E S O O n l y	Control of the Field Stabilization System components (STRAP system, communication link to M6, liquid cooling). This system is used for Field Stabilization. The control is deployed on the Sensor LCU. This sub-system belongs to the ESO delivery. The device is connected to the connectors defined in [AD 03]. Field Stabilization System interfaces: The applicable documents for the FSS interface are [AD 03] and [AD 04].
	Item	From	To	Signal	Description	Pin
	COMMUNICATION:
	1	LCU	ATS	STRAP board console For maintenance only	RS232 Port	W31
	APD HEAD CONTROL:
	10	LCU	ATS	STRAP APD Head control lines	I/O lines to STRAP VME board
	11	LCU	ATS	STRAP APD Head signal lines	See [AD 03] and [AD 04]
	APD HIGH VOLTAGE:
	20	LCU	ATS	High Voltage lines	See [AD 03] and [AD 04]
	APD GATE CONTROL:
	30	LCU	ATS	APD gate control +	contact closed to close the APD gate Digital Output
	31	LCU	ATS	APD gate control -	Common
	32
	33	LCU	ATS	APD gate control 50W coax	50W coax
	34

E S O O n l y	Field Stabilization System Software Interface: The applicable document for the FSS software interface is [RD 07].
	Item	From	To	Signal	Description	Pin
	CONFIGURATION:
	2	LCU	ATS	STRAP Static Configuration (Can not be modified while APD is active)	Static parameters: Open/Close loop APD Gain Diagnostic sampling period Number of cycles Hook-function name etc ... (TBD) SW Command
E S O O n l y	3	LCU	ATS	STRAP Dynamic Configuration (May be modified while APD is active)	Dynamic parameters: Guide Reference Point Interaction Matrix Gate for APD gain control etc ... (TBD) SW Command
	CONTROL:
	4	LCU	ATS	Start STRAP	start APD acquisition with current configuration SW Command
	5	LCU	ATS	Stop STRAP	stop APD acquisition SW Command
	6	LCU	ATS	Gate APD gain	turn gate on/off for APD gain control (used in chopping mode when alternating between object and sky) SW Command or Digital Output
	7	LCU	ATS	Update Interaction Matrix	update interaction matrix (for derotating M6 corrections) SW Command
	8	LCU	ATS	Request Interaction Matrix	retrieve actual interaction matrix SW Command
	9	LCU	ATS	Update Reference Point (see Note 1 below)	update the APD reference point SW Command
	STATUS & DIAGNOSTICS:
	10	ATS	LCU	STRAP Status	get STRAP status SW Command / DB attribute
	11	ATS	LCU	STRAP diagnostics parameters	Diagnostics parameters: r0, t0, FWHM, SNR, centroid, extrema etc ... (TBD) SW Command / DB attribute
	12	LCU	ATS	Error Vector (see Note 2 below)	request the instantaneous Error Vector SW Command
	SYNCHRONIZATION:
	13	LCU	LCU	Function Hook (see Note 3 below)	hook a user-defined function synchronous to the APD control loop API Function
	Note 1: The guide reference point is theoretically the optical center of the APD sensor. Since the FSS Translation Stage is a tracking axis, its position will be updated while tracking. However, it might be necessary to interpolate its position between 2 updates. This is achieved by offsetting the APD reference point synchronously with the Translation Stage control loop. The offset shall be less than 1/2 Airy disk (i.e. approx. 0.2" on the sky) so as not to loose the object. Note 2: In order to compensate for tracking drift, the absolute offset of M6 is queried by the M6 Control Loop and sent to the telescope Alt/Az axes. The relative slow correction speed of the main axes allows not to recenter M6 but let the FS loop closed and active, that will bring M6 back to the center. Note 3: The ATCS Requirements specify the need of synchronizing the acquisition system with the guiding loop. On the UTs, this is implemented between the TCCD system and the AG/FS loops by means of a user-defined function hook that is invoked at each exposure. The details of the function are application specific, the interface is TBD (shall try to match the existing one). The function shall have access to the actual parameters describing the data acquired during this cycle (error vector, SNR, FWHM etc...).

Last modified: Wed Sep 20 15:24:28 METDST 2000