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Picard Consortium meeting – PMOD/WRC, Davos, 29-30 Nov 2010
Diarad_SovaP instrument performance
( IRMB C. Conscience
 Radiometric equations
 Ground characterizations
 Flight calibrations
Tasks to finalize
for S. Dewitte )
Picard Consortium meeting – PMOD/WRC, Davos, 29-30 Nov 2010
A02, A03 Radiometric equations
Ideal radiometer :
 Pcl  Po 
SI  

 A 
Real radiometer :
 Pcl  Po   C1  C6 .1  C2  
SI  C5 
  C3  C4
'
  eff . A.1      ' '. cos  
Pcl 
Pcl _ t1  P cl _ t 3
2
“It becomes absolute when all corrections are characterized and
the measurements are traceable to international standards.”
Picard Consortium meeting – PMOD/WRC, Davos, 29-30 Nov 2010
Radiometric equation
•
 Precision aperture : A
 Power measurements : P
 Cavity efficiency : αeff
 Corrections
–
–
–
–
–
–
–
–
–
–
 Pcl  Po   C1  C6 .1  C2  
SI  C5 
  C3  C4
'
  eff . A.1      ' '. cos  
C1 : wires heating effect
C2 : precision of the servo-system
C3 : shutter emission
C4 : mirror emission
C5 : optical effects (diffraction, scattering, backscattering )
C6 : sensors thermal equilibrium
Δ : mirror free thermal dilatation
Δ' : mirror thermo-mechanical effects
Δ'' : mirror initial deformation due to the fixture torque
cos θ : depointing
Picard Consortium meeting – PMOD/WRC, Davos, 29-30 Nov 2010
Ground characterizations
 Electrical
–
–
–
–
–
–
–
–
characterisations :
Current measurement Resistor, R100 , in the lab.
Reference voltages, V1-->V6, V'1-->V'6 during Th.Vac.
Heating Resistor, R120 , during Th.Vac.
the sensitivity is measured in air & vacuum
Determination of parasitic Resistors, rc & rd , based on sensor sensitivity.
Adjusting power equilibrium of the cavities
Adjusting sensors equilibrium
Calibration of thermometer sensor
 Optical characterisations :
–
Quasi cylindrical tube profile
–
Cavity bottom uniformity
–
Cavity reflectance
 Mechanical characterisations :
–
Precision aperture, A, measured by NIST & NPL
Picard Consortium meeting – PMOD/WRC, Davos, 29-30 Nov 2010
Electrical characterization : Calibration voltages
Vn  a0  a1.Tres  a2 .Tres
2
Picard Consortium meeting – PMOD/WRC, Davos, 29-30 Nov 2010
Electrical characterization : Heater resistor
- A third order model of the heater resistor was established during the Th.Vac,
and is valid for [-30°C  45 °C], with a traceable AGSE. This model serves also for
quality control of the acquisition chains.
2
3
R120  a0  a1.Tbase  a2 .Tbase  a3.Tbase
Ohm
Rd(Tbase) en Rad05
120.34
120.335
120.33
120.325
120.32
120.315
120.31
120.305
120.3
120.295
120.29
120.285
120.28
120.275
120.27
120.265
120.26
Rd
45
40
35
30
25
20
15
10
5
0
-5
-10
-15
-20
-25
-30
°C
Picard Consortium meeting – PMOD/WRC, Davos, 29-30 Nov 2010
Electrical characterization : Heater parasitic resistor
Current flowing through the wires and the soldered
joints produce a small power that is detected by
the sensor and thus must be taken into account
in the radiometric equation.
Charaterization done with traceable DVM, and
based on the sensivity of the detector
R parasitic  rc  rd
[mOhm]
u [mOhm]
rc,left
3.23
0.15
rd,left
3.70
0.16
rc,right
3.86
0.29
rd,right
2.70
0.21
Picard Consortium meeting – PMOD/WRC, Davos, 29-30 Nov 2010
Optical characterization :
C5 : Correction factor for optical effects
Diffraction on precision aperture (δ’)
Scattering around the intrance aperture (Σ)
Backscattered radiation from volume between shutter
and precision area (Σ')
1
C5 
  ' '
Σ
7.5 10-6
from Solcon, to be updated
Σ’
45 10-6
from Solcon, to be updated
δ’
500 10-6
to be updated by NIST calculation
Picard Consortium meeting – PMOD/WRC, Davos, 29-30 Nov 2010
Mechanical characterization : Precision Apertures
 Area measured by NIST at 20°C
–
based on optical method
Aperture Sun side
 NPL has measured 4 diameters at 20°C
–
–
Aperture Sensor side
based on a mechanical method
with a measure of the departure from roundness
Picard Consortium meeting – PMOD/WRC, Davos, 29-30 Nov 2010
Mechanical Correction : free dilatation Δ
  2.k .(T  T0 )  k 2 .(T  T0 )2 
negligible
Δ = 0,00021 @ T = 32 °C
k
8.6 ppm/°C
Titanium
T0
20.0 °C
NPL, NIST
T
22°C  32 °C
Diarad in
flight
Picard Consortium meeting – PMOD/WRC, Davos, 29-30 Nov 2010
Flight calibration : corrections C3&C4
This correction has been calculated from the first stellar pointing.
–
~ - 1,15 W/m² ( loss of energy when the shutter is opened & T mirror decreases )
Tright shutter (closed)
Solar pointing
Stellar pointing
Tleft shutter (opened/closed)
ΔP = L_(shutter + mirror)
Picard Consortium meeting – PMOD/WRC, Davos, 29-30 Nov 2010
Flight calibration : corrections C3&C4
ΔTog = -13 °C
ΔTmg = -1.5 °C
Picard Consortium meeting – PMOD/WRC, Davos, 29-30 Nov 2010
Flight calibration : acquisition system
Sensor
V6
M
U
X
Amplifier
V/F
Counter
V1
During the 3’ that lasts a radiometric cycle, 6 calibration voltages are fed
into the acquisition system to calibrate it. A linear equation is established
between each counter and the 6 voltages.
Picard Consortium meeting – PMOD/WRC, Davos, 29-30 Nov 2010
Flight calibration : acquisition system
V_channel = A . counts + B
switch off/on
First switch on
Coefficients A, and B since the beginning of the mission : they track
variations in the acquisition system. The effect of the decreasing of the
Temperature of the V/F, due to “eclipses”, is visible in the green circles.
Picard Consortium meeting – PMOD/WRC, Davos, 29-30 Nov 2010
Uncertainty of the SI measurements in A02, A03
Uncertainty in [PPM]
u
Left cavity
Right cavity
Traceable
A
107
117
yes
Thermal effects
Δ
30
30
literature
Thermo-mechanical effects
Δ’
250
250
Fixation effects
Δ’’
250
250
αeff
190
190
C5
110
110
Solar pointing
Cos
TBAnalysed
TBAnalysed
Shutter correction
C3
39
39
Diaphragm correction
C4
19
19
Static error of the servo
C2
1.2
1.2
Sensor thermal equilibrium
C6
TBAnalysed
TBAnalysed
Wire heating effect
C1
0.8
1.5
yes
294
518
yes
Aperture
Cavity
absorption factor
Optical effects
Electrical chains
Combined uncertainty
Uc
523
677
Expanded uncertainty (k =2)
U
1046
1354
not yet
yes
Picard Consortium meeting – PMOD/WRC, Davos, 29-30 Nov 2010
Tasks to be finalized
WP1 : Optical corrections (Σ, Σ’, σ) need to be updated for SovaP
 WP2 : Depointing correction
–
Analyse CNES report for depointing between SovaP and reference surface.

WP3 : shutter & mirror corrections
Analyse in details stellar pointings to improve the correction.

WP4 : efficiency of the cavity

Extra calibration of tiles has been asked
 WP5 : corrections Δ’ , Δ’’ need to be characterized

Description of new setup and test is requested
 WP6 : estimate the global Uncertainty of the SI measurement
–
Case of A08 ( other radiometric equation for this mode ).