I can seem to capture a graph comming from a optical spectrum analyser on labview 5 comming through GPIB

[jeff_au]

Already build a interface for the spectrum analyser but it's only displaying half of the spectrum graph on LabVIEW 5

[craigr]

Jeff,

Check and see if the graph axis range is large enough for the data you want to display. You may only need to increase the range of the graph. If that is not the problem, more information would be required to give any further recommendations. Are you using an instrument driver? What instrument are you trying to communicate with? Does this behavior occur with all data, or just certain ranges? You may need to check the input specifications (such as range) given to the instrument to insure that it is outputing the correct values as well.

Regards,
Craig R.

[jeff_au]

Hi Craig,

Thanks alot for your reply. We are currently building an optical spectrum analyser interface using LabVIEW 5. On the interface you can set your start wavelength and your stop wavelenght. Basicly, it allow the user to find the range that best suits their needs. Unfortunately for some reason, the graph (x-y graph) in LabVIEW 5 can only display half the graph. For example, if the range is from 700nm to 1700nm the graph would only display 700nm to 1200nm. The data acquisition is done through the GPIB/IEEE 488 drivers which seems to be working fine (we test it with other instruments). We can't seem to change the range of the graph like you mentioned simply by stretching the graph.
Thanks again for your reply and hope to hear from you soon.
Jeff

[Dennis_Knutson]

The XY Graph can display any range you want. How are you determing the range? With XRange.Minimum and XRange.Maximum property nodes? Or do you have autscaling turned on? On the front panel, you don't stretch a graph to inrease the range. All that does is make the graph larger. Use the text tool to select the first or last number on the range and enter a new value if you don't have autoscaling turned on. If you're getting the x array values from the instrument, have you verified that you're getting the numbers you expect?

[jeff_au]

Hi Dennis,

Actually the graph that we are using is already set to autoscale X so I think it may already be in the right scaling range. It still has problems displaying the complete graph.
Thanks for you help anyway:)
Jeff

[Dennis_Knutson]

Then I would suggest that you look at the raw data being retrieved from the instrument and how you're converting it for the display on the graph. The data comes across the gpib as strings so there could be a bug in the conversion to numbers or maybe the data is being truncated. While the instrument itself might display the entire range, often you have to specify exactly how much of that to transfer.

[jeff_au]

Hi Dennis,

We are using the Icon "GPIB receive" to retrieve the data from the optical sprectrum analyser. The data are then pass through the icon "spreadsheet spring to array" which converts the strings so that it's compatible with the graphic array. On the "GPIB receive" icon we limited the count function to 2770 because increasing this number any more will results in system saturation and the result is a flat line zero on the graph. So what do you think?
Jeff:)

[Dennis_Knutson]

Without knowing the actual instrument and the command set, it's pretty hard to say. When you say "GPIB Recieve", do you mean the GPIB Read function and is 2770 the byte count? Or are you using an instrument driver provided by NI or the manufacturer? What do you mean by "system saturation"? Have you looked at the raw data returned. This is easy to do with a probe or creating a string indicator. This should be done directly on the GPIB/VISA Read function. If the raw data is not representative of the entire spectrum, then it's probably time to dig into the instrument programming manual and see if your read command is incorrect.