MATLAB: “Attempt to reference field of non-structure array” error when using Makemid Command

makemidrohde and schwarz

I am trying to use makemid for creating MATLAB instrument driver for my Rohde and Schwarz Signal Analyzer. I have installed the IVI driver for the same. It gives me the following error "Attempt to reference field of non-structure array" error!. I am unable to understand what causes this error.

the syntax for using makemid command is makemid('Driver name','file name')

Best Answer

I'm not really sure, because your question does not give much specific information about your situation (such as the actual name of the driver, that would be nice to have). My best guess: you are trying to access some kind of driver file using this thing you provided:

makemid('Drivername','filename')

And the following is the case:

It could be that in your 'filename' you have for example the full path of your file as follows:

'C:/whatever/your/folder/is/where/that/driver/is/located/yourfilename.mdd'

If your file is not a file with the extention .mdd, but for example a .txt file, this could give erros if you do not specify the file extention in the filed 'type'. Another possibility is that the name of your file 'yourfilename' accidentally contains a dot (i.e.: 'your.filename.mdd'). That might cause MATLAB to read it as a struct (while it is not) and therefore throws you an error.

Related Solutions

MATLAB: Cannot connect to instrument using IVI driver

Since I do not have the actual instrument, I was not able to try it out with one - but I was able to successfully connect using simulation mode of the IVI driver. I used R2010b for the following:

>> iviInfo = instrhwinfo('ivi')
   iviInfo = 
                  LogicalNames: {}
                    ProgramIDs: {'AgilentRFPowerMeter.AgRFPM'}
                       Modules: {'AgRFPowerMeter'}
    ConfigurationServerVersion: '1.7.0.12115'
      MasterConfigurationStore: [1x59 char]
                   IVIRootPath: [1x36 char]

The command listed above will result in a structure where ProgramIDs field will list all the installed IVI-COM driver while the Modules field will list all the IVI-C driver installed on your computer.

As it is seen from the output, I had only installed one driver from the link posted and that driver installs both an IVI-C as well as an IVI-COM driver for the Agilent Power Meter.

To use these installed IVI-C and IVI-COM drivers in MATLAB, you will need to have/create a MATLAB Instrument Driver (which is a layer around those drivers). Depending on which driver (IVI-C or IVI-COM) you plan to use, you would call the makemid command (makemid = Make MATLAB Instrument Driver).

 >> makemid('AgRFPowerMeter','MATLAB_IVI_C_Driver.mdd');

The command above creates an MATLAB Instrument Driver for the IVI-C driver - AgRFPowerMeter (listed in the Modules field). The second argument is the name for the created MATLAB Instrument Driver.

Similarly if you plan to use the IVI-COM driver to communicate with your instrument you would create the MATLAB Instrument Driver using the ProgramID of the IVI-COM driver:

 >> makemid('AgilentRFPowerMeter.AgRFPM','MATLAB_IVI_COM_Driver.mdd');

Once you have the *.mdd file, you can create a device object using the syntax:

 >> deviceobj = icdevice(<name_of_my_mdd_file>,<instrument_visa_address>);

So, if you plan to use the IVI-C driver (note that if you are not using simulation mode, you can avoid the 'optionstring' and 'simulate=true' arguments):

 >> ivicobj = icdevice('MATLAB_IVI_C_Driver','GPIB0::5::INSTR','optionstring','simulate=true');
 >> connect(ivicobj);

While if you plan to use the IVI-COM driver:

 >> ivicomobj = icdevice('MATLAB_IVI_COM_Driver','TCPIP0::my-instrument-hostname::INSTR','optionstring','simulate=true');
 >> connect(ivicomobj);

Remember, if is important to get the instrument's VISA address correct for connect to pass in non-simulation mode. You can get the instrument's VISA address from the VISA Vendor's utility - for example NI's Measurement and Automation Explorer and/or Agilent's Connection Expert.

Hope this helps.

-Ankit

MATLAB: How to create and use a MATLAB Instrument Driver (.mdd) file for use with the Agilent MXA/EXA or PSA series Signal/Spectrum Analyzer

The IVI-COM drivers for the Agilent MXA/EXA series of Signal Analyzers and PSA series of Spectrum Analyzers implement special interfaces known as Measurement Personalities. The ability to create a MATLAB Instrument Driver (.mdd) file from an IVI-COM driver that implements personalities is not available in Instrument Control Toolbox 2.7 (R2008b).

To work around this issue, follow these steps:

(1) Visit the following Agilent webpage:

http://www.agilent.com/find/matlab_sa

Download the file linked at the bottom of the page labeled "Supported MATLAB driver for EXA, MXA, and PSA", and save it as an MDD (.mdd) file in your working directory.

(2) Create an instrument object using the ICDEVICE command:

% hwobj is an interface object you have successfully created

d = icdevice('<mdd_file_name>.mdd', hwobj)

% RsrcName is a VISA resource name/string

d = icdevice('<mdd_file_name>.mdd', 'RsrcName');

(3) If instrument object creation is successful, query for the instrument ID by issuing the following command in MATLAB:

>> get(d,'Identify')

Where 'Identify' is a property of the instrument object as defined by the MDD file, and wraps around the "*IDN?" command. To browse the MDD file for a complete list of Properties and Functions as defined by the instrument driver, you can issue the following command:

>> midedit('E4440A.mdd');

(4) Download the materials linked on the same Agilent webpage. They can be downloaded via the link labeled "MATLAB technical kit..." at the bottom of the webpage. Explore these examples to proceed to further use MATLAB with your Agilent instrument.

Best Answer

Related Solutions

MATLAB: Cannot connect to instrument using IVI driver

MATLAB: How to create and use a MATLAB Instrument Driver (.mdd) file for use with the Agilent MXA/EXA or PSA series Signal/Spectrum Analyzer

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