Overcurrent control VI for Xantrex XHR 300-3.5 DC Power Supply

[disbecknell]

I'm attempting to use LabVIEW 8.0 to control a Xantrex XHR 300-3.5 DC Power Supply for an electrochemistry experiment.  I wish to write a VI program that allows me to set a desired voltage and max allowable current.  What I have in mind is a while loop that compares the measured output current with the max allowable current that the user sets, and if the measured current is less than max allowable the program will step up the voltage by some increment until the desired output voltage is reached.  I'm having trouble deciding how I will implement this program.  The Xantrex power supply driver comes with all the necessary tools, I believe, such as a set voltage and set max current VI, I just need help or advice on how I should wire them together.  Any ideas are appreciated, questions if something is still unclear.

Thanks
-Andrew

[Adam W]

Hi Andrew,

Just to confirm, are you able to communicate succesfully with your instrument?  As far as the VI set you are using goes, is it an instrument driver?  Does it come with any example VIs?  That might be a good place to start.  Oftentimes there will be examples that use the other instrument VIs that are a good reference for building your own code.  As for comparisons inside the while loop, you could use shift registers and a case structure to implement what you are trying to do.  Take the current iteration's current value, compare it to the max value, and wire the boolean output to the case structure.  The true/false cases can be incrementing the voltage, or ending the VI, etc.  A state machine architecture might even be an option here, though I don't know if it's necessary.

Hope this helps!

Adam W
Applications Engineering
National Instruments

[disbecknell]

Adam,

Sorry for the lapse in communication, I'm a student and left for summer vacation after my last posting.  Now I'm back at work, attempting to complete what I started.

Yes, I am able to communicate with the power supply through LabVIEW.  There is an example VI that allows you to set the desired voltage and current, as well as an over-voltage protection value.  It outputs the measured voltage and current, and returns an error if Set Voltage > OVP.
The configuration VI's that come with the instrument driver are: Config Current, Config Voltage, Config OVP, Config Time Delay, Config Current Soft Limit, and Config Voltage Soft Limit.
Attached are screenshots of both.

I have a little knowledge of algorithms, but I'm lost in LabVIEW right now.  Please let me know, in as much detail as possible, if I can modify the example VI to accomplish what I want or how I should build one that will.

Thanks
-Andrew

[Scott_G]

Andrew,

In the first screenshot you sent, you have all the values you need to compare the actual voltage and current to the desired.  As far as the programming, if you right click on the block diagram you will have a functions pallette.  You want to use the programming pallete and use the comparison and structures groups.  In Labview, there are also examples you can work from if you go to help--find examples.  In the example finder you can do a search for comparison or case structure.  This should get you started.