How do digital mulitimeters (DMM) measure capacitance through their typical 10M Ohm input/output impedance? Providing a logic level of 3.3V, attempting to measure 1F would mean a time constant of...
Measure 100pF, or 1 nF, with and without your small cap in parallel. If the meter still offers poor resolution when measuring higher capacitance, build a small RC oscillator round an HC14, and measure the frequency with your oscilliscope.
This circuit doesn't give you absolute capacitance values, but if you need that, you can do a calibration step to compute a lookup table that maps counter/timer values to capacitance. To increase the dynamic range of measurements, you can do autoranging using the circuit on the right hand side.
I have built a circuit to measure a capacitor's capacitance using the τ = R·C formula (see schematic below). simulate this circuit – Schematic created using CircuitLab When I open the switch ...
Why would you want to measure capacitance to determine if a capacitor is broken? It might be a bit old-fashioned, but it's easier to determine by looking at the voltage with an oscilloscope. However, to make a point germane to your question: look up the differences between resistance and reactance.
3 Another answer, given that you have a frequency counter, would be to build an oscillator using the 555 timer, and measure the frequency. Switch in a few standard resistors (1k, 10k, 100k etc) and check with a known capacitor how close the "frequency calculation" formula is to reality.
5 simulate this circuit – Schematic created using CircuitLab I'm trying to determine the capacitance of a sensor, but the oscilloscope's internal capacitance is loading the measurement too much. What is an appropriate method to determine a low picofarad capacitance using an o'scope in this situation? (o'scope internal capacitance is 24pF).
Am I calculating total input capacitance or gate capacitance or none of the above? And are my calculations even correct to begin with. The point of this is that I want to know what gate capacitance...
To add to this answer, the way capacitance meters measure capacitance is by applying a small (generally 30 mV peak) AC voltage and measuring the resulting current. This gives you an impedance, and that's then converted to capacitance that's displayed on the screen. Good LCR meters will also separate out the reactive and resistive components of the impedance to give you the ESR as well; simple ...
