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  1. question about ABB ACS800 control

    Looking again at accel rates for internal vs. external control - I see that with internal control (top,  in attached pic),  speed ramp is in fact very linear,  but when set to external (encoder) control (bottom )- accel ramp is not linear, but rate increases over time.  Y-scale is RPM ( X 0.1,  so really going to 740 RPM).  Purple line at bottom of graphs show motor torque (%, also x 0.1 - so really going to 100%).  Total time to speed (740RPM) end up to be 12.5 sec when set to internal , and about twice that for external.    
  2. question about ABB ACS800 control

    Thanks for the ideas to look at.  In terms of accel rate - based on expected motor torque and the inertia which I have as load - while set to internal control and max accel parameters,   I am getting pretty much the exact accel rate which I would expect.  Both for internal and external (encoder) control - the ramp is very linear.  The only problem is...  that while set to external speed control that ramp is half the slope of when set to internal speed control (and half of what I should be getting...). Yes,  I was looking for other parameters which might somehow be influenced by the external vs. internal decision - but as of yet,  I have not been able to find anything which looks like it might be playing a role in this behavior.  
  3. question about ABB ACS800 control

    I am not a drive person (far from it...),  but I am working on a project using a number of ACS800 drives.  On one drive (only seeing this issue on one drive,  as far as I can determine) - when I specify a target speed and also specify maximum acceleration - there is a (significant) difference in terms of the accel time whether I have the drive set to internal speed control vs. external (encoder) control.  It takes almost exactly twice as long to get up to speed when set to external vs. internal.  (And problem with keeping it set to internal is that we lose accuracy at higher speeds,  and also at very low speeds...).  The most obvious issue would be a bad or improperly set encoder module,  but speed of motor is correct (as measured by tach) whether using internal or external.  Encoder module was also swapped for new one,  with no difference.   The only parameter that I am changing is speed by external encoder vs. internal  (I think that it is parameter 98.01).  Would anyone have any idea as to what could be causing this?   Thanks for any ideas!