VEGAS "Square-Wave" (Non)-Problem in the Data Manager


When looking at the output of the VEGAS data manager, occasionally the output will look like a fluctuating square-wave, as shown below:

Screenshot with DF saw.png

If your data manager looks like this, do not worry, things are likely fine.

This looks like the signal from the calibration source, but the frequency of the wave can be much longer than the desired frequency. In the example shown above, the switching frequency was less than 1s, though the observed wave is ~5~10s. Changing the switching frequency can change the frequency of the wave, and it have a larger envelope with which it follows (see right side of Bank A in the above figure).

Cause and Solution/Reason to Ignore

Do not fret! This may look bad, but it is a non-problem. The data manager is just checking the output from VEGAS at a slower frequency than VEGAS is switching, causing some aliasing. Let's say the data manager checks VEGAS every 0.65 seconds (it is often neither an easy or regular interval), and VEGAS is switching the cal between on and off every 0.3s. At first, the data manager reads when the calibrator is on. 1.3, 1.95, 2.6, 3.25, and 3.9 seconds later, the data manager still reads when the calibrator is on. The next data manager reading, at 4.55s, this trend then switches, and the data manager will read the VEGAS output only when the calibration is off, leading to a lower power reading, and the square-wave looking trend to the VEGAS data monitor power readings.
Topic revision: r1 - 2014-08-18, AdamKobelski
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