Resistance on my Extech 380193 LCR meter - Page 1
Forum section: electronics / testgear

author: Dan Moos
author_rank: Frequent Contributor
timestamp: June 17, 2023, 11:06:36 pm
content: Since I don't believe this meter measures ESR, when I'm measuring a reactive component and have 'R' as my secondary meaurement, exactly what resistance am I reading?Also, this meter only has 1k and 120 Hz freq settings. To me, that seems like quite a limitation. 1 k seems awful low to me. Is this reason enough to find a better one? My interests run the gamut of the hobby, including wanting to dabble in RF.

author: Martin72
author_rank: Super Contributor
timestamp: June 17, 2023, 11:17:24 pm
content: Hi,120Hz(one way rectified mains frequency) is more for the "high" value capacitors/inductors, 1khz is a very common testfrequency, but will be too low when you want to determine components for RF use.A meter up to 100khz or more should be suitable.The higher the testfrequency, the more expensive the meter will be.Edit:QuoteYou could check it in this way:Displayed Capacitor value, when you use the formular for XC = 1/2*pi*f*capacity and the result is more or less similar to the displayed resistance, then it´s not the ESR.

author: Dan Moos
author_rank: Frequent Contributor
timestamp: June 18, 2023, 12:42:17 am
content: QuoteSo you are suggesting its reading the XC at the freq I'm set for? The numbers don't work for that.

author: srb1954
author_rank: Super Contributor
timestamp: June 18, 2023, 12:46:34 am
content: Quote from: Dan Moos on June 17, 2023, 11:06:36 pmIt does measure ESR of the component under test when set to the SER mode.You can do a simple experiment:Measure an electrolytic capacitor and note the C and R measurements. R is the ESR of the capacitor. Add another 1resistor in series with the capacitor and you should note that the resistance reading has increased by 1indicating that the ESR has increased because of the additional series resistor.On the 1kHz frequency setting this meter has a resolution of 0.1pF and 0.1uH so it is suitable for most component measurement applications. Where it is not suitable is for measuring the D or Q of RF components at somewhere near their normal operating frequency. As the losses in most components increase with frequency the D and Q readings at 1kHz will not accurately represent the actual losses seen in real operation. For improved accuracy of D and Q readings at higher frequencies you will need a RF bridge, which is considerably more expensive than the average hand-held LCR meter. Or you could use a VNA with a component test fixture.

author: Dan Moos
author_rank: Frequent Contributor
timestamp: June 18, 2023, 02:24:11 am
content: QuoteI just tried what you said, but with a 150p ceramic and a 1k resistor. Meter set for capacitance, series, 1 Khz R in the secondary measurement spot. The resistance did jump by 1k. But at 120 hz, the R value went up over 10 times. Is ESR that freq dependent?

author: TimFox
author_rank: Super Contributor
timestamp: June 18, 2023, 03:00:25 am
content: For a 150 pF C0G ceramic capacitor,Q=Xseries/Rseriesof the capacitor may not change much with frequency.However, the reactanceXscales as 1/f.By simple algebra, the series resistance should go up by about 8x from 1000 Hz down to 120 Hz.

author: srb1954
author_rank: Super Contributor
timestamp: June 18, 2023, 04:36:32 am
content: Quote from: Dan Moos on June 18, 2023, 02:24:11 amYour measurements might be pushing the meter beyond its accuracy capabilities. At 120Hz a 150pF capacitor has an 8.8Mreactance so adding an extra 1kresistor in series with that is hardly going to make any difference in the total impedance. The LCR meter may not have the internal maths resolution to discern such a small change accurately.Normally for small value capacitors you would use the PAR mode and determine the losses from the D (dissipation factor) measurement. ESR measurements are generally more commonly used for lower impedance measurements such as found with larger or electrolytic capacitors.

author: TimFox
author_rank: Super Contributor
timestamp: June 18, 2023, 01:35:18 pm
content: Also, I have found over many years, using a wide range of instruments, that it is difficult (not totally impossible) to measureQ> 1000 (D< 10-3= 0.1%) accurately.

author: mawyatt
author_rank: Super Contributor
timestamp: June 18, 2023, 03:25:33 pm
content: If one looks at how Q is measured (actually computed, not directly measured), in most quality modern bench type LCR meters, it's no surprise that high Q values are questionable.The mentioned LCR measurement usually involves some form of "synchronous sampling" to reduce the effects of noise and unwanted signals, also with some averaging, and utilize high resolution accurate ADCs (even the handheld DER-5000 has a equivalent 4.5 digit ADC, the TH2830 and IM3536 have 5.5~6.5 digit eqv. ADCs). The actual measurement is from the voltage and current of the DUT, where the current is deduced from a ~ virtual ground port Lcur, and sensed by Lpot, which scales and computes the DUT impedance with Hcur and Hpot values.With Q the absolute value of Tan of the DUT Impedance Z angle, and the sensitivity of Q can be accessed as the derivative of Q wrt the DUT Impedance angle or dQ/dtheta = 1/[Cos^2(angle)], and the Cos function is most sensitive (slope) to the angle at +-90 degrees, and it's squaredThen a Q of 1000 results in an angle of 89.9427 degrees, and a measurement/computational error of 0.1% results in a Q assessment of ~390 (sensitivity of 10^6), not 1000, and a simple linear error assessment would assume a Q of 999 or 1001, not 390!Using this same conditions a Q of 100 would result in an angle of 89.42706 degrees, and a 0.1% error would be a Q of ~86.5 (little better, sensitivity of 10^4), and a Q of 10 would have an angle of 84.28941 degrees and with a 0.1% error a Q of ~9.854 (much better, sensitivity of 10^2).This is why we don't use "Q" much to define or represent a single component, but for filter use seems to be a much better parameter as theBW/FcFc/BW.Anyway, as we older "seasoned" folks have learned, "Know Thy Instrument", or "THI" for quality, reliable, and repeatable measurementsBest,