Build Your Own Total System Power Analyzer

Overall Score

The advantage of taking an off the shelf DAQ system, such as the LabJack U3HV, and employing it in this project is the ease of collecting and saving the data. The U3HV ships with a fairly powerful data acquisition software package, while the software has nowhere near the flexibility and utility of the industry standard (LabView), it provides all the needed functionality required for this project.

The software provides for both streamed (hardward time acquisition) and software polling. In software polling mode, data can be collected at roughly 100 Hz across all 8 channels, in stream mode data can be acquired as fast as 6000 Hz per channel (or a total of 48 KHz sampling rate). Sampling rate determines the time resolution of the system, and the higher the sampling rate the more detailed structure one can observe in the time evolved signal. For this project we stick to the software polling methodology since that will give plenty of data; however, interesting behavior can also be found by sampling faster, and when the need arises these methods can and will be used.

DAQ Factory Express not only serves to collect the data from the LabJack U3HV, but also has a substantially robust scripting language. As such, the raw output from the sensors in volts can be convered via the calibration data to actual amps, and knowing voltage, directly to power. Furthermore, DAQ Factory Express allows for user defined graphs and output variables which can be programmed to produce a nice utility for the entire build. A screen capture of the channel configuration, main output screen and the calibration/configuration screens are shown below.

For most of the data collection, the polling frequency was actually set to 100 Hz, and 5 samples averaged to produce a single point yielding an effective sampling rate of approximately 20 Hz. Simple boxcar averaging is akin to a high pass filter, unfortunately higher frequency signal is rejected (be it actual noise or true signal). Again, as various situations warrant these sampling and averaging methods, it can be configured as needed to extract the useful information when desired.

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