I use a NI PXI 1033 chassis which contained two NI PXI 5402 generators.
In one of my applications, these generators are synchronized and generate sinus signals at 500 kHz and 5 V with a 180° phase difference.
No problem to generate these signals with a fixed frequency, but I need to modify "on the fly" the frequency and keep the 180° phase difference. So my problem is that when the signals frequency is modified, with my solution (based on an FGEN example) the phase difference is modified too in an uncontrollable way.
I’d like to find a solution that would allow me to keep the 180° at each iteration of the while loop and have signals without interruption. I use LabVIEW 8.6, NI-FGEN VI and the synchronization is done with PXI trigger line. Maybe there are some tips with the trigger to make this possible?
Changing the frequency on the fly is only software dependant, so you can't be sure that you ask both cards to change frequency at exactly the same time. That's why your signals aren't in phase.
Tha only solution you have is to stop and laucn your generation again using the same trigger for the 2 cards, but you will have a continuous DC signal (last value of your sine) between the stop and start.
How about using one signal source and a transformator with two (identical) output windings?
Or use two identical amplifiers with differntial inputs and drive one on the positive and one on the negative input? (the phase shifts of both amps must match, so a transformator would be my first try)
About the solution of using one generator with tranformator or amplifiers, It could be a good solution but the test norm does not allow me to do this.
The only software solution is to change frequency with launch and stop at each changement, it works but but it's time constraining for my test.
Thanks for your help,