1. Seismic sensors in PACMAN
Peter Novotny
1st PACMAN workshop
3rd February 2015, CERN

2. Seismic sensors in PACMAN - Peter NOVOTNY - 3rd February 2015
Outline
Why seismic sensors in PACMAN
How seismic sensors work
PACMAN requirements to sensors
State of the art seismic sensors
Current work
Conclusions
Seismic sensors in PACMAN - Peter NOVOTNY - 3rd February 2015

3. 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
Cultural noise
Micro seismic
peak
Seismic sensors in PACMAN - Peter NOVOTNY - 3rd February 2015

4. 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.
Seismic sensors in PACMAN - Peter NOVOTNY - 3rd February 2015

5. How seismic sensors work?
Theoretical principle
Transducer
Seismic sensors in PACMAN - Peter NOVOTNY - 3rd February 2015

6. Transducers Seismic sensor with electromagnetic transducer Transducer
Seismic sensors in PACMAN - Peter NOVOTNY - 3rd February 2015

7. Seismic sensors in PACMAN - Peter NOVOTNY - 3rd February 2015
Types of transducers
Resistive
Capacitive
Piezoelectric
LVDT - Linear variable differential transformer
Optical (Interferometers, encoders)
Elmg. – coil + magnet
Eddy current …
Seismic sensors in PACMAN - Peter NOVOTNY - 3rd February 2015

8. Seismic sensors in PACMAN - Peter NOVOTNY - 3rd February 2015
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
Seismic sensors in PACMAN - Peter NOVOTNY - 3rd February 2015

9. PACMAN requirements for sensor
Bandwidth = 0.1Hz – ≈200 Hz
Resolution ≤ 0.1nm
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
Seismic sensors in PACMAN - Peter NOVOTNY - 3rd February 2015

10. 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
Force balanced optical
accelerometers
Seismometers
MEMS
accelerometers
Piezo-accelerometers
Seismic sensors in PACMAN - Peter NOVOTNY - 3rd February 2015

11. Seismic sensors in PACMAN - Peter NOVOTNY - 3rd February 2015
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
Seismic sensors in PACMAN - Peter NOVOTNY - 3rd February 2015

12. Seismic sensors in PACMAN - Peter NOVOTNY - 3rd February 2015
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
Seismic sensors in PACMAN - Peter NOVOTNY - 3rd February 2015

13. 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
Seismic sensors in PACMAN - Peter NOVOTNY - 3rd February 2015

14. Seismic sensors in PACMAN - Peter NOVOTNY - 3rd February 2015
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
Our requirements:
Bandwidth
Weight and size
Magnetic resistance
Price
High self noise
Resolution
MEMS realisation
Final product
Seismic sensors in PACMAN - Peter NOVOTNY - 3rd February 2015

15. Promising candidates
Short period seismometer
CP ZM500
Short period seismometer
Guralp CMG-6T
Force balanced optical
accelerometers
PACMAN
CP ZM500
CMG-6T
Optical acc.
Bandwidth [Hz]
0.1 – 1k
[nm/s2/√Hz] 4
0.3
2.5 20
Measurements and tests need to be done to check requirements fit.
Seismic sensors in PACMAN - Peter NOVOTNY - 3rd February 2015

16. Noise in seismic sensors
!Noise is the most limiting parameter of sensor resolution!
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
Seismic sensors in PACMAN - Peter NOVOTNY - 3rd February 2015

17. Noise comparison Acquisition hardware noise is also very important
and should be below sensor noise.
Seismic sensors in PACMAN - Peter NOVOTNY - 3rd February 2015

18. Seismic sensors in PACMAN - Peter NOVOTNY - 3rd February 2015
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 …
Seismic sensors in PACMAN - Peter NOVOTNY - 3rd February 2015

19. Seismic sensors in PACMAN - Peter NOVOTNY - 3rd February 2015
Current work
Measurements and data processing
Seismic sensors in PACMAN - Peter NOVOTNY - 3rd February 2015

20. Seismic sensors in PACMAN - Peter NOVOTNY - 3rd February 2015
Next steps
Development of the optimum sensor for PACMAN
Integration into the PACMAN bench.
Analysis of the performances and robustness.
Seismic sensors in PACMAN - Peter NOVOTNY - 3rd February 2015

21. Seismic sensors in PACMAN - Peter NOVOTNY - 3rd February 2015
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.
Seismic sensors in PACMAN - Peter NOVOTNY - 3rd February 2015

22. Thank you for your attention!

23. Backup slides

24. How does seismic sensor work?
Transfer functions:
𝑇 𝑤𝑦 = 𝑌 𝑊 = 𝑟𝑒𝑙𝑎𝑡𝑖𝑣𝑒 𝑑𝑖𝑠𝑝𝑙𝑎𝑐𝑒𝑚𝑒𝑛𝑡 𝑎𝑏𝑠𝑜𝑙𝑢𝑡𝑒 𝑑𝑖𝑠𝑝𝑙𝑎𝑐𝑒𝑚𝑒𝑛𝑡
Laplace
transform
𝑇 𝑤 𝑦 = 𝑌 𝑊 = 𝑟𝑒𝑙𝑎𝑡𝑖𝑣𝑒 𝑣𝑒𝑙𝑜𝑐𝑖𝑡𝑦 𝑎𝑏𝑠𝑜𝑙𝑢𝑡𝑒 𝑣𝑒𝑙𝑜𝑐𝑖𝑡𝑦
𝒎 𝒚 +𝒄 𝒚 +𝒌𝒚=−𝒎 𝒘
Natural
frequency
Two important things coming out from this equation
Natural frequency of oscillator which is one of important limiting factors for sensors
Transfer functions which describe frequency dependant relation between absolute and relative motion
From TF it’s obvious which relations are interesting for us (and those are three with flat characteristic)
!! – what doeas it mean for us? we know TF but we also need to measure this relative motion
𝝎 𝟎 = 𝒌 𝒎
𝑇 𝑤 𝑦 = 𝑌 𝑊 = 𝑟𝑒𝑙𝑎𝑡𝑖𝑣𝑒 𝑑𝑖𝑠𝑝𝑙𝑎𝑐𝑒𝑚𝑒𝑛𝑡 𝑎𝑏𝑠𝑜𝑙𝑢𝑡𝑒 𝑎𝑐𝑐𝑒𝑙𝑒𝑟𝑎𝑡𝑖𝑜𝑛
𝝎/𝝎 𝟎
!! Information about absolute motion is in relative motion!!

25. Few sensors and their producers
type of sensors
GURALP
Seismometers
ion
geophones
Sercel (Mark Products)
Kinemetrics (Streckeisen)
Seismometers + FBA
Nanometrics
REFTEK
Lennartz electronic
Metrozet
Eentec
FDBCK MET geophones + FBA
SINUS
Piezo-velocity sensor
GeoSIG
geophones + FBA
Endevco
accelerometers
Wilcoxon
DYTRAN
DJB Instruments
MMF
Brüel & Kjær
PCB
COLIBRYS
METTECH
MET
GEOTECH INSTRUMENTS
To give you idea how the sensors looks like
Not exhaustive list

26. Secondments High precision mechanic manufacturer
3 months starting in April 2015
Project:
Measurement and adjustment techniques for precision applications
Development of the seismic sensor for stabilisation of the Final Focus (of CLIC)
Equivalent of 7 months
(already started)
Their measuring and control system
In regards to secondments
LAPP – one of the things they are working on is a .1.odsek
DMP produce high presicion