Loop drops when connected wireless (NI 9191)

Question

Hi,
I cannot figure out why a NI cDAQ 9191 chassis has connection drops when connected wireless and works
perfectly when connected thru LAN.
I wrote a little test VI to check the connection accuracy. The chassis has a NI 9375 I/O module plugged in.
A Moxa AWK3121 is used as wireles access point. What I do is check 5 digital inputs and control 3 digital outputs.
The outputs are continuously placed on/off at a different rate. I use an event loop and a main loopt that communicates
to the chassis at a loop rate of 10ms.
The chassis, laptop and Moxa A.P. are all close together on my desk. The Wifi signal is excellent.
Now, the code i written is probably not optimal.
But...  If I start with connecting the chassis with a LAN cable to my laptop, Wifi Disabled, Linked Local. The communication is perfect.
No drops between the loops and the real time.        
No communication errors. Runtime was 52 minutes.
Second test. Connected the chassis to the Moxa A.P. with LAN cable. Laptop connected wireless to the Moxa A.P.
Chassis still in Link Local. Ik can access the chassis in MAX. No problem.
When I run my test, I immediately see loop pauzes. After one minute there can be already a difference of 20 sec.
between calculated looptime and real time. Sometimes the active light on the chassis goes off and on.
When the active light is out, the loop is on hold. (Wich is normal as I assume the DAQ VI's are waiting for response.)
After appr.10 minutes the error -50405 "No Transfer in progress because transfer was aborted by client".
If I look at the timings there is already a difference of more then 5 minutes between the loop timing and the real time.
As last I tested with the chassis and the PC connected wireless to the Moxa A.P.
I did not get the -50405 error, but again loop drops. After 10 minutes there was a shift of 2 minutes.
Has anyone experience with wireless connections with the NI 9191 chassis?
Can I change my code? Did I mis something? (I'm a newbie to Labview)
Any help or suggestions would be appreciated.
Thanks in advance.
Frankie.
Labview 2014 SP1 (32bit) on Windows 7 Enterprise (X64)
Chassis and Moxa all updated to the latest firmware.
Solved!
Go to Solution.
Attachments:
Chassis919Tester.vi ‏51 KB
Symmetrical_Pulse_Generator.vi ‏55 KB

Answer 1

I am not clear on whether you are connecting the two together "in it's own little network" (which implies "router" and not "AP") or if you are connecting to the LAN through the wireless device (in which case it is entirely appropriate to refer to the wireelss device as an "AP").  Your last post about hot spots is what confused me.
But as you said, the biggest worry is the active light.  Try using a different router/AP.  I've seen routers overheat and reset themselves before due to inadequate heat sinking.  i.e., Someone (not me, I swear!) dropped the AP and knocked the heat sink off the chip.
As for the delay, if you are indeed using the Moxa as an AP, are you sure you're connecting to your AP?  If you're connected to a hotspot instead, your throughput will be at least halved - and maybe even 1/4 bandwidth if your AP happens to have connected to a different hotspot than you did.  If you are using it as a router, try differnt bands or channels to see if you can get around any interference your company wireless network might be generating.
In general, conclude that wireless isn't the best way to connect test devices together.
Bill
(Mid-Level minion.)
My support system ensures that I don't look totally incompetent.
Proud to say that I've progressed beyond knowing just enough to be dangerous. I now know enough to know that I have no clue about anything at all.