APD Sensor

• Control of the STRAP APD Quad-Cell Sensor.
  The device is controlled via the VMESTRAP board.



• The control is deployed on the Sensor LCU.

Hardware Interface:

The hardware interfaces are described in [AD 08], and more detailed information can be found in the STRAP documentation [AD 03] and [AD 04].

Software Interface:

The available commands for controlling the APD Sensor are described in the STRAP User Manual [RD 07].

Item	From	To	Command/Action	Parameter		Unit	Note
				Command	Reply
STRAP SETUP:
1	ATCS	STRAP	Write setup values to STRAP LCU database Interaction Matrix Diagnostic Period M6 Offset X,Y Sky Back Ground Integration Time Filter Frequency Send command NWSETUP	intMatrix[0-3] diagBufferLen spotOffsetX/Y skyBackground intTime thomsonFreq		[S.I.] ms arcsec ph/s ms Hz	1
STRAP DIAGNOSTIC MONITORING LOOP:
2	ATCS	STRAP	Trigger on DB event from STRAP diagnostic loop Read diagnostic data from STRAP LCU database Mean Values RMS values Status data		meanValue[0-7] rmsValues[0-7] status.<attr>		2
START STRAP ACQUISITION:
3	ATCS	STRAP	Send command OPENGAT Send command SETCTRL	TRUE TRUE			3
STOP STRAP ACQUISITION:
4	ATCS	STRAP	Send command SETCTRL Send command OPENGAT	FALSE FALSE			4
DISPLAY GUIDE DETECTOR SIGNALS:
5			UIF widgets available for guide detector signals display on WS				5
SET GUIDE REFERENCE POINT:
6			Not supported by firmware yet The Guide Reference Point will be managed by the Translation Stage				6
APD CONTROL LOOP:
7	ATCS	STRAP	Send command SETCTRL (Open Loop)	FALSE			7
8	ATCS	STRAP	Send command SETCTRL (Close Loop)	TRUE			8
APD GATE CONTROL:
9	ATCS	STRAP	(Write gate value in STRAP LCU database) Send command OPENGAT (Open Gate at n%)	gate = n TRUE		%	9
10	ATCS	STRAP	Send command OPENGAT (Close Gate = 0%)	FALSE
UPDATE INTERACTION MATRIX:
11	ATCS	STRAP	Write IM values in STRAP LCU database Send command NWSETUP	intMatrix[0-3]		[S.I.]	10
M6 CHOPPING CONTROL:
12	ATCS	STRAP	Timer Trigger to Phase ON Write M6 offset values in STRAP LCU database Send command NWSETUP Send command OPENGAT Send command SETCTRL	spotOffsetX/Y   TRUE TRUE		arcsec	11
13	ATCS	STRAP	Timer Trigger to Phase OFF Write M6 offset values in STRAP LCU database Send command NWSETUP Send command OPENGAT Send command SETCTRL	spotOffsetX/Y   FALSE FALSE		arcsec

Note 1: In [RD 07], the list of setup parameters is described in detail.
The skyBackground value is to be corrected from the Neutral Density filter set in the beam.

Note 2: The synchronization mechanism is based on LCU database event. Foreseen is a synchronization as for the TCCD software: a user-defined function shall be invoked each time new diagnostic data is available from the STRAP board. Similar interface is recommended (data buffer passed to the function). This function shall trigger the FS Loop task.
The FS Control Loop will also monitor the system status as of the database attributes (list is TBD).

Note 3: This sequence of commands does not correspond to the final implementation of the STRAP LCU software. It shall be replaced by the commands STRTCLP/STRTOLP/STRTCGS or START <CloseLoop | OpenLoop | Calibrate>.
The command STRTCGS is performing the necessary calibration on a new GS (automatic setting of internal parameters and integration time).
Check STRAP behaviour when spot is lost in Closed Loop (cloud passing by for example): No correction shall be sent to M6. The diagnostic data shall contain an additional flag indicating that no correction was sent. It is ATCS responsibility to decide to open the loop (stop acquisition).
STRAP must find a way to react timely on this event. This might impact on the STRAP firmware.

Note 4: This sequence of commands does not correspond to the final implementation of the STRAP LCU software. It shall be replaced by the command STOP.

Note 5: The UIF widgets are not available yet. The diagnostics must be updated on LCU DB (see setup parameter diagBufferLen). The update of the LCU database with the diagnostic data shall be activated each time the acquisition in Open or in Closed loop is started.

Note 6: The guide reference point is theoretically the optical center of the APD sensor. Since the Translation Stage is a tracking axis, its position will be updated during tracking. However, it might be necessary to interpolate its position between 2 updates, by offsetting the APD reference point synchronously with the Translation Stage control loop. Further investigation of the tracking accuracy of the Translation Stage is necessary; early estimates makes the dynamic APD offsetting not mandatory.
Check cost for firmware change to support this feature.

Note 7: The mirror M6 is preset to the setup parameters spotOffsetX and spotOffsetY.

Note 8: It takes 8 integration cycles to stabilize.

Note 9: The gate can be controlled either by SW or by Digital I/O.

Note 10: Mathematical analysis shall show how accurate therefore how often the IM shall be updated. The effective IM is the product of the configuration matrix IM(0) with the rotation matrix IM(a).

Note 11: ATCS is master of the synchronization. The spotOffsetX/Y values for Phase ON are either (0,0) or the previous tilt angles when switching to Phase OFF (TBC). Depending on the performances, it might be necessary to implement this feature in the STRAP firmware (TBC).

Future Releases of STRAP SW:

The following features shall be made available and commands shall be preferred: The STRAP SW must be brought to VLT Standards and comply with the SW device conventions.

Item	From	To	Command/Action	Parameter		Unit	Note
				Command	Reply
SPECIFIC COMMANDS and FEATURES:
1	ATCS	STRAP	Send command SETUP	Setup Parameters			12
2	ATCS	STRAP	User-Defined Hook function	Diagnostic Data Structure
3	ATCS	STRAP	Send command STRTCLP / STRTOLP / STRTCGS Send command START	OpenLoop/CloseLoop/Calibrate			13
4	ATCS	STRAP	Send command STOP
9 10	ATCS	STRAP	Send command SETGATE	Open/Close/n
11	ATCS	STRAP	Send command SETIM	a		degree	14
12 13	ATCS	STRAP	Send command PHASCHP	On/Off			15
STANDARD COMMANDS:
20	ATCS	STRAP	Standard command INIT				16
21	ATCS	STRAP	Standard command STANDBY STRAP LCU SW executes command SHUTDWN				17
22	ATCS	STRAP	Standard command ONLINE STRAP LCU SW executes command SETTEMP STRAP LCU SW executes command SETHV	TRUE TRUE			18

Note 12: The values of the sky background must be corrected for the ND filter transmission.

Note 13: The command STRTCGS performs the calibration procedure to be done once for each new GS. It yields the determination of the integration time, loop gain, gating, etc...
After discussion, the Neutral Density filter is left out of STRAP responsibility. ATCS shall set the appropriate ND filter corresponding to the GS magnitude.

Note 14: For enforcing the concept of data hiding, it is recommended to communicate the APD-M6 rotation angle only to the STRAP LCU Software. This avoids ATCS to have knowledge of IM(0) and risk to modify it unexpectedly.

Note 15: The command name stands for Phase Chopping. The M6 chopping position (in M6 coordinate system) must be given for each phase switching, because the APD and M6 are located on planes subject to field rotation.

Note 16: This command is essential for Release 1. This command shall perform the initialization procedure of STRAP (determination of the configuration/setup parameters: temperature, high voltages, etc...).

Note 17: This STRAP command is part of the operations performed by the STRAP LCU Software to switch the state of the STRAP device to STANDBY.

Note 18: These STRAP commands are part of the operations performed by the STRAP LCU Software to switch the state of the STRAP device to ONLINE.

Last modified: Wed Feb 16 17:25:42 MET 2000