The basic idea is that the sound card outputs a sine wave (about 1 kHz default) that drives a voltage divider made of a known reference resistor (say, 1k) in series with the DUT. The sound card stereo inputs monitor the voltage at the top of the resistor, and the top of the DUT. The (complex) voltage across the resistor allows the determination of the current, which also flows through the DUT, so the complex impedance of the DUT can be found via Ohm's law.

To calibrate, you only need to know the value of the resistor (read if from a good DMM), then there are 3 buttons you click on one by one:

1) Resistor shorted, no DUT2) Resistor present, no DUT

3) DUT shorted.That allows the macro to determine the sound card input impedance, which is otherwise in parallel with the DUT, and compensate for that in subsequent operation. With a 1k reference, and a typical sound card impedance of 15k, this allows reading DUT resistance above 1 Meg.

The big (resizeable) meter shows R (ESR) and X by default, labelled with proper units (Ohms, K, M, pF, nF, uF, uH, mH, H). You can change one line in the macro to include DF (or Q for inductors) as well. One button saves a reading to a log file; another saves notes/comments.

Regarding the original question about typical ESR values, I was puzzled for a long time about the fact that ESR was always inversely proportional to C, such that a 47 pF cap might show an ESR over 500k.

Turns out that the basic impedance measurement doesn't distinguish between series and parallel connections of the real and complex impedance components, so you have to help it out by toggling a "Series" button to "Parallel" based on your judgement. Typically, this turns out to be pretty simple: Use the default Series for electrolytics, and use Parallel for 1 uF and below. That 47 pF cap reading then shows a parallell (leakage) resistance well over a Megohm.

Full write-up from the Help system is at , including a screen shot, photo of a simple test fixture, and circuit diagrams.

Best regards,

Bob Masta DAQARTA v7.60 Data AcQuisition And Real-Time Analysis