PCSGU250 Bode plotter for closed loop gain measurement

I’ve been attempting to use the PCSGU250 to measure the closed loop response of a 24V output switch mode power supply. I’m attempting to use a method similar to what is discused here: http://www.maxim-ic.com/app-notes/index.mvp/id/3245 So far the measurements look erronious. The phase data is very noisy and while the bode plotter is running the display I see on the scope screen is noisy. I suspect that noise might be influencing the measurments.

In on older topic on the discusion board http://forum.velleman.eu/viewtopic.php?f=11&t=3215&hilit=bode+average it looks like an averaging feature was added to the PCGU1000/PCSU1000. Is there a similar feature available for the PCSGU250?

Indeed, if there is a lot of noise in teh signals it can affect the Bode plotter test results. The analyzer measures the total RMS output of the device under test as the output response. Also the phase measurement has difficulties to define the phase between the signals.

Averaging may help a little.

The averaging option for the Bode plotter is now added to the PCLab2000LT version 1.11.
Here is the link to download the setup program:
velleman.eu/downloads/files/ … _setup.zip

For averaging you need the triggering to set on.
You may use either the input CH1 or CH2 as the triggering source.
In the oscilloscope Options -> Average menu select the number of acquisitions to average.
In the Bode plotter select Options -> Wait Time to select the proper time for the trace to stabilize after each frequency step.
In the Bode Plotter select Options -> Allow Averaging.

Also you may select in the oscilloscope Options -> Trigger Options -> Noise Reject.