PFIS Home -> Documents -> Code 3140: Control System

Southern African Large Telescope

Prime Focus Imaging Spectrograph

Interlock Specification and Design Document

SALT-3140AS0015

Jeffrey W Percival

Modification Record
Version Date Comment
1.2 09 Sep-2002 -
2.0 25-Sep-2002 Remove NI 7334 motion control interlocks
2.1 18-Oct-2002 Add Etalon detentes, update articulation detente, heaters, and RS232
2.2 08-Nov-2002 Assign codes to interlocks, rename home and index items
2.3 03-Dec-2002 Update etalon latch management, filter magazine
2.4 02-Jan-2003 Add shutter state table; use interlock tables generated from controls data base
2.5 04-Feb-2003 Add articulation state table & interlocks
2.6 07-Apr-2003 Update shutter voltage timing
2.7 30-Sep-2003 Update Relay & Stepper Interlocks
2.8 13-Jan-2004 Update tables to reflect LabVIEW code
3.0 23-Aug-2005 Update symmetric push/pull pneumatics; put ilock table in-line
3.1 06-Sep-2005 Remove Etalon & Grating Insert updates; can't implement them
Repair partial update: add ArtHome&DetenteCaught to ET & GR ins & rem

Introduction

This document specifies all the actuator interlocks required to prevent misuse of or harm to the Prime Focus Imaging Spectrograph.

It also describes the instrument safemode, and gives procedures for recovery into safemode.

A complete list of actuators and sensors can be found here.

The interlock charts below describe how to prevent commanding PFIS into an illegal state. The interlocks are grouped into hardware interlocks and software interlocks. Hardware interlocks are implemented in hardware. Each hardware interlock is also implemented in software, so that a hardware interlock is activated only in the event of a software failure. Additional interlocks are implemented in software.

NOTE: we refer to the boolean indicators from a logical, not electrical, point of view. "True" and "asserted" mean that the sensed condition is present. Whether that condition is actually active-high or active-low (1 or 0) is irrelevant here.

Hardware Interlocks

Hardware relay interlocks prevent actuators from being activated in a dangerous condition.

Hardware Relay Interlocks

In order to close a relay, certain requirements must be met. This table gives AND conditions for each relay. For example, the first entry below means that the relay P.5.1-R.1 must not be closed, and its solenoid not energized, unless the sensor S.5.1-B.7 is asserted (logically true), meaning that the elevator is at a station.

The interlocks are shown here.

Hardware Stepper Interlocks

Motion Control interlocks (forward and reverse limits) are managed by the National Instruments 7334 motion control cards. This section covers additional interlocks not managed by the 7334s.

The stepper direction terminology we use is "forward" and "reverse", so that we match the boards and documention from National Instruments (NI). NI defines "forward" to be clockwise as you face the tip of the motor shaft.

The interlocks are shown here.

Hardware Interlock Table

Mech. # Actuator Code Item Interlock Code Comment Item Type
1 PDS-R.4 Etalon 1 Controller AC\ P.9.3-B.3 NOT Etalon 1 Door Open relay
1 PDS-R.5 Etalon 2 Controller AC\ P.9.4-B.3 NOT Etalon 2 Door Open relay
5 P.5.1-R.1 Slitmask Fetch\ S.5.1-B.6 OR Slitmask Elevator Station relay
5 P.5.1-R.1 Slitmask Fetch\ P.5.1-B.1 OR Slitmask Fetched relay
5 P.5.1-R.2 Slitmask Stow\ S.5.1-B.6 OR Slitmask Elevator Station relay
5 P.5.1-R.2 Slitmask Stow\ P.5.1-B.2 OR Slitmask Stowed relay
5 P.5.2-R.1 Slitmask Insert\ S.5.1-B.3
Slitmask Elevator Home relay
5 S.5.1-FWD Slitmask Elevator Fwd P.5.1-B.1 OR Slitmask Fetched stepper
5 S.5.1-FWD Slitmask Elevator Fwd P.5.2-B.2 AND Slitmask Removed stepper
5 S.5.1-FWD Slitmask Elevator Fwd P.5.1-B.2 OR Slitmask Stowed stepper
5 S.5.1-REV Slitmask Elevator Rev P.5.1-B.1 OR Slitmask Fetched stepper
5 S.5.1-REV Slitmask Elevator Rev P.5.2-B.2 AND Slitmask Removed stepper
5 S.5.1-REV Slitmask Elevator Rev P.5.1-B.2 OR Slitmask Stowed stepper
6 P.6.1-R.1 HWP Insert\ P.6.5-B.1
QBL Inserted relay
6 P.6.3-R.1 QWP Insert\ P.6.1-B.1
HWP Inserted relay
6 S.6.1-FWD HWP Rotate Fwd P.6.2-B.2
HWP Detente Removed stepper
6 S.6.1-REV HWP Rotate Rev P.6.2-B.2
HWP Detente Removed stepper
6 S.6.2-FWD QWP Rotate Fwd P.6.4-B.2
QWP Detente Removed stepper
6 S.6.2-REV QWP Rotate Rev P.6.4-B.2
QWP Detente Removed stepper
7 P.7.2-R.1 Shutter Assist\ P.7.1-B.1
Shutter Opened relay
9 P.9.1-R.1 Etalon 1 Insert\ P.9.3-B.2
Etalon 1 Latch Removed relay
9 P.9.1-R.2 Etalon 1 Remove\ P.9.3-B.2 OR Etalon 1 Latch Removed relay
9 P.9.1-R.2 Etalon 1 Remove\ P.9.1-B.2 OR Etalon 1 Removed relay
9 P.9.2-R.1 Etalon 2 Insert\ P.9.4-B.2
Etalon 2 Latch Removed relay
9 P.9.2-R.2 Etalon 2 Remove\ P.9.4-B.2 OR Etalon 2 Latch Removed relay
9 P.9.2-R.2 Etalon 2 Remove\ P.9.2-B.2 OR Etalon 2 Removed relay
9 P.9.3-R.1 Etalon 1 Latch Remove\ P.13.1-B.3 AND Articulation Detente Caught relay
9 P.9.3-R.1 Etalon 1 Latch Remove\ S.13.1-B.3 AND Articulation Home relay
9 P.9.3-R.1 Etalon 1 Latch Remove\ P.10.1-B.2 AND Grating Removed relay
9 P.9.3-R.1 Etalon 1 Latch Remove\ S.10.2-B.3 AND Grating Rotate Home relay
9 P.9.4-R.1 Etalon 2 Latch Remove\ P.13.1-B.3 AND Articulation Detente Caught relay
9 P.9.4-R.1 Etalon 2 Latch Remove\ S.13.1-B.3 AND Articulation Home relay
9 P.9.4-R.1 Etalon 2 Latch Remove\ P.10.1-B.2 AND Grating Removed relay
9 P.9.4-R.1 Etalon 2 Latch Remove\ S.10.2-B.3 AND Grating Rotate Home relay
10 P.10.1-R.1 Grating Insert\ P.13.1-B.3 AND Articulation Detente Caught relay
10 P.10.1-R.1 Grating Insert\ S.13.1-B.3 AND Articulation Home relay
10 P.10.1-R.1 Grating Insert\ P.9.3-B.1 AND Etalon 1 Latch Inserted relay
10 P.10.1-R.1 Grating Insert\ P.9.1-B.2 AND Etalon 1 Removed relay
10 P.10.1-R.1 Grating Insert\ P.9.4-B.1 AND Etalon 2 Latch Inserted relay
10 P.10.1-R.1 Grating Insert\ P.9.2-B.2 AND Etalon 2 Removed relay
10 P.10.1-R.1 Grating Insert\ S.10.1-B.6 AND Grating Magazine Station relay
10 P.10.1-R.1 Grating Insert\ S.10.2-B.3 AND Grating Rotate Home relay
10 P.10.1-R.2 Grating Remove\ P.13.1-B.3 AND Articulation Detente Caught relay
10 P.10.1-R.2 Grating Remove\ S.13.1-B.3 AND Articulation Home relay
10 P.10.1-R.2 Grating Remove\ S.10.1-B.6 AND Grating Magazine Station relay
10 P.10.1-R.2 Grating Remove\ P.10.1-B.2 OR Grating Removed relay
10 P.10.1-R.2 Grating Remove\ S.10.2-B.3 AND Grating Rotate Home relay
10 S.10.1-AWO Grating Magazine AWO\ S.10.1-R.1 NOT Grating Magazine Blake Release\ stepper
10 S.10.1-R.1 Grating Magazine Blake Release\ S.10.1-AWO NOT Grating Magazine AWO\ relay
10 S.10.1-STEP Grating Magazine Step P.9.3-B.1 AND Etalon 1 Latch Inserted stepper
10 S.10.1-STEP Grating Magazine Step P.9.1-B.2 AND Etalon 1 Removed stepper
10 S.10.1-STEP Grating Magazine Step P.9.4-B.1 AND Etalon 2 Latch Inserted stepper
10 S.10.1-STEP Grating Magazine Step P.9.2-B.2 AND Etalon 2 Removed stepper
10 S.10.1-STEP Grating Magazine Step S.10.1-R.1 AND Grating Magazine Blake Release\ stepper
10 S.10.1-STEP Grating Magazine Step P.10.1-B.2 AND Grating Removed stepper
10 S.10.2-STEP Grating Rotate Step P.9.3-B.1 AND Etalon 1 Latch Inserted stepper
10 S.10.2-STEP Grating Rotate Step P.9.1-B.2 AND Etalon 1 Removed stepper
10 S.10.2-STEP Grating Rotate Step P.9.4-B.1 AND Etalon 2 Latch Inserted stepper
10 S.10.2-STEP Grating Rotate Step P.9.2-B.2 AND Etalon 2 Removed stepper
12 P.12.1-R.1 Filter Insert\ S.12.1-B.6
Filter Magazine Station relay
12 S.12.1-FWD Filter Magazine Fwd P.12.1-B.2
Filter Removed stepper
12 S.12.1-REV Filter Magazine Rev P.12.1-B.2
Filter Removed stepper
13 P.13.1-R.1 Articulation Detente Remove\ S.13.1-AWO NOT Articulation AWO\ relay
13 P.13.1-R.1 Articulation Detente Remove\ P.9.3-B.1 AND Etalon 1 Latch Inserted relay
13 P.13.1-R.1 Articulation Detente Remove\ P.9.1-B.2 AND Etalon 1 Removed relay
13 P.13.1-R.1 Articulation Detente Remove\ P.9.4-B.1 AND Etalon 2 Latch Inserted relay
13 P.13.1-R.1 Articulation Detente Remove\ P.9.2-B.2 AND Etalon 2 Removed relay
13 S.13.1-AWO Articulation AWO\ P.13.1-B.3
Articulation Detente Caught stepper
13 S.13.1-R.1 Articulation Blake Release\ S.13.1-AWO OR NOT Articulation AWO\ relay
13 S.13.1-R.1 Articulation Blake Release\ P.13.1-B.3 OR Articulation Detente Caught relay
13 S.13.1-STEP Articulation Step S.13.1-R.1 AND Articulation Blake Release\ stepper
13 S.13.1-STEP Articulation Step P.13.1-B.2 AND Articulation Detente Removed stepper

Self-consistency Checks

PFIS has a sharp distinction between configuring and exposing. There are no modes that require a continuously changing state of an actuator. Even in fast polarimetry, the waveplates are stopped and detented between motions. This provides many points in time, even during exposures, at which the state of the instrument is fixed, and the relationships between actuators and sensors are known and are able to be checked.

These checks can't be performed in hardware, because they are transiently violated during actuator motions. The software knows when the instrument is in a quiescent state, so the checks will be performed in software.

Sensor Self-checks

Some actuators move between opposite, mutually exclusive states. For example, a mask can either be in or out, but not both or neither. These checks can be done in software, using an exclusive-OR test.

Note that these conditions represent impossible, not undesirable, states. Undesirable states are avoided with hardware interlocks, and interlock failures are sensed according to the state checking section below. Impossible states cannot happen even if you defeat the interlocks. It is a physically unrealizable state, and hence can be used to diagnose the sensors or state of the hardware.

These pairs of sensors must satisfy an exclusive-OR condition. One or the other, but not both and not neither. This check is done in software.

Code Item Complement Item
P.5.1-B.1 Mask Fetched P.5.1-B.2 Mask Stowed
P.5.2-B.1 Mask Inserted P.5.2-B.2 Mask Removed
P.6.1-B.1 HWP Inserted P.6.1-B.2 HWP Removed
P.6.2-B.1 HWP Detente Inserted P.6.2-B.2 HWP Detente Removed
P.6.3-B.1 QWP Inserted P.6.3-B.2 QWP Removed
P.6.4-B.1 QWP Detente Inserted P.6.4-B.2 QWP Detente Removed
P.6.5-B.1 QBL Inserted P.6.5-B.2 QBL Removed
P.7.1-B.1 Shutter Opened P.7.1-B.2 Shutter Closed
P.7.2-B.1 Shutter Assist On P.7.2-B.2 Shutter Assist Off
P.9.1-B.1 Etalon 1 Inserted P.9.1-B.2 Etalon 1 Removed
P.9.2-B.1 Etalon 2 Inserted P.9.2-B.2 Etalon 2 Removed
P.9.3-B.1 Etalon 1 Latch Inserted P.9.3-B.2 Etalon 1 Latch Removed
P.9.3-B.2 Etalon 1 Latch Removed P.9.3-B.1 Etalon 1 Latch Inserted
P.9.4-B.1 Etalon 2 Latch Inserted P.9.4-B.2 Etalon 2 Latch Removed
P.9.4-B.2 Etalon 2 Latch Removed P.9.4-B.1 Etalon 2 Latch Inserted
P.10.1-B.1 Grating Inserted P.10.1-B.2 Grating Removed
P.11.1-B.1 Beamsplitter Inserted P.11.1-B.2 Beamsplitter Removed
P.12.1-B.1 Filter Inserted P.12.1-B.2 Filter Removed
P.13.1-B.1 Articulation Detente Inserted P.13.1-B.2 Articulation Detente Removed

State Checking

At any given time, the instrument must satisfy some constraints on its current state. For example, if "Mask Stowed" is asserted, then so must "Mask Removed". The condition should have been prevented by the hardware interlocks, so these conditions can serve as indications of interlock failure. These checks are implemented in software..

Code Item Constraint Item Mech. #
P.5.1-B.1 Mask Fetched

5
P.5.1-B.2 Mask Stowed P.5.2-B.2 Mask Removed 5
P.5.2-B.1 Mask Inserted P.5.1-B.1 Mask Fetched 5
P.5.2-B.1 Mask Inserted S.5.1-B.3 Mask Elevator Home 5
P.5.2-B.2 Mask Removed

5
S.5.1-B.1 Mask Elevator Fwd Hard

5
S.5.1-B.2 Mask Elevator Rev Hard

5
S.5.1-B.3 Mask Elevator Home S.5.1-B.6 Mask Elevator Station 5
S.5.1-B.4 Mask Elevator Station 1 S.5.1-B.3 Mask Elevator Home 5
S.5.1-B.5 Mask Elevator Station 2 S.5.1-B.3 Mask Elevator Home 5
S.5.1-B.6 Mask Elevator Station S.5.1-B.3 Mask Elevator Home 5
P.6.1-B.1 HWP Inserted P.6.5-B.1 QBL Inserted 6
P.6.1-B.2 HWP Removed P.6.3-B.2 QWP Removed 6
P.6.2-B.1 HWP Detente Inserted

6
P.6.2-B.2 HWP Detente Removed

6
P.6.3-B.1 QWP Inserted P.6.1-B.1 HWP Inserted 6
P.6.3-B.2 QWP Removed

6
P.6.4-B.1 QWP Detente Inserted

6
P.6.4-B.2 QWP Detente Removed

6
P.6.5-B.1 QBL Inserted

6
P.6.5-B.2 QBL Removed P.6.1-B.2 HWP Removed 6
P.6.5-B.2 QBL Removed P.6.3-B.2 QWP Removed 6
S.6.1-B.1 HWP Encoder Index

6
S.6.2-B.1 QWP Encoder Index

6
P.7.1-B.1 Shutter Opened

7
P.7.1-B.2 Shutter Closed P.7.2-B.2 Shutter Assist Off 7
P.7.2-B.1 Shutter Assist On P.7.1-B.1 Shutter Opened 7
P.7.2-B.2 Shutter Assist Off

7
S.8.1-B.1 Focus Fwd Hard

8
S.8.1-B.2 Focus Rev Hard

8
P.9.1-B.1 Etalon 1 Inserted S.13.1-B.3 Articulation Home 9
P.9.1-B.1 Etalon 1 Inserted S.10.2-B.3 Grating Rotate Home 9
P.9.1-B.1 Etalon 1 Inserted P.10.1-B.2 Grating Removed 9
P.9.2-B.1 Etalon 2 Inserted S.13.1-B.3 Articulation Home 9
P.9.2-B.1 Etalon 2 Inserted S.10.2-B.3 Grating Rotate Home 9
P.9.2-B.1 Etalon 2 Inserted P.10.1-B.2 Grating Removed 9
P.9.3-B.2 Etalon 1 Latch Removed S.13.1-B.3 Articulation Home 9
P.9.3-B.2 Etalon 1 Latch Removed S.10.2-B.3 Grating Rotate Home 9
P.9.3-B.2 Etalon 1 Latch Removed P.10.1-B.2 Grating Removed 9
P.9.3-B.3 Etalon 1 Door Open

9
P.9.4-B.2 Etalon 2 Latch Removed S.13.1-B.3 Articulation Home 9
P.9.4-B.2 Etalon 2 Latch Removed S.10.2-B.3 Grating Rotate Home 9
P.9.4-B.2 Etalon 2 Latch Removed P.10.1-B.2 Grating Removed 9
P.9.4-B.3 Etalon 2 Door Open

9
P.10.1-B.1 Grating Inserted P.9.1-B.2 Etalon 1 Removed 10
P.10.1-B.1 Grating Inserted P.9.3-B.1 Etalon 1 Latch Inserted 10
P.10.1-B.1 Grating Inserted P.9.2-B.2 Etalon 2 Removed 10
P.10.1-B.1 Grating Inserted P.9.4-B.1 Etalon 2 Latch Inserted 10
P.10.1-B.1 Grating Inserted S.10.1-B.6 Grating Magazine Station 10
P.10.1-B.2 Grating Removed

10
S.10.1-B.1 Grating Magazine Fwd Hard

10
S.10.1-B.2 Grating Magazine Rev Hard

10
S.10.1-B.3 Grating Magazine Home

10
S.10.1-B.4 Grating Magazine Station 1

10
S.10.1-B.5 Grating Magazine Station 2

10
S.10.1-B.6 Grating Magazine Station

10
S.10.2-B.1 Grating Rotate Fwd Hard

10
S.10.2-B.2 Grating Rotate Rev Hard

10
S.10.2-B.3 Grating Rotate Home

10
S.10.2-B.4 Grating Rotate Home 1

10
S.10.2-B.5 Grating Rotate Home 2

10
P.11.1-B.1 Beamsplitter Inserted

11
P.11.1-B.2 Beamsplitter Removed

11
P.12.1-B.1 Filter Inserted S.12.1-B.6 Filter Magazine Station 12
P.12.1-B.2 Filter Removed

12
S.12.1-B.1 Filter Magazine Fwd Hard

12
S.12.1-B.2 Filter Magazine Rev Hard

12
S.12.1-B.3 Filter Magazine Home

12
S.12.1-B.4 Filter Magazine Station 1

12
S.12.1-B.5 Filter Magazine Station 2

12
S.12.1-B.6 Filter Magazine Station

12
P.13.1-B.1 Articulation Detente Inserted

13
P.13.1-B.2 Articulation Detente Removed

13
P.13.1-B.3 Articulation Detente Caught

13
S.13.1-B.1 Articulation Fwd Hard

13
S.13.1-B.2 Articulation Rev Hard

13
S.13.1-B.3 Articulation Home

13

Limit Checks

Any no time should any limits be asserted. Here are the limits. These are fed into the National Instruments 7334 motion control card, which prevents motion into a limit.

Hard Limits
Limit Code Avoidance Action
Mask Elevator Fwd Hard S.5.1-B.1 Home Indicator Move Rev
Mask Elevator Rev Hard S.5.1-B.2 Cable Encoder Move Fwd
Focus Fwd Hard S.8.1-B.1 LVDT Move Rev
Focus Rev Hard S.8.1-B.2 LVDT Move Fwd
Grating Magazine Fwd Hard S.10.1-B.1 Cable Encoder Move Rev
Grating Magazine Rev Hard S.10.1-B.2 Cable Encoder Move Fwd
Filter Elevator Fwd Hard S.12.1-B.1 Home Indicator Move Rev
Filter Elevator Rev Hard S.12.1-B.2 Cable Encoder Move Fwd
Articulation Fwd Hard S.13.1-B.1 Home Indicator Move Rev
Articulation Rev Hard S.13.1-B.2 Open Loop* Move Fwd

* Open loop means that an incremental encoder will be initialized as part of a power-up sequence, and then that encoder will be subsequently relied upon to avoid the hard limits without any additional indicators. The hard limits will be avoided during initialization by using a center switch to indicate the hunt direction, and a home indicator to reset the encoder. The hard limits themselves, of course, provide the next level of protection for the hardware.

Initialization and Safing

To initialize PFIS or recover it from an unknown state, perform these steps.

  1. Apply power to the PXI Chassis
  2. Reset the motion control cards
  3. Turn off power to the stepper motors
  4. Turn off power to the pneumatic solenoids
  5. Command all pneumatic relays to the off state
  6. Apply power to the pneumatics
  7. Execute the sensor self-checks, the limit checks, and the state checks.
  8. Apply power to the stepper motors
  9. Recover the slitmask mechanism into a safe state
  10. Recover the grating mechanism into a safe state

At the end of this procedure, PFIS indicators should be in a safe state.

This table specifies the indicators that must be asserted for the PFIS to be in a safemode state.

Mech. # Sensor Code Item
5 P.5.1-B.1 Mask Fetched
5 P.5.2-B.2 Mask Removed
5 S.5.1-B.3 Mask Elevator Home
6 P.6.1-B.2 HWP Removed
6 P.6.2-B.1 HWP Detente Inserted
6 P.6.3-B.2 QWP Removed
6 P.6.4-B.1 QWP Detente Inserted
6 P.6.5-B.2 QBL Removed
7 P.7.1-B.2 Shutter Closed
7 P.7.2-B.2 Shutter Assist Off
9 P.9.1-B.2 Etalon 1 Removed
9 P.9.2-B.2 Etalon 2 Removed
9 P.9.3-B.1 Etalon 1 Latch Inserted
9 P.9.4-B.1 Etalon 2 Latch Inserted
10 P.10.1-B.2 Grating Removed
10 S.10.1-B.3 Grating Magazine Home
10 S.10.2-B.3 Grating Rotate Home
11 P.11.1-B.2 Beamsplitter Removed
12 P.12.1-B.2 Filter Removed
12 S.12.1-B.3 Filter Magazine Home
13 P.13.1-B.1 Articulation Detente Inserted
13 S.13.1-B.3 Articulation Home
13 S.13.1-R.1 Articulation Blake Release\

State Tables and Diagrams

Some of the PFIS mechanisms are complicated enough to require state information: the slitmask, the grating, and the filter mechanisms.

Slitmask State Table

Slitmask State Table
State # State Name Fetched Inserted Home
S2 Station - Mask - - -
S1 Home - Mask - - X
S0 Unknown - X -
S0 Unknown - X X
S3 Station + Mask X - -
S4 Home + Mask X - X
S0 Unknown X X -
S5 Inserted X X X

Waveplate State Table

The waveplate pneumatics are a little tricky. There are 3 legal states: unpolarized, linear, and circular. These states are achieved with 3 pneumatics, which therefore provide 5 unwanted states. We need to move from state to state in particular order, and to move from an illegal state to a legal state in the fastest way, which is to change the state of exactly one of the 3 pneumatics.

Waveplate State Table
State QWP Inserted HWP Inserted QBL Inserted State Name Next State Next Action
S1 - - - Open S2 QBL Insert
S2 - - X QBL, Not Useful S3 or S1 HWP Insert or ~QBL Insert
S0 - X - conflict S1 ~HWP Insert
S3 - X X Linear S4 or S2 QWP Insert or ~HWP Insert
S0 X - - conflict S1 ~QWP Insert
S0 X - X conflict S2 ~QWP Insert
S0 X X - conflict S4 QBL Insert
S4 X X X Circular S3 ~QWP Insert

QWP: Quarter-wave Plate
HWP: Half-wave Plate
QBL: Quarter-wave Blank (used for linear polarimetry)

Note that of the four illegal states, three of them require opening a relay instead of closing one. With a power failure, the mechanism automatically springs into the Open state.

Shutter State Table

The shutter has states because of the pneumatic assist. The pneumatic assist actuator allows the shutter solenoid to be turned off during an exposure. The shutter is kept open by the pneumatic, whose control solenoid is in a cooled control box. The pneumatic assist actuator can be disabled, so that the shutter can be used with only its solenoid, during short and repetitive exposures.

The sequence of events is this:

1. The shutter open command (P.7.1-R.1) is asserted by the software.

2. The electronics applies the full opening voltage to the shutter solenoid. This circuitry has digital logic built into it, so that it relaxes into the standby voltage after 0.5 seconds.

3. Upon detection of the shutter open indication (P.7.1-B.1), the circuitry asserts the pneumatic assist (P.7.2-R.1) if enabled by the digital output P.7.2-D.1.

4. When the shutter assist on indication (P.7.2-B.1) is detected, the power is cut to the solenoid. Note that the software is still asserting the shutter open bit.

5. When the shutter open bit is de-asserted, the shutter assist pneumatic is returned to its normally off position.

Shutter State Table
State Shutter Assist Enable Shutter Assist On Shutter Open Actions
0 - - - Solenoid off
Pneumatic off
1 - - X Solenoid on
Pneumatic off
2* - X - Solenoid off
Pneumatic on
3* - X X Solenoid on
Pneumatic on
4 X - - Solenoid off
Pneumatic off
5 X - X Solenoid on
Pneumatic on when shutter is open
Solenoid off when assist is sensed
6* X X - Solenoid off
Pneumatic on
7* X X X Solenoid on
Pneumatic on

* = Not a normal state

Grating State Table

Grating State Table
State # State Name Magazine Station Rotate Home Inserted
0 Select Grating X X -
1 Insert Grating X X X
2 Rotate Grating X - X
3 Rotate Home X X X
4 Remove Grating X X -

Filter State Table

Filter State Table
State # State Name Filter Station Inserted
0 Select Filter X -
1 Insert Filter X X
4 Remove Filter X -

Articulation State Table

Articulating the camera arm requires careful use of the articulation brake and motor power.

Articulation State Table
State # State Name Detente Removed Detente Caught Detente Inserted Motor Killed Brake Released
0 Safe - X X X -
1 Motor On - X X - -
2 Remove Detente X - - - -
3 Brake Off X - - - X
4 Insert Detente - X - - X
5 Motor Off - X X X X
6 Brake On - X X X -