LCR Meter - What does R measure on a capacitor? - Page 1
Forum section: electronics / beginners

author: killingtime
author_rank: Regular Contributor
timestamp: September 29, 2021, 06:51:44 pm
content: Hi,I was looking at a spec sheet for an LCR meter that doesn't have 'ESR' as a measured parameter. It has L,C,R & Z (primary), and D,Q (secondary). There is no DCR range either (resistance at 0Hz).8399362.s21i.faiusr.com/61/ABUIABA9GAAgzfKMggYosdCQnQQ.pdfTrying to work out if the unit could measure the ESR of a capacitor.Q: What does the resistance range (R) of an LCR meter actually measure when you put a capacitor with some ESR across the terminals, with 'series mode' selected? Assume almost no leakage.I'd like to think that any LCR meter is able to distinguish between the R and X of a capacitor and just give you the R value. Is it that simple?To confuse matters, some LCR meters like the DE-5000 have both an 'R' range and 'ESR/EPR' range.Reading LCR manuals doesn't help; all provide the example of a resistor across the terminals then the 'R' range is selected.One final question; what's the benefit of having a 100KHz range on an LCR meter?I know you're meant to test the DUT at the frequency it's going to be used at in circuit - OK, but why stop at 100KHz? Caps work at radio frequencies (MHz), so the 100KHz seems a bit arbitrary.100Hz - PSU smoothing applications after the full wave rectifier - mains supply.1k/10KHz audio applications.100KHz - switch mode PSU applications?Thanks.

author: TimFox
author_rank: Super Contributor
timestamp: September 29, 2021, 07:22:04 pm
content: From your post, to get ESR of a capacitor with that unit, you measure “C” (primary) and “D” or “Q” (secondary) at the test frequency and compute the ESR from those two numbers. For low Q (say,Q< 10), there is a problem, since the capacitance for the parallel and series models is different. I refer you to the usual textbooks for the formulae.Stopping at 10 kHz or 100 kHz is just a practical matter of extra cost and difficulty of measurements at 1 MHz and above. Good RF impedance meters can go up to 1 GHz, but that requires careful fixturing of the device under test.Yes, a “true” LCR meter can distinguish between R and X inR + jX, but different digital instruments have different capabilities of what parameters can be displayed.

author: bob91343
author_rank: Super Contributor
timestamp: September 29, 2021, 08:54:52 pm
content: It's easy. The R you measure on the R range is the ESR as long as the capacitance has negligible reactance at the measuring frequency. If not, some relatively simple calculation is necessary. The frequency has to be low enough so that the ESL is negligible.

author: Capernicus
author_rank: Frequent Contributor
timestamp: September 29, 2021, 10:52:27 pm
content: if you add a resistor, does it drop the reactance of the capacitor being tested?

author: bob91343
author_rank: Super Contributor
timestamp: September 30, 2021, 01:27:47 am
content: The reactance should be independent of any added resistor.

author: MarkF
author_rank: Super Contributor
timestamp: September 30, 2021, 09:57:09 am
content: This video may give you some insight:

author: killingtime
author_rank: Regular Contributor
timestamp: September 30, 2021, 10:47:08 am
content: @TimFox - Yes, but I'd have to calculate the ESR manually that way, every time with a calculator. Looking for the meter to display the ESR.@bob91343 - 'The R you measure on the R range is the ESR as long as the capacitance has negligible reactance at the measuring frequency..' . So what is actually being measured on the R range then (my original question)? The R part of complex impedance (R - xj)@Capernicus - I don't know. I don't have the meter. Looking to buy one.@MarkF - It was a help, but the guy in the video is using a VNA that outputs a R - jX value. There is no R,C or L range on that instrument. You deduce the LCR from the complex impedance notation, which makes it easy.The issue is that many low end LCR meters don't display a complex impedance. They give you a R, C and L range instead and output one value. The instrument linked does anyway. My question is, what is that value for R?Let me put the question another way.When measuring a cap on the R range, does an LCR meter display;1. The R component only of the complex impedance (R - jX) or,2. The magnitude of overall impedance 'Z' (vector sum of resistance and reactance), or3. Something else.

author: TimFox
author_rank: Super Contributor
timestamp: September 30, 2021, 01:45:24 pm
content: Your meter isn't designed to do directly what you want.Either:Use a calculator.Buy a different meter, e.g. DER DE-5000, that has an explicit ESR reading.

author: The Electrician
author_rank: Frequent Contributor
timestamp: September 30, 2021, 02:29:53 pm
content: Quote from: killingtime on September 30, 2021, 10:47:08 amAccording to the specs you gave in post #1, this meter can display two parameters at once: L-Q, C-D, R-Q, and Z-Q. R is the real part of the impedance (ESR) and Z is the magnitude of the complex impedance.This is the oldest LCR meter made by Applent; it's probably the company's first LCR meter. Check out that 7-segment display! And, even though it's still available on amazon, the price is $500+; not a good deal.Applent has much better and newer meters:https://applent.en.alibaba.com/productgrouplist-212870894/LCR_Digital_Meter.html?spm=a2700.shop_index.88.21Several other manufacturer's have LCR meters that are newer and less expensive, as you must have noticed. Have you found an AT2811 for sale really cheap? Why are you considering it in particular?

author: Jwillis
author_rank: Super Contributor
timestamp: September 30, 2021, 04:17:22 pm
content: If you interested I've been using theMastech 5208 LCR Tester. They're around $200 . Think I paid around $400 for mine on Amazon around 4 or 5 years ago . They're not the newest on the line but they are so easy to use and fairly accurate. Easy to calibrate. Haven't had a problem with mine for a few years now. Don't much care for the way the test leds connect but its not the worst I've seen . Software is a simple and basic .Manual explains everything really well. Worth checking out .

author: bob91343
author_rank: Super Contributor
timestamp: September 30, 2021, 04:20:18 pm
content: When you measure a capacitor on the R range it will show the complex Z magnitude. This approximates the ESR if the reactance is small compared to the impedance. You can verify it by measuring the D on the capacitance range; if it's small then your ESR reading may be off.My question is, what is the purpose of measuring ESR accurately? If you want to characterize a capacitor, you need more sophisticated measuring equipment. If you just want to know if the capacitor is defective, the ESR measurement gives some information.

author: The Electrician
author_rank: Frequent Contributor
timestamp: September 30, 2021, 05:19:06 pm
content: Quote from: bob91343 on September 30, 2021, 04:20:18 pmThe meter has a Z range, so why would it show |Z| (complex Z magnitude) on the R range? Wouldn't it make sense to show |Z| on the Z range, and show ESR (Rs) on the R range?

author: bob91343
author_rank: Super Contributor
timestamp: September 30, 2021, 06:08:28 pm
content: The purpose of the R range is to measure resistors. Since your unit measures R at some frequency, rather than at DC, its display isn't defined if you are measuring a capacitor. However, in many or most cases, measuring R of a capacitor indicates the ESR as long as the measurement isn't polluted by the capacitive reactance.Think of it this way. If you put a resistor in series with a capacitor and measure the combination, at DC you get an open circuit (or actually the insulation resistance of the dielectric). When you use a low frequency, the charging and discharging of the capacitor results in a resistance reading. If the meter is calibrated in Ohms and does not measure phase, it will probably give a reading based on the volltage that appears and the current it supplies. If the frequency is high enough, or the capacitance large enough, the voltage across the capacitor is very low and the reading you get is based on the ESR, since that's where most of the voltage is developed. (This ignores ESL, which comes into play at higher frequencies.)So the reading at dc is high and as you raise the frequency it shows some value which starts to drop with higher frequency. At some point, the capacitance becomes such a low reactance that its effect on the reading is minimal and the resistance reading is lowest, indicating ESR. As you raise the frequency further, the ESL comes into play and the reading increases again. But by this time the capacitance doesn't enter into the measurement unless its a low value. Measuring ESR of a 47 pF capacitor is difficult because the capacitance interferes at low frequencies and the ESL dominates at very high frequencies so the only way to measure ESR is to take readings at different frequencies and do some calculation. All components have self resonant frequencies that can further complicate things.So the answer to the original question is the usual 'it depends'.

author: Capernicus
author_rank: Frequent Contributor
timestamp: September 30, 2021, 06:11:21 pm
content: Capacitors have about as much resistance as a transistors collector and emitter (i.e. naff all.) Thats unless its been charged then its infinite.But is it actually still measurable in millohms or something? Thats actually a confusing thing to try and read cause the capacitor would fill up so quick that u couldn't even read it!I think youd have to use a very high frequency ac to do that, so it stays neutral in the centre to get the resistance reading, but tiny capacitors would be the hardest to read the resistance of.

author: TimFox
author_rank: Super Contributor
timestamp: September 30, 2021, 06:33:15 pm
content: A good (non-electrolytic) capacitor has a negligibly high parallel resistance for most applications, but most capacitors have a measurable series resistance, which is a function of frequency.When sending a high alternating current through the capacitor, the capacitance does not dissipate power, but the resistance does.Electrolytic capacitors have relatively high series resistance at the frequencies where they are used, perhaps 10% of the reactance value (for D = 10%), and that is an important limitation for use in rectifier filter circuits.With mediocre capacitors (X7R ceramic and polyester/Mylar film), you can usually measure the ESR at frequencies below, say, 1 kHz on a decent meter (D roughly 1%).

author: The Electrician
author_rank: Frequent Contributor
timestamp: September 30, 2021, 07:14:24 pm
content: Quote from: bob91343 on September 30, 2021, 04:20:18 pmIf the meter shows the complex Z magnitude on the R range, what does it show on the Z range?

author: The Electrician
author_rank: Frequent Contributor
timestamp: September 30, 2021, 08:35:26 pm
content: Quote from: bob91343 on September 30, 2021, 06:08:28 pmYou are not up-to-date on how modern LCR meters work. Here are some good references:http://componentsengineering.com/wp-content/uploads/pdfs/LCR-Measurement-Primer.pdfhttp://hotstreamer.deanostoybox.com/temp/AgilentImpedanceMeasurementHandbook.pdf

author: killingtime
author_rank: Regular Contributor
timestamp: October 01, 2021, 12:00:20 pm
content: After a bit more research, I'm beginning to conclude that the R on any LCR meterthat can distinguish phase (display D or Q)is actually the same thing as ESR, when the meter is in series mode.The term 'ESR' is just another way of defining 'R' when in series mode for any complex impedance. I can't see it being anything else. What threw me initially was that some LCR meters (like the DE-5000) have an R range and ESR range, and wondered if they might be different parameters. The ESR range seems to be just a convenience secondary range, to save you having to jump out of the C range (when measuring caps), and into the R range with series mode selected.For those that have suggested R would be Z(mag), well it's possible, but your LCR meter would then be rubbish as measuring any resistor with a large reactive component - like a high ohmic value wirewound resistor. If the same meter can display Q or D, then it knows about signal phase across the DUT, so it should be able to calculate R and distinguish that from X. Why then wouldn't you display R, given that there is already an dedicate Z(mag) range?A real world test for this would be to measure a cap on the R range, and then add a series resistor (non-reactive) with a ohmic value similar to that of the cap reactance (at the frequency your measuring at). If the R reding goes up by the resistor value, your R range is actually measuring the R part of a complex impedance. If the reading is way out, then the meter is measuring something else like Z(mag).It's possible that in spite of the above, some LCR meters don't display only R on the R range. There might be something quirky in the meter design for resistance measurement; someting that has been 'assumed' by the designer, but not documented. I guess you just have to run the above test.Thanks for the replies and links.

author: Jwillis
author_rank: Super Contributor
timestamp: October 01, 2021, 05:32:45 pm
content: All the ranges ''L" , "C" , and "R" are in AC mode . As you know , every passive component exhibits an ESR (equivalent series resistance ), ESL (equivalent series inductance )and ESC (equivalent series capacitance) . The ESL and ESC really don't have much meaning until you get into high frequencies.The ESR of a resistor is of course the value of the resistor. When you add a resistor in series with a capacitor , the displayed ESR of the circuit becomes the sum of the the two ESR's at the frequency of the test . If you try to measure the same circuit in DCR you get either an open circuit or the sum of the DC resistance of the resistor and the capacitor depending on the maximum measuring specifications of the meter . The DC resistance of a capacitor can be extremely high . Up in the mega Ohm range or more .When you measure the resistance of a resistor on a LCR meter you can choose two main ranges . The R range which is in AC at a specified frequency and the DCR which is DC resistance at zero hertz . There should be little difference between the displayed values . But these values can be more accurate than a standard multimeter because of the 4 point measuring .

author: The Electrician
author_rank: Frequent Contributor
timestamp: October 01, 2021, 11:38:58 pm
content: Quote from: killingtime on October 01, 2021, 12:00:20 pmYou never did answer my earlier question "Several other manufacturer's have LCR meters that are newer and less expensive, as you must have noticed. Have you found an AT2811 for sale really cheap? Why are you considering it in particular?"An LCR meter that can't distinguish phase when measuring would be like a scalar network analyzer, as opposed to a vector network analyzer. I haven't run across a meter that can measure AC resistance without also measuring phase. Such a thing might have existed a long time ago, but nowadays it's so easy to measure phase at audio frequencies that every low cost LCR meter manufacturer does it. If an LCR meter says it makes measurements at the standard frequencies of 100 Hz, 120 Hz, and 1 kHz (at a minimum), and says it displays R, then when a capacitor is the component being measured that R is the real part of the impedance, the ESR. DCR is a different thing--some meters measure it, some don't, and if they do, it is usually designated R (or DCR), with AC resistance designated Rs or Rp.I explained a lot of this, including why the so-called ESR meters can only measure the ESR of high value capacitors (values above a few uF) in another thread:https://www.eevblog.com/forum/projects/impedance-lcr-esr-meters/msg459252/#msg459252I see universal assertions about capacitor parameters, such as "ESR is constant with frequency", or "ESR varies with frequency", or "ESR decreases with frequency", "capacitor DF is constant with frequency", etc. One shouldn't make such universal assertions and you can see some of the many variations in capacitor behavior here:https://www.eevblog.com/forum/projects/capacitor-measurements-on-an-impedance-analyzer/msg178362/#msg178362

author: killingtime
author_rank: Regular Contributor
timestamp: October 02, 2021, 06:21:48 pm
content: Quote from: The Electrician on October 01, 2021, 11:38:58 pmYep, I was offered a good deal on one. That's the only reason.That post you linked to is well written and quite helpful. I have a portable VNA for antenna work (3GHz), but it only has one range; everything referenced to 50 Ohms, so any reading below 5 Ohms or above 500 Ohms becomes questionable, even after calibration. Still better than nothing. Makes you realise just how basic LCR meters are. The have more than one range though for better accuracy, so it's a trade off.Regards.

author: tpowell1830
author_rank: Frequent Contributor
timestamp: October 03, 2021, 06:35:06 pm
content: Quote from: killingtime on September 29, 2021, 06:51:44 pmThis fellow has excellent tutorials and this one is on measuring ESR and he is a forum member.

author: killingtime
author_rank: Regular Contributor
timestamp: October 04, 2021, 08:03:31 pm
content: Good video. Easy to follow explanation and method.Presumably, the 'step voltage' (square wave) method used will only work if the ESL (series inductance) is low enough not to distort the reading. This method relies onthe cap having almost no capacitive reactance on the edge of the square wave (larger caps better, faster wave edge better), leaving only R, and inductive reactance which will also be largest at the rising edge.Although the square wave frequency he's using is low (200KHz), the frequency on those wave edges will be a lot higher. Faster wave edges will have a greater effect on ESL.I guess you'd see any ESL on the Oscope trace though as a higher initial trace voltage, which reduces over time as inductive reactance fall away. I think I see that in the video. There are some very tall, narrow and faint spikes at the wave edges. Anyone else see that? Doesn't reduce the practicality of the method though so long as you know what to look out for.