CFHT Logo   Autofill User's Manual


   

  • Introduction:  
    • The autofill system comprises of an Allen Bradley SLC500 PLC based controller to automatically fill the EEV Dewar mounted on the ESPADONS Spectrograph.   The controller is mounted on the wall inside of the slit room.  Sensors and other cabling feed into the spectrograph room to allow control, some feedback, and filling of  EEV. 
    • Refer to  Block Diagram
    • Refer to Schematic Diagram
  • Basic Theory of Operation
    • Upon start of a fill cycle, the controller will wait a few seconds and then sense either Dewar 1 or Dewar 2 Flow sensor's temperature reading.  This temperature reading is a surface mount RTD taped directly to the output side of the control solenoid.  If there is LN2 flow, the temperature reading should immediately  start to decrease.
    • The controller will continue to watch this flow temperature to insure continued LN2 flow.  If this temperature starts to rise significantly, then the controller determines the tank is empty and automatically flags this tank as being empty and switches over to  the other tank.
    • The LN2 flow will continue until the Exhaust Flow temperature drops below -195 degrees C.  This is an indication that EEV is full and is purging excess LN2 out of the exhaust port.   The LN2 flow is kept on for a few additional seconds to insure this was not a "burp" and EEV is indeed full. 

  • The system has the following features:
    • 2 Storage Dewars - Allows filling of  EEV for up to 9 days.  When one of the storage dewars empties, the controller automatically senses the loss of LN2 flow and will automatically switch over to the second storage dewar. 
    • Handset control/status:
      • Autofill Handset
      • LEDs ON/OFF Switch - (Illuminate the LED indicators to give current status)
      • New Dewar Switch - Used to reset the the status bit after replacing an empty storage dewar with a new one.
      • Dewar 1 and Dewar 2 Empty LEDs
      • Vacuum Too High LED (Vacuum level is too high to allow a safe filling)
      • Pressure Relief 1 and Pressure Relief 2 LED (The pressure relief  sensor on the vent side of the storage dewar is too high).
      • Mode Switches (When pressing any of these switches, the LED indicator will illuminate to indicate a switch press):
        • Off/Cancel - Stop the automatic control of the autofill system.
        • Man Fill - Manually start a fill sequence.  When EEV is full, stop the LN2 flow and revert back to the Off/Cancel mode.
        • Auto Fill - Sense when either EEV or exhaust temp has risen above a predetermined set point.  At this time, the controller automatically commences with a fill cycle.  When EEV is full, stop LN2 flow and stay in Auto Fill mode.
        • Sched Fill - Also can be referred to as "Interval" or "Cycle" fills.   Start filling at certain predetermined times of day.  This time can be automatically calculated based on # of cycles per 24 hour period or set in registers.   In this mode, the fill cycle will start at a predetermined time of day.  When EEV is full, stop LN2 flow and stay in Sched Fill mode.
          • # Cycles (Display) - Selects number of intervals or cycles in a 24 hour period.  This can be 1, 2, 3 or 4.
            • 1 - Once every 24 hours.
            • 2 - Twice in 24 hours.
            • 3 - Three times in 24 hours.
            • 4 - Four times in 24 hours.
  • Operation:
    • It is assumed all the necessary connections are made.  If there are any questions, please refer to  Block Diagram
    • The PLC's power (in the slit room) should be on. 
    • The dewar (EEV) should be pumped and mounted on the instrument. 
    • You should have two (2 ea) liquid nitrogen storage dewars in place.  Procedure on how to replace storage dewar  on system.
    • Move the LEDs ON/OFF switch to the ON position.
      • Make sure none of the LED error indicators are set.  If they are, you must first remedy the situation before you will be allowed to start a fill. 
    • For EEV's case, you should see "2" in the LED display to the right of # Cycles/24 Hours switch.  This means the autofill system will fill EEV two times in 24 hours.  Currently (16 February 2006) we are filling at 07:30 and 1630 hours.  If there is any doubt about this, contact Grant. 
    • When you are satisfied things are connected and on with two full storage dewars hooked up, you can now press:
      • Sched Fill - This will put the system into Scheduled Fill mode.
      • Now press Man Fill:  This will start LN2 flow into EEV.  When EEV becomes full, the controller will stop LN2 flow and revert back to Sched Fill mode. 

  • ========================  Useful Information =======================
  • Autofill Status
  • LN2 Tank Replacement Procedure
    • Procedure on how to replace storage dewar  on system.
  • Autofill PLC - 83.70  (You may enter the PLC's IP address into a web browser and monitor the various data registers).
    • PLC Data Register Definitions:
      • Temperatures (Degrees C):
        • F20:0 - Flow Temp 1
        • F20:1 - Flow Temp 2
        • F20:2  - Exhaust  Temp
        • F20:9 - Dewar Temp
      • Vacuum Data
        • F23:0 - Vacuum Value (Torr)
        • F23:1 - Max Vacuum Value Threshold. (Used to determine if filling is OK)
        • F23:2 - Max vacuum gauge volts. (Determine if vacuum gauge volts is valid)
          • Value (volts) = (F23:2*10)/32767
        • F23:3 - Min vacuum gauge volts. (Determine if vacuum gauge volts is valid)
          • Value (volts) = (F23:3*10)/32767
      • Command Register
        • N10:0 - Fill Mode
          • 0 - Off/Cancel
          • 1 - Manual Fill
          • 2 - Auto Fill
          • 3 - Schedule (Interval) Fill
        • N10:1 - 1 - 4 Intervals per 24 hours
      • B22:0 - Status Register
15
 14
 13
 12
 11
 10
 9
 8
 7
 6
 5
 4
 3
 2
 1
 0
Pressure
Relief 2
Error
 Pressure
Relief 1
Error
 No LN2 Flow
 Both Dewars Empty
 Dewar 2 Empty
 Dewar 1 Empty
 Ambient Temp
Error
 Exhaust
Temp
Error
 Flow 2 Temp
Error
 Flow 1 Temp Error
 Amb RTD Error
 Exhaust RTD Error
 Flow 2 RTD
Error
 Flow 1 RTD Error
 Vac Too  High
 Vac Gauge Volts Error
      • B22:1 - Some Status
15
 14
 13
 12
 11
 10
 9
 8
 7
 6
 5
 4
 3
 2
 1
 0
Software
Reset
 No Vacuum
Gauge Enable (Set  for no Vac Gauge)
 Auto Time Control
0 - User defined  fill times.
(N50:10, N50:21, N50:22, N50:23)
Based on # Cycles
(N10:1)

1 -Equal time intervals.
(6, 8, 12, 24 hours)
Based on # Cycles (N10:1)

 Auto Fill Mode
0 - Trigger on Exhaust Temp (F20:15)
1 - Trigger on Dewar Temp (F20:16








Dewar 2
Valid
 Dewar 1 Valid
 Dewar 0 Valid
(No Valid Dewars)
      • Date Stuff
        • N50:10 holds the integer value for "Hour" of start time.  This is in 24 hour format.
        • N50:11 holds the integer value for "Minute" of start time. 
        • N50:12 holds the integer value for "Seconds" of start time but I don't actually use this.  It's just there.
        • N50:13 holds the integer value for  Last Fill "Hours"
        • N50:14 holds the integer value for Last Fill "Minutes"
        • N50:15 holds the integer value for Last Fill "Seconds"