REW Beta Release Impedance Measurement 5.2 beta34

[Alexander Nowak]

Hi,

playing around with the impedance measurement i found out that's a good advice to RTFM. But that's the smaller part.

after trying to calculate the TSPs of a chassi, i think that REW is showing the impedance graph round about 3 Ohm too high.
Try to measure the Rleads results in a line at about 3 Ohms. The R-DC, which is calculated by REW in the TSP calculation tool, ist about 3 Ohms under the shown graph. when i try to put in the value picked out of the graph, REW tells me, that the DC resistance value is greater than the minimum Impedance. The given maximum value is the correct DC resistance of the chassi. But it is 3 Ohms under the shown minimum impedance.
Measuring resistors between 10 and 100 Ohms results in the ('correct value'+3Ohms).

I hope, you understand, what I try to describe.

Am I doing a mistake during my measurements, or is there a bug?

I tried to find a thread like this, but I did not found one. I hope you can help me.

Alex

 

[John Mulcahy]

Impedance measurements with beta 34 are working fine for me, so probably some issue with your setup. What sense resistor value are you using? If the input channels are swapped the results tend to have the sense resistor value added to them (e.g. for a 100R sense resistor everything reads 100R too high). What was the result of the impedance calibration?

 

[Alexander Nowak]

Thank you for your ideas.

Impedance calibration is fine. When I change one input gain it ends with an error.
I am using a resistor of 100 Ohm (98,2 Ohms, 17W) and the correct value is put into REW for R-sense. R-input is 10kOhms and it is given too.
It seems to be an offset of the measurement and i can't change it. Even if I take out the measurement input, so that there is no Signal and the calculation should be round about 0 Ohms, I get a straight line at 3 Ohms -_-. Even if I measure a 1 Ohm resistor I got a straight line at 4 Ohms.

For the 3 Ohm issue it also doesn't matter if I am using an external amplifier or the headphone output of the Audio Interface.
I do not think that there is an problem with my audio interface, but I am using a Persons Studio 26. At the moment i have no other interface at hand.

 

[Alexander Nowak]

I don't know what to say.... yesterday I rebooted the mac about 3 times and nothing changes...today in the morning, I updated it and rebooted again. ... Long story short: I don't know why, but it seems to work and i did not change anything on the setup. Maybe i'll font out what was wrong.

 

[John Mulcahy]

Quite strange. The lead resistance value is subtracted from all measurement results, so in theory a negative lead resistance value could cause that but the REW control only allows zero or positive values to be entered.