FM-ILT Resultsof the PACS FM1 Chopper

Markus Nielbock

Ulrich KlaasJeroen BouwmanHelmut DannerbauerJürgen SchreiberUlrich Grözinger

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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

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Chopper

Angular Calibration

19.07.2007

Goal 1: chopper position sensor read-out vs. rotation angle, i. e. ROU()

ZEISS: ZEISSFPU

FM-ILT: CSLFPU

FM-ILT: FPROU

ZEISS and DECMEC amplification factors

DECMEC conversion UFP 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°

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Chopper

19.07.2007

Goal 2: ROU = 0 for = 0°

define mechanical zero-point (Idrive = 0 mA) as = 0°

not identical with optical zero-point (optical axis)

measure ROU (equivalent to UFP) at = 0°

subtract zero-point offset from DECMEC read-out (CALU table)

Angular Calibration

original relation

mech

. Z

P

ZP corrected relation

nominal

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Chopper

19.07.2007

Angular Calibration

redundant

stored in two PCSS calibration files:PacsCal_ChopperAngle_FM_2_0.fitsPacsCal_ChopperAngleRedundant_FM_2_0.fits

access in JIDE with:from cal import *readCal(“AngularCalibration”, version=“FM_2_0”)readCal(“AngularCalibrationRedundant”, version=“FM_2_0”)

ROUFP() non-linearseparated 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°)

6th order polynomial fit

4th order polynomial fit

Marku

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Chopper

Static and Dynamic Properties

19.07.2007

Open-loop chopping (e. g. in SFT):

a) derive electro-mechanical characteristics of chopper systemb) good tool to detect possible damage of chopper

1. Rotational Eigenfrequency () and Oscillation Damping ()

close to values determined during module level tests at ZEISS

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Chopper

Static and Dynamic Properties

19.07.2007

2. Specific Torque (S)

FS

represents rotatability of chopper, i. e.:

S I

a) S decreases with rising deflectionb) behaves similar to ZEISS measurementc) higher by 3% compared to ZEISS, by 1% for redundant operations

less current neededd) smooth and monotonous relation with angle

no apparent chopper damage

Conclusion:

The FM1 chopper seems intact.

Marku

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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.

Marku

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Chopper

Performance

19.07.2007

1. Chopping at calibration sources (± 8°), nominal DECMEC

transition time: 23 msduty 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

Marku

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Chopper

Performance

19.07.2007

2. Chopping in sky window (± 4°), nominal DECMEC

transition time: 19 msduty cycle: 62%

specifications not met for 10 Hz chopping

symmetric in positive and negative anglescurrent peaks tolerable

+4°

-4°

If chopping at 5 Hz: 81% duty cycle

stable within rms = 2.7 rou

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Chopper

Performance

19.07.2007

3. Chopping in sky window (± 4°), redundant DECMECredundant nominal

behaviour similartransition time and duty cycle identical to nominalcontroller 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?

Marku

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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 ?

blu

ere

d

6 rou

7 rou

detector read-out begins on chopper movementchopper reaches end position after 24 msfirst 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.

Marku

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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