Low g iMEMS® Accelerometers


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To introduce ADI’s accelerometer solution and its iMEMS low-g accelerometer portfolio

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Low g iMEMS® Accelerometers

  1. 1. Low g iMEMS ® Accelerometers <ul><li>Source: ANALOG DEVICES </li></ul>
  2. 2. Introduction <ul><li>Purpose </li></ul><ul><ul><li>To introduce ADI’s accelerometer solution and its iMEMS low-g accelerometer portfolio </li></ul></ul><ul><li>Outline </li></ul><ul><ul><li>General accelerometer knowledge </li></ul></ul><ul><ul><li>ADI’s solution </li></ul></ul><ul><ul><li>iMEMS accelerometer portfolio </li></ul></ul><ul><ul><li>Detailed examination of the ADXL345 </li></ul></ul><ul><li>Content </li></ul><ul><ul><li>15 pages </li></ul></ul>
  3. 3. What is Accelerometer? <ul><li>Acceleration is a physical characteristic of a system. </li></ul><ul><li>The control system uses the measured acceleration to control for changing dynamic conditions. </li></ul><ul><li>An accelerometer is a sensor that measures acceleration. </li></ul><ul><li>The accelerometer is used to measure </li></ul><ul><ul><li>Acceleration </li></ul></ul><ul><ul><li>Vibration </li></ul></ul><ul><ul><li>Shock </li></ul></ul><ul><ul><li>Tilt </li></ul></ul>
  4. 4. Five Types of Motion Sensing <ul><li>Acceleration measures the change in velocity in a unit of time. </li></ul><ul><ul><li>Acceleration with a negative value is known as deceleration. </li></ul></ul><ul><li>Vibration can be thought of as acceleration and deceleration that happens quickly and in a periodic manner. </li></ul><ul><li>Shock is acceleration that occurs instantaneously. </li></ul><ul><li>Tilt or inclination is the angle displacement from a defined reference. </li></ul><ul><li>Rotation is a measure of angular rate motion. </li></ul>Accelerometer Acceleration Vibration Shock Tilt Gyroscope Rotation
  5. 5. MEMS Accelerometers <ul><li>The MEMS accelerometers use differential capacitors to measure g-force. </li></ul><ul><li>If an accelerative force is applied, then the capacitance will change. </li></ul>
  6. 6. Gravity Measurements <ul><li>g-Level: the acceleration value. </li></ul><ul><ul><li>+1g is the acceleration measurement for gravity which is equal to 9.8m/s 2 . </li></ul></ul><ul><li>A low-g sensing range is less than 20g and deals with motion a human can generate. </li></ul><ul><li>A high-g sensing range is useful for sensing motion related to machines or vehicles. </li></ul>
  7. 7. Key Parameters of MEMS ® Acceleration <ul><li>Measurement range </li></ul><ul><ul><li>The level of acceleration supported by the sensor’s output signal specifications </li></ul></ul><ul><ul><li>Specified in ± g </li></ul></ul><ul><li>Sensitivity </li></ul><ul><ul><li>The ratio of change in acceleration (input) to change in the output signal </li></ul></ul><ul><li>Nonlinearity </li></ul><ul><ul><li>The measurement of deviation from a perfectly constant sensitivity </li></ul></ul><ul><li>0G Bias </li></ul><ul><ul><li>specified the output level when there is no acceleration </li></ul></ul><ul><li>Noise </li></ul><ul><ul><li>random deviation from the ideal output </li></ul></ul><ul><li>Bandwidth </li></ul><ul><ul><li>The highest frequency signal that can be sampled without aliasing by the specified Output Data Rate </li></ul></ul>
  8. 8. ADI Low g iMEMS Accelerometer Portfolio 3 to 6 160 2.5 PWM ±10 30 %/g +/- 1.2g 2 ADXL213 3 to 6 110 2.5 Analog ±4 1000 mV/g +/- 1.7g 2 ADXL203 3 to 6 110 2.5 Analog ±4 1000 mV/g +/- 1.7g 1 ADXL103 2.4 to 6 320 2.5 Analog ±10 57 mV/g +/- 18g 2 ADXL321 1.7 to 2.75 - 1.6 Digital ±10 up to 256 LSB/g +/- 2/4/8/16g 3 ADXL346 2.0 to 3.6 - 1.6 Digital ±10 up to 256 LSB/g +/- 2/4/8/16g 3 ADXL345 1.8 to 3.6 300 1.6 Analog ±10 300 mV/g +/- 3g 3 ADXL335 1.8 to 3.6 250 1.6 Analog ±10 420 mV/g +/- 2g 3 ADXL327 1.8 to 3.6 250 1.6 Analog ±10 57 mV/g +/- 16g 3 ADXL326 1.8 to 3.6 250 1.6 Analog ±10 174 mV/g +/- 5g 3 ADXL325 Voltage Supply (V) Noise Density (µg/rtHz) Typical Bandwidth (kHz) Output Type Sensitivity Accuracy (%) Sensitivity Range # of Axes Product
  9. 9. ADXL345 Digital Accelerometer <ul><li>Ultra low power </li></ul><ul><ul><li>40 µA in measurement mode </li></ul></ul><ul><ul><li>0.1µA @ standby mode </li></ul></ul><ul><li>Power consumption scales automatically with bandwidth </li></ul><ul><li>User-selectable resolution: up to 13-bit @ ± 16g </li></ul><ul><li>Tap/double tap detection </li></ul><ul><li>Activity/inactivity monitoring </li></ul><ul><li>Free-fall detection </li></ul><ul><li>Built-in FIFO minimizing host processor load </li></ul><ul><li>SPI and I 2 C digital interface </li></ul>3 ±10n/a Up to 256LSB/g ±2/ 4 / 8 / 16g 1.6KHz Digital # of Axes Sensitivity Accuracy (%) Sensitivity Range Bandwidth Output Type
  10. 10. Motion Sensing Alarm with ADXL345 <ul><li>Activity and inactivity sensing detect the presence or lack of motion. </li></ul><ul><li>ADXL345 has built-in detection of activity and inactivity. </li></ul>ADXL345 generates inactivity interrupt Store inactivity state in controller Wait for activity interrupt ADXL345 generates activity interrupt Request user passcode to continue operation
  11. 11. Fall Detection <ul><li>Falls where lots of rotation happens are normally preceded by a large shock. </li></ul><ul><li>Integration of acceleration tells you if there is a large change in velocity. </li></ul><ul><li>ADXL345 has a built-in threshold detection feature and a FIFO that facilitates this function. </li></ul>FREE_FALL interrupt asserted Wait for ACTIVITY interrupt Wait for INACTIVITY interrupt Generate fall alert Wait for ACTIVITY interrupt Wait for INACTIVITY interrupt Generate critical fall alert
  12. 12. Tap Detection <ul><li>Tap sensing is capable of detecting single and double taps. </li></ul><ul><li>Three register values have to be set up: </li></ul><ul><ul><li>Latent register </li></ul></ul><ul><ul><li>Window register </li></ul></ul><ul><ul><li>THRESH_TAP register </li></ul></ul>ADXL345 generates first tap interrupt Wait for second tap interrupt Start different operations
  13. 13. Connecting with Processors <ul><li>Figure 1 3-wire SPI connection </li></ul>Figure 2 4-wire SPI connection Figure 3 I 2 C connection
  14. 14. Development Tools <ul><li>Ultralow power ADXL345 accelerometer </li></ul><ul><li>Universal Inertial Sensor Motherboard </li></ul><ul><li>DUT specific Satellite board for evaluation </li></ul><ul><li>Standard USB cable for power and communications </li></ul><ul><li>PC based Graphical User Interface </li></ul><ul><li>User reprogrammable firmware capability </li></ul>
  15. 15. Additional Resource <ul><li>For ordering iMEMS Low g Accelerometers, please click the part list or </li></ul><ul><li>Call our sales hotline </li></ul><ul><li>For more product information go to </li></ul><ul><ul><li>http://www.analog.com/en/mems/low-g-accelerometers/products/index.html </li></ul></ul><ul><li>Visit Element 14 to post your question </li></ul><ul><ul><li> www.element-14.com </li></ul></ul><ul><li>For additional inquires contact our technical service hotline or even use our “Live Technical Chat” online facility </li></ul>