Change in Impedance measurement calculation ?

[trobbins]

Hi John, I am running V5.40 Beta 42, and was just doing some impedance sweeps and noticed an approx 4.4x inaccuracy for C and L calculated levels (both L and C are ~4.4x lower in value) for a variety of my metrology standards. It's been nearly three years since I last used REW's impedance tool for measuring some metrology standards, and the calculated part values/impedances back then were accurate. I cross-checked past saved mdat files (that used 5.20.5) by running them on present V5.40 and the past mdat file calculates as the correct value when run on V5.40. I confirmed the resistance standards were accurate, and the reference R used for calibration gave a repeated accurate measurement. I repeated the calibration procedure and measured the same results for resistance accuracy and capacitance inaccuracy. I am using the same impedance jig and soundcard and connection setup. I can post an old and new mdat for an example same reference cap if that is of assistance.
Ciao, Tim

 

[John Mulcahy]

I just checked my reference components (R, L, C) with the current beta 66 and all measure normally, no change.

 

[trobbins]

Thanks for checking - much appreciated.

I'm still a bit flummoxed. I updated to beta 66. Rebooted soundcard. Repeated calibrations (I get 100.5 ohm for O/C, which help indicates is as expected; I get 30mohm for S/C; I get 10R for reference as expected, and phase responses out to 96kHz all typical). Swapped inputs. Then swapped PC's and all was nominal on other PC. So back to original laptop and played around more. Measurement came good when I changed sample rate from 192 to 96k. Went back to 192k rate and measurement was still good. So something quirky perhaps with my asio or soundcard or subtle settings for those, so I will do some more cross-checks. Obviously my end and I should have done some more cross-checking first - doh.