Accelerometer Sensors Presented by: Mohammad Zand Seyed Mohammad Javad Moghimi K.N.T. University of Technology
Outline: Accelerometer Introduction Background Device market Types Theory Capacitive sensor Piezoelectric sensor Signal Conditioning Conditioning Circuits Standard ICs Miscellaneous Extra Information Sensor Manufactures Conclusions References
Background: MEMS Micro Electro Mechanical Systems Small devices that perform the same function as larger mechanical systems Usually machined out of silicon Accelerometers Devices that are used to measure acceleration Used for airbag sensors, etc.
Device Market: Primary Market Automobile Airbag Sensors Approximately 50 million sensors/year Sensors sell for approximately $10 each Secondary Markets Computer Joysticks Military Applications Amusement Park Technology
Types: 1. Potentiometric 2. LVDT 3. Variable Reluctance 4. Piezoresistive 5. Capacitive 6. Piezoelectric capacitive transducers strain gage transducers optical transducers (laser interference measurement) resistive transducers electromagnetic transducers
Piezoelectric Types: i. Shear system ii. Compression system iii. Bending or Flexure system
Piezoelectric Advantages: 1. Extremely wide dynamic range, almost free of noise - suitable for shock measurement as well as for almost imperceptible vibration. 2. Excellent linearity over their dynamic range. 3. Wide frequency range, high frequencies can be measured. 4. Compact yet highly sensitive. 5. No moving parts - no wear. 6. Self-generating - no external power required. 7. Great variety of models available for nearly any purpose. 8. Integration of the output signal provides velocity and displacement. ent.
Comparing Piezoelectric with others: Sensor Type Advantage Disadvantage Piezoresistive Electrodynamic - measures static acceleration - also for static measurement - limited resolution because of resistive noise - only for low and medium frequencies - supply voltage required - only for low frequencies Capacitive - measures static acceleration - cheap manufacturing with semiconductor technology - low resolution - fragile
Comparing Piezoelectric Types: Shear Compression Bending Advantage - low temperature transient sensitivity - low base strain sensitivity - high sensitivity-to to- mass ratio - robustness - technological advantages - best sensitivity-to to- mass ratio Drawback - lower sensitivity-to to- mass ratio - high temperature transient sensitivity - high base strain sensitivity - fragile - relatively high temperature transient sensitivity
Theory: Capacitive sensor Change in Capacitance due to the Lateral Movement of the Plates Change in Capacitance due to the Change in Plate Separation Parallel Plate Capacitor A General Accelerometer Two Objects in Space Differential Capacitor
Theory: Piezoelectric sensor Rx = Resistance of piezo Cx = Capacitance of piezo Cc = Capacitance of cable Charge Q amplifying (charge) = d F circuit Ca = Capacitance of amplifier circuit Ra = Resistance of amplifier circuit Useful frequency range
Conditioning Circuit: Capacitive
Conditioning Circuit: Piezoelectric Charge Output Sensors - high output impedance, piezoelectric sensors (without built-in in electronics) which typically require external charge or voltage amplifiers for signal conditioning. Internally Amplified Sensors - low impedance, piezoelectric force, acceleration and pressure type sensors with built-in in integrated circuits. (ICP is registered trademark of PCB Piezotronics,, Inc. which uniquely identifies PCB's sensors which incorporate built-in in electronics.)
Conditioning Circuit: Piezoelectric Advantage Drawback ICP Compatible Sensors - Fixed sensitivity regardless of cable length and cable quality - Low-impedance output can be transmitted over long cables in harsh environments - Inexpensive signal conditioners and cables - Intrinsic self-test function - Withstands better harsh conditions like dirt and humidity - Constant current excitation required (reduces battery operating hours) - Inherent noise source - Upper operating temperature limited to <120 C Charge Mode Sensors - No power supply required - ideal for battery powered equipment - No noise, highest resolution - Wide dynamic range - Higher operating temperatures - Smaller sensors possible - Limited cable length (< 10 m) - Special low noise cable required - Charge amplifier required
Conditioning Circuit: Piezoelectric ICP principle
Conditioning Circuit: Piezoelectric Charge Amplified System Schematic
Standard ICs: MAX1455 (MAXIM)
Extra Information: Accelerometer Mounting Accelerometer Cabling Accelerometer Selection (Metra Mess) MEMS Datasheets Applications More about signal conditioning TEDS
Availability in IRAN: مجتمع الکترونيک سيليکون: (www.siliconec.com) (Silicon74@Yahoo.com) Tele Fax:+98 21 6712720 (5 Lines) ADXL202 (Analog Devices) 400,000 Rials ADXL210 (Analog Devices) 490,000 Rials
Sensor Manufactures:
Conclusions: There are so many types of accelerometers for so many applications. It s s applications extends in many tasks. The price varies between a few ten dollars to few thousand dollars. MEMS version is smaller, lighter, and cheaper than traditional alternatives.
References: 1. Stanford university 2. MIT university 3. Metra Mess- und Frequenztechnik Radebeul 4. PCB Piezotronics 5. National Instruments 6. Berkeley University 7. ENDEVCO Corporation 8. Sensorland.com 9. Honeywell International 10. Analog Devices 11. Maxim 12. Delphi
? Questions?
Accelerometer Mounting: Typical reasons of coupling errors Resonance frequencies of different mounting methods a Accelerometer probe b Insulating flange c Magnetic clamp Mounting methods for accelerometers d Adhesive mounting (no wax) e Stud mounting
Accelerometer Cabling: Sensor Insulated mounting sensor Methods without mounting of insulation cable avoids tie-down causes ground a ground loops loop
Accelerometer Selection: Criteria Accelerometer Properties Selection chart for acceleration: < 10 g 10-200 g 200-1000 g 1000-10000 g > 10 000 g Amplitude Range KB12(V) KS48 KS76/77 KD37V-42V KB103 KS813 KS74/80 KS50-52 KD37-42 KS91/94/95 KS513 KS943 KS93 KD29 KD93 Choose resonant frequency and linear frequency range Selection chart for upper 3 db frequency limit: Frequency Range < 200 Hz KB12(V) 0,2-10 khz KD41/42(V) KS48 KS813 KB103 10-15 khz KD37/38(V) KS50-52 KS513 KS80 15-25 khz KS76/77 KS93/94/95 KD29 KS943 KS74 > 25 khz KS91 KD93 Accelerometer weight <1/10 the weight of test object. Choose miniature accelerometers for light objects. Selection chart for sensor weight: Weight of Test Object < 3 g KS91/93 KS94/95 3-20 g KD29 KD93 KS943 20-50 g KS76/77 KD37/38(V) KB103 KS74 50-100 g KD41/42(V) KS50-52 KS813 KS513 KS80 > 100 g KB12(V) KS48 Temperature Transients, Base Strain, Magnetic Fields, Extreme Acoustic Noise Humidity and Dust Measurement of Vibration Velocity and Displacement Assess influence, choose sensor according to characteristics, choose shear type accelerometers when temperature transients or base strain may occur, stainless steel versions for strong magnetic fields Industrial accelerometers with protection grade IP67 Single and double integration, below 20 Hz use shear type accelerometers
MEMS:
Datasheets: Q-Flex QA3000 (Honywell( Honywell) MEMS MS7000 (Colibrys( Colibrys) GP-383 (Columbia Research Laboratories, Inc) ADXL202E(Analog Devices) Model 66A50 TEDS(Endevco) APA300 (Star Micronics America, INC)
Applications:
More about signal conditioning: Metra Mess: Charge Amplifiers M68 Series ICP Conditioning Module M32
TEDS: ENDEVCO : i-teds Accelerometer Model 66A50, A11, A12 Smallest Triax with TEDS IEEE P1451.4 TEDS Light Weight (5.5 gm) Single Cable Milli-g's Resolution Hermetically Sealed Titanium Housing Case Isolation Option