Issue with random phase multi-sine wavefrom generation using PXI-5412

[dtiew]

Hi, 

I am trying to generate random phase multi-sine waveform using PXI-5412 14-Bit 100M/s AWG on LabVIEW8.0.

The version of LabVIEW8.0 for PXI-5412 comes with a sample VI on multi-tone waveform generation. There is no issue with the sample VI when I tried it out with different combination of frequency and amplitude.

Since I need the phase to be random for each frequency component, I had to rip up the tone cluster comprising 3 elements, i.e. frequency, amplitude and phase, that is feeding the waveform generator, and rebundle the cluster with elements of frequency elements reading from a CSV file using a FOR loop, a fixed amplititude value and a random phase number generated from a random number generatoror (formula: pi - 2pi x rand). When observed the generated multi-sine waveform on PXI-5112 100MHz Digital Oscilloscope, it was observed that the waveform would change with the range of frequency being tested.  However, the amplitude of the waveform is always ~1.4V (guess it is always default to 1 V x sqrt(2)).  There is no such issue when testing the same combination of frequency and amplitude using the sample VI without modification.

Attached please find the sample VI,  the ripped up version and the CSV file that I used. Is there anything wrong with the 1D array of cluster of 3 elements that I built and assembled causing the waveform generator to ignore the input value of amplitude and possibly the input value of the phase as well (as it seemed that the amplititude is always set to the default value)?

The other issue that I observed on both sample VI and ripped up version is about the sampling info.  The waveforms displayed on PXI-5112 Digital Oscilloscope always default to 10 cycles no matter how changed the sampling frequency and number of samples.  For example, if the frequency is 10 Hz, sampling frequency is 1000 Hz, and I set the number of samples to 10000.  I supposed to get 10000/100  = 100 cycles.  However, I could see only 10 cycles no matter how I changed.  What should be the correct way to change the number of cycles?

Really appreiciate your help and advice. Thanks.

[KateB · Accepted solution]

1. Phase unit is in degree (-180 to 180), not -pi to pi.
2. Normalize Waveform.vi always normalize your signal amplitude. You can remove it to use your desired amplitue, but need to make sure that it's not above 5412 spec.

[dtiew]

Thanks for the info.

One I changed the phase formula for phase unit in degrees, the random phase multi-sine waveform is working fine now.

However, I am still seeing that the peak value on the niScope seems to be amplitude x sqrt(2). For example, if I specify the amplitude to be 2, I will get peak value of 2 x 1.414 = 2.8.  Is this the case?