Here are a couple of sites you might find interesting: http://www.cliftonlaboratories.com/Documents/Crystal%20Motional%20Parameter= s.pdf covers measuring motional parameters http://www.oscilent.com/spec_pages/PNDescrpt/ESR_Mode.htm covers calculating ESR from the motional parameters. It seems to me that if the question is overdriving the crystals, you=20 would want to know the minimum ESR, in order to calculate max voltage. =20 At 1.4K, max voltage is a paltry 37mV. Is your circuit operating at=20 that low of a voltage? Kerry Richard Prosser wrote: > On 15 March 2011 16:28, Harold Hallikainen wrote= : > =20 >> Instead of trying to measure the current, I wonder if you can measure th= e >> differential voltage using a couple scope probes. That seems a lot easie= r >> 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 th= ey >> maybe even give a maximum recommended differential voltage across the >> crystal? >> >> Harold >> >> >> >> >> -- >> =20 > 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 =20 --=20 Internal Virus Database is out-of-date. Checked by AVG Anti-Virus. Version: 7.0.289 / Virus Database: 267.11.13 - Release Date: 10/6/05 --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .