Seeking understanding of what an LCR meter can measure beyond L, C, and R - Page 1
Forum section: electronics / testgear

author: ballsystemlord
author_rank: Frequent Contributor
timestamp: May 21, 2023, 06:14:50 pm
content: LCR meters will read a variety of additional parameters to just LCR.For example, Conductance, Susceptance, and Admittance. These can be calculated by inputting the reciprocal of the resistance, reactance, and impedance. So would having a meter that would compute these parameters for you be of any advantage in real-world-usage?Tequipmenthttps://www.tequipment.net/lcr-meters-impedance-measurement-products/lcr-meters/, in addition to several common parameters, lists Rdc and Rac as things that LCR meters can measure. But isn't Rac just Reactance? Isn't Rdc just resistance? Am I not understanding something, or are they just using different abbreviations for things?Interestingly, (and not that I'd spend this much on a meter), but higher end meters, like this onehttps://www.tequipment.net/Instek/LCR-8201/LCR-Meters/, don't list ESR as one of the parameters that they measure. Why? Is it just hidden somewhere deep inside of their manuals (I did search the datasheet. Not a mention of the word ESR.) or is ESR something that should be seen on separate lines, one for resistance, and the other for reactance and then we manually enter/compute what our circuit will do when exposed to a part with that reactance and resistance?Thanks!

author: TimFox
author_rank: Super Contributor
timestamp: May 21, 2023, 06:56:01 pm
content: According to the datasheet you posted for the full-priced LCR-8201, it can displayCseries;Cparallel; ACRseries; and ACRparallel, among other parameters.A maximum of four parameters can be displayed simultaneously."ESR" is merely a synonym for the series resistance in a series R-C model of a component, i.e. ACRseries.At a single frequency, any two-terminal capacitor-looking object can be modeled as eitherCseriesin series withRseries, orCparallelin parallel withRparallel.In the latter model, you may use the conductanceGparallel= 1 /Rparallel, at your convenience.These units compute the displayed parameters from the inherent measurement of eitherR+ jXorG+ jB.Elementary circuit theory discusses how these vary with frequency.

author: Martin72
author_rank: Super Contributor
timestamp: May 21, 2023, 08:41:13 pm
content: Here´s a pdf where all questions will be answered:Agilent Impedance Measurement Handbook

author: mawyatt
author_rank: Super Contributor
timestamp: May 21, 2023, 10:06:59 pm
content: Quote from: TimFox on May 21, 2023, 06:56:01 pmActually the LCR measurement values are not R + jX but simply DUT voltage and current as vectors (digitized versions of magnitude and angle of sinusoids, with multiple samples taken, then sinusoid reconstructed), R +JX and all other parameters are computed from such!!Also a proper capacitance model should include ESL as well as ESR for a capacitor to help represent the series resonate effect, without such the "effective" capacitance can not change with frequency, and we know many types of capacitors do vary over their expected operating frequency range, thus the inclusion of ESL to represent such.Best.

author: TimFox
author_rank: Super Contributor
timestamp: May 22, 2023, 03:34:15 am
content: Quote from: mawyatt on May 21, 2023, 10:06:59 pmI got that upside-down.With LCR meters using the basic mechanism of the GenRad Digibridges, the "low" end of the component connects to a virtual ground to measure the device current, while the "high" end is driven by a known value of AC voltage.Using a phase-sensitive detector on the device current, and dividing by the voltage value gives the admittanceY=G+ jB, whereGcomes from the "real" (in-phase) component andBcomes from the "imaginary" (quadrature phase) component of the current, where the phase reference for the detector comes from the voltage.That summarizes the actual measurement, but the built-in computation starts with these two values and applies appropriate calibration (including fixturing) to calculate the displayed values.

author: pdenisowski
author_rank: Super Contributor
timestamp: May 22, 2023, 11:00:15 am
content: As some of the other posters have pointed out, modern, high(er) end LCR meters essentially measure the phase angle between voltage and current and calculate L, C, R, and related quantities from that phase shift.A lot of the differentiation between LCR meters is in things like measurement frequency, measurement accuracy, bias, and additional functions like frequency sweeps, transformer measurements, binning, etc., as well as fixtures, interface, and ease of use.It's really hard to go back to using a handheld LCR meter (and I've used most of them) after using a benchtop LCR meter

author: ballsystemlord
author_rank: Frequent Contributor
timestamp: May 27, 2023, 11:37:38 pm
content: I watched the 2 videos, and read the PDF up to the point where they describe the theory of operation of LCR meters. I now have more questions than I did before...I didn't get one of my original questions answered. I know I wasn't clear enough on the ESR bit, but I thought I explained myself well enough on the others. I'll try rewriting them...Is having the meter itself compute Conductance, Susceptance, and Admittance a useful feature you should pay extra for, or is it just handy once in a while?Is Rac just another way of saying Xc/Xl (e.g. Marketing had the idea of calling it Rac), or is it some special other measurement?Some higher end meters don't mention that they measure ESR, why?Thanks!

author: Martin72
author_rank: Super Contributor
timestamp: May 28, 2023, 12:50:14 am
content: Hi,QuoteOur sourcetronic LCR (and many others) also has no explicit parameter displayed as ESR, but measures it anyway.And that is the parameter R.This describes the real part of a complex resistor.If you measure a capacitor and have R displayed, it is nothing else than ESR.

author: mawyatt
author_rank: Super Contributor
timestamp: May 28, 2023, 01:32:29 am
content: Quote from: Martin72 on May 28, 2023, 12:50:14 amBe careful here, many LCR meters can display RP which is the Parallel Equivalent, where ESR is Equivalent Series Resistance, or Series Equivalent. Most lab grade LCR meters don't measure device parameters directly, they measure the DUT vector current and vector voltage across the DUT, then compute all the device parameters from such.Best,

author: TimFox
author_rank: Super Contributor
timestamp: May 28, 2023, 02:45:18 am
content: Note that for a real capacitor with a reasonable Q value, the equivalent parallel and series resistancesRPandRSare very different.

author: ballsystemlord
author_rank: Frequent Contributor
timestamp: May 28, 2023, 03:31:22 am
content: Quote from: TimFox on May 28, 2023, 02:45:18 amWhich, of course, brings us to the question, what's the actual resistance if series and parallel produce such different results?(It's probably academic, but it's still interesting.)

author: TimFox
author_rank: Super Contributor
timestamp: May 28, 2023, 01:44:21 pm
content: The wrong question.For the component ("capacitor"), the choice between series and parallel models depends on the circuit you are designing:Typically, the series model is easier to calculate in a power-supply filter capacitor, but the parallel model is easier to calculate in an RLC parallel-resonant circuit.For the guts of the device ("dielectric"), the basic physics is often better described withQ= 1/D, which is a somewhat weak function of frequency for many materials.The component also has parasitic resistances (connections in series and leakage in parallel) packaged along with the dielectric.At a fixed frequency, there is no difference in operation between the series and parallel models.

author: coromonadalix
author_rank: Super Contributor
timestamp: May 28, 2023, 03:18:58 pm
content: aaaaaand the serial or parallel DUT can be impacted by all parts around it or are in the same circuit, it is not an absolute way to troubleshoot

author: jwet
author_rank: Frequent Contributor
timestamp: May 28, 2023, 08:56:11 pm
content: These alternate inverted units are not just arithmetic - they can be more useful in certain ranges- for instance- if you were measuring 1 milli ohm and had three digits, would you like to see .001 ohms or 983 Siemens (or mhos in the day). This used to be more important when units had fixed LED displays and hardware defined interfaces. Make sure the instrument covers the range you need, this will make sure it can measure it. In the above example, a modern unit might display 1.02 milli-ohm (the inverse of 983 mhos)

author: ballsystemlord
author_rank: Frequent Contributor
timestamp: May 28, 2023, 11:45:58 pm
content: Thanks, guys. That just leaves the last one:Is Rac (Resistance AC) just another way of saying Xc/Xl (e.g. Marketing had the idea of calling it Rac), or is it some special other measurement?(I give a link with examples in the OP.)Unless you have anything to add regarding the other 2:https://www.eevblog.com/forum/testgear/seeking-understanding-of-what-an-lcr-meter-can-measure-beyond-l-c-and-r/msg4883012/#msg4883012

author: The Electrician
author_rank: Frequent Contributor
timestamp: May 29, 2023, 12:26:36 am
content: Quote from: ballsystemlord on May 28, 2023, 11:45:58 pmMost of the high end LCR meters don't use the term Rac. The usual term is Rs, which is the resistive part of the series equivalent model. Rp is the resistive part of the parallel equivalent model. Rac and Rs and ESR are the same thing.Here is a list of what the Keysight E4980A can display. The E4980A is a very high end LCR meter currently available from Keysight:

author: Martin72
author_rank: Super Contributor
timestamp: May 29, 2023, 12:53:17 am
content: QuoteIt was a few decades ago, but I had once learned that the impedance is the AC resistance.

author: mawyatt
author_rank: Super Contributor
timestamp: May 29, 2023, 01:16:14 am
content: Impedance is usually referred to as Z, and a complex number as R +jX, where X is the Reactance and + for Inductive and - for Capacitive. R of course is the Real part and Resistance.Also note that X can not dissipate energy, only R can do this, so the "Loss" in an Impedance Z is solely due to the Real part R.Best,