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MAGIC Interface Issues. Patrick Brown , Blackett Laboratory, Imperial College. MAGIC – Magnetometer from Imperial College. Purpose Dual tri-axial magnetoresistive sensor measures magnetic field vector local to spacecraft in frequency range 0-10Hz Role of magnetometer

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Magic interface issues
MAGIC Interface Issues

Patrick Brown,

Blackett Laboratory,

Imperial College


Magic magnetometer from imperial college
MAGIC – Magnetometer from Imperial College

Purpose

Dual tri-axial magnetoresistive sensor measures magnetic field vector local to spacecraft in frequency range 0-10Hz

Role of magnetometer

Contribute to spacecraft attitude determination

Measurement of local field direction for pitch angle determination

Detection and characterisation of local waves and structures

Parts

Outboard sensor head

Electronics board

Inboard sensor (on electronics board)

Harness (UCB supplied)


Magnetoresistive magnetometer (Single axis)

3axis Fluxgate

Single axis MR

  • Implementation – analogue closed loop

  • Bipolar driving to maintain optimum detectivity

  • Requires current pulse of 4A for 2ms

  • Dynamic Offset compensation employed


Magic instrument datasheet
MAGIC Instrument Datasheet

  • Two instrument modes – Science A/B (high res) and Attitude (lower res)

  • Switch to science modes when power allows



Sensor head outboard sensor
Sensor Head (Outboard Sensor)

CINEMA Boom very light

MAG Harness requires at least 17 lines

Boom can only support very thin gauge wire

Line loss on 4A pulse too large

Solution MAGIC Sensor Head

Install sensor drive electronics with sensor

Inboard sensor in mounted directly on PCB

Plastic packages (most likely implementation)

Ceramic version

MAGIC Test Harness


Mechanical interface issues
Mechanical Interface Issues

Sensor head mechanical interface design led by UCB

Harness supplied by UCB

Magnet wire with Aracon outer braid

Aracon slightly magnetic

Last 10cm near head will be silver over copper

Provisional Integration Plan

UCB Manufacture harness with flying wires

Imperial integrate harness to sensor head/add non magnetic braid piece

Imperial install MAGIC connecter for test and calibration

Imperial remove bus connector prior to delivery

UCB or Imperial add bus connector following head installation on boom

Harness Connector at MAGIC PCB – MDM25Way

Sensor head mass: <20g (if potted)

Strain Relief

No Connector

Prototype Sensor Head: Dimensions (cm) 2x2x2.5(h)

  • Inboard sensor in mounted directly on MAGIC card

  • MAGIC PCB Single PC104 card, Mass ~ 150g, clearance 1cm each side

Latest UCB Drawing


MAGIC Harness Connections

17 wires

  • 3 x 2 Differential Sensor out (Bx, By, Bz)

  • 3 x 2 Feedback (Bx, By, Bz)

  • 1 x Thermistor (RTN reference to GND)

  • 1 x Bridge Voltage (12V or 5V reference to GND)

  • 1 x Drive Clock

  • 1 x Drive Voltage (16V RTN reference to GND)

  • 1 x GND


Magic data command interface
MAGIC Data & Command Interface

Interface to bus via ADS1216

8 channel, 24 bit Delta-Sigma architecture with 8 I/O registers

Has the required channel number, range and H/W control potential

Control interface via SPI

PGA, and on board Sinc filters

Low power consumption ~ a few mW

Issues

MAGIC requires the bus to sample the MAGIC data at some TBC rate i.e. switching the MUX at the required cadence

Baseline that MAGIC filtering is performed on board ADC

No CS needed on dsPIC33 if ADS1216 only SPI device

To minimise processing load on bus controller recommend dedicated bus connections for NDREDY and ADC RESET



MAGIC Bus Interface Connections initial difficulties

  • Connector – Pins on a standard PC104 connector are OK but if opportunity exists for a smaller dedicated connector would take that option


Magic cmdh bus requirements
MAGIC CMDH Bus Requirements initial difficulties

Channel switching of ADC add acquisition of data

7 channels in total OB (Bx, By, Bz) IB (Bx, By, Bz) OB Temp

Not all channels accessed in all modes (default mode is OB and Temp only)

Potential switching of sinc filter, read of ADC register status

Packetization and time stamping

MAGIC commanding via SPI to ADC but also prefer if commanding can control rail switching on the bus


MAGIC Functional Commanding initial difficulties

Assume: 1. MAGIC On when 5V and 3.3V rails are up2. 12V and 16V are switched off by bus on start up


Icd clarification current efforts
ICD Clarification: Current Efforts initial difficulties

ADC

ADS1216 development work ongoing

Have switched relay via I/O lines

Priority task to get continuous sampling (up to 200Hz) by MSP430 over SPI

Then start MAGIC code development

MAG

Investigating if Attitude Mode can be run on a 3.3V Bridge

Finalise Functional Block Diagram

Generate Three axis schematic

Build three axis breadboard

Calibration and Interference test of proto-sensor head

THERMAL

Initial thermal mode indicated in-flight temp range of -50oC to +120oC

Once three axis calibration complete temp test will be made with unpotted and potted sensor

Other Issues for Discussion – Schedule & Magnetic Cleanliness Plan


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