Latency and the 7i43
29 May 2011 02:30 #10143
by centaur
Latency and the 7i43 was created by centaur
Hi folks - just how important is latency when using the Mesa 7i43 card? I can understand that latency is critical when asking the CPU to generate step/dir pulses but I am not certain how latency effects the 7i43 in servo configuration.
Any thoughts?
Thanks
Any thoughts?
Thanks
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29 May 2011 04:16 - 29 May 2011 04:18 #10146
by PCW
Replied by PCW on topic Re:Latency and the 7i43
Jitter/latency is never good but is less important in servo systems.
Jitter/latency will show up as a noise input to the position part of the PID loop (the velocity estimate does not suffer the same noise if you use the encoders velocity estimate) The magnitude of this noise is JV (Jitter x Velocity). For example at 120 IPM and 50 usec of jitter this noise amounts to 1/10000"
This noise could be mostly eliminated, making the servo less succeptable to host jitter if the PID loop used the actual extrapolated position based on the actual sample time not the calculated time, but the error is small enough on most systems to be swamped by other errors
Jitter/latency will show up as a noise input to the position part of the PID loop (the velocity estimate does not suffer the same noise if you use the encoders velocity estimate) The magnitude of this noise is JV (Jitter x Velocity). For example at 120 IPM and 50 usec of jitter this noise amounts to 1/10000"
This noise could be mostly eliminated, making the servo less succeptable to host jitter if the PID loop used the actual extrapolated position based on the actual sample time not the calculated time, but the error is small enough on most systems to be swamped by other errors
Last edit: 29 May 2011 04:18 by PCW.
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