Breakpoint Modulus and Sync with DAQ

[SciWare]

I’m engineering a system that will drive a sample in x and y through a raster pattern under a displacement measuring laser in order to generate a 3D profile of the sample. This system synchronizes motion and DAQ to perform this function, basically I want to clock the DAQ at every N encoder pulses (either X or Y).

The motion hardware I’m using is a PCI-7332 and the measurement from the laser goes into a PCI-6221.

I’m looking at one of the shipped examples that implies that you can do this called

examples\Motion\FlexMotion\RTSI.llb\RTSI with DAQmx (breakpoint-external scan clock).vi

This example setups up a modulus breakpoint that is mapped to a RTSI line that you then map as the DAQ sample clock source, This is all good.

However if you look in the while loop where it is polling the status it appears that it has to programmatically re-arm the breakpoint after every time it is fired with Enable Breakpoint Output.flx. If this is so then my application layer needs to manage this, which is not what I want, I want the hardware to just mange this.

Unfortunately I’m is a situation where I don’t yet have full access to the system so I can’t tinker and figure it out.

The other option if would be to map the encoder axis to a RTSI line and then into the DAQ clock, which is fine except its going to oversample, I like the Modulus Breakpoint approach as it is neater.

I would be most grateful for some direction

[Jochen]

Hello Kurt,

the breakpoint feature of the PCI-7332 requires software rearming and there is no way around that. Fast onboard rearming is only available with NI 7350 boards, like the PCI-7352.  NI 7350 board provide a maximum periodic breakpoint rate of 4 MHz per axis. You could ask your local NI branch for a hardware upgrade.

The other option is routing the encoder signal to the RTSI, but this might have some drawbacks (e. g. micro-oscillations on the encoder causing unsolicited DAQ readings).

I hope that helps,

Jochen Klier

National Instruments

[SciWare]

Thanks Jochen

Unfortunately I dont think out client will allow us to go to the 7350, so I think the way to go is to clock off the encoder. Perhaps another way would be to clock off the stepper motor, that way we wont get jitter.

[Jochen]

Kurt,

using the stepper output signal seems to be a good option then. Cabling is a bit more complicated, as this signal can't be routed to the RTSI lines, but it's a better choice in terms of synchronisation quality.

Regards,

Jochen