GBT OPERATIONS PROCEDURES

 Number: OP-01
Title: Maintenance and Testing Support Last Revision: 4 Nov 02

Warning

Ensure personnel safety through effective communications. Let people know of telescope movements, before they're made!

Fall protection is required at several PMU/PCT connection locations. 

General

The following procedures are designed primarily to support maintenance and testing activities. 

Antenna Azimuth and Elevation Moves Using M&C

    Azimuth moves at a set rate:

STEP

 ACTION
1 From the Antenna Control window tabs:
  • Set the main axis coordinate mode to Encoder Az/El
  • Zero out any local pointing corrections
  • Deselect Refraction and Pointing Model corrections 
2 If moving from a specific point (A) to another point (B) at a set rate, move the antenna to your starting position (A). Otherwise, go to next step. 
3 Ensure Azimuth drive is enabled (Disable the elevation drive).
4 From the Antenna Control tab:

Enter the desired movement rate in the Azimuth field (ArcMin/Min), (Positive value=CW move; Negative value=CCW move), (See conversion table below for sample rates and formulae)

5 From the Antenna Monitor window, Managers menu, open the Antenna Acquire Data window:
  • Determine how many degrees you want to move then convert this distance to an appropriate scan length using the following formula:    

Degrees to Move × Degrees Per Minute × 60 = Scan Length in Seconds

  • Enter the value obtained in the scan length field of the Antenna Acquire Data window 
6 When ready to begin the move, press the Start button in the Antenna Acquire Data window. The antenna will move in azimuth at the set rate for the time specified. 
7 To move at the same rate back to the original starting point:
  • Change the sign (+ or -) in the rate field
  • Press the Update button to set the starting point as the current location
  • Enter the same movement rate and scan length determined in steps 4 and 5
  • Press the Start button to begin the move
8 To continue making additional moves back and forth at a set rate just repeat step 7. 
Degree Per Min to Arc Minutes Per Min Conversion Table 
Deg/Min = Arc Min/Min   Deg/Min = Arc Min/Min   Deg/Min = Arc Min/Min   Deg/Min = Arc Min/Min
1

 

 60 11

 

 660 21

 

 1260 31

 

 1860
2

 

 120 12

 

 720 22

 

 1320 32

 

 1920
3

 

 180 13

 

 780 23

 

 1380 33

 

 1980
4

 

 240 14

 

 840 24

 

 1440 34

 

 2040
5

 

 300 15

 

 900 25

 

 1500 35

 

 2100
6

 

 360 16

 

 960 26

 

 1560 36

 

 2160
7

 

 420 17

 

 1020 27

 

 1620 37

 

 2220
8

 

 480 18

 

 1080 28

 

 1680 38

 

 2280
9

 

 540 19

 

 1140 29

 

 1740 39

 

 2340
10

 

 600 20

 

 1200 30

 

 1800 40

 

 2400
Additional Conversion Formulae

Arc Minutes Per Minute to Degrees Per Minute:  Arc Min/Min   ÷   60   =   Degrees Per Minute

Degrees Per Minute to Arc Minutes Per Minute:   Deg/Min   x   60 Arc Min/Deg  =  Arc Min/Min

    Elevation moves at a set rate:

STEP

 ACTION
1 From the Antenna Control window tabs:
  • Set the main axis coordinate mode to Encoder Az/El
  • Zero out any local pointing corrections
  • Deselect Refraction and Pointing Model corrections 
2 If moving from a specific point (A) to another point (B) at a set rate, move the antenna to your starting position (A). Otherwise, go to next step. 
3 Ensure Elevation drive is enabled (Disable the Azimuth drive).
4 From the Antenna Control tab:

Enter the desired movement rate in the Elevation field (ArcMin/Min), (Positive value=Upward move; Negative value=Downward move), (See conversion table above for sample rates and formulae)

5 From the Antenna Monitor window, Managers menu, open the Antenna Acquire Data window:
  • Determine how many degrees you want to move then convert this distance to an appropriate scan length using the following formula:    

Degrees to Move × Degrees Per Minute × 60 = Scan Length in Seconds

  • Enter the value obtained in the scan length field of the Antenna Acquire Data window 
6 When ready to begin the move, press the Start button in the Antenna Acquire Data window. The antenna will move in elevation at the set rate for the time specified. 
7 To move at the same rate back to the original starting point:
  • Change the sign (+ or -) in the rate field
  • Press the Update button to set the starting point as the current location
  • Enter the same movement rate and scan length determined in steps 4 and 5
  • Press the Start button to begin the move
8 To continue making additional moves up and down at a set rate just repeat step 7. 

Antenna Azimuth and Elevation Moves Using a PMU   

STEP

 ACTION
1 Pass control to the PMU. At the OCU, bring up the Control menu and set Az/El Ctrl to PMU
2 At the elevation drive deck or azimuth truck, connect the PMU to the available port. Note: If moving in elevation, the stow pin must first be retracted using the MSU in the servo room
3 Activate the PMU by pressing the ACTIVE button 
4 Select the desired rate (HI or LO)
5 Enable the specific axis to move by pressing its ENABLE button
6 Move the axis by rotating its control knob in the desired direction 
7 Monitor the move closely to avoid exceeding limits or running over a PMU cable 

Moving the Sub Reflector

    Movement via the OCU

STEP

 ACTION
1 Select the Control menu and set SCU Ctrl to OCU and Feed Arm Ctrl to SCU
2 Select the SRPosition menu
3 Change values for X,Y,Z, Xt, Yt, or Zt as desired then select Execute
4 Monitor the move via the Axis-Cmd-Feedbk window
5 Monitor the faults window for problems 

    Movement via the PMU

STEP

 ACTION
1 Pass control to the PMU. At the OCU, bring up the Control menu and set SCU Ctrl to OCU and Feed Arm Ctrl to PMU
2 At the receiver room (SCU cabinet, left side) or sub reflector access deck, connect the GBT Subreflector PMU (3 plug) or standard PMU (single plug) into the labeled port.
3 Activate the axis to move by pressing the ACTIVE button associated with it 
4 Select the desired rate (HI or LO)
5 Enable the specific axis to move by pressing its ENABLE button.
6 Move the axis by pressing the RETract or EXTend button (3 plug PMU) or turning the AZ or EL knob (single plug PMU) .
7 Monitor the move closely to avoid exceeding limits 

    Movement via the PCT

STEP

 ACTION
1 Pass control to the PCT. At the OCU, bring up the Control menu and set: OCU control to PCT,  SCU Ctrl to OCU, Feed Arm Ctrl to SCU
2 At the receiver room (SCU cabinet, left side) or sub reflector access deck, connect the PCT to the labeled port 
3 Plug in/Turn on the PCT. To repaint (fill) the screen, press CTRL E then press P (screen will fill and mimic OCU screen) 
4 The subreflector can now be run the same as if from the OCU (see Movement via the OCU, steps 2-5)

    Movement via M&C (assumes M&C already has control)

STEP

 ACTION
1 In the Antenna Control window, Drives tab, Disable azimuth / elevation drives; Enable subreflector motors 
2 In the Antenna Control window set the SubReflector Mode to XYZ
3 Select the Subr XYZ Ctrl tab and enter desired values in the X, Y, Z, Xt, Yt, or Zt fields or use the slide bars  
4 Press the Move To button to initiate the move
5 Monitor the move via the Subr XYZ Ctrl tab or Optics Monitor windows
6 Monitor the message window for problems
7 Use the E-Panel Stop or Abort buttons to terminate the move if needed 

Moving Prime Focus X, Focus, and Polarization

    Movement via the OCU

STEP

 ACTION
1 Select the Control menu and set SCU Ctrl to OCU and Feed Arm Ctrl to SCU
2 Select the PFPosition menu
3 Change values for X (inches), Focus (inches), or Pol (degrees) as desired then select Execute
4 Monitor the move via the Axis-Cmd-Feedbk window
5 Monitor the faults window for problems 

    Movement via the PMU

STEP

 ACTION
1 Pass control to PMU. Select the Control menu and set SCU Ctrl to OCU and Feed Arm Ctrl to PMU
2 At the prime focus service shelter, connect the PMU to the available port.  Notes:
  • Port location requires fall protection
  • Lower port instructions: AZ=PFF Focus; EL=PFF Pol; POL=Boom in/out
  • Upper port instructions: AZ=PFF X movement; EL=Turret rotate; POL=Turret Pin in/out
3 Press the ACTIVE button 
4 ENABLE the control knob or button corresponding to the axis to move. See step 2 notes.
5 Monitor the move closely to avoid exceeding limits 

    Movement via the PCT

STEP

 ACTION
1 Pass control to the PCT. At the OCU, bring up the Control menu and set: OCU control to PCT,  SCU Ctrl to OCU, Feed Arm Ctrl to SCU 
2 At the receiver room (SCU cabinet, left side) or prime focus service shelter, connect the PCT to the labeled port 
3 Plug in/Turn on the PCT. To repaint (fill) the screen, press CTRL E then press P (screen will fill and mimic OCU screen)  
4 Prime focus axis can now be moved the same as if using the OCU
5 Monitor the move via the Axis-Cmd-Feedbk window
6 Monitor the faults window for problems 

    Movement via M&C (assumes M&C already has control)

STEP

 ACTION
1 In the Antenna Control window, Drives tab, Disable azimuth / elevation drives; Enable prime focus motors 
2 In the Antenna Control window set the SubReflector Mode to Prime
3 Select the Prime Focus Ctrl tab and enter desired values in the Focus, Polar, or X fields or use the slide bars
4 Press the Move To button to initiate the move
5 Monitor the move via the Prime Focus Ctrl tab or Optics Monitor windows
6 Monitor the message window for problems
7 Use the E-Panel Stop or Abort buttons to terminate the move if needed 

Moving the Prime Focus Boom

    Movement via the OCU

STEP

 ACTION
1 Select the Control menu and set SCU Ctrl to OCU and Feed Arm Ctrl to SCU
2 Select the BoomPosition menu
3 Select Extend or Retract by pressing the space bar then select Execute (it takes approximately 4.5 minutes)
4 When the move is complete, the status window will show the following messages:
  • PFF Stowed
  • Boom Retracted Limit
  • Boom Decel Retract
  • Boom Brake Set
5 Monitor the faults window for problems 

    Movement via the PMU

STEP

 ACTION
1 Pass control to the PMU. Select the Control menu and set SCU Ctrl to OCU and Feed Arm Ctrl to PMU
2 At the prime focus service shelter, connect the PMU to the lower port.  Notes:
  • Port location requires fall protection
  • Lower port instructions: AZ=PFF Focus; EL=PFF Pol; POL=Boom in/out
3 Press the ACTIVE button 
4 ENABLE the control knob or button corresponding to the axis to move. See step 2 notes.
5 Monitor the move closely to avoid exceeding limits 

     Movement via the PCT

STEP

 ACTION
1 Pass control to the PCT. At the OCU, bring up the Control menu and set: OCU control to PCT,  SCU Ctrl to OCU, Feed Arm Ctrl to SCU 
2 At the prime focus service shelter, connect the PMU to the labeled port 
3 Plug in/Turn on the PCT. To repaint (fill) the screen, press CTRL E then press P (screen will fill and mimic OCU screen)  
4 Prime focus boom can now be moved the same as if using the OCU
5 Monitor the move via the Axis-Cmd-Feedbk window
6 Monitor the faults window for problems 

    For boom movement via M&C, refer to the procedure titled "Antenna Control Via The M&C System".

Moving the Turret

    Movement via the OCU

STEP

 ACTION
1 Ensure the telescope is in Access position (Check for Turret Horizontal message in status window)
2 Select the Control menu and set SCU Ctrl to OCU and Feed Arm Ctrl to SCU
3 Select the TUPreset menu
4 Enter the number corresponding to the receiver to rotate into position then select Execute
5 Monitor the move via the Axis-Cmd-Feedbk window
6 When the move is complete, the status window will show the following messages:
  • Turret Horizontal
  • Turret Stow Pin Extended
  • Turret Locked
7 Monitor the faults window for problems

    Movement via the PMU

STEP

 ACTION
1 Ensure the telescope is in Access position (Check for Turret Horizontal message in status window)
2 Pass control to the PMU. Select the Control menu and set SCU Ctrl to OCU and Feed Arm Ctrl to PMU
3 At the receiver room or prime focus service shelter, connect the PMU to the labeled port.  Notes:
  • Receiver room (SCU cabinet, left side)
  • Prime focus service shelter port location requires fall protection. Upper port instructions: AZ=PFF X movement; EL=Turret rotate; POL=Turret Pin in/out
4 Press the ACTIVE button 
5 Select the desired rate (HI or LO)
6 ENABLE POL to retract or extend the turret locking pin. Note: CCW retracts; CW extends 
7 To rotate the turret, ENABLE the EL control knobs. Note: DN moves the turret CCW; UP moves it CW 
8 Monitor the move closely to avoid exceeding limits 
9 If a limit is exceeded, hold down the EL ENABLE button while rotating the control knob to back it out of the limit

    Movement via the PCT

STEP

 ACTION
1 Pass control to the PCT. At the OCU, bring up the Control menu and set: OCU control to PCT,  SCU Ctrl to OCU, Feed Arm Ctrl to SCU 
2 At the receiver room (SCU cabinet, left side) or prime focus service shelter, connect the PCT to the labeled port 
3 Plug in/Turn on the PCT. To repaint (fill) the screen, press CTRL E then press P (screen will fill and mimic OCU screen)  
4 The turret can now be moved the same as if using the OCU
5 Monitor the move via the Axis-Cmd-Feedbk window
6 Monitor the faults window for problems 

    For turret movements via M&C, refer to the procedure titled "Antenna Control Via The M&C System".

Receiver Changes and Subreflector Maintenance

    Gregorian Receiver Changes

STEP

 ACTION
1 Pull the turret locking pin.
2 Rotate the turret to the position desired by the mechanics or receiver engineer.
3 Reinsert the locking pin if possible.
4 When finished, rotate and lock into position the next receiver scheduled to be used.

    PF Feed Changes  

STEP

 ACTION
1 With the prime focus boom retracted, set the POL, X, and FOCUS as follows:
  • POL = -94 Degrees
  • X = 34 inches
  • FOCUS = 47.5 inches
2 After the receiver change, test all axis to ensure they are functioning correctly.

    Subreflector Maintenance (Greasing)

STEP

 ACTION
1 Ensure the subreflector is already stowed. If not, stow it prior to greasing. 
2 The mechanics will now grease and wipe down the exposed tube surfaces of the different axis.
3 When asked to move the subreflector, move the Y axis to -10. The mechanics will continue wiping down the exposed tube surfaces.
4 When asked to move the subreflector again, move the X axis to +10. The mechanics will finish wiping down the exposed tube surfaces.
5 When the mechanics are done, use the SRSTOW option on the OCU/PCT to stow the subreflector.

Prepared by: Dave Rose

Last modified: 4Nov02