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MAGIC Interface Issues

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

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  1. MAGIC Interface Issues Patrick Brown, Blackett Laboratory, Imperial College

  2. 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)

  3. 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

  4. MAGIC Instrument Datasheet • Two instrument modes – Science A/B (high res) and Attitude (lower res) • Switch to science modes when power allows

  5. Note: IB sensor & electronics not identical to OB

  6. 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

  7. 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

  8. 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

  9. 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

  10. ADS1216 testbed now operating at Imperial after some initial difficulties • Currently accessed at an individual sample level via a Linux box • Next step is continuous sampling via Linux and connection to MSP430 • Envisage uplink of ADC pseudocode to CINEMA FTP server

  11. MAGIC Bus Interface Connections • Connector – Pins on a standard PC104 connector are OK but if opportunity exists for a smaller dedicated connector would take that option

  12. MAGIC CMDH Bus Requirements 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

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

  14. ICD Clarification: Current Efforts 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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