Duty-cycle and phase measurement of quadrature encoder outputs using PXI-6602

[WDAI]

Hi,

I'm working on a project where I need to verify the frequency, duty-cycle, and phase of a quadrature encoder outputs, which is attached to a motor. The encoder has 3 outputs Ch.A, Ch.B and Index (Z). I'm able to measure the frequency using a PXI-6602 counter/timer module with the example "Meas-Dig Frequency-Low Freq 1 Ctr.vi", but I'm still struggling with the duty-cycle measurement of Ch.A and Ch.B, and Phase measurement between Ch.A and Ch.B, and Between Ch.A and Z if possible.  What would be the best way to measure duty-cycle and phase using a PXI-6602?

Thanks,

Willie

[Kevin_Price]

I'd be looking to capture edge timing for all the digital transitions in question.  Since a counter task requires you to specify one edge or the other, you may need to create 2 counter tasks per signal, each being sensitive to one transition direction.  Because they will be input (measurement) tasks that need their start times synced, you'll need to configure an arm-start trigger for all of them.  Another problem that arises is that your board can only use DMA transfers for 3 of your tasks, the other 3 would need to use interrupts.

You might want to consider using a board that has digital ports capable of change detection such as an X-series board.  Then you could do the job with 1 digital input task and 1 counter input task.

By the way, are you trying to characterize the motor or the encoder?  If you're characterizing the encoder, you'd better know going in that some (maybe much) of the variation you measure will be due to non-ideal motor motion rather than intrinsic encoder variations.

-Kevin P

[WDAI]

Hi Kelvin,

Thanks for your reply and inputs. I'll try what you suggested.

I'm trying to characterize the motor using the feedback of the encoder. You were right, the output of the encoder varies due to the type of the motor and how the motor is controlled.

Thanks,

Willie