PXI-5402 generates error on arbitrary function

[lt@tbio.dk]

My PXI-5402 will not allow me to use the NIFGEN Express Arbitrary Function Generator in Labview 8.2. It reports "Device not found". The card works fine with the FGEN SOFT FRONT PANEL and it also works fine in Labview 8.2 when using Frequency Lists for generating various waveforms. However, the examples as e.g. the NiFGen_Sweep_Generator_Example.vi reports following "Invalid Output Mode - NIFGEN_VAL_OUTPUT_ARB not supported on this Signal Generator." when I try to use the "Arbitrary Waveform"

Any help appreciated

Lars

[Nick_Storton]

Hi Lars,

The PXI-5402 is an Arbitrary Function Generator which means it will only produce periodic waveforms in a mode called Direct Digital Synthesis (DDS). In DDS mode, a fixed size memory (called lookup memory) stores one cycle of a periodic waveform. This waveform must contain exactly the same number of samples as the lookup memory size (no more, no less). A phase accumulator indexes into the lookup memory. For each cycle of the device sample clock, the sample of the waveform in lookup memory that is addressed by the phase accumulator is output. The accumulator is then incremented by the value in the frequency control word (FCW). By adjusting the Frequency proerty / attribute, NI-FGEN will calculate the corresponding FCW and you can vary the output frequency of the waveform in lookup memory. The phase accumulator increments in smaller steps for smaller FCWs. Accordingly, you need more samples to output one cycle of the waveform, so the frequency is lower. A higher FCW results in a higher output frequency. In DDS mode, the sample clock does not vary with the frequency of the waveform generated. At higher frequencies, some waveform samples in lookup memory are skipped; at lower frequencies, some samples output multiple times in succession. With this in mind you can see that this device will not support Arbitrary waveform or Arbitrary Sequence mode you would use it in DDS mode and download your user defined waveform into lookup memory. It is well worth re-stating here that DDS based generators will not necessarily output all samples of the pattern in lookup memory depending on the output frequency, if you need to ensure that every sample is output you will need to use an Arbitrary Waveform Generator such as the PXI-5421.

Hope this helps,

Nick