How can I stop my RF Signal Generator output from switching on and off for every command sent?

[bgushiken]

I'm having a problem with my LabView code changing the power and frequency settings on my Anritsu Synthesized Signal Generator. I'm using an Agilent USB to GPIB converter to control the devices and using the IO Libraries to manually send commands.

The problem that I'm facing is that for every command that I send to the generator using a VISA write vi in LabView, the generator actually switches the output on and off so one can hear the relay switching constantly. When I send the frequency and power change commands manually via the IO Libraries application, it does the command properly without the RF output switching. Any ideas on how I can stop the switching from happening? Should I be using a vi other than VISA Write in order to sove my problem?

[BerkO]

Hello Bgushiken,

Can you post the VI that you are using?

[bgushiken]

Here's the actual loop vi that tries to accurately set the voltage on the signal generator. We have to do it this way since the amplifier that we're using may not be linear accross the voltage ranges. This loop usually runs a few times so you can see that the signal generator will start clicking constantly everytime we set a different power level.

[BerkO]

Hello Again,

I forgot to ask, could you also tell us what model your instrument is? Clicking doesn't necessarily mean that it is actually switching the output ON or OFF.  The relay that is switching the output almost always is and should be seperate from the relays that adjust the power levels that you are setting.  One good way to test if it really is turning the output on or off is connecting a scope to the output and configuring and changing the power settings that make the clicking noises.

[bgushiken]

Hi Berk,

It's a Anritsu 68369A/NV.

We've done inital tests with the signal generator connected to a power meter and we can definitely see to the output drop eveytime we hear the clicking. We've also switched the power and frequency using the front panel and by manually sending commands via the Agilent IO controls application, and the clicking does not happen. I guess this is the reason why we're looking at the possiblity the VISA Write.vi adds extra commands but we are not able to see exactly what is being sent to the signal generator.

[Dennis_Knutson]

Since there is no loop in this code, could you also provide the main VI where this subVI is getting called?

p.s. Though it would make no difference to your problem, why are you using a sequence structure? Everything is defined by data flow and the sequence structure does nothing. Use the Time Delay function instead of the Wait (ms) or create a Wait (ms) with error in/error out connections.

[bgushiken]

Thanks for the suggestion Dennis. Defininitely good to know.

Here's the higher level subvi that calls the subvi I sent previously.

[AnalogKid2DigitalMan]

Right clicking on the pink text boxes on the block diagram and selecting '\' Codes display show some inconsistency in terms of use of spaces- displayed as \s. Do not know if this is correct formatting or not.

[O_Proulx]

Hello bgushiken,

You can test visa without LabVIEW by going to tools -> NI-VISA -> VISA interactive control in Measurement and Automation Explorer.  You will be able to send your GPIB commands from there.  This may help in narrowing down the problem. 

As for the exact problem, you explained that everytime a VISA command is sent to the instrument, the output is switched on and off.  Does the instrument read the command successfully anyways?  (Is the output set to the value you wanted?)  If not, then it may be possible that your instruments requires a EOS at the end of each command.  You can manually add the proper character at the end of each command or using the message base settings of a VISA property node to add it automatically at each write. 

Let us know the results of these tests.

[Albert.Geven]

Hi

maybe you are initializing the visa over and over again?