I am confused about measuring capacitance - Page 1
Forum section: electronics / beginners

author: nangalakula
author_rank: Contributor
timestamp: April 30, 2025, 11:50:24 pm
content: I am confused about measuring capacitance.E.g. if I measure a ~ 30pF one. My component tester (DSO-TC4) shows 27 pF. Which looks the correct value.My multimeter (2C53P) shows first 5-6 pF and after a while, I've just realized... if I move my wireless mouse or I use my wireless keyboard maybe after a minute it goes up to ~13 pF.My other meter (peaktech 2030) shows 40 pF with just the meter probe connected. And abot 110 pF when the 30 pF capacitor is connected.So first the multimeter shows a much lower value, second its shown value fluctuates a lot depending what is going on near the place of the measurement.

author: u666sa
author_rank: Frequent Contributor
timestamp: April 30, 2025, 11:55:24 pm
content: TC4 measures using DC. Plus you don't have an LCR meter. Measuring capacitance gives you nothing since you don't know ESR. You could measure a critical cap and the cap meter will show you proper value, and you'd think everything is fine, but in reality that cap could be bad, and that bad cap could be your problem.Get an LCR meter. Hantek 1833C for big caps and Nano VNA H4 for tiny caps. There other alternatives. But these two will be the best money you ever spend in terms of return on the stuff you fix with them.

author: ledtester
author_rank: Super Contributor
timestamp: May 01, 2025, 01:56:40 am
content: Quote from: nangalakula on April 30, 2025, 11:50:24 pmIt's hard to accurately measure such a low capacitance. You'll have better luck in the nanofarad and above range.QuoteYour Peaktech has a "REL" button which you can use to account for stray capacitance.Then again, according to this page:https://peaktech-rce.com/en/digital-multimeters/650-peaktech-2030-digital-multimeter-6000-counts-bar-graph-1000v-true-rms.htmlthe lowest range is 60 nF. This means it will only give you back a capacitance value in multiples of 10pF. Also the +/- 20 digit possible error means there could be up to 200pF error in the reading.Again - it's hard for this meter (and most meters) to measure such a low capacitance.

author: Haenk
author_rank: Super Contributor
timestamp: May 01, 2025, 06:40:42 am
content: And remember: Even your test leads will add a couple (maybe even tens) of pF - likely does not matter when measuring nF or uF, but with very small capacities, that's a huge error margin.For accurate measurements, a good LCR meter is required, though the exact value of these small caps might only matter in RF/HF applications anyway, so maybe "any value" is good enough and you don't need to measure...

author: coromonadalix
author_rank: Super Contributor
timestamp: May 01, 2025, 06:27:17 pm
content: and to add ... you may or would need a good test fixtureone who can hold smd's or the ones you slide the part in ... as written, leads can create problems, they add resistance or inductance or capacitance effects or a mix of all, human presence or anything else who can induce errorsyes lcr's with the possibility of nulling out the error with a REL functionbench or handheld meters are not precise (up to a certain extent) the computed values are mostly charge with time related results, but an dedicated lcr is the right path, esr dcr many test frequencies, inductances etc ...all component testers have limited precision, and the parts they use are maybe 1% precision ...

author: nangalakula
author_rank: Contributor
timestamp: May 01, 2025, 06:34:14 pm
content: Thanks a lot guys.This "REL" really made it. I missed I have such. Now the peaktech shows totally reasonable values.10 pF -> using the "REL" shows .01 nF1 nF -> 1 nF100 nF -> 99.6 nFI have an LCR meter. I've just ordered one which had a reasonable price (for me), ET4410. I tried it out and shows good values even for these small ones. But well... I think some more learning is in front of me before I really understand what I see on the LCR meter. So I want to first understand these simpler meters.I've checked how to read the values written on the capacitor. And on my 10 pF, I have written 10 and a small circle on the bottom of the numbers. I understand that if two numbers are written then it is the pF value. So om my 10 pF 10 means 10 pF. But I haven't found what this small circle means. Please can you help, what does this small circle mean?

author: ledtester
author_rank: Super Contributor
timestamp: May 01, 2025, 10:10:00 pm
content: The final zero could be part of a 3-digit capacitor code.See this page:https://www.wikihow.com/Read-a-Capacitorunder "Reading Compact Capacitor Codes".So "100" means 10x10^0 = 10x1 = 10pf.

author: veedub565
author_rank: Frequent Contributor
timestamp: May 03, 2025, 10:26:58 am
content: Quote from: u666sa on April 30, 2025, 11:55:24 pmI bought an ESR meter for this very reason.https://www.peakelec.co.uk/acatalog/esr70-capacitor-esr-meter.html

author: MrAl
author_rank: Super Contributor
timestamp: May 03, 2025, 12:54:24 pm
content: Quote from: nangalakula on April 30, 2025, 11:50:24 pmHi,Unfortunately, some things you cannot measure very well unless they are combined with the actual application they were intended to be used with.Power inductors are the most notorious. They have various specs and you won't get a good idea what they can do unless you hook them up in the application that you are going to use them in. Then you can measure some values and see if everything adds up to the value of the inductor you assumed it had. An example would be a buck or boost circuit.With capacitors, it's kind of the same thing although some are more lenient than others. The key point is to put them into the actual application, and even on the actual PC board they were intended to be used with. Then measure the frequency or the voltage or whatever you need to and then calculate back to the capacitor value. If the capacitor value, in that circuit, is what you thought it was then you are good to go. For example, an oscillator circuit. If you use a capacitor to generate a frequency, then that frequency should reflect that capacitor value according to the analysis of the circuit and any parasitic components. If it is different, then you have to investigate and determine if the cap is the wrong value or something else is wrong.There could be tests that you develop to test certain caps that will be known to reflect how they work in a given circuit. You would establish that test by using the cap in the circuit, then test using a test jig, then correlate the results. If you did everything right, the values you measure in the test circuit will tell you if the component will work in the actual application circuit.We always have to remember that for a lot of tests we are always working with the lumped circuit element model. That's a sort of simplified model, and also with some parasitic components.