Difference between revisions of "Pre-processing LFI"

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== The LFI scientific telemetry ==
 
== The LFI scientific telemetry ==
 
Each LFI radiometer provides two analog outputs, one for each amplifier
 
Each LFI radiometer provides two analog outputs, one for each amplifier
chain. In a nominal configuration, each output yields a sequence of alternating
+
chain. In a nominal configuration, each output yields a sequence of alternating <math>V_{sky}</math>, <math>V_{load}</math> signals at the frequency of the phase switch. By changing the phase switches configuration, the output can be a sequence of either <math>V_{sky}</math> or <math>V_{load}</math> signals.
<math>V_{sky}</math>, <math>V_{load}</math> signals at the frequency of the phase switch. By changing the
+
 
phase switches configuration, the output can be a sequence of either <math>V_{sky}</math> or
+
The conversion from analog to digital form of each radiometer output is performed by a 14 bits Analog-to-Digital Converter (ADC) in the Data Acquisition Electronics unit (DAE). The DAE transforms the signal in the range [-2.5 V, +2.5 V]: first it applies a tunable ''offset'', <math>O_{DAE}</math>, then it amplifies the signal with a tunable ''gain'', <math>G_{DAE}</math>, in order to make full use of the resolution of the ADC, and finally the signal is integrated. To eliminate phase switch raise transients, the integration takes into account a ''blanking time'', i.e. a blind time in the integrator where data are not considered. The default value of the blanking time is 7.5 <math>\mu s</math>. Both the <math> O_{DAE}</math>, the <math>G_{DAE}</math> and the blanking time are parameters set through the LFI on-board software. The equation applied to transform a given input signal <math>V_{in}</math> into an output <math>V_{out}</math> is:
<math>V_{load}</math> signals.
 
  
The conversion from analog to digital form of each radiometer output is performed by a
 
14 bits Analog-to-Digital Converter (ADC) in the Data Acquisition Electronics
 
unit (DAE). The DAE transforms the signal in the range [-2.5 V, +2.5 V]: first
 
it applies a tunable ''offset'', <math>O_{DAE}</math>, then it amplifies the signal
 
with a tunable ''gain'', <math>G_{DAE}</math>, in order to make full use of the
 
resolution of the ADC, and finally the signal is integrated. To eliminate
 
phase switch raise transients, the integration takes into account a ''blanking time'',
 
i.e. a blind time in the integrator where data are not
 
considered. The default value of the blanking time is 7.5 <math>\mu s</math>. Both the
 
<math> O_{DAE}</math>, the <math>G_{DAE}</math> and the blanking time are parameters set through
 
the LFI on-board software. The equation applied to transform a given input
 
signal <math>V_{in}</math> into an output <math>V_{out}</math> is:
 
  
 
<math>
 
<math>
Line 34: Line 21:
 
</math>
 
</math>
  
with <math>{G_{DAE} = 1, 2, 3, 4, 6, 8, 12, 16, 24, 48}</math>, <math>O_{DAE}</math> is one of 255 possible offset steps from +0 up to +2.5 V and where <math>Z_{DAE}</math> is a small offset introduced by the DAE when applying a
+
 
selected gain. The values of <math>G_{DAE}</math> and <math>O_{DAE}</math> are set by
+
with <math>{G_{DAE} = 1, 2, 3, 4, 6, 8, 12, 16, 24, 48}</math>, <math>O_{DAE}</math> is one of 255 possible offset steps from +0 up to +2.5 V and where <math>Z_{DAE}</math> is a small offset introduced by the DAE when applying a selected gain. The values of <math>G_{DAE}</math> and <math>O_{DAE}</math> are set by
 
sending, through specific telecommands, the DAE Gain Index (DGI) and the DAE
 
sending, through specific telecommands, the DAE Gain Index (DGI) and the DAE
 
Offset Index (DOI) associated to the desired values.
 
Offset Index (DOI) associated to the desired values.
Line 42: Line 29:
 
V</math>, so that the quantization step is <math>q_{ADC}=5.0/2^{14} = 0.30518</math> mV. The quantization
 
V</math>, so that the quantization step is <math>q_{ADC}=5.0/2^{14} = 0.30518</math> mV. The quantization
 
formula is
 
formula is
 +
  
 
<math>
 
<math>
 
P = \text{round} \left(\frac{V_{out} + 2.5}{q_{ADC}} \right),
 
P = \text{round} \left(\frac{V_{out} + 2.5}{q_{ADC}} \right),
 
</math>
 
</math>
 +
  
 
and the output is stored as an unsigned integer of 16 bits.
 
and the output is stored as an unsigned integer of 16 bits.
  
The digitized scientific data is then processed by the Radiometer Electronics
+
The digitized scientific data is then processed by the Radiometer Electronics Box Assembly (REBA) which runs the LFI on-board software. For each LFI detector, the REBA processes the data in the form of time series which are split into telemetry packets. To satisfy the LFI assigned telemetry budget limit of 53.5 Kbps, the REBA implements 7 acquisition modes (processing types) which reduce the scientific data rate by applying a number of processing steps. The following figure illustrates the main steps of the on-board processing and the corresponding processing types (PTypes).
Box Assembly (REBA) which runs the LFI on-board software. For each LFI detector, the REBA processes the data in the form of time series which are split into telemetry packets.
+
 
 +
[[File:ptypes.png]]
 +
 
 +
; ''PType 0'': in this mode the REBA just packs the raw data of the selected channel without any processing.
 +
; ''PType 1'': consecutive <math>V_{sky}</math> or <math>V_{load}</math> samples are coadded and stored as unsigned integers of 32 bits. The number of consecutive samples to be coadded is specified by the <math>N_{aver}</math> parameter.

Revision as of 16:21, 17 October 2012

Overview[edit]

The first processing level of the LFI DPC is the so called Level 1. The source data of the Level 1 software includes:

  • raw housekeeping telemetry packets retrieved from different satellite subsystems: the LFI instrument, the Sorption cooler, the HFI instrument and the Central Data Management Unit (CDMU).
  • the LFI raw scientific telemetry
  • Additional auxiliary data provided by the MOC and the Flight dynamics:
    • The Attitude History File (AHF)
    • Time correlation data (time correlation coefficients and time couples)
    • The Sorption cooler out of limit data

Only a subset of the raw housekeeping telemetry packets is daily processed and converted into TOIs, i.e. those relevant to the LFI DQR production and the estimation of the LFI instrument systematic effects.

The LFI scientific telemetry[edit]

Each LFI radiometer provides two analog outputs, one for each amplifier chain. In a nominal configuration, each output yields a sequence of alternating [math]V_{sky}[/math], [math]V_{load}[/math] signals at the frequency of the phase switch. By changing the phase switches configuration, the output can be a sequence of either [math]V_{sky}[/math] or [math]V_{load}[/math] signals.

The conversion from analog to digital form of each radiometer output is performed by a 14 bits Analog-to-Digital Converter (ADC) in the Data Acquisition Electronics unit (DAE). The DAE transforms the signal in the range [-2.5 V, +2.5 V]: first it applies a tunable offset, [math]O_{DAE}[/math], then it amplifies the signal with a tunable gain, [math]G_{DAE}[/math], in order to make full use of the resolution of the ADC, and finally the signal is integrated. To eliminate phase switch raise transients, the integration takes into account a blanking time, i.e. a blind time in the integrator where data are not considered. The default value of the blanking time is 7.5 [math]\mu s[/math]. Both the [math] O_{DAE}[/math], the [math]G_{DAE}[/math] and the blanking time are parameters set through the LFI on-board software. The equation applied to transform a given input signal [math]V_{in}[/math] into an output [math]V_{out}[/math] is:


[math] V_{out} = G_{DAE}(V_{in} + O_{DAE}) + Z_{DAE} [/math]


with [math]{G_{DAE} = 1, 2, 3, 4, 6, 8, 12, 16, 24, 48}[/math], [math]O_{DAE}[/math] is one of 255 possible offset steps from +0 up to +2.5 V and where [math]Z_{DAE}[/math] is a small offset introduced by the DAE when applying a selected gain. The values of [math]G_{DAE}[/math] and [math]O_{DAE}[/math] are set by sending, through specific telecommands, the DAE Gain Index (DGI) and the DAE Offset Index (DOI) associated to the desired values.

The ADC quantizes the [math]V_{out}[/math] uniformly in the range [math]-2.5 V \le V_{adc} \le +2.5 V[/math], so that the quantization step is [math]q_{ADC}=5.0/2^{14} = 0.30518[/math] mV. The quantization formula is


[math] P = \text{round} \left(\frac{V_{out} + 2.5}{q_{ADC}} \right), [/math]


and the output is stored as an unsigned integer of 16 bits.

The digitized scientific data is then processed by the Radiometer Electronics Box Assembly (REBA) which runs the LFI on-board software. For each LFI detector, the REBA processes the data in the form of time series which are split into telemetry packets. To satisfy the LFI assigned telemetry budget limit of 53.5 Kbps, the REBA implements 7 acquisition modes (processing types) which reduce the scientific data rate by applying a number of processing steps. The following figure illustrates the main steps of the on-board processing and the corresponding processing types (PTypes).

File:Ptypes.png

PType 0
in this mode the REBA just packs the raw data of the selected channel without any processing.
PType 1
consecutive [math]V_{sky}[/math] or [math]V_{load}[/math] samples are coadded and stored as unsigned integers of 32 bits. The number of consecutive samples to be coadded is specified by the [math]N_{aver}[/math] parameter.

(Planck) Low Frequency Instrument

Data Processing Center

(Planck) High Frequency Instrument

Command and Data Management Unit

[ESA's] Mission Operation Center [Darmstadt, Germany]

Attitude History File

Daily Quality Report

analog to digital converter

LFI Data Acquisition Electronics

LFI Radiometer Electronics Box Assembly