sddsfeedforward

• description: sddsfeedforward performs feedforward on process variables. Feedforward essentially means that one or more process variables are set according to a predetermined function of other process variables. In sddsfeedforward, the user supplies a series of tables that are used to interpolate values of a single actuator as a function of a single readback. Any number of tables may be given, so that any number of actuators may be driven by any number of readbacks. Each actuator is, however, driven by only one readback. One readback may drive any number of readbacks.

• example:

  sddsfeedforward ID1GapCompensation.sdds -interval=10,s
  

  where the file ID1GapCompensation.sdds contains the following data:

  ReadbackName = ID1:Gap             ActuatorName = S1B:H1:CurrentAO  
   ReadbackValue  ActuatorValue 
  ------------------------------
         150.000          0.000 
         100.000          0.000 
          50.000          1.000 
          40.000         10.000 
          30.000         20.000 
          20.000         35.000 
          15.000         74.000 
          11.000         99.000
  

  At each iteration step, ID1:Gap is read and sddsfeedforward intepolates a new value for S1B:H1:CurrentAO based on this table, which it writes to the PV.
• synopsis:

  sddsfeedforward <inputfile>
         [-interval=<real-value>] [-steps=<integer=value>]
         [-verbose] [-dryRun]
         [-averageOf=<number>[,interval=<seconds>]] 
         [-testValues=<SDDSfile>]
         [-ezcaTiming=<timeout>,<retries>]
         [-runControlPV=<string>] [-runControlDescription=<string>]
         [-CASecurityTest]
  

• files:
  • input file:

    The input file is an SDDS file with the following elements:

    • Parameters
      • ReadbackName -- Required string parameter giving the name of the readback for this table. This is the process variable that is read from EPICS. Its value is used to interpolate a new value for the actuator.
      • ActuatorName -- Required string parameter giving the name of the actuator for this table. This is the process variable that is set by the program according to interpolation with the readback values.
      • ReadbackChangeThreshold -- Optional floating-point value giving the amount by which the process variable named in ReadbackName must change from the previous iteration's value in order for a change to be made for the actuator. Most useful if the readback is a little noisy and one doesn't want the actuator to be changed pointlessly. If the same process variable is named as readback for several actuators, then the smallest value of the change threshold is the one used.
      • ActuatorChangeLimit -- Optional floating-point value giving the maximum amount by which the actuator should be changed in a single iteration. If several actuators have the same readback process variable, then they are limited together by the most constraining of the limits. In such a case, the vector of changes is scaled to bring all the changes within the respective limits.
    • Columns
      • ReadbackValue -- Required floating-point column giving values of the readback for an interpolation table.
      • ActuatorValue -- Required floating-point column giving values of the actuator for an interpolation table.

  • test values file:

    To make sddsfeedforward more robust, one can implement tests on any process variable, not necessarily those involved in the feedforward itself. If any of the tests fail, then the feedforward is suspended until the test suceeds. The test consist of checking whether a process variable is within a specified range or not. The testValues file has three required columns and one optional one:

    • ControlName -- Required string column giving process variables names to test.
    • MinimumValue, MaximumValue -- Required floating-point columns, defining a valid range for corresponding PVs. It is an error if MinimumValue $>$ MaximumValue.
    • SleepTime -- Optional floating-point column, specifying sleep (or pause) time before attempting another test.

• switches:
  • interval=<real-value> -- Specifies the interval in seconds between readings. The time interval is implemented with a call to usleep between calls to the control system. Because the calls to the control system may take up a significant amount of time, the average effective time interval may be longer than specified.
  • steps=<integer-value> -- Number of iterations for the feedforward before normal exiting.
  • verbose -- prints out a message when data is taken.
  • dryRun -- readback variables are read and computations are performed, but the control variables aren't changed.
  • averageOf=<number>[,interval=<seconds>]] -- Specifies averaging of the readback values, giving the number of readings to average and the interval in seconds between the readbacks.
  • testValues=<file> -- An SDDS file containing minimum and maximum values of PV's specifying a range outside of which the feedforward is temporarily suspended. The contents of the file are described above.
  • ezcaTiming[=<timeout>,<retries>] -- Sets EZCA timeout and retry parameters.
  • runControlPV=<string> -- Gives the name of a process variable to use for workstation-independent process control via the Run Control facility.
  • runControlDescription=<string> -- Gives a text description to write to the Run Control record for process identification.
  • CASecurityTest -- Specifies that before writing values to EPICS, a test should be done of the state of Channel Access security on the process variables, to see if the process is permitted to write values.

• see also:
  • sddsexperiment
• author: M. Borland, ANL