EveryCircuit - Measuring capacitance

9 years ago

C = Q * V or in words: " Capacitance equals Charge times Voltage". For Charge it's C : V = Q and for Voltage it's C : Q = V. If it helps you...

hurz

9 years ago

@Karsten, Q=C*U ; C capacitance in Farad ; U is voltage [V] (german) ; Q is electric charge Coulomb in [As]. But still the question how to measure. There are many ways to do. All depends on the C how big or small it is and what measure equipment you have available.

UncleRick

9 years ago

I would think you would start with a measurement of voltage or current, against time, OR, voltage & current, against time. That's just a guess.

ingandrestamayo

9 years ago

In a simple circuit you have a curve ( with a linear voltage supply), the curve is like a inverse logaritm. At the 63% of the full voltage in the curve you find the tao. The tao is the product of resistence and capavitance. If you have the tao and the resistance cou could find the cappacitance in faradios. This is part of the differential ecuations subjet.

hurz

9 years ago

But all these tips we have to assume the equipment and the math skills, right? Who can make an A to Z tutorial for all methods to measure and calculate capacitances? I'm to lazy over Xmas for that ;p

GingerKing

9 years ago

Depends on the accuracy needed sir. The easiest way (i think) is to send a sine wave through the mystery cap. Holding the frequency fixed at #### Hz and measuring the current through the cap will allow you to calculate the capacitance. (Assuming you known the voltage of sine wave) Equation is Z = 1/(jwc). --> Z = -j/(2*pi*f*c) and Z = V/I (ohms law)... ok i just arrived at the movies to see star wars. Ill finish this later. Maybe

NateDogg1232

9 years ago

I don't have the equipment (only 14, and broke), and I may have the math skills.

NateDogg1232

9 years ago

This was more of a seeking knowledge type thing.

hurz

9 years ago

GingerKing, yes but think about different types of caps in size and polarity (electrolyte ones and low AC freq plus DC offser to measure) and high freq for little ceramic cap in pF range were you need a scope or special voltmeter. And start with ckmplex math is also a little above most users here. All in all this is a very long/big tutorial from basics to smith charts.... Only my 2 cents

ingandrestamayo

9 years ago

How is the capacitance? A tube? A red ball? There are 3 numbers somewere? Becouse you can google the capacitance with this tree or four numbers in the case it have. Is very diffucult to know the capacitance withough a multimeter or an ociloscope

GingerKing

9 years ago

I made you a circuit that involves math and a stop watch. Its called "capacitance measurement". Have fun

hurz

9 years ago

Great, GK check my comment on that.

selman

9 years ago

Have anybody seen @hunar's cap measurement circuit

hurz

9 years ago

"Made In Kurdistan"? For my taste already to much implementation details which will overload EC capabilities. Think about a device to measure caps in a range of 1pF to 1mF. This can not be done with a single method. We should first do some theory and discuss which method to use to measure a complex impedance at what range of Z. Hunars circuit can then easily be implemented in a little arduino device much more useful then hundreds of shit gates and SSDs ;-)