Keyboard Shortcuts
ctrl + shift + ? :
Show all keyboard shortcuts
ctrl + g :
Navigate to a group
ctrl + shift + f :
Find
ctrl + / :
Quick actions
esc to dismiss
Likes
Search
OT: who has access to a professional capacimeter?
|
OT: who has access to a professional capacimeter? Sorry to be OT, I write here because 'more' likely we are professional electronics. Wonder if anyone can 'make me a great pleasure, I will send by mail a capacitor 100 / 1000uF him fit me with a capacimeter value professional and informs me by e-mail, no need to send it back. My problem: I am an electronic Hobbyist and economic use meters, but each one measuring capacitor shows me a very different value (also 20%). I homebuilt a capacimeter from 100.000uF and need a capacity 'of known value to calibrate it. I tried to measure a capacitor with a bridge RLC but the frequencies of 10-100-1000Hz shows me three completely different values. Someone and 'willing to do this to me please? I live in Italy, please contact me at my email: "bertolimarco2004 snail libero.it" Thanks in advance. Marco |
||
|
I almost always make a circuit
that somehow relate the signals back to the accuracy of a resistor. Use an 'active' circuit to win twice. A generator, KNOWN resistor [1%] KNOWN frequency(s), measure RELATIVE voltage readings: Vac1=input and Vac2=voltage across cap. Then make certain the multiple values you get make sense No Function Generator? Use your SoundCard. it is accurate. No scope? Use your SoundCard check whether Daqarta will work for you: Bob Masta DAQARTA v7.60 Data AcQuisition And Real-Time Analysis www.daqarta.com Scope, Spectrum, Spectrogram, Sound Level Meter Frequency Counter, Pitch Track, Pitch-to-MIDI FREE Signal Generator, DaqMusiq generator Science with your sound card! No need to 'buy' anything. Nor, end up trusting an instrument whose accuracy cannot be verified easily regards robert --- LTspice@... wrote: From: "zio_bapu@... [LTspice]" <LTspice@...> To: <LTspice@...> Subject: [LTspice] OT: who has access to a professional capacimeter? Date: 02 Aug 2015 02:22:21 -0700 OT: who has access to a professional capacimeter? Sorry to be OT, I write here because 'more' likely we are professional electronics. Wonder if anyone can 'make me a great pleasure, I will send by mail a capacitor 100 / 1000uF him fit me with a capacimeter value professional and informs me by e-mail, no need to send it back. My problem: I am an electronic Hobbyist and economic use meters, but each one measuring capacitor shows me a very different value (also 20%). I homebuilt a capacimeter from 100.000uF and need a capacity 'of known value to calibrate it. I tried to measure a capacitor with a bridge RLC but the frequencies of 10-100-1000Hz shows me three completely different values. Someone and 'willing to do this to me please? I live in Italy, please contact me at my email: "bertolimarco2004 snail libero.it" Thanks in advance. Marco |
||
|
Who needs professional accuracy? Most aluminium electrolytics have a tolerance on -50/+100% so your 100uf could be between 50uf and 200uf.
toggle quoted message
Show quoted text
For 90% of testing I have a cheap Arduino based tester like the one reviewed here:- I must say its magic. Stuff must anything in and you get a result. Sometimes it syas its broken, and usually it is. No good for caps over 100uf but I have other ways to measure them. Dave -----Original Message----- |
||
开云体育Le 02/08/2015 11:22, zio_bapu@...
[LTspice] a écrit?:
?That is not surprising because, indeed, capacitance varies with frequency. In addition, most capmeters are based on a basic impedance measurement and the simplistic assumption that the equivalent model of a real-world" capacitor is a perfect cap with a leakage resistance in parallels and a series resistance. Reality is much more complex, particularly with electrolytic caps. As someone else mentioned, there is no practical need for great accuracy in measurement of electrolytics, but I understand you want to calibrate your tester. I would say the most accurate method is measuring the discharge time. Let's say you have a nominal 10 000 uF cap discharging into 1kohm, the TC is 10 seconds. After 10s, the cap discharges a 37% of the initial value, after 20s, to 13.7%. This can be easily metered with an analog meter ( a DMM has too much latency). You can easily achieve better than 5% accuracy with this method.
|
||
|
It's hard to beat the little impedance meter boards on eBay for about $25 now. If ?you have a scope and signal generator, you can build a traditional bridge circuit with just a few parts. The reference will be a small close tolerance film cap that should be easy to find. There's a plan for a simple but accurate bridge here-
and lots more cap fundamental stuff here-? Aluminum electrolytic caps show various odd effects with frequency, but at any single frequency the simple series or parallel models work OK. The standard frequency for measurement is usually 120 Hz, where losses will be low. At 1 kHz or more, you'll see losses increase greatly and Cp will serve you better than Cs. ? |
||
|
-------------------------------------------- On Sun, 8/2/15, zio_bapu@... [LTspice] <LTspice@...> wrote: Subject: [LTspice] OT: who has access to a professional capacimeter? To: LTspice@... Date: Sunday, August 2, 2015, 3:22 AM OT: who has access to a professional capacimeter? Sorry to be OT, I write here because 'more' likely we are professional electronics. Wonder if anyone can 'make me a great pleasure, I will send by mail a capacitor 100 / 1000uF him fit me with a capacimeter value professional and informs me by e-mail, no need to send it back. >
I have a Quadtech 1659 RLC Digibridge & would be happy to test it. But I think postage for you would be expensive. Alternately you could do it with a scope: Jim |
||
|
Making electronic hobby and not for work buy multimeters made in china, one of them was pointing a capacitance value 'halved, I open it and find that the Chinese guy had forgotten to calibrate it. Same with an Inductance meter. Maybe I'm not lucky! Other multimeters display values all different, even 20%. I wonder: Is there 'be trusted to buy those capacitance meters? |
||
|
John Woodgate
In message <mpo32e+16aibk2@...>, dated Mon, 3 Aug 2015, "zio_bapu@... [LTspice]" <LTspice@...> writes:
I wonder: Is there 'be trusted to buy those capacitance meters?Not from where you have bought them. Don't buy a meter. Use one of the methods for measuring capacitance you have already been given in this thread. -- OOO - Own Opinions Only. With best wishes. See www.jmwa.demon.co.uk When I turn my back on the sun, it's to look for a rainbow John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK |
||
开云体育Le 03/08/2015 17:58, zio_bapu@...
[LTspice] a écrit?:
?This has already been answered. When the real capacitor is close enough to the basic "one C- two R" model, they generally can be trusted, although different measurement frequencies are likely to give slightly different values. As for electrolytics, they cannot be trusted to give an accurate value, because such a concept does not exist; as I mentioned earlier, their capacitance varies with frequency, but also electrolytic show significant DA (dielectric absorption), a non linear phenomenon that makes the apparent capacitance change over time. In addition, capacitance decreases with time, but some regeneration can happen, and it also varies significantly with temperature. These issues are known from the beginning, that's why electrolytics are not to be used in applications where their value is critical, as in filters (although many cheap loudspeaker manufactures use NP lytics in their passive x-overs). From their inception, designers have commonly used a factor 10.
|
||
|
John Lawvere
I'm skeptical of black-box capacitance meters. Connect a square-wave source, resistor, and capacitor in series, with grounded end of source? and one end of cap in common, and watch charging/discharging of cap voltage?with an oscilloscope. Measure half-life of exponential decay, calculate time constant, and solve?for capacitance. Remember that total resistance is sum of resistor you put in circuit plus generator resistance of square wave source. If you plan to do this a lot--especially with small caps--you should do some "calibration" runs with several accurately known small caps: find capacitance of o'scope probe. On Monday, August 3, 2015 9:39 AM, "Jerry Lee Marcel jerryleemarcel@... [LTspice]" wrote:
?
Le 03/08/2015 17:58, zio_bapu@...
[LTspice] a écrit?:
?This has already been answered. When the real capacitor is close enough to the basic "one C- two R" model, they generally can be trusted, although different measurement frequencies are likely to give slightly different values. As for electrolytics, they cannot be trusted to give an accurate value, because such a concept does not exist; as I mentioned earlier, their capacitance varies with frequency, but also electrolytic show significant DA (dielectric absorption), a non linear phenomenon that makes the apparent capacitance change over time. In addition, capacitance decreases with time, but some regeneration can happen, and it also varies significantly with temperature. These issues are known from the beginning, that's why electrolytics are not to be used in applications where their value is critical, as in filters (although many cheap loudspeaker manufactures use NP lytics in their passive x-overs). From their inception, designers have commonly used a factor 10.
|
||
to navigate to use esc to dismiss