capture E4406 EVM measurement screen

[Evan_2008BJ]

Hi distinguished NI engineers,
           Nowadays , I attemps to setup EVM test in our lab. All seems ok except screen capture problem.From the E4406 programming manual ,this insturment supports screen capture functionality.

           This commands says it would provide a view of numeric results and a ploar constellation graph in the two windows.How i can realize that in labview, my experience for this is limited.

          Could anyone raise me a hand? Thanks.

[Dennis_Knutson]

You seem to be asking a couple different questions. First, does the command work? I mean, does the screen change to reflect what you want?

Second, you are doing a read but you haven't issued any command to the instrument to send any data. You would need to issue a query (i.e. something with a '?' at the end.

Third, you mention a screen capture but you are not issuing any command that tells the instrument to perform such an operation. That's a command you will have to look up and then find the command to transfer it to the pc.

Fourth, when you finally do issue a query and do a read, you will have to convert the string returned into numeric data before it can be displayed on a graph.

Fifth, a LabVIEW graph will not correctly display a polar plot. You will probably have to use the picture indicator to display this. Look at the shipping examples. Do a search for 'polar'. You may be able to do a normal trace on the instrument, fetch that, and display the data in LabVIEW without setting up the instrument to do it. I suspect this will be faster than setting up the instrument, doing a capture, transfering the capture, and then converting the capture to be displayed in LabVIEW.

I can't help much more beyond this. I don't have the instrument (or even the manual) to experiment with.

[Richard_2008]

Hi Dennis,
                Sorry for reply late. I will clarify something~~

You seem to be asking a couple different questions. First, does the command work? I mean, does the screen change to reflect what you want?

(The command really work.)

Second, you are doing a read but you haven't issued any command to the instrument to send any data. You would need to issue a query (i.e. something with a '?' at the end.

(I have already configured the command"DISPlay:EEVM CONStln" to the VISA write. Do you mean i still need to issue the command to Visa Read before get the expected graph?)

Third, you mention a screen capture but you are not issuing any command that tells the instrument to perform such an operation. That's a command you will have to look up and then find the command to transfer it to the pc.

(I already issue the command"DISPlay:EEVM CONStln" command to perform the command and also configure the measurment before display the screen.I was a bit lost.What kind of command you think i need to put it into? Because i think the sequence is clear:configure the measurment-->conduct the measurement-->capture and display the result.)

Fourth, when you finally do issue a query and do a read, you will have to convert the string returned into numeric data before it can be displayed on a graph.

(Yes ,I'll remember this rule to get the graph.)

Fifth, a LabVIEW graph will not correctly display a polar plot. You will probably have to use the picture indicator to display this. Look at the shipping examples. Do a search for 'polar'. You may be able to do a normal trace on the instrument, fetch that, and display the data in LabVIEW without setting up the instrument to do it. I suspect this will be faster than setting up the instrument, doing a capture, transfering the capture, and then converting the capture to be displayed in LabVIEW.

(All i want is to capture the whole measurment screen, Do you think it make sense?Maybe i do not care whether it's a polar plot or other kind of graph.)

           Thanks a lot for your replay and patience.

Evan

[Dennis_Knutson]

You probably need to spend some time learning how instrument control works. Studying the manual for the instrument is one place. There are also tutorials on the developer zone but basically, you have commands and queries. A command tells the instrument to perform some action but does not place any data in the buffer to be read by the pc. A query tells the instrument to maybe perform some action but to also place data in the buffer. For example, if you were programming something simple such as a DMM, you might issue a command such as SETUP:VOLTS DC to tell it switch to a DC voltage measurement mode. If you were to do a read after this, you would not have any data. If you issued a SETUP? and then did a read, the instrument would return a VOLTS DC string. Most instruments these days use a standard protocol called SCPI. With SCPI, a '?' at the end of the command is the key to telling the instrument to place data in the buffer for a transfer. In your code, you have issued a command to tell it to switch display modes. In order to get the screen information, you would then have to issue a query. I don't have this instrument or the manual, but with some spec analyzers, it would be a command like TRACE?. To do a screen capture, if the instrument supports it, you might have to issue a special command to tell the actually perform a screen capture (as opposed to just reading trace data).

[Richard_2008]

Hi ,

     Thanks for your explanation. Still have some focus~~~

       A. You menitoned if i used the querry instead of complete commmand, I can get the expected result from buffer .If I understand correct , the sequence could be like this:issue a command such as SETUp:VOLTs DC--->issue a querry :SETUp ?-->Read data in the buffer.

       B. Where can get the instrument control tutorials in your sites?

BR,

Evan

[Richard_2008]

Hi Dennis,

                If i want to fetch certain measurement result , despite issue the complete command for instance "MEASurement:EEVM",is it neccsary to issue the command follwing the command as well?

Thanks.

Evan

[Dennis_Knutson]

If the command does not end with a '?', it is not a query.

Check out http://zone.ni.com/devzone/cda/tut/p/id/4359

and from Agilent - http://adn.tm.agilent.com/index.cgi?CONTENT_ID=1821

[Richard_2008]

Hi Dennis,

                   I made an example to fetch certain measurement result( GSM EVM test).

                   First, specify the certain measruement---"MEASure:EEVM 6"

                   Second,use the querry---"MEASure:EEVM ?" to transfer the data

                   Third, use the fetch command---"FETCh:EEVM ?" to capture the measurement result.

                   Do you think the sequence is make sense?

[Dennis_Knutson]

I can't really judge the VI you've written since I don't have the instrument manual to look at. Carefully study the syntax of the commands in the programming manual. You may be able to do a MEAS:EEVM 6? which will intiatiate the measurement and tell the instrument to return the values. That would eliminate the other two commands. You would probably not need the FETCH if you issue the MEAS command. A MEAS usually tells the instrument to initiate a measurement cycle (i.e. trigger and then read). A FETCH usually does not do an initiate. For example, if you had an instrument with 2 channels, a MEAS:CH 1? would cause the instrument to trigger and take a measurement. To get the data from channel 2, you would just do a FETCH:CH 2? to get results only without doing another trigger.

[Richard_2008]

Thanks Dennies,

                          So now I am understand the querry functionalilty. The next problem is if the command does not capture the screen , how can i realize it ? I want to capture the Constlen graph of the EVM test on the GUI , how can i do it? I refer to the Agilent PSA series driver ,which made by NI, but it still does not work. Do you have similar source code share with me?

                           I use the instrument :E4406(Vector singal analyzer) for measurement. I enclosed the instrument manual for your referrence.Thanks.

                          (I'm sorry i have to compress the manual and change the extension as txt because of your website policy, Cloud you please change back to .rar and go through the manul?)

BR,

Evan