Now that I have a programmable psu, dc load, oscilloscope and multimeter, it's time to build a flexible test bed. It's main purpose is to specify efficiency of switch mode regulators. But with some tweeking itcan also be used to measure ripple of a power supply under load. It's going to be a flow that can step through voltages, then sweeps the load over a range,makes measurements and log them to a spreadsheet.
The flow will be able to loop this process once, or continuous until the STOP button is pressed. Scope and DMM are optional. If you uncheck the Active box, they aren't used in the flow. You may notice that it looks similar to previous LabVIEW flows I blogged about. It is. But while those were for a single purpose, I'm trying to keep this one as generic and versatile as I can manage. |
The flow uses the instruments I have i the lab: a Rigol DM832A psu and DS1054Z oscilloscope. Keithley DMM6500 and home grown dc load.
Because the psu and load use fairly standard SCPI commands, they can be easily switched out for another brand / make.
The oscilloscope and DMM have setup that's more specific. But because they are optional in the flow, you could leave them inactive and add your own measurement commands.
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The Control Part
The blocks in read control the process. You can set begin and step values for supply and load.
When you execute the process, it will start from the start psu and load setting.
It will then run over the load ramp, and when finished, increase the voltage.
On and on until the number of steps are executed.
If you uncheck Single Run, it will restart the whole process from the initial sessions until you STOP it.
During the execution, the active settings are displayed and updated while the loop is running.
The Measure Part
Here you can set the parameters of scope and DMM. These blocks also show the measurements at runtime.
The oscilloscope one can obviously use more parameterising. It runs on a fixed channel with predefined range.
Time will tell what I want to make flexible.
The DMM has some more options, mainly related to filtering and ranging.
Behind the Scenes
The measurements are logged to a spreadsheet. There are more values writtenthan shown on the display.
The psu and dc load measurements are also logged.
The LabVIEW project is attached to the blog.
The attached pdf has a readable version. Here's the decent sized DMM6500 initialisation block (klick to enlarge):
 | labviewflow.pdf |
