SSWG Meeting 2006 May 8

SSWG May ’06: SAMS

SSWG Meeting 2006 May 8

Agenda

• SAMS Hardware overview

• SAMS Software overview

• System status – performance to date

• Future work

SSWG Meeting 2006 May 8

Milestones for SAMS

  Temperature span (C)

Relative Humidity (%)

Alignment RMS tiptilt (arcsec)

Milestone 1 3.2 < 66 0.1

Milestone 2 6.4 < 86 0.1

Historical records suggest this will require no realignment on 45% of nights and no more than 1 realignment per night for 70% of nights.

This should cover ~75% of nights with no realignment necessary and 90% with no more than 1 realignment required.

SAMS Hardware

• Hardware reliability has been impeccable except for 1 manufacturing defect since installation ( numerical module has since been repaired)

• 15 Sensors have burnt since commissioning the 4th and 5th rings of the array – represents a sensor failure rate of 3.1%

• Burnt sensors are systematically replaced and drifting sensors are continually being investigated and fixed.

• 96% of sensors work correctly, the balance consists of 9 burnt and 12 drifting sensors.

• 2 segments have been coated and passed the capacitance test after coating.

• 3 sensors did however fail shortly after being put back into service – damage may have been caused by improper handling, further investigation required

SSWG Meeting 2006 May 8

SAMS Software

• The LabView portion of the system is stable and working reliably since the upgrade ( Oct 2005)

• The upgraded rack software has solved all of the delay and spurious measurement issues ( jumps and severe offsets)

• Phase 1 of the MACS sensor rejection software is complete

• Future software development will focus on refining the sensor rejection software

SSWG Meeting 2006 May 8

SAMS Software – Disabling drifting sensors

•Sensor Drifting: Disable sensor to avoid growth of FoM

•Possible to disable wrong sensor. Need more sophisticated approach. Working on it.

SSWG Meeting 2006 May 8

Array Control• 91 segments, 273 actuators, 480 edge sensors• Capacitive edge sensors measure voltages related to gap (G) between segments and relative height (H) of transmitter, receiver pair on adjacent edges

• G = GPOL(VG) where VG = gap voltage• H = SPOL(G) * VH + OPOL(G)• GPOL, SPOL, OPOL are 3rd order polynomials e.g., OPOL(G) = a3G

3 + a2G2 +a1G +a0

• Sensor height – actuator position: H = AS (A is a 480x273 matrix -> geometry)• Inverse problem: actuator positions from sensor heights: S = (ATA )-1 ATH

• SAMS integrates for 4 minutes -> H ; S -> tip, tilt, piston• Rows corresponding to drifting, bad sensors removed from A matrix• 4 segments constrained in piston to control global tip,tilt,piston and GRoC• Figure of Merit (FOM): rms difference between observed, expected H

• Error budget: 0.3asec(EE50) -> rms tiptilt ~0.1asec

SSWG Meeting 2006 May 8

Mode Correction

SSWG Meeting 2006 May 8

Mode Correction – Tried and rejected

Observed

Corrected usingsame night’s coefficients

Corrected usinglast night’s coefficients

SSWG Meeting 2006 May 8

Pseudo-heights

• Allow for local non-uniformities in truss deformation with change of T• Hp = H + H ; H = G = (G – G0) (OPOL -> OPOL`)• S = (AT•A)-1 AT Hp

SSWG Meeting 2006 May 8

Example Test: 2006-03-14Rms Tip/Tilt as measured by CCAS – first iteration polynomials drift 0.28 arcsec/2.5°C

SSWG Meeting 2006 May 8

2006-03-14 Pseudo-height polynomials (1) (from 2005 10 27) 0.14 arcsec/2.5°C

SSWG Meeting 2006 May 8

2006-03-14 Pseudo-height polynomials, 2nd iteration (from 2006 03 14) 0.06 arcsec/2.5°C. Maximum rms TT ~ 0.1 arcsec.

SSWG Meeting 2006 May 8

2006-03-13 Pseudo-height polynomials (1) and (2). <0.1arcsec/2°C.No hysteresis, but very little effect of revised polynomials – T gradients?

SSWG Meeting 2006 May 8

  

 

END

2006-03-14

SSWG Meeting 2006 May 8

  

 

END2006-03-13

SSWG Meeting 2006 May 8

  

 

Environmental Effects - Humidity

• Reference sensors on Sital blocks in cage below primary• 3 different fixed gaps cover range in actual array, fixed heights

SSWG Meeting 2006 May 8

SSWG Meeting 2006 May 8

SAMS Ongoing Investigations

• FEM analysis of effect of T gradients• Real-time polynomial modification to include environmental effects• Work session at Fogale (JWM(SAAO), BL and AC(Fogale))• Refinement of polynomials per sensor• Incorporation of RH data• Investigate use of wavefront sensing

SSWG Meeting 2006 May 8

  

 

END

SSWG Meeting 2006 May 8

Other things?

• modes, effect of sensor error on tt error• excess noise• effect of disabled sensors• mode correction à la JS

SSWG Meeting 2006 May 8

Test procedure

• Align primary; rms Tiptilt ~0.06 arcsec• Zero SAMS• Control segments with SAMS in closed loop• Observe primary with CCAS; record tip, tilt, piston

• Remove global Tip/Tilt, GRoC from SAMS data• Estimate true piston by least-squares• Compute SAMS height errors