Minimum frequency step duration and Minimum List Length for frequency lists in NI 5406 signal generator

[joseaasturias]

Hello,

We need to feed an RF amplifier with a function generator in order to create plasma in a Ion source. The pulse length of the signal must be 1ms long, and repeated twice per second.

Nowadays we are working in the following way: We turn of the RF with a f0 frequency (aprox 1.995 MHz). After 20us we send a trigger signal that switches to a f1 frequency (aprox 2.005 MHz).  We keep this frequency for the rest of the pulse.  However, the plasma we generate is not "constant" or stable during the whole pulse. If we modify smoothly the frequency during the pulse we could improve it.


What we would like to do: use frequency sweep: instead of using this frequency hopping, we would like to go smoothly from f0 to f1 (frequency sweep). And then again from f1 to f2.

As we have a PXI for data analysis, we are thinking about using the Arbitrary Function Generator from NI: NI 5406 which allows frequency sweeping. However, in the specifications, this is not very clear, and i have some questions:

- We can create a "frequency list". In the NI website below, it shows that the "Minimum Step Duration" is 1.28us, which would be ok for us (i understand that the "Minimum Step Duration" is the minimum time between 2 frequencies). However, the manual of the device "NI PXI/PCI-5402/5406 Specifications" says the frequency list has a  Step Duration from 1 ms to 21s. Which one is correct??

-  It also says that the "Minimum List Length " is 1s. For us, we would need a list shorter that 0.5 seconds (we need to repeat the same pulse twice per second.). Is it possible to make what we want??

- In the end, we would like implement a control loop that modifies the frequency list  in real time.

http://zone.ni.com/reference/en-XX/help/370524L-01/nisignal_generators_help/features_by_device_smc/


Thanks for your help.
Best regards,
Jose.

[Elizabeth_K. · Accepted solution]

Hi Jose,

You are correct about the documentation's inconsistencies. The minimum step duration used to be 1ms, but was changed to 1.28 µs at driver version 2.6. The help document was changed to reflect that, but the specifications were not. I will make sure that gets fixed.

The minimum list length is not listed in the specifications, and the most recent version of the NI Signal Generators Help (driver version 2.9) lists the minimum list length as 1 step. The help changed at driver version 2.6.1 to clarify that the 1 s meant 1 step. I'm attached a screenshot of the most recent help.

There is an example installed with the NI-FGEN driver called "Fgen Sweep Generator.vi". I would recommend starting from that for your application.

I hope that clears up some of the inconsistencies in our documentation. Please let us know if you have any more questions.

Elizabeth K.

Signal Generators Product Support Engineer

[joseaasturias]

Thanks a lot for your help. It clarifies everything!

Jose.