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<== Date ==> <== Thread ==>

Subject: RE: VAL field in Motor record Default unit
From: "Mooney, Tim M." <mooney@aps.anl.gov>
To: Matt Dentinger <mdentinger43@gmail.com>, "tech-talk@aps.anl.gov" <tech-talk@aps.anl.gov>
Date: Sun, 12 Feb 2017 07:29:45 +0000
Hi Matthew,

The VAL field is the position you want the motor to move to.  You choose the units you want for the VAL field, and then you set the MRES (motor resolution) field to be the distance, in those units, that the motor will move when it's driver gets one step pulse. (You should also set the EGU field to some string that will tell the user what units you chose for the VAL field.  The EGU field isn't used for any other purpose.)

Other background information: the motor's running speed (VELO) is in EGUs per second.  The motor's acceleration time (ACCL) is the number of seconds you want it to take for the motor to get from its base speed (VBAS) to its running speed (VELO). Stepper motors have a resonant speed that you want to avoid.  If you set VBAS to be higher than the resonant speed, the motor will leap immediately to the base speed, avoiding the resonance, and then accelerate from there to the running speed.  This is why short moves are slow, and longer moves are faster.



Tim Mooney (mooney@aps.anl.gov) (630)252-5417
Beamline Controls Group (www.aps.anl.gov)
Advanced Photon Source, Argonne National Lab


From: tech-talk-bounces@aps.anl.gov [tech-talk-bounces@aps.anl.gov] on behalf of Matt Dentinger [mdentinger43@gmail.com]
Sent: Saturday, February 11, 2017 8:52 PM
To: tech-talk@aps.anl.gov
Subject: VAL field in Motor record Default unit

Dear Tech-Talk,

   Hi, I am a student at the University of Washington and I am learning how to navigate and use EPICS programming.  For the task at hand I will not be able to use encoders, making use of absolute positioning impossible, so I was wondering what default unit the VAL field was in.  Through some testing it seems the larger the value, the faster the motor moves so I guessed that it might be a number that somehow represents revolutions per second (or another given time).  Hope you can shed some light on my issue.  Also, haven't subscribed yet, but I may have to depending on how this project continues.  Thanks again.

  Best,
  
     Matthew Dentinger

Replies:
Re: VAL field in Motor record Default unit Joey Thai
References:
VAL field in Motor record Default unit Matt Dentinger

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