continuously varying frequency generation

[abeach_FTL]

Hi there,

I have a requirement to be able to drive four independant sine waves (1Hz - 30kHz) into a Unit Under Test.I need to have the ability to continuously vary these in terms of amplitude and frequency.

Our system currently makes use of an PXI-8106RT controller and a PXI-6259 to generate three independant sine waves (0.1Hz - 100Hz) on a 10ms processing frame under LabWindows/CVI running on LabVIEW RT. To do this the controller is generating three 10ms waveforms and then squirting them at the card, every cycle. Obvioulsy there is quite a bit of processing involved with this even when using sine wave generation function ("SineWave()"). This is only one of a number of tasks the system has to perform. Will our current architecture be able to handle the new requirements or do we need to look at something different (buy four function generators)?

Cheers

[Liam_A]

Hello there,

This can depend on several factors, such as the memory set up of your PXI 8106RT and what the other processes are that are being carried out also. The architecture you have used can also be a factor such as whether different tasks are being carried out simultaneously and what timing you have used.

It might be a good idea to post some of this information up here for us to see.

[abeach_FTL]

I have calulated that if I assume we need to produce samples at 20 times the Fmax to accurately reconstruct the waveform then it will be 600000 samples per second per channel. So across 4 channels, I am looking at 2.4MS/s which from looking at the 6259 spec does not seem possible for 4 channels (1.25MS/s).

The rest of the system is using:

- 6723 to generate analogue dc outputs

- 6513 Discretes

- 6514 Discretes

- 6229 to generate 4 analagoue dc outputs (16 bit DAC)

- NAII 75DS2 Synchro / Resolver

- AIM ACX429-16 (ARINC 429)

- AIM ACX1553-2 (MIL-STD-1553B).

Everything is running within the 10ms frame rate.

I have looked at the 6358 X series which seems to offer a much higher throughput for analogue outputs but is a lot more expensive. That is as much as I can tell you as I am a systems engineer not a software guy.

Hope this helps.

[Liam_A]

Hi there again,

You are correct with your assumptions concerning the throughput of the cards. Be careful in your selection of a new one however as the 6358 is only available in the PXIe format. To get the required throughput, you may have to consider a 14 bit card rather than a 16 bit.