one end is grounded (e.g., measuring the input of an amplifier that can tolerate the roughly 600 mV rms AC voltage).The input is not protected (see other threads about this unit), so you must be careful to ensure the capacitor under test is fully discharged.For good results, you should do the open/short calibration, with the test leads you are using, before starting measurements after powering on.Comparing mine to good capacitors gives results well within the manufacturer’s specification.

author: tautech
author_rank: Super Contributor
timestamp: September 08, 2021, 09:35:39 pm
content: EsquaredNeeding similar to you some years back and also venturing into SMD a good set of SMD smart tweezers was chosen for their overall versatility.Now comes the cries that you can't use them on TH or bigger components......Prior to getting the tweezers I used a borrowed old school LCR bridge so tweezer accuracy was checked against it and was found to be more than acceptable for my needs which have changed little over the years.Good tweezers aren't cheap but are fast, compact and convenient should bench space be an issue.

author: kripton2035
author_rank: Super Contributor
timestamp: September 08, 2021, 09:40:32 pm
content: the TL-22 tweezers that come with the (deree)-de5000 (if you take care to order them both at the same time) are nice and solid.

author: TimFox
author_rank: Super Contributor
timestamp: September 08, 2021, 10:31:31 pm
content: The TL-22 are good: four wires brought from unit to tips.You need some simple method (like a tiny piece of plastic) to hold the tips apart (placed away from the contacts) when doing the "open circuit" calibration.

author: fishwhispers
author_rank: Contributor
timestamp: September 09, 2021, 01:34:54 am
content: Quote from: Esquared on September 08, 2021, 08:52:45 pmDepending whether you are in "series" or "parallel" mode it should be..."Resistance = The Equivalent Series Resistance, or Equivalent Parallel Resistance".It's not the same as the Z measurement, which is the "real" part of impedance (On the BK 880 at least). Here are a couple pictures showing a 47uF cap. The first shows the Equivalent Series Resistance "R", since the meter is in "series" mode. (1.9ohms)And the second picture shows the "Z" measurement for the same cap, (29.5ohms)

author: David Hess
author_rank: Super Contributor
timestamp: September 09, 2021, 12:10:17 pm
content: Quote from: kripton2035 on September 08, 2021, 09:40:32 pmAnd the TL-21 kelvin clips are cheap enough to buy an extra set for the adapter to make your own.

author: TimFox
author_rank: Super Contributor
timestamp: September 09, 2021, 01:33:29 pm
content: "Z" is not the real part of the impedance, but the (positive) magnitude of the complex-valued impedance. (For a capacitor, the real part of the impedance is the ESR, the imaginary part is the capacitive reactance.)

author: fishwhispers
author_rank: Contributor
timestamp: September 09, 2021, 03:58:25 pm
content: Whoops! Well I’m learning stuff here. Sorry for adding to the confusion.

author: The Electrician
author_rank: Frequent Contributor
timestamp: September 09, 2021, 04:03:00 pm
content: Using a bench LCR meter (Hioki IM3570) the derivation of various quantities from a basic impedance measurement can be illustrated. This instrument can make measurements with precision (7 digits) exceeding its accuracy spec (5 digits). This level of precision can be used to select matched components with precision greater than the instrument's accuracy.This meter makes the assumption that the parameter called Z (impedance) is actually |Z| (impedance magnitude), and the parameter called Y (admittance) is actually |Y| (admittance magnitude).Given the following relationships:The term ESR (equivalent series resistance) is labeled Rs on this meter. Another quantity which might be called EPR (equivalent parallel resistance) is labeled Rp on this meter; this quantity is not displayable on any handheld meter I'm familiar with.Here are several measurements of a 47uF electrolytic capacitor made at 1 kHz. The first image shows the parameter labeled "Z" on the meter, but it's really "|Z|". All the handheld meters I'm familiar with make this same assumption, that the user will realize that the displayed parameter is really |Z|, not Z. Also shown are the two parts of the complex valued Z. The real part is labeled "Rs", and the imaginary part is labeled "X".This image shows the same capacitor, with the real and imaginary parts of Z shown separately but a minute later. The values are slightly different than the previous image due to the air currents in the room changing the temperature of the capacitor. The 7 digit precision of the meter is able to show this. Touching the capacitor really changes the measurement.:Here is the same capacitor but with admittance parameters. Note that the EPR (equivalent parallel resistance) is not the real part of the admittance (which has units of siemens), but rather the reciprocal of the real part of the admittance:

author: TimFox
author_rank: Super Contributor
timestamp: September 09, 2021, 04:14:13 pm
content: One advantage of bench LCR meters over the (less expensive) handhelds is that you have more choices of the (computed) parameters to display. My DE-5000 will display magnitude and phase angle of the impedance, capacitance or inductance (series or parallel model), with Q or D or with equivalent (series or parallel) resistance. It will not display the components X and R, nor B and G, which would be useful (but are calculable from what can be displayed). The only real problem with the DE-5000 is that if the “inductor” is capacitive at the test frequency (i.e., above self resonance), it displays a positive value of inductance corresponding to the magnitude of the reactance. To check that, you need to look at magnitude and phase (which can be a positive or negative angle).

author: fishwhispers
author_rank: Contributor
timestamp: September 09, 2021, 04:24:11 pm
content: Ok interesting. I think I understand Z now, but let me see if I can repeat it back in a super layperson way.If the complex impedance is a vector on a 2D plane, the "Z" parameter displayed on LCR meters in the magnitude of that vector (which will always be positive). This would also explain why "Z" doesn't change when you switch between "parallel" and "series" mode, because the angle of the vector is changing but its magnitude is staying the same. Both ESR and EPR would be represented by one axis in this 2D plane and reactance would be represented by the other axisIs that correct?

author: The Electrician
author_rank: Frequent Contributor
timestamp: September 09, 2021, 04:37:55 pm
content: Quote from: fishwhispers on September 09, 2021, 04:24:11 pmThe angle of Z doesn't change when you switch between series and parallel. Set your meter to display the angle (theta) and while measuring a capacitor switch the modes; you'll see that the angle doesn't change.

author: TimFox
author_rank: Super Contributor
timestamp: September 09, 2021, 04:59:08 pm
content: Almost correct. To be clear, the equations below use vector (bold-face) notation for complex variables such asZ, and plain italic for real variables such as the magnitudeZand the componentsRandX.The series model is described by the impedanceZ=R+jX, which can also be described using the magnitudeZand the associated phase angle θ.The parallel model is described by the admittanceY= 1/Z=G+jB, where the components are "conductance" and "susceptance".The magnitudes are related byY= 1/Z, and the phase angle of the admittance is the negative of the phase angle of the impedance.Note thatRis not equal to 1/G. TheQvalues of the two models are equal.

author: The Electrician
author_rank: Frequent Contributor
timestamp: September 09, 2021, 05:05:56 pm
content: Quote from: TimFox on September 09, 2021, 04:59:08 pmlWho are you responding to? The Electrician, or fishwhispers?On the DE-5000 the symbol for AC resistance is not just a plain "R", it is "Rs" or "Rp" depending on mode, so I have to take back what I said about no handheld meter displaying Rp--the DE-5000 does.

author: fishwhispers
author_rank: Contributor
timestamp: September 09, 2021, 05:33:46 pm
content: I assume it was me since I asked if I was correct.Ok, it sounds like I have some homework to do. I'm having a hard time building up an intuitive model for the difference between "parallel" and "series" as they relate to Z and Y. I'm not sure why a "the negative of the phase angle" for Y would still show same theta on the meter as Z. But there's probably just some math that I don't quite understand.Thanks for guidance! Sorry for telling you the wrong thing Esquared. Hopefully things got cleared up for you in the end.

author: The Electrician
author_rank: Frequent Contributor
timestamp: September 09, 2021, 06:27:48 pm
content: Quote from: fishwhispers on September 09, 2021, 05:33:46 pmYour meter doesn't display Y so you shouldn't expect to see the angle of Y. Did you do the little exeriment I suggested? Put that 47uF cap back in the meter, set it to display Z and theta and switch the mode between series and parallel. Theta should not change sign.

author: fishwhispers
author_rank: Contributor
timestamp: September 09, 2021, 07:02:41 pm
content: Yes, I did try it. You are correct, the theta stays the same.Also that makes sense that it doesn't show Y because the units show as Ohms regardless of whether you choose "series" or "parallel" mode.

author: TimFox
author_rank: Super Contributor
timestamp: September 09, 2021, 09:34:45 pm
content: Quote from: The Electrician on September 09, 2021, 05:05:56 pmTo "The Electrician".On the DE-5000, which does not displayY, the common readouts for capacitance (for example) are for an ideal capacitor in series with a resistor (series mode), or for an ideal capacitor in parallel with a resistor (parallel mode). The units in both readout modes are farads and ohms. Similarly for inductance. The two capacitance values are not equal (reasonably close with high Q), and the two resistor values are far apart with high Q.

author: The Electrician
author_rank: Frequent Contributor
timestamp: September 09, 2021, 11:17:12 pm
content: Quote from: TimFox on September 09, 2021, 09:34:45 pmSo what was I not correct about?