Download Swarm CEFI-LP Calibration Plan

Swarm CEFI-LP Calibration Plan
SW-TN-IRF-EF-001
[email protected]
v.1.1
2006-04-24
Document history
Version
Date
0.1
2006-04-18
1.0
2006-04-21
1.1
2006-04-24
Comment
Draft based on proposal.
Corrections to section 3 from Lennart.
Standardized document number
Contents
1.
2.
Functional testing and calibration concept ....................................................................................... 1
Unit ground test and calibration ....................................................................................................... 1
2.1 Setup ............................................................................................................................................... 1
2.2
Test scenario ............................................................................................................................. 2
2.3
Calibration scenario .................................................................................................................. 2
3. Ground tests at system level ............................................................................................................. 3
3.1 EMC ............................................................................................................................................... 3
3.2 Instrument verification during system tests .................................................................................... 3
4. LP in-orbit offset determination ....................................................................................................... 3
5. In-orbit calibrations to physical quantities........................................................................................ 3
1. Functional testing and calibration concept
The LP calibration philosphy is as follows:
- All fundamental ground calibrations of the electronics are done at LP level, i.e. on the bench in
Uppsala. This includes the complete frequency response of the instrument and determination of
temperature-dependent offsets. (Section 2)
- Integrated ground tests (CEFI and Swarm level) are used mainly for verification of instrument
integrity, EMC environment and timing in the complete chain. (Section 3)
- Instrument internal offsets are regularly determined (and, for some measurements, corrected for)
on-board using dedicated calibration sequences including sweeping over open probe. (Section 4)
- Calibration factors and error corrections depending on probe-spacecraft-plasma interactions are
determined manually in flight, mainly during the commissioning phase. This includes comparison
between the two probes, to CEFI ion measurements, and to external data sources like EISCAT. A
calibration mode with higher data rate for increased time sweep time resolution is occasionally
used also after the commissioning period. (Section 5)
2. Unit ground test and calibration
2.1 Setup
The planned setup for LP level functional and calibration tests is shown in Figure 1.
2.2 Test scenario
An external analogue signal is applied to the probes via a plasma simulator. Normally it is a DC level
or a sine wave with varying frequencies and amplitudes. An arbitrary generator is used to generate
those signals. In a typical functional test the test sequence is controlled from the experimenter laptop
via a LAN interface. It first sets the LP instrument via the CEFI or spacecraft simulator to a suitable
mode, and then it commands the instrument. The LP-EGSE PC then reads the telemetry data from the
spacecraft simulator, decodes the data, and compares the result with the applied stimuli signal.
2.3 Calibration scenario
The calibration will be performed with the setup shown in Figure 1. The calibration consists of
different calibration sequences. Each sequence contains commands for the LP and stimuli commands
for the LP-EGSE instruments. The measured data are collected from the CEFI simulator and LP-EGSE
respectively and stored in files on the experimenter laptop. During the calibration all different modes
for the CEFI LP instrument are executed. In each mode the stimuli for the probes are DC levels or sine
waves with useful amplitudes and frequencies for the instrument. The test sequences will run at the
experimenter laptop and the LP is in this setup controlled from a CEFI simulator
Figure 1. The setup of the CEFI LP instrument during ground calibration and functional testing (unit
level, not integrated with the full CEFI instrument or s/c).
3. Ground tests at system level
3.1 EMC
The LP instrument will require a dedicated test, preferably performed in an EMC chamber, to verify
low system noise levels. We estimate that the test will last for a half day including set-up. LP
operations are simple, mainly concentrating on waveform capture at constant bias, and require only
passive stimulus (via protective cover, see Section 3.2).
3.2 Instrument verification during system tests
In order to verify instrument integrity and timing a subset of the calibration sequences used on LP level
will be repeated during LP integration into CEFI and at the CEFI integration into the SC. These tests
will require active stimulus.
We will also monitor LP data during all integrated EMC and thermal vacuum tests. These tests
requires only passive stimulus. We expect to have passive stimulus connected to the probe via the
probe protective cover also for support of CEFI and SC functional tests.
4. LP in-orbit offset determination
A bias voltage sweep, with the input relay opened, is performed in order to determine the non-linearity
effects and offsets in the signal path up to the ADC. The resulting error values, from each bias step, are
stored in a matrix and used for correction of data sample before sent to telemetry. This method, of inorbit calibration of data, has successfully been used in the Rosetta LAP instrument. This will be run
regularly on board. Data are transmitted to Earth for calibration of bias sweep data, but also used
onboard for offset removal during processing in the FPGA
5. In-orbit calibrations to physical quantities
In the commissioning phase we will verify and adapt the routines for conversion of continuous 2 Hz
normal mode (NM) to physical quantities using a higher telemetry mode performing potential sweeps
with about 128 data points (words) every few seconds. This calibration should be updated periodically
during the mission to verify the probe accuracy.
IRF has access to use the EISCAT incoherent scatter facility in northern Scandinavia for measurements
of a number of physical parameter (Ne, Te, Ti, magnetic field-aligned velocity and electric field) in the
ionospheric F-region. We will us this to verify and adapt the theoretical expressions for reduction of LP
data to physical parameters (density and temperature) during commissioning. Other cross-calibration
activities during commissioning will include probe intercomparison and comparison to CEFI ion data.