Some notes on EnsemblePSOFly.db

2014-09-26 21:06:43 +00:00
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+Commands to tell the Aerotech Ensemble to output pulses every {delta} units,
+beginning at scan_start and ending at scan_end.  Note that the Ensemble fires
+pulses at positions n*delta from the position at which the PSOCONTROL X ARM
+command was invoked.  Thus, the pre-fly position of the motor must be an
+integer multiple of {delta}.
+
+{start} = scan_start - {delta}
+{end} = scan_end + {delta}/2
+
+
+PSOCONTROL X RESET                             ' Reset PSO.
+PSOPULSE X TIME 50,25                          ' Define a pulse of width
+                                               ' 50 usec, with 25 usec
+                                               ' on time.
+
+PSOOUTPUT X PULSE WINDOW MASK                  ' Set PSO output type to PULSE.
+                                               ' PSO pulses are masked by
+                                               ' the window.
+
+PSOTRACK X INPUT 1                             ' Track primary encoder for
+                                               ' axis.
+
+PSODISTANCE X FIXED {delta} UNITS              ' Set the incremental firing
+                                               ' distance ((units).
+
+PSOWINDOW X 1 INPUT 1                          ' Track primary encoder for
+                                               ' Window 1.
+
+PSOWINDOW X 1 RANGE {start},{end} UNITS        ' Set the fixed range (in units) for
+                                               ' the window.
+
+' Note that the following command establishes the origin for
+' distance-based output pulses as the motor's current position.
+' (i.e., it simply clears a counter that will be clocked by encoder pulses.)
+PSOCONTROL X ARM                               ' Enable PSO and start tracking.
+
+<user moves the motor from start to end>
+
+PSOWINDOW X 1 OFF                              ' Turn off window.
+PSOCONTROL X OFF                               ' Stop PSO tracking.
+
+
+
+------------------------------------------------------------------------------
+Start, end positions, etc.
+
+Before the motor's fly motion begins, the motor is moved to the "taxi" position,
+which is chosen so that the motor can accelerate to constant speed before data
+acquisition begins.  For constant acceleration from a possibly nonzero base
+speed, the acceleration distance is given by
+
+	accelDist = accelTime * (baseSpeed + slewSpeed)/2
+
+In EPICS motorRecord PVs, this is
+
+	accelDist = motor.ACCL * (motor.VBAS + M.VELO)/2
+
+Data acquisition occurs at N locations during the motor motion, where
+	N = (endPos - startPos) / scanDelta
+The locations are given by
+	dataStart + i*scanDelta*dir
+where i is an integer in the range [0, N-1], and
+	dir = (endPos-startPos)>0 ? 1 : -1
+
+Because of the way the Ensemble motor controller's position-synchronized output
+is implemented, dataStart is determined by the taxi position and the
+pulse-window open and close positions, such that the taxi position must be an
+integer multiple, M, of scanDelta away from dataStart.
+
+The taxi position must also be at least accelDist away from dataStart, giving a
+lower limit on M:
+
+	taxi = dataStart - M*scanDelta*dir <= dataStart - accelDist*dir
+	M >= accelDist/scanDelta
+	M = ceil(accelDist/scanDelta)
+
+
+-------------------------------------------------------------------------------
+
+The Ensemble PSO output is RS422, via an interface cable that ends with a female
+DB9 connector with an entirely custom pinout that includes 5V power.  If
+conversion to TTL is needed, the following chips and boards seem useful:
+
+Analog Devices ADM483E chip
+
+Linear Technology LTC485 chip
+
+Microbotics SLC10422-TTL board
+
+-------------------------------------------------------------------------------