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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 ).