Frequency plot using ComponentWorks++

[jkn]

Hi:
I am trying to develop a VI for a Spectrum Analyser (HP8566B) using ComponentWorks++. The prototype I developed (using NI example) can send primitive commands and read the output. My question is in displaying Frequency plots. I understand that if I get a Vector of x and y values I can plot the graph using CNiGraph. But how do I get a vector of values from the instrument. (Since I am only familiar with the primitive commands which return only a single value). I am sure somebody has done this before. Is it possible to get a vector of values from the instrument?

[Jason F.]

Well sort of, you can send commands to the spectrum analyzer that will cause it to return a dataset representing its currently displayed waveforms. After you receive this array of points you can then parse the data into a Vector for plotting.

The best way to show you how to do this, is for you to take a look at an instrument driver that is on our website for the hp8566b. This driver contains a function called hp8566b_read_wvfm_array that will cause it to return a set of data points representing its traces on its display. I have included it with this post, but you can also get it from the following site (scroll down til you see your model #):

http://search.ni.com/search/query.html?lk=2&rq=1&nh=500&rf=3&qm=1&ql=&pw=595&qp=%2BContentType%3AInstrumentDriver+%2BID
NetManufacturer%3A%22Hewlett-Packard%2C+Agilent+Technologies%22&qt=&layout=IDNet

It was developed to be used in CVI, but since it has a C file as its source file you can open it in either CVI or VC++ (I suspect you have both since you have CW++). Or if you want you can use the ComponentWorks Instrument Driver Factory (you should be able to find it in the Start menu under Measurement Studio >> Utility Programs) to build the driver into a dll with CVI and then you can just call its functions dynamically in your C++ app.

[jkn]

Thanks a lot. That is what I did exactly. It is working fine now. The only thing that wasn't clear on the hp8566b.c file (driver) was this:
Inside the function It uses "03:TA" as the command to get the 1001 sized array of values. When I tried this, I was getting valid values only very rarely. Most other times I was getting -100 for all the 1001 values. This perplexed me a lot. Later when I read the instrument manual again (I am a software guy - not familiar with the instrument) I found the TS command for doing a sweep. When I changed "03:TA" to "TS;03;TA", it started working consistently.
Thanks Jason for your detailed reply.