What makes load resistor too high/low for impedance measurement? Also colors and background?

[jeffamm]

Hi guys, love this product, wish I had it when I was back getting my EE degree, couple of questions

I don't understand what activates the warning message for load resistor too high or too low?  I haven't found the guidance for what it should be - is it supposed to be some percentage of the expected impedance range?  Is it meant to be a current limit? 

I'm measuring a small RLC network and getting both "too high" and "too low" warnings at nearly the same frequency points (2-3 each) near resonance of the circuit.  That's with a 10k ohm load resistor and a network impedance that runs from 3k to 40k ohms from audio 20Hz to 20kHz.  The curve looks smooth so I've mostly been ignoring it, but If my measurement is off due to the load I'd like to fix it (but don't know what to do with conflicting warnings).  

If I just live with the warnings can I suppress the display of the warnings, so they're not visible when I take screen captures for my presentation?

Also, new topic - can I make the traces for Z, R and X different colors from each other?  I only see how to change the color in a way that changes all of them to still be the same.

2nd new topic - can I change the background of the display to be white instead of the dark grey.  I think I've seen some screen caps posted that were white but don't see how to change.

 

 

 

[attila]

Hi @jeffamm

The resistor too low/high warnings are shown where the relation between reference resistor and load impedance is at extremes, above 200 or below 1/200.
In this condition the measurement might be wrong or have too much error and suggest you to repeat the analysis with a lower or high reference resistor value.
The resistor too low or high is decided based on capacitive or inductive identification of the load, but this might be wrong guess at extreme relations.

[jeffamm]

Attila, thank you for your response.  I wanted to re-post with a couple of screen shots so you could see what I'm seeing.  I'm measuring an RLC network from 20Hz to 20kHz.  I did compensation open/closed on my setup first.   Both of the attached curves are of the same network.  The second plot below is what I ran first, with a 10k resistor, and my concern was for getting both too high and too low warnings at the same point, around the peak of the curve.  So I tried it with a 1k resistor and my measurements are very different, including the frequency of the peak.   If I understand your answer about 200 or 1/200th I think I'm well within that range since with a 10k load resistor I'm measuring from 7k to 50k ohms. But I'm a bit unsettled about whether I can consider these measurements to be accurate when the load resistor changes the results so significantly.   I'd appreciate any thoughts, tips, corrections etc.

thanks

Jeff

 

 

 

[attila]

Hi @jeffamm

Looking at it again, the resistor too low/high warning is shown when the input gain/attenuation is below 1/200 or above 200, or the absolute value of input phase is above 89deg or below 1deg. These you can see in input/decibel and phase / input phase views.
For your experiment the warning is probably due to phase warning. This warning is valid if you are looking at simple capacitive or inductive components where reactance should be much higher than resistance.
It looks like you are analyzing a more complex circuit, so you can ignore this warning.