EPICS routine for conditioning ED1, ED2 high voltage 
         ---------------------------------------------------- 

         High voltage on the DRAGON electrostatic dipoles may be raised 
 gradually using an EPICS routine which monitors the anode and cathode 
 currents, the tank pressure and the x-ray rate.  This allows for slow 
 conditioning of the ED's under computer control. 

         An EPICS page, called from the Optics|Condition ED1 option of the 
 DRAGON menu bar, allows the initialization, launching, monitoring or 
 stopping of HV conditioning. 

         Each of the 4 monitored parameters (anode current, cathode 
 current, pressure, x-rays) must be within a range specified by 2 numbers 
 ("Too Low" and "Low") before a voltage increase will take place.  An 
 upward step in voltage (by "Upstep" kV) will be considered by the control 
 loop once every "Uptime" seconds. 

         The need to step voltage back down because of heavy conditioning 
 is considered once every "Downtime" seconds.  The HV setpoint will be 
 reduced by "Downstep" kV if any of the 4 parameters lies in the range 
 between "High" and "Too High". 

         If any parameter lies between "Low" and "High", it is neither a 
 cause for a down-step nor license for an up-step in HV.  The control loop 
 should sit at the same voltage setpoint until another Uptime or Downtime 
 seconds have elapsed. 

         If any parameter is found to be higher than "Too High" the routine 
 exits from the control loop, on the assumption that something has gone 
 wrong with a readback or some other unexpected hardware failure has 
 happended.  Similarly, going below "Too Low" terminates the loop. 

         Conditioning terminates also if the user clicks the Stop button on 
 the conditioning page, or if some other agent (user or Scaling 
 routine) changes the Setpoint value from the value last set by the 
 HV Conditioner. 


 To set up HV Conditioner: 
 - manually determine the HV Setpoint at which signs of conditioning appear 
   and enter this number as VSTART (in kV). 
 - choose the voltage at which conditioning should end as VSTOP (in kV). 
 - choose the step size for voltage increases (in kV).  Suggested: 0.01 
 - choose the minimum interval between steps up (in seconds). Suggested: 60 
 - choose step size and interval for voltage decreases.   
   Suggested: 0.05 kV and 30 sec 
 - specify the effective resistance of the HV stack (MOhms = V/uA).  We 
   are interested in the net current after stack current is subtracted, 
   using this constant.  Suggested: 6000 
 - specify the TooLow, Low, High, TooHigh limits of anode current 
   and cathode current (uAmps).  Suggested: -10, 5, 20, 50   
 - specify the limits on pressure (in Torr). 
   Suggested: 0.7E-9, 5.0E-7, 3.0E-6, 3.0E-5 
 - specify the x-ray rates.  Suggested: 2, 500, 5000, 300000 

 Start the conditioning by clicking on "Condition DRA:ED1" (or :ED2). 
 A watchdog timer should start counting up from 0 and keep counting as long 
 as the control loop has not been terminated.  The read-back voltages and 
 currents as well as the Setpoint voltage are displayed in each of the 
 Anode and Cathode boxes.  In each of the 4 boxes a green triangle will 
 point up if everything is OK to step up the HV, or will point down if the 
 HV should be stepped down.  If the control loop is terminated because of 
 one parameter staying out-of-range, a red "stop sign" is displayed for 
 that parameter.  The value which caused abnormal termination should appear 
 in the last part of the log file, which can be displayed by clicking on 
 "View log". 

 Dave Hutcheon 
 26 Feb 2003