How do I correctly time while loops using SCPI and VISA/Ethernet communication to send DC current Values to a Power supply?

I'm rather new to using labview and I having an
issue with a test Data Aquisition lab I'm trying to setup using a
Keithley 6221 AC/DC current source and a basic PCI M-series NI-DAQmx.
First of all, I'm looking to update the current value on a power
supply at a rate of atleast 10Hz and I'm using SCPI commands and VISA
communication through ethernet to do so. Attached below is the VI I
have written.
The issue I'm having is this:
My VI will
loop through the values fine in software, or so it seems. I am unable
to get the Power supply to update sequentially if I don't set my loop
delay to anything greater than 130ms. If I try to run the loop faster
it starts skipping values instead of counting 1,2,3,4,5,1,2,...etc. it
goes 1,2,4,5,2,4,1,2 on the display of the power supply and my DAQ unit
also skips these values so I know that the number just isn't getting
read to the Power supply in time. I was wondering if this was due to
my sloppy programming or if it is a hardware issue, my computer or the
method of communication to the power supply? Is this due to the fact
that I'm using ethernet and VISA communication? Is there a faster way
to communicate or is GPIB faster? Any input at all would be extremely
helpful.
On a side note: Right now I'm using an pre-determined
array of values that I can update on the fly but in the future this
with be put into a closed-loop control system. The value for the
power supply output will be determined by the loop and sent that way.
Attachments:
basic DC loop 6221 Keithley.vi ‏145 KB

Also, one of the string constants is NOT set to '\' Codes Display. Here is an alternative method of calculating the index. I removed the DAQ and VISA stuff since I could not run it.
Lynn
Attachments:
basic DC loop 6221 Keithley.2.vi ‏16 KB

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Message Edited by devchander on 01-10-2006 06:15 AM
Message Edited by devchander on 01-10-2006 06:19 AM
Attachments:
arrayinouttestnewfinalnew4.vi ‏59 KB
arrayinouttestnewfinal.vi ‏63 KB

How do I correctly time while loops using SCPI and VISA/Ethernet communication to send DC current Values to a Power supply?

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