FM-ILT Resultsof the PACS FM1 Chopper
Markus Nielbock
Ulrich KlaasJeroen BouwmanHelmut DannerbauerJürgen SchreiberUlrich Grözinger
Marku
s Nie
lbock – FM
-ILT R
esu
lts of P
AC
S FM
1
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
Marku
s Nie
lbock – FM
-ILT R
esu
lts of P
AC
S FM
1
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°
Marku
s Nie
lbock – FM
-ILT R
esu
lts of P
AC
S FM
1
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
Marku
s Nie
lbock – FM
-ILT R
esu
lts of P
AC
S FM
1
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
s Nie
lbock – FM
-ILT R
esu
lts of P
AC
S FM
1
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
Marku
s Nie
lbock – FM
-ILT R
esu
lts of P
AC
S FM
1
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
s Nie
lbock – FM
-ILT R
esu
lts of P
AC
S FM
1
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
s Nie
lbock – FM
-ILT R
esu
lts of P
AC
S FM
1
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
s Nie
lbock – FM
-ILT R
esu
lts of P
AC
S FM
1
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
Marku
s Nie
lbock – FM
-ILT R
esu
lts of P
AC
S FM
1
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
s Nie
lbock – FM
-ILT R
esu
lts of P
AC
S FM
1
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
s Nie
lbock – FM
-ILT R
esu
lts of P
AC
S FM
1
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
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