I need help from peopple understanding better these things. So, I would like to measure for example the capacitance of some capacitor. How should I do that? How about tolerance, is it even possible? What about resistors, how to measure the resistance and tolerance?
Thank you in advance for helping me stupid..
-Kimmo-
Thank you in advance for helping me stupid..
-Kimmo-
You can measure larger value caps with a 12.6V or 6.3V filament transformer, an AC voltmeter, and a 50k potentiometer. Put the R and C in series with the secondary and apply mains voltage to the transformer primary. Adjust the pot until the voltage drops across the R and C are equal. Disconnect and measure the resistance of the pot. Then C = 0.159/f*R, where C is the capacitance, f is the line frequency, and R is the measured resistance of the pot. A capacitance meter is much easier, especially for smaller value caps. Every multimeter will measure resistance.
Tolerance isn't really measured because it is a range. It is the amount that the component will vary from the specified value, ie a 5% tolerance 100 ohm resistor should measure between 95 ohms and 105 ohms.
Tolerance isn't really measured because it is a range. It is the amount that the component will vary from the specified value, ie a 5% tolerance 100 ohm resistor should measure between 95 ohms and 105 ohms.
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Another thread here took me to Conrad's page for a capacitance bridge. This is an expansion of my procedure above, and provides for a wider range and more accurate measurement.
You can also do this much simpler with a soundcard, a dead pair of headphones (for the cord, plug it into your PC speaker out), a fixed resistor (8-10 ohms) and a multimeter.
hook the resistor and capacitor in series on one channel and do as sofaspud recommends. Vary frequency using a tone generator program until the voltage drop is the same and calculate C.
Tolerance in percent is simply 100 x (M-V)/V
M=measured value
V=specified value
Even then, the measurement is thrown off by wiring resistance and ESR. For values that large, a time constant method would be better.
Hello,
OK, but let's make a try.
10,000µF at 100Hz is 0.16Ω.
So, you will need a very low resistor and a power amplifier to make this measurement.
Not, that easy :
In that case you put a 1000R in series and time how long it takes to charge to 63% of supplied voltage from initial 0V.
t = R * C
Seconds, Ohms, Farads
The best way to measure capacitance for run of the mill DIY is to buy a DVM which includes some capacitance ranges. These only cost a little more than a basic DVM.
'Tolerance' is not a component parameter, but a batch parameter. You can't measure it. The best you can do is check whether a batch is consistent with the stated tolerance. For example, if you measured 100 resistors and they were all within 0.5% of nominal they could be 0.5% resistors or a lucky sample from 1% resistors or out-of-spec samples from 0.1% tolerance.
'Tolerance' is not a component parameter, but a batch parameter. You can't measure it. The best you can do is check whether a batch is consistent with the stated tolerance. For example, if you measured 100 resistors and they were all within 0.5% of nominal they could be 0.5% resistors or a lucky sample from 1% resistors or out-of-spec samples from 0.1% tolerance.
+1 on this method. Here is a little more detail.
I used this recently on some larger power supply caps. Works like a charm. I have a power supply that I can set to constant current operation, so I used that instead of a resistor. Just make sure that the time constant you are trying to look for is at least 20 seconds long so that you can record it accurately.
You set up the charging circuit and connect a DVM across the cap. At the same time that you apply DC power you start the count-up timer. When the voltage reading reaches 63% of the supply voltage, you stop the timer or record the elapsed time. The voltage will continue to rise, so you have to keep an eye on the DVM, which may only be updating every 0.5 seconds. Since you know R and t you can easily calculate C.
-Charlie
With constant current you need to use the following formula:
C = i * dt / dV
Farads
Amperes
Seconds
Volts
( d is delta )
example:
A 1A current will change the Voltage on a 1 Farad cap by 1 Volt in 1 second. (definition of 1 Farad)
I picked up an LCR meter for £25 at Farnell UK | Electronic Components | Electronic Parts
It wasn't terribly good at measuring small inductances but at least give an idea of the LCR value.
I recently got into semiconductor analysers and bought a couple and have found them invaluable.
It wasn't terribly good at measuring small inductances but at least give an idea of the LCR value.
I recently got into semiconductor analysers and bought a couple and have found them invaluable.
For small values there is this pretty nice PIC-based little measurement tool that is sold on Ebay. There was a thread about it here about a half year ago or so:
http://www.diyaudio.com/forums/equipment-tools/224329-another-ebay-gadget.html
This seems to be pretty accurate and is definitely affordable.
Small capacitance values can be measured on basic multimeter operating as a microammeter with a simple multimeter adapter: this one will give ~1µA/pF, and the scale factor can easily be modified.
If a function generator is used as a squarewave source, the circuit simplifies to two diodes and one cap
If a function generator is used as a squarewave source, the circuit simplifies to two diodes and one cap
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