Why can't labVIEW communicate simultaneously with all of my six RS 485 devices ?

Question

Hi everyone,
i'm writing a VI that is able to read out 8 sensors from 6 devices connected by RS 485. I'm using the VISA subVI for that. 
My trouble is, the more devices I connect at the same time, the slower the 8 sensor readings are coming in. One device takes 5 seconds and all six take 18 seconds, when they really should take 5 seconds, too. It seems to me, that labVIEW, the way I use it, can only read and/or write one device at the time. Is there a why to make labVIEW faster ?
To be more exact about my diagram. I simply have open/write/read/close structure in a subVI which is called by a subVI that handles progression of the commands and the output strings. This subVI is called 6 times in a one while loop in my main program.
I experimented with putting all device-work flows in one sequence structure, but there it became very obvious that more devices slow down the "rhythm" of my VI. 
Any help is appreciated.
cheers
I attach the middle subVI
Attachments:
CallSensors.vi ‏19 KB

Answer 1

PI-Control wrote:To be more exact about my diagram. I simply have open/write/read/close structure in a subVI which is called by a subVI that handles progression of the commands and the output strings. This subVI is called 6 times in a one while loop in my main program.
You open/write/read/close each time you communicate?  That will wreak havoc on your performance.  You should open the port once at the start of the program and then close it once at the end.  You can read/write as much as you want in between.  Opening and closing ports repeatedly can really slow you down.
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