Thread Subject: Problems with the tekvisa.dll in instrument control toolbox

Hi,

I am trying to use Matlab to communicate to a Tektronix spectrum analyser. Both the spec an and the PC are running v3.3.2.7 of the Tek VISA server/client software.

When I type "rtsa = visa('tek','TCPIP::168.254.109.8::INSTR') at the command line in Matlab I get the following error message.

"??? Error using ==> visa.visa at 239
Invalid RSRCNAME specified. Type 'instrhelp visa' for more information"

I cannot see any problems with my command format based on the examples in the VISA documentation.

Can anyone help??

Regards,
Joe

"Joseph " <jo.winter@dfat.gov.au> wrote in message <gvt3fb$rji$1@fred.mathworks.com>...
> Hi,
>
> I am trying to use Matlab to communicate to a Tektronix spectrum analyser. Both the spec an and the PC are running v3.3.2.7 of the Tek VISA server/client software.
>
> When I type "rtsa = visa('tek','TCPIP::168.254.109.8::INSTR') at the command line in Matlab I get the following error message.
>
> "??? Error using ==> visa.visa at 239
> Invalid RSRCNAME specified. Type 'instrhelp visa' for more information"
>
> I cannot see any problems with my command format based on the examples in the VISA documentation.
>
> Can anyone help??
>
> Regards,
> Joe

Hi Joe,

It looks like the instrument is not correctly configured and identified by the Tek VISA application. For a resource string to work in MATLAB, it needs to be identified/configured in the VISA application first.

Once configured, you can take the VISA resource string from the VISA application itself.

Hope this helps

-Ankit

Ankit,

Thankyou for your response.
Based in your advice I tried configuring the VISA application on my PC for the RTSA. It seems the tool for doing this is the "OpenChoice Instrument Manager". However this application is unable to see any instruments connected to the network if I only have the VXI-11 server running on the RTSA. However if I enable sockets, OpenChoice can see the IP socket - Matlab however is still unable to recognise the resource.

I know in earlier versions of VISA there was a configuration tool, however I have not found any documentation on how to configure VISA to recognise a resource other than using the OpenChoice tool provided with the VISA application.

Any pointers?

Cheers
Joe

Ankit,

Well like most of these issues it usually the programmer rather than the tool that is at fault.

TCPIP is not one of my strong points - my network guy suggested I change my addresses to be 192.168.1.x. Well surprise, surprise, everything started working as described in the help documentation. Something to do with "private" IP addresses. I'll need to go back and refresh my knowledge of IP addressing.

Thanks again for your help.

Cheers
Joe

Hi Joe,

Yes -- you're seeing a "classic" issue with controlling instruments over TCP/IP. The computer "discovers" the instrument using a protocol called UDP, which can only be used locally (it won't cross a router), but it can see everything. However, communication happens using the TCP/IP protocol, which will cross routers if it needs to, and they are configured correctly. However, to accommodate large scale networks, TCP/IP allows you to break down your physical network into a number of virtual sub-nets. You were on one sub net, your instrument was on another, and the two can't "see" each other. When you changed the computer's address, you moved onto the instrument's subnet.

-Rob