PACS CQM/AVM ILT

AVM/CQM ILT – test results 1

PACS IQR 13 Jan 2005

PACS CQM/AVM ILTResults of functional/performance/ calibration tests



Major (science) requirements on PACS

Detectors: Sensitivity, Detector/readout noise (NEP), Dynamic Range

Image Quality: blur, distortion, misalignment

Spectral resolution, wavelength range, filter bands, photometric accuracy, ....

Chopper: frequency, duty cycle, stability on plateau, position accuracy, range (throw)

Calibration Sources: time constants, stability, emissivity

Stray Light: homogeneous, inhomogeneous

See

PACS Science Requirement Document

PACS Instrument Requirement Document

More PACS Sub-unit specifications and requirements documents...



Two cryogenic test phases (19-23 July, 6 Sep-29 Oct)

- Functional and Performance tests of all mechanisms, detectors, array read-outs, sensors and sources (Test/Analysis Reports), including Test Optics

- Calibration tests ( calibration files, reports)

- S/W tests and improvements (QLA, TA, IA, e.g. visualization, detector sorting, de-compression)

- Tests/debugging of warm electronics (e.g. DEC/MEC)

- Tests of command scripts (Tcl, CUS), On-Board Control Procedures (OBCPs), Astronomical Observation Templates (AOT)



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I) S/W and Warm Electronics



Detector Sorting Bolometer (IA Display Tool)

- Bolc Simulator Test Pattern reconstructed- Figure by IA Display tool

Bolometer Red

Bolometer Blue



Detector Sorting Spectrometer


PACS IQR 13 Jan 2005Detector Sorting Spectrometer (Status Ge:Ga arrays pixel performance (SCOS

result))


PACS IQR 13 Jan 2005Detector Sorting Spectrometer (Status Ge:Ga arrays pixel performance (SCOS

result))



PACS - QLA



IA Plot / Display

- Setting & saving Plot settings- Labels, Axis, zooming, hardcopy, plotsymbols, ...- Plot to PS without rendering- Well documented



II) Functional/Performance tests and instrument characterisation









Cross-reference: major (science) requirements on PACS vs. PCD

Detectors: Sensitivity 3.2.1, 3.2.6, 4.3.8

Detector/readout noise (NEP) 1.1.11, 1.1.12, 1.2.10

Dynamic range 1.2.3, 4.3.6

Image Quality: blur, distortion,

misalignment, PSF, ... 3.1.2, 3.1.3, 3.1.4, 4.1.1, 4.1.2, 4.1.3

Spectral resolution 4.2.2

Chopper: frequency, duty cycle, stability on plateau,

position accuracy, range (throw) 0.7.5, 0.7.6, 0.7.13, 2.3.2

Calibration Sources: time constants,

stability, emissivity 0.7.11, 0.7.12

Stray Light, ghosts: 3.1.5, 3.1.6, 4.2.4



II A) Photometer functional tests and characterisation



Performed tests (photometer)

- 0.7.1 FPU thermal behaviour (photometer)

- 0.7.2 Test of cooler recycling and operation

- 0.7.4 Verify function of bolometer detectors

- 0.7.5/6 and 2.3.2 Verify function of PACS chopper / performance test / duty cycle

- 0.7.7 Verify function of photometer filter wheels

- 0.7.11/12 Verify function of internal calibration sources / performance test

- 1.1.1 Control optimum pixel bias setting

- 1.1.10 Measure time constants after a flux change

- 1.1.11 Measure the low frequency noise

- 1.1.12 Measure the bolometer Noise Equivalent Power (NEP)



- 2.2.3 Optimum positioning of chopper on internal reference sources (bolometer)

- 2.5.1 Temporal stability of internal calibration sources

- 2.5.3/0.7.12 Time constants: heat-up & cool-down times of internal calibration sources

- 3.1.1 Central pointing position (photometer)

- 3.1.2 Relation between chopper position and angular displacement on sky

- 3.1.4 Photometer Point Spread Function (PSF)

- 5.1.1 OBCP and AOT tests

- many ad hoc tests (including tests of test equipment/test optics)

Conclusion: Tests were often hampered by DECMEC problems. Bolometer sufficiently tested for CQM ILT

purposes



Example 1 - Chopper FT, duty cycle

Analysis of the waveform of the chopper modulation for different chopping frequencies and chopper deflections both for rectangular (two-position) and triangular (three-position) chopping.

Duty cycle requirements:

- On sky: >80% for 0-10 Hz chopping frequency

- On Cal. Sources: > 70% (larger throw)



Actual chopper position vs. Time

(here: 0.8 Hz, ±1.2 degrees)

Fluctuations well within spec



Mean duty cycle for different chopping frequencies vs. chopping throw

Here: square modulation



Comparison to measurements of Zeiss

Compared to CQM measurements shorter swinging-in phase with smaller amplitude. Plateaux much smoother. Requirements fulfilled for all frequencies and deflections.

poorly adjusted DEC/MEC control parameters ?



Example 2 – PACS Calibration Sources

Analysis of the time constants and stability of the two internal calibration sources.



Heat-up and temperature plateau behaviour (after DECMEC adjustments)



Emissivity of calibration sources measured against OGSE cryogenic blackbody.Values close to design value.



Example 3 – Bolometer flat field and offset

s(i, j, p, T) = o(i, j) + g(i, j) × f(i, j, p, T)

Image of the offset Image of the flat-field (gain)

measured signal input signal

p=chopper position T=temperature

Module 5

Module 1 Module 2

Discarded pixels



Example 4 – Photometer Field of ViewChopper Step-Scan Across PACS FOV

• “Astronomical” field = cold OGSE BB• Internal calibrators set to 70 K (left) and 90 K (right)• No flatfielding applied

-0,20

-0,19

-0,18

-0,17

-0,16

-0,15

-0,14

-0,13

-0,12- 0,15 - 0,10 - 0,05 0,00 0,05 0,10 0,15



Example 4 - Chopper Step-Scan Across PACS FOV



OGSE BB1

OGSE BB2

Chopper position



• “Point source”: hole with equiv. diam. 7” (~2 pixels) in front of external blackbody

• Blue photometer, on-array chopping + nodding to remove very uneven OGSE background, no flat-field

Example 5 - First Point Source Image (Blue Photometer)

dead/bad subarrays+ beam

- beam

• “Point source”: hole with equiv. diam. 7” (~2 pixels) in front of external blackbody, on-array chopping+nodding

• “Point source”: hole with equiv. diam. 7” (~2 pixels) in front of external blackbody, on-array chopping+nodding

• Same source, “line scanning” mode, unprocessed data



Sigma of a 2D gaussian fit to the PSF of measured and simulated data

PSF wider than expected (25-50%). This discrepancy clealy needs investigation. Part (most?) of it may be due to the imperfect focus of the PACS/OGSE setup and to the non-nominal plate scale.

Strehl ratio can not be determined reliably right now.



Summary of preliminary analysis:

- OGSE external focus off the design position

- PSF wider than expected (25-50%)

- Misalignments (1-4 degrees) between XY stage, chopper, arrays and subarrays

- Plate scale of the OGSE/PACS setup (mm on XY stage vs. pixels on detector array) is 10% off the design value. Assumed explanation: caused by de-focus.

Several of these results imply modifications of OGSE setup, test procedure and/or planning of FM tests. But there are no implications for CQM IST at this point.



Example 6 – Time constants after switch-on

OGSE BB1 (29K) and 2 (6.5K), OGSE chopper wheel at 500mHz



Example 6 – Time constants after switch-on

• Bolometer signal roughly stabilized within 2 hours after the switch-on

• Implications for observing strategy will be discussed at AOT workshop



Example 7 – Bolometer Responsivity, Noise Spectrum, NEP

Responsivityon OGSE BBs1 x 1010 V/W

1/f knee ~0.125 Hz

Noise density 5 µV/Hz1/2

NEP = 5 x 10-16 W/Hz1/2,as measured at subunitlevel tests



Example 7 – Bolometer Responsivity, Noise Spectrum, NEP



II B) Spectrometer functional tests and characterisation



Performed tests (spectrometer)

- 0.7.1 FPU thermal behaviour (spectrometer)

- 0.7.3 Verify function of Ge:Ga detectors, CREs, detector heaters and related temperature sensors; many CRE tests for testing of compression/de-compression, DECMEC etc.

- 0.7.5/6 Verify function of PACS chopper (spectrometer), performance test

- 0.7.7 Verify function of spectrometer filter wheels

- 0.7.8 Verify function of grating

- 0.7.11/12 Verify function of internal calibration sources / performance test

- 1.2.1 Optimum detector bias settings

- 1.2.3 Dynamic range per selected integration capacitor

- 1.2.4 CRE check-out voltage

- 1.2.6 Detector dark current

- 1.2.11 Linearity of CRE readout

- 2.3.2 Duty cycle of chopper waveforms



- 2.3.3 Optimum positioning of chopper on internal reference sources (spectrometer)

- 2.5.2 Spatial stability of internal calibration sources

- 4.1.1 Spectrometer central pointing position and grating alignment

- 4.1.3 Spectrometer PSF

- 4.2.1 Grating wavelength calibration

- 4.3.2 Flux reproducibility internal sources

- 4.3.4 Flux reproducibility external sources

- 4.3.5 Linearity with flux

- 4.3.8 Relative Spectral Response Function spectrometer

- 5.2.1/2 OBCP tests, calibration AOT

- Spectral map focal plane

- Attempts with external laser

- many ad hoc tests (in particular to debug DECMEC, CRE tests)

Conclusion: Tests were often hampered by DECMEC problems (including CRE settings) and by spectrometer filter wheel being stuck.



Example 8 – grating drive performance

Oscillations within specs



Example 9 – grating wavelength calibration

Against water vapor absorption spectrum,

Input source: external BB, 25.4mm, T=730C,

absorption path in air: ~20 cm







The S/N on quite a number of pixels and a number of lines has been very poor, such that substructure in the continuum may cause apparent shifts of the measured peak positions.

Strongly fringed pixels in the red section have not been used in this analysis.

The accuracy of the reference water spectrum is limited, air temperature and pressure have not been monitored and no other air species than H2O have been included in the calculations. Some small systematic offsets for blended water lines may therefore be present in the reference list.

Given these problems, no attempt has been made to improve further on the calibration accuracy, by fitting correction polynomials to individual modules/pixels. The present accuracy for the red spectrometer is of the order of a resolution element while for the blue section it is better, more of the order half to a third of a spectral resolution element.



Example 10 – Fringes



Example 11 – Spectral resolution and Instrumental Profile



Example 12 – Spectral Leakage and Ghosts

2nd order leaking into 1st order (dichroic cut-off), plus 0th order ?

3rd order leaking into 2nd order (blue filter cut-off)

Strong narrow features beyond band limit (?)



Example 12 – Spectral Leakage and Ghosts

Multiple reflections of 2nd order leaking into 1st order (?)

Angular dependent filter transmission (?)



Example 13 – grating health checks/change in behaviour

Hall sensors vs. Grating position over time

Spectrum vs. Grating position over time

(This occured after DECMEC malfunction had driven grating against hard stop at full speed)



• “Point source”: hole with equiv. diam. 7” (~1 pixel) in front of external blackbody

• Blue spectrometer, (source on) – (source off)(averaged over the 16 spectral channels of each spatial pixel)

Good agreementwith predicted PSF

Example 14 - First Point Source Image (Spectrometer)



Example 16 – Signal/Noise Measurements (Red Module, QM5)

Measurement in detector testcryostat (MPE electronics)

Measurement in PACS(DECMEC)

S/N ratio as measured during module tests re-established during ILT with full signal/data chain



Example 16 – Signal/Noise Measurements (Blue Module)

Measurement in PACS(DECMEC)

(FM42)

Measurement in detector testcryostat (MPE electronics)



Example 17 – Optimum Detector Bias

The purpose of these calibration test (1.2.1 and 1.2.2) is to find the optimum bias voltage and temperature range where the detector operates under stable conditions and the NEP shows a minimum.

During CQM tests the heater on the blue detector array housing was not functional, therefore the detectors were kept at FPU temperature without active regulation. The optimisation procedure under these circumstances was restricted to a bias scan at constant FPU temperature.

In this DRAFT version no NEP was calculated but σ(si/|median(s)|) was derived instead, where si represents the the individual slopes on subramps and |median(s)| is the absolute value of slopes median. This measure is proportional to the NEP, the derived minima will not change when switching to NEP.



Example 17 – Optimum Detector Bias

The mean value in the red is ~75 mV. The mean value in the blue is ~200 mV.

blue red

Preliminary!



III) OBCPs, AOT definition



At present the following Observing modes are offered by PACS: - Line Spectroscopy - Range Spectroscopy - Dual band photometry - Single band photometry (basically as fall back or for parallel mode with SPIRE)

They will be commanded via On-Board Command Procedures (OBCPs), e.g.

- OBCP8: Grating Line scan with 2 or 3 position chopping- OBCP5: Photometry with 2 or 3 position chopping with dither- OBCP 10: Internal calibration I



Each AOT consists in principle of: - AOT specific setup - OBCP - Change_Setup - OBCP - Change_Setup - OBCP - ... - ... - Change_Setup - OBCP - AOT specific reset



- One example for an AOT (chopped photometry) was already implemented as CUS script (incl. OBSID and BBID).

- OBCPs (the AOT building blocks) and dedicated AOT tests were performed in ILT.

- A (2-day) workshop is planned (17-18 January 2005) to discuss further strategies for the (intimately linked) issues of AOT design, calibration files, and data analysis

- Next Milestones:- End 2004: Proof of concept- Mid 2005: Deliver parameter sets/AOT definitions and observing time calculator - - - End 2005: update calibration files (e.g. sensitivities) for time calculator



HSPOT communicates with the CUS Engine.

All parameters are passed from HSPOT to the CUS Engine.

Any calculations are done in the CUS Engine, because all logic is contained in the CUS script.

PACS will not provide a stand-alone time calculator but a first version of the AOT logic. The AOT logic is implemented in CUS scripts. AOT execution times will be calculated there. In addition to the time calculator the CUS engine will also contain a noise estimator (based for now on theoretical expectations).



Cross-reference: major (science) requirements on PACS vs. PCD

Detectors: Sensitivity 3.2.1, 3.2.6, 4.3.8

Detector/readout noise (NEP) 1.1.11, 1.1.12, 1.2.10

Dynamic range 1.2.3, 4.3.6

Image Quality: blur, distortion,

misalignment, PSF, ... 3.1.2, 3.1.3, 3.1.4, 4.1.1, 4.1.2, 4.1.3

Spectral resolution 4.2.2

Chopper: frequency, duty cycle, stability on plateau,

position accuracy, range (throw) 0.7.5, 0.7.6, 0.7.13, 2.3.2

Calibration Sources: time constants,

stability, emissivity 0.7.11, 0.7.12

Stray Light, ghosts: 3.1.5, 3.1.6, 4.2.4

Documents

PACS CQM/AVM ILT