The Manufacturing challenge -Is it a challenge? Research, Design, Development and the Manufacturing of Broadband Seismometers Cansun Güralp

Present requirements from broadband sensor design Realistic Fundamental Requirements of a broadband sensor system –Fundamental noise level of the sensor needs to be below the Low Noise Model –Spurious resonance's of the design has to be well outside the required seismic spectrum –Frequency response –Sensor calibration has to be an ‘absolute’ calibration –Linearity –Cross axis rejection –Single sensor for each site to cover the complete Seismic spectrum

Must be a feedback sensor system –The feedback system should be able to provide different types of sensor response to accommodate differing requirements. –The system fundamental resonance must be controlled with feedback –Open loop system would have substantially large sensor masses –Open loop systems response will be different form each other, every sensor would have to be individually trimmed to give the required response. Present requirements from broadband sensor design

Practical Requirements 1.Sensor size 2.Operation of sensor remotely 3.Sensor frequency response that can be modelled with a single transfer function 4.Single sensor to cover the complete seismic spectrum 5.Peripheral equipment to make the sensor a useful and portable product (Borehole, Holelock, Digitisers) 6.Temperature of operation 7.Ease of set up, installation and transportability 8.Sensor calibration facility

Low Noise Modal and Sensor Noise (Theory) CMG-1T Brownian Noise Brownian Noise – Usher, Güralp 1978 Sensor Transducer and Electronic Noise – Güralp 1978

Packaging Requirements 1.Modularity 2.Flexibility 3.Ability to provide units as Surface, Borehole and Ocean bottom system. 4.Portability 5.Over all size of the sensor

Manufacturing – The Solution 1.Simple design 2.Clear understanding of the fundamental principles and the relationship between design and the theory - Feedback, electronic design, materials, and testing methods 3.Minimise number of components within the design that effects the sensor performance so that manufacturing principles can be applied with ease.

Manufacturing Difficulties: Complex and multiple materials tends to be inconsistent with requirements of mechanical stability Complicated assembly Very complicated spring systems Extremely expensive machining for production purposes Cannot be used as a single sensor, i.e. Vertical and Horizontal component Not a versatile design as it tries to address a particular solution.

Manufacturing Difficulties: To many parts within the design which leads to manufacturing difficulties. To many parts within the design which leads assembly difficulty Zero length spring that can have high frequency and long period spurious modes of resonance's. Open loop system

Manufacturing Difficulties: Top heavy design where the centre of gravity is too high Open loop system that is likely not to meet the required specifications

Manufacturing, Present Design: Does not rely on special manufacturing techniques and equipment Separate Vertical or horizontal sensor Modular design Ease of assembly Reproducible in large quantities

Manufacturing, Present Design: Vertical or horizontal sensor Modular, can be integrated with hole locks of different design. Ease of assembly as a system at the installation site. Can be a complete seismic station, (weak + strong motion) which the borehole sensor incorporates Strong Motion accelerometer.

Manufacturing, Present Design: Modular, can be integrated with hole locks of different design. Ease of assembly as a system at the installation site. Three or single jaw holelocks can be used depending on the type of installation

Manufacturing, Present Design: The design can be modified to suite other applications. OBS and deep sea borehole instrumentation, (OBH)

Manufacturing, Present Design: The design can be modified to suite other applications. Portable and easily recoverable OBS system.

Manufacturing of Broadband Sensors Sensors are available in large quantities. To date over 2059 CMG-3 type instruments have been manufactured over 255 (3T / 3ESP / 3TB) and production rate of over 719 broadband instruments (all models).

Manufacturing of Broadband Sensors Sensor response from 360 sec to 100 Hz available. Sensor noise from 20 Hz to >100 sec as portable sensor. (Measured sensor noise levels not theoretical.) Transportable 220 mm ( 9 inches) high 168 mm diameter Weight compact 11.5 KG Durability: stainless steel construction, with O rings can be immersed in fluid for prolonged periods. Operation: all functions remotely controllable. Low power: less than 1 watt.

Production Set-up Purpose built factory Isolated floor section from rest of the building. Building regulations

Production Set-up Clean Rooms and Laminate Flow Cabinets: Investment is very costly

Production Set-up Rigorous internal staff training on sensor assembly and staff training on the understanding of how NOT to build broadband sensors. Internal detailed assembly documentation is essential Sensor test set up A cluster of boreholes to test borehole units Pits and piers Vault test facility with wide band transmission of data.

Production Set-up Measurement system: Response measurement of large number of sensors For example a 360 sec velocity sensor frequency response can take 2 hours for 3 components.

Calibration Automated ‘Absolute’ Calibration

Facilities Production

Facilities Testing: Environmental & Quality

Facilities Automated Frequency response and Calibration

Facilities Vault facility

Facilities Borehole Testing

Facilities Customers given detailed training

Design and Evolution Design and evolution of Sensors is REQUIRED for a mass producible Sensor system, with continuous research and development. The design staff has to be present at all times so that the production and technical issues are resolved without delay The use of latest design tools must be invested in, including training of production staff. The design of any Sensor has to incorporate a producible and cost effective solution

Personnel Requirements Dedicated personnel must all be trained in the art of manufacturing precision instrumentation. A company ethos has to be defined and accepted by all the personnel. Essential to eliminate the BLACK ART associated with broadband sensor assembly and production. Must be closely linked to the Research & Development team. Ideally experience is required in the operation and running of the seismic stations.

Research & Development Team Cybernetics, Control Systems with Mathematics and Instrument Design PhD University of Reading Cybernetics, Control Systems with Engineering Mathematics BSc University of Reading Mathematics and Computer Science PhD University of Cambridge Physics BA University of Cambridge Chemistry PhD Cambridge Computer Science / Electronic and Electrical Engineering MSc Imperial College, London / BSc University of Strathclyde Electronic and Electrical Engineering BEng. Imperial College, London

Results achievable with present design Sensor suitable to detect signals from Tides to 100 Hz Single sensor that covers the complete seismic spectrum Modular, can be used as a borehole, surface and OBS type sensor system. Cost effective even when compared to digitisers Large quantities can be produced.

Sensor Noise (Testing) To record Earth tides Sensors need very good LP performance (5 days of raw 1 sps data)

Sensor Noise (Testing) Mass position data (Raw 4 sps data)

Sensor Noise (Testing) Testing at UK factory (3 production verticals)

Sensor Noise (Testing) Verifiable (USGS ASL)

Sensor Noise (High Freq) Verifiable (Sandia National Laboratories)

Sensor Results from Three Component Autonomous ± 30 DEGREES self levelling OBS system with internal digitiser. Red trace CMG-1 Z installed in OBS package, Blue trace STS1 Z installed on pier

“Quiet day” “Stormy day”

Sensor Noise (New Sites) New locations highlight importance of good performance (Plots – USGS ASL)

Current Research & Development Projects 1.Very high temperature Broadband sensor, continuous operation at 175 Degrees Centigrade. CMG-3T High temperature sensor can operate at 150 degrees; this is being improved. 2.Very low temperature sensor to operate at –55 degrees centigrade. 3.Very High Frequency feedback sensor (1Hz to 5K Hz) 4.Unbreakable sensor for Mars, in collaboration with UCLA. Patented

Current Research & Development Projects 5. Only Horizontal Acceleration responsive sensor, to remove tilt component, from surface installations and even from borehole sensors. 6. Strong Motion Velocity sensor with long period 100 sec response up to 100 Hz 7. CMG-1T sensor system with digital output that will incorporate inherently digital transducer. 8. Development of new calibration techniques. 9.Direct Digital Instrument and digital transducer with a dynamic range > 155 dB (Patent pending) 10. More than 25 % of annual turn over is fed back into R&D and invested in the companies infrastructure.

Current Broadband Sensor Challenge Acceptance of new concepts and ideas that will allow complete seismic system simplification this being digital output broad band sensors.