Is there a way to determine exactly where a breakpoint occurs?

Question

Hello everyone:  I am having trouble getting my head around this problem I am having, so I'm hoping someone here has run into something like this and has a tip for me.
I have a PXI-7354 that I am using to control a rotary stage which has an 8000 lpr encoder, and a 10:1 reduction gear, so I have 80,000 lpr effectively.
I am using the 7354 to generate a Breakpoint Pulse every 100 encoder counts, so I should be getting 800 pulses per revolution.  (I use the breakpoint pulses to trigger a second device and aPXIe-5122 data acquisition card to synchronize the production and acquisition of a data record.)
However, and here's the problem:
When I rotate 1 revolution, I see 799 pulses
When I rotate 2 revolutions, I see 1598 pulses
When I rotate 3 revolutions, I see 2397 pulses
etc. 
I am losing 1 pulse per revolution. I haven't figured this out yet, as I am using periodic breakpoints with a whole number of breakpoints as a period.
THe problem is that I "count" the number of breakpoint pulses that I get in order to derive the angular position where the breakpoint occurs.  For instance, if I start at 0 degrees, and I have 0.45 degree spacing between breakpoints, after 10 pulses, I should be at 4.05 degrees.  After 100 pulses, I should be at  44.55 degrees.
As I am missing one count per rev, however, my derived angular position is incorrect.
I need a way to determine the actual position of each breakpoint.  The most obvious way to do this is to use the HS capture functionality of the board, and I could (further) share the breakpoint pulse with the HS Capture input on the motion card to do HS capture, but is there any way to do this internally on the 7354?
Thanks for looking at this, any help is appreciated.
Wes
Wes Ramm, Cyth UK
CLD, CPLI
Solved!
Go to Solution.

Answer 1

Thanks for your response, Matt.
I have already got the BP signal going to my external device via a UMI-7774, so this is not a problem.  The tricky part of this question is whether there is an easy way to "share" the BP information with the HS Capture INPUT line so that I can grab a HS position when the BPs are generated, so that I'd have a buffer of ACTUAL position, rather than relying on the BPs being in the correct location (and DERIVING the instantaneous position of the BPs by counting the BPs).  It seems that it is NOT possible to share the signal by routing the BP1 Out simultaneously to the external UMI 7774 pin AND to either the HS Capture INPUT OR to my data acquisition card.  I know that I can route my encoder signal and other things to my DAQ card, but this won't help me in this case.  Furthermore, I can only have 1 BP per axis, so it isn't possible to replicate that functionality on a second BP generator.
I am working on setting up a third device to count the pulses generated by the 7354 when I exercise the stage through motion, so I'll have more data later today.
I'll post here any findings.
Thanks again,
Wes
Wes Ramm, Cyth UK
CLD, CPLI