digital vs analog control

Digital Vs Analog control

M HewitsonGEO ISC MeetingHannover, Feb 2010

Wednesday, January 27, 2010

Digital Control, GEO ISC Meeting, Hannover, Feb 2010

Contents

• Pros and cons of Analog and Digital Control• Overall areas of work• What do we need in 10 years from now?• Other random thoughts

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Cons of analog control

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•Slow development•difficult to do accurate design

•tolerances of electronic components

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•tolerances of electronic components•Hard to do complicated controls

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•tolerances of electronic components•Hard to do complicated controls•Interference

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•tolerances of electronic components•Hard to do complicated controls•Interference•Hard to modify

•testing alternatives is difficult

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•testing alternatives is difficult•Hard to build in comparative logic

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•testing alternatives is difficult•Hard to build in comparative logic•Hard to build in ‘intelligence’

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•testing alternatives is difficult•Hard to build in comparative logic•Hard to build in ‘intelligence’•Hard to ‘back-up’

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•testing alternatives is difficult•Hard to build in comparative logic•Hard to build in ‘intelligence’•Hard to ‘back-up’•Hard to do MIMO

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Pros of analog control

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•Robust•doesn’t (often) break down•doesn’t crash

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•Dynamic range•‘easier’ to avoid being limited by ‘self’ noise

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•Continuous processing•no inherent band-width limits

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•Hard to modify

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•Hard to modify•Available diagnostic instrumentation is good

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Pros of digital control

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• Flexibility• can do really complicated

controllers• easy to modify• quick to develop• easy to make back-up

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• Can build in lots of logic• intelligence for switching

states• locking logic• adaptive filtering

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• Diagnostics• in particular, remote• off-line testing and

diagnostics• store signals

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• Can do lots of DIO

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• Can do lots of DIO• Can do MIMO

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• Can do lots of DIO• Can do MIMO• Error detection

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• Can do lots of DIO• Can do MIMO• Error detection• Signal generation and

injection

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• Can do lots of DIO• Can do MIMO• Error detection• Signal generation and

injection• Control interfaces are more

precise

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Cons of digital control

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• Easy to break• backup, backup, backup!

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• Hard to do ‘fast’ loops• limited to about 10kHz UGF with current technology

• can get really fast ADC/DAC cards, but processing and integration becomes an issue

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• Interference?

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• Interference?• Dynamic range

• best systems limited to about 20-bit• typical systems more like 10-14-bit• often need good whitening, both at ADC and DAC

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• Software interfaces are currently not as user-friendly as real knobs and switches

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• Software interfaces are currently not as user-friendly as real knobs and switches

• Software instrumentation not as advanced as analog

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When I’m 64....

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When I’m 64....

• Control will be adaptive• more advanced use of control theory, control engineers

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When I’m 64....


• Observatories will become more ‘self-controlling’• built-in failure/recovery modes

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When I’m 64....



• Greater use of distributed and parallel computing• cpu farm, cluster, GPUs

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When I’m 64....




• We will have powerful human interfaces, visualisation and diagnostic tools• real-time instrumentation in hand-held devices• clean, scalable, modern-looking control interfaces

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When I’m 64....





• We will have high-resolution, high sample-rate, distributed analog-digital interfaces• high-quality A/D, D/A modules

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When I’m 64....






• Communication over real-time wifi• driven by entertainment industry - internet TV

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When I’m 64....






• Communication over real-time wifi• driven by entertainment industry - internet TV

• Tighter coupling between data analysis and instrument control• tracking of signals, IFO operation modes responding to external triggers

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Areas of activity

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Experiment



Areas of activity

8

Experiment

ADC DAC DIO ADC DAC DIO



Areas of activity

8

Experiment


Timing



Areas of activity

8

Experiment


Communication

Timing



Areas of activity

8

Experiment


Communication

Real-time Processing Async Processing

Timing



Areas of activity

8

Experiment


Communication


DiagnosticsControl Control

Timing



Areas of activity

8

Experiment


Communication



Timing

Scripting interface



Areas of activity

8

Experiment


Communication



Timing

Scripting interface

GUI GUI



Areas of activity

8

Experiment


Communication



Timing

Scripting interface

GUI GUIAPI



Areas of activity

8

Experiment


Communication



Timing

Scripting interface

GUI GUIAPI Real-time instrumentation



Future Requirements

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Future Requirements

• How fast do we want/need to make loops?• split loops, down/up mixing• MSPS chips available

• can we process that? • GPUs?

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Future Requirements



• How much resolution do we need?• typically get 16-bit or 24-bit (sigma-delta)

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Future Requirements




• How much processing power?• loop/control complexity• sample-rate• sample resolution• number of channels• inter-process communication

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Future Requirements




• How much processing power?• loop/control complexity• sample-rate• sample resolution• number of channels• inter-process communication

• Good software!• it should be nice to use, powerful, flexible, robust

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Other thoughts

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Other thoughts

•Should look at audio systems

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Other thoughts

•Should look at audio systems•Research in to adaptive systems for IFO control

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Other thoughts

•Should look at audio systems•Research in to adaptive systems for IFO control•MIMO systems

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Other thoughts

•Should look at audio systems•Research in to adaptive systems for IFO control•MIMO systems•Reduce hardware to sensors and actuators

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Other thoughts

•Should look at audio systems•Research in to adaptive systems for IFO control•MIMO systems•Reduce hardware to sensors and actuators•Embedded dedicated controls

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Other thoughts

•Should look at audio systems•Research in to adaptive systems for IFO control•MIMO systems•Reduce hardware to sensors and actuators•Embedded dedicated controls•Feedforward techniques, Kalman filtering

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Other thoughts

•Should look at audio systems•Research in to adaptive systems for IFO control•MIMO systems•Reduce hardware to sensors and actuators•Embedded dedicated controls•Feedforward techniques, Kalman filtering•Instrumentation and visualisation

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Other thoughts

•Should look at audio systems•Research in to adaptive systems for IFO control•MIMO systems•Reduce hardware to sensors and actuators•Embedded dedicated controls•Feedforward techniques, Kalman filtering•Instrumentation and visualisation•Digital control means more data

•storage, data access

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digital vs analog control

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