1. FM-ILT Results of the PACS FM1 Chopper Markus Nielbock Ulrich Klaas Jeroen Bouwman Helmut Dannerbauer Jürgen Schreiber Ulrich Grözinger

2. Markus Nielbock – FM-ILT Results of PACS FM1 Chopper Calibration Overview 19.07.2007 1. Angular Calibration (PICC-MA-TR-021) mechanical zero-point (rest position) position sensor read-out vs. rotation angle 2. Static and Dynamic Properties (PICC-MA-TR-023) specific torque rotational eigenfrequency open-loop oscillation damping 3. Performance transition time vs. rotation angle duty cycle synchronisation with detector read-out current consumption

3. Markus Nielbock – FM-ILT Results of PACS FM1 Chopper Angular Calibration 19.07.2007 Goal 1: chopper position sensor read-out vs. rotation angle, i. e. ROU(  ) ZEISS:FM-ILT: ZEISS and DECMEC amplification factors DECMEC conversion U FP to ROU provided by ZEISS Chopper User Manual Recipe to derive angular calibration,but zero-points do not match. Goal 2: ROU = 0 for  = 0°

4. Markus Nielbock – FM-ILT Results of PACS FM1 Chopper 19.07.2007 Goal 2: ROU = 0 for  = 0° define mechanical zero-point (I drive = 0 mA) as  = 0° not identical with optical zero-point (optical axis) measure ROU (equivalent to U FP ) at  = 0° subtract zero-point offset from DECMEC read-out (CALU table) Angular Calibration original relation mech. ZP ZP corrected relation

5. nominal Markus Nielbock – FM-ILT Results of PACS FM1 Chopper 19.07.2007 Angular Calibration redundant stored in two PCSS calibration files: PacsCal_ChopperAngle_FM_2_0.fits PacsCal_ChopperAngleRedundant_FM_2_0.fits access in JIDE with: from cal import * readCal(“AngularCalibration”, version=“FM_2_0”) readCal(“AngularCalibrationRedundant”, version=“FM_2_0”) ROU FP (  ) non-linear separated into three parts: 1. sky range (± 4.1° = 3’ on sky) 2. neg. calibration source range (< -4.1°) 3. pos. calibration source range (> +4.1°) 6 th order polynomial fit 4 th order polynomial fit

6. Markus Nielbock – FM-ILT Results of PACS FM1 Chopper Static and Dynamic Properties 19.07.2007 Open-loop chopping (e. g. in SFT): a) derive electro-mechanical characteristics of chopper system b) good tool to detect possible damage of chopper 1. Rotational Eigenfrequency ( ) and Oscillation Damping (  ) close to values determined during module level tests at ZEISS

7. Markus Nielbock – FM-ILT Results of PACS FM1 Chopper Static and Dynamic Properties 19.07.2007 2. Specific Torque (S) FS represents rotatability of chopper, i. e.: SI a) S decreases with rising deflection b) behaves similar to ZEISS measurement c) higher by 3% compared to ZEISS, by 1% for redundant operations  less current needed d) smooth and monotonous relation with angle  no apparent chopper damage Conclusion: The FM1 chopper seems intact.

8. Markus Nielbock – FM-ILT Results of PACS FM1 Chopper Performance 19.07.2007 established by chopping with varying PID controller parameters Goal 1: duty cycle of ≥ 80% for science observations (± 4.1°) and chopping at 10 Hz Goal 2: duty cycle of ≥ 70% for calibration observations (~ 8°) and chopping at 5 Hz  10 ms transition time  30 ms transition time PID optimisation affected by oscillations of unknown origin  change of suppression filter required new set of PID parameters, only a few days for testing in FM-ILT 3 PID optimisation done for: ± 4.1° ± 8.5° both nominal and redundant Degraded mode (reduced set of drive coils) tests missing so far.

9. Markus Nielbock – FM-ILT Results of PACS FM1 Chopper Performance 19.07.2007 1. Chopping at calibration sources (± 8°), nominal DECMEC transition time: 23 ms duty cycle: 77% +8° -8°  specifications met symmetric in positive and negative angles current peaks tolerable linearisation of read-out sensor in DMC software stable within rms = 3.5 rou

10. Markus Nielbock – FM-ILT Results of PACS FM1 Chopper Performance 19.07.2007 2. Chopping in sky window (± 4°), nominal DECMEC transition time: 19 ms duty cycle: 62%  specifications not met for 10 Hz chopping symmetric in positive and negative angles current peaks tolerable +4° -4° If chopping at 5 Hz: 81% duty cycle stable within rms = 2.7 rou

11. Markus Nielbock – FM-ILT Results of PACS FM1 Chopper Performance 19.07.2007 3. Chopping in sky window (± 4°), redundant DECMEC redundant nominal behaviour similar transition time and duty cycle identical to nominal controller parameters can be easily converted Question: Can we chop faster? Maybe after modifying oscillation suppression filter. No time! Question: Can we live with the performance achieved?

12. Markus Nielbock – FM-ILT Results of PACS FM1 Chopper Performance 19.07.2007 4. Synchronisation with detector readout (spectrometer) chopping period between calibration sources: 5s lossless compression spectrometer read-out: full 250 Hz sampling 10 ramps per chopper plateau To what extent does chopping affect the detector signal ? blue red 6 rou 7 rou detector read-out begins on chopper movement chopper reaches end position after 24 ms first 6 – 7 read-outs of chopper plateau affected Question: How do we deal with this? a) discard first 7 read-outs (on-board software) b) discard whole ramp (significant loss of data) suggestions, feasibility studies Remark: Issue remains even for a faster chopper.

13. Markus Nielbock – FM-ILT Results of PACS FM1 Chopper Summary 19.07.2007 1. angular calibration achieved for nominal and redundant 2. chopper seems intact 3. duty cycle of 80% for chopping at 5 Hz 4. first 7 spectrometer read-outs of each chopper plateau affected by chopper movement Outlook: Control parameter verification and further optimisation planned for IST

14. Markus Nielbock – FM-ILT Results of PACS FM1 Chopper Title 19.07.2007