Planck Pre-Launch Status Papers - APC - Université Paris Diderot ...

M. Bersanelli et al.: Planck pre-launch status: Design and description of the Low Frequency InstrumentFig. 22. Schematics of the grounding scheme of LFI.Table 11. LFI characteristic internal frequencies.Fig. 23. Schematics of the cryoharness serving HEMT biasing, phaseswitch biasing, and temperature sensors. Heat loads on the 20 K stageare minimised by intercepting heat with the V-grooves.compression (by a factor of 2.4 for at least the 95% of thepackets) performed in the REBA SPU (Sect. 4.5), the sciencedata volume is 36.12 Kbps, increased to 37.88 Kbps by packetingoverheads. An additional contribution of up to 5.06 Kbpscomes from the so-called “calibration channel”: for diagnosticpurposes, one LFI channel at a time will be transmitted to theground without compression. Adding 2.57 Kbps of housekeepingleads to a total budget of 45.41 Kbps for LFI, well withinthe allocated 53.5 Kbps (see Table 12). It is critical that the (average)2.4 compression factor be achieved with an essentiallylossless process, which requires careful optimisation of the parametersthat control the on-board compression algorithm in theSPU (Maris et al. 2009). After telemetry transmission, the datawill be treated through LFI DPC “Level 1” (Zacchei et al. 2009)for real-time assessment, housekeeping monitoring, and data decompression.Then the time-order information (TOI) will beν Origin Unit1Hz ........... Housekeepingacquisition frequency DAE BEU1Hz ........... Synchronisationsignal DAEBEU,REBA10 Hz . . . . . . . . . . Internal timer SCS1kHz.......... Lockingclocks SCS4096 Hz . . ..... PhaseSwitch FEM,DAEBEU100 kHz . . . . . . . 5 V & 12 V DC/DC SCS131 072 Hz . . . . . DC/DC converters DAE Power box131 072 Hz . . . . . On-board clock signal DAE BEU, REBA131 072 Hz . . . . . LOBT clock SCS200 kHz . . . . . . . 12 V DC/DC SCS1MHz ......... CommandlinkfromtheBEUbox DAEpowerbox1MHz ......... Internaltransferofdigitaldata DAEBEU,REBA8MHz ......... ADCclock SCS10/80 MHz . . . . . 1355 serial data digital interface DAE BEU, REBA16 MHz . . . . . . . . DSP processor clock SCS17.46 MHz . . . . . Clock frequency of the DSP REBA20 MHz . . . . . . . . Sequencer internal clock DAE BEUTable 12. LFI data rate summary.30 GHz 44 GHz 70 GHzNumber of detectors . . . . . . . . . . . . . . . . . 8 12 24Angular resolution (nominal) ......... 33 ′ 24 ′ 14 ′Beam crossing time [ms] . . . . . . . . . . . . . 92 64 39Sampling rate [Hz] . . . . . . . . . . . . . . . . . . 32.51 46.55 78.77Science data rate [Kbps] . . . . . . . . . . . . . 8.32 17.87 60.49Total science data rate . . . . . . . . . . . . . . . 86.69 Kbpsafter compression . . . . . . . . . . . . . . . 36.12 KbpsTotal LFI data rate . . . . . . . . . . . . . . . . . . 45.41 Kbpsgenerated and processed by the successive analysis steps in theDPC pipeline.Page 19 of 21