On 15 March 2011 16:28, Harold Hallikainen wrote: > Instead of trying to measure the current, I wonder if you can measure the > differential voltage using a couple scope probes. That seems a lot easier > than trying to measure the current. Then calculate the drive power based > on the ESR of the crystal. Do they give a typical and minimum ESR? Do the= y > maybe even give a maximum recommended differential voltage across the > crystal? > > Harold > > > > > -- Thanks for the input. Yes, I do have typical and max ESR values (1k4 and 3k5) for the crystal but have had difficulty in the past getting correlation between differential voltage measurements and the recommended current probe measurements. The ESR resistance is in series with the reactive components of the crystal and so there is a significant phase shift. It might work if I had an equivalent parallel resistance value but I don't, and the crystal equivalent circuit lumped component values are not readily available either. Also the drive voltage is close to a square wave while the output voltage is nearly sinewave so I'm not sure a direct rms difference (or rms conversion of the difference) is appropriate. And the output node is quite high impedance so is sensitive to any loading at all. The various manufacturer app notes etc always use either a current probe or a series resistance to derive crystal current but I'm not having too much luck this time. Thanks, Richard Prosser --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .