Seismic sensors in PACMAN

Peter Novotny1st PACMAN workshop

3rd February 2015, CERN

Seismic sensors in PACMAN - Peter NOVOTNY - 3rd February 20152

Outline

• Why seismic sensors in PACMAN• How seismic sensors work• PACMAN requirements to sensors• State of the art seismic sensors• Current work• Conclusions

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Why we need seismic sensor?

• Ground is shaking all the time even if we don’t see or feel it.

Power Spectral Density of ground motion for different sites

Micro seismicpeak

Cultural noise

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Why we need seismic sensor?

• When measuring beam position with nm resolution we need to know how this ground motion propagate through the bench and influence our measurements.

• Therefore we want to measure ground motion at different positions of the bench.

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How seismic sensors work?

Theoretical principle

Transducer

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Transducers

Seismic sensor with electromagnetic transducer

Transducer

• Resistive• Capacitive• Piezoelectric• LVDT - Linear variable differential transformer• Optical (Interferometers, encoders)• Elmg. – coil + magnet• Eddy current• …

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Types of transducers

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Sensor parameters

• Bandwidth – fmin - fmax

• Sensitivity S – conversion factor from D,V,A to Volts• Self noise N – determine resolution• Resolution R = N/S – smallest measureable value• Dynamic range – Max/Min measureable value• Active/passive – need of power supply• Weight and dimensions• Robustness against magnetic stray field and radiation

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PACMAN requirements for sensor

• Bandwidth = 0.1Hz – ≈200 Hz• Resolution ≤ 0.1nm (rms@1Hz) which means high sensitivity and low self-noise• Stray magnetic fields resistance

different mg. field on the ground than on the magnets• Dynamic range ≥ 80dB

from 0.1nm to at least 1µm• Weight < few kg & compact size

to fit inside the bench

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State of the art sensors

Different types of sensors for different use like:• Natural ground motion measurement (tides,

waves)• Earthquakes monitoring• Oil and gas exploration• Building, bridges structural monitoring • Nuclear test ban treaty monitoring • …

Geophones

Seismometers

Piezo-accelerometers MEMSaccelerometers

Force balanced optical accelerometers

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Geophones

• Output voltage proportional to ground velocity

above natural frequency.• Simple and compact solution • Low noise but also low sensitivity

Our requirements: Low noise Weight and size Price× Sensitivity× Resolution× Bandwidth× Magnetic resistance

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Seismometers

• Output voltage is proportional to ground velocity in certain frequency bandwidth.

• Utilise the feedback control of mass position to extend bandwidth to low frequencies.

Our requirements: Very low noise Resolution• Bandwidth• Weight and size

× Magnetic resistance

× Price

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Piezo-accelerometers

• Output voltage is proportional to ground acceleration below natural frequency.

• High self noise at lower frequencies

Our requirements: Bandwidth Weight and size Magnetic resistance• Price× High self noise at

low freq.× Resolution

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MEMS accelerometers

• Output voltage is proportional to ground acceleration below natural frequency. (similar freq. characteristic as piezo-acc.)• High self noise because of light mass.

Principle

MEMS realisation

Final product

Our requirements: Bandwidth Weight and size Magnetic resistance Price× High self noise× Resolution

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Promising candidates

Force balanced optical accelerometers

Short period seismometer CP ZM500

Measurements and tests need to be done to check requirements fit.

Short period seismometer Guralp CMG-6T

PACMAN CP ZM500 CMG-6T Optical acc.

Bandwidth [Hz] 0.1 - 200 0.1 - 100 0.1 - 100 0.1 – 1k

Noise@1Hz [nm/s2/√Hz] 4 0.3 2.5 20

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Noise in seismic sensors

Sources of noise:• Thermomechanical (Brownian) noise

• Molecular collisions with mass• Thermoelectrical (Johnson) noise

• Random thermal excitation of charge carriers• Other semiconductor electronic noise

• Schottky noise• Flicker 1/f noise

• Discretisation noise• ADC converters

!Noise is the most limiting parameter of sensor resolution!

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Noise comparison

Acquisition hardware noise is also very important and should be below sensor noise.

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Current work

• Characterization of the seismic sensors available on the market and those developed by Laboratories

• Comparison of their TF, S/N ratio and bandwidths • Investigation of alternative and innovative approaches:

– Optical transducers (Interferometers, Fibre Bragg grating)– Molecular Electronic Transducers (MET)– Tunnelling effect– Noise reduction in MEMS accelerometers– …

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Current work

• Measurements and data processing

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Next steps

• Development of the optimum sensor for PACMAN• Integration into the PACMAN bench.• Analysis of the performances and robustness.

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Conclusions

• We need seismic sensors to know how GM has influence on the beam position measurement.

• Many state of the art sensors exist but were designed for different purposes (don’t match PACMAN requirements).

• Some of them seem promising.• Measurements needs to be done to test their performance.• Investigation of new technologies and possible improvements.• Development of optimum senor for PACMAN, integration to

bench and analysis of its performance.

Thank you for yourattention!

Backup slides

How does seismic sensor work?

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𝝎𝟎=√ 𝒌𝒎

Laplacetransform

Naturalfrequency

𝑇𝑤𝑦=𝑌𝑊

=𝑟𝑒𝑙𝑎𝑡𝑖𝑣𝑒𝑑𝑖𝑠𝑝𝑙𝑎𝑐𝑒𝑚𝑒𝑛𝑡𝑎𝑏𝑠𝑜𝑙𝑢𝑡𝑒𝑑𝑖𝑠𝑝𝑙𝑎𝑐𝑒𝑚𝑒𝑛𝑡

Transfer functions:

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= 𝑟𝑒𝑙𝑎𝑡𝑖𝑣𝑒𝑣𝑒𝑙𝑜𝑐𝑖𝑡𝑦𝑎𝑏𝑠𝑜𝑙𝑢𝑡𝑒𝑣𝑒𝑙𝑜𝑐𝑖𝑡𝑦

𝑇 �̈� 𝑦=𝑌�̈�

=𝑟𝑒𝑙𝑎𝑡𝑖𝑣𝑒𝑑𝑖𝑠𝑝𝑙𝑎𝑐𝑒𝑚𝑒𝑛𝑡𝑎𝑏𝑠𝑜𝑙𝑢𝑡𝑒𝑎𝑐𝑐𝑒𝑙𝑒𝑟𝑎𝑡𝑖𝑜𝑛

!! Information about absolute motion is in relative motion!!𝝎 /𝝎𝟎

Few sensors and their producers

Producer type of sensorsGURALP Seismometersion geophonesSercel (Mark Products) geophonesKinemetrics (Streckeisen)

Seismometers + FBA

Nanometrics SeismometersREFTEK SeismometersLennartz electronic SeismometersMetrozet Seismometers + FBA

EentecFDBCK MET geophones

+ FBASINUS Piezo-velocity sensorGeoSIG geophones + FBAEndevco accelerometersWilcoxon accelerometersDYTRAN accelerometersDJB Instruments accelerometersMMF accelerometersBrüel & Kjær accelerometersPCB accelerometersCOLIBRYS accelerometersMETTECH METGEOTECH INSTRUMENTS Seismometers

Secondments

• Development of the seismic sensor for stabilisation of the Final Focus (of CLIC)

• Equivalent of 7 months (already started)• Their measuring and control system

• High precision mechanic manufacturer

• 3 months starting in April 2015• Project:

• Measurement and adjustment techniques for precision applications