TCPIP FETC

[Detox92]

Hi,

I am currently trying to use Labview to realtime view EVM RMS measurement via TCP IP.

Equipment is N9000A CXA

Connection is good. 

I send the following command :FETC:EVMQ?

I then read the returned string.

My problem is i get a returned sting 6.314648714E+01,6.390706248E+01,1.968745911E+02,2.266368866E+02,4.752113439E+01,4.816966443E+01,2.591475191E+01,2.614784611E+01,-5.273332042E+00,-3.076437569E+01,-4.199448479E+01

but sometimes i get an error message telling m: The network operation exceeded the user-specified or system time limit.

I understand the error but dont understand why one moment i recieve a measurement and the next i do not.

I have tried playing with delay times.

Thanks for any help

Alex

[mikeporter]

There are a number of things that could be going on. There could be other errors occurring, but you don't have any of your error clusters connected.

Next, a TCP/IP network is not deterministic. The amount of time it takes to do something can vary dramatically, What timeout values have you used? Are you sure the device is seeing the request and responding in a timely manner?

Related to that point, what is your network topology? Remember that you are sharing the network bandwidth with everybody else using it.

Mike...

[Detox92]

Hi Mike,

Thanks for the response.

I am using errors in my real vi this was just a simple vi to check what was happening.

I tried timeouts varying from 500ms all the way up to 5000ms.

When i run it in Highlight Execution Mode, it seems to be alot more stable.  

The networking is via a switch but nothing but a couple of other machines attached.

I dont know if i can use CRLF instead of immediate for determine when it stops looking for new data but so far i have ahd no joy.

Thanks again.

Alex

[mikeporter]

It would make sense that it would seem more stable with highlighting turned on: you aren't querying the remote device as often so there are fewer chanced for error.

You could try doubling the timeout to 10 sec, but what about the remote device itself? Is it seeing the command and responding?

Mike...

[Detox92]

I think some of the time it is yes as i get a valid response. 

How would i go about checking?

[mikeporter]

What is the device you are talking to? Does it have any way of showing when it receives a request? When the reponse timesout do you get any data back? By tem way, what is FETC?

Mike...

[Detox92]

The device is a spectrum analyzer. Agilent N9000A CXA

It recieve SCPI commands an Agilent language i think. FETC means FETCh data.

When it times out i get no data.

Thanks again!

Alex

[Dennis_Knutson]

Why don't you try the driver for that instrument (Help> Find Instrument Drivers). Your for loop with that count does not make much sense. The driver uses VISA which is simpler than your code and its probably more robust.