Piezoresistive Pressure Transducers <ul><li>Source: Freescale </li></ul>
Introduction <ul><li>Purpose </li></ul><ul><ul><li>This training module provides basic knowledge of pressure sensors, and ...
Pressure and Pressure Measurement  <ul><li>Fluid pressure can be defined as the measure of force per-unit-area exerted by ...
Static vs. Dynamic Pressure Systems Static Pressure Systems P abs   =   P   +   ( ρ   x   g   x   H) P abs :   the   absol...
Pressure Sensors Basics
Basic Structure of Freescale’s Pressure Sensor
Fully Integrated Pressure Sensor Schematic
Design Considerations for Different Levels of Sensor Integration <ul><li>Priced higher than compensated / uncompensated de...
MPXH Series <ul><li>Features </li></ul><ul><li>Pressure ranges up to 300 kP </li></ul><ul><li>Temperature compensated from...
MPXV and MPXA Series <ul><li>Features </li></ul><ul><li>•  Pressure ranges up to 250 kPa </li></ul><ul><li>•  Temperature ...
Noise Considerations <ul><li>Two Types of noise in a piezo-resistive integrated pressure sensor </li></ul><ul><ul><li>Shot...
Interfacing Pressure Sensors to MCUs
Implementing Auto-Zero Function <ul><li>A zero pressure reference condition must be known to exist in the system. </li></u...
Additional Resource <ul><li>For ordering the pressure sensors, please click the part list or </li></ul><ul><li>Call our sa...
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Piezoresistive Pressure Transducers

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Introduction of basic knowledge of pressure sensors and Freescale's featured products and their applications

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Piezoresistive Pressure Transducers

  1. 1. Piezoresistive Pressure Transducers <ul><li>Source: Freescale </li></ul>
  2. 2. Introduction <ul><li>Purpose </li></ul><ul><ul><li>This training module provides basic knowledge of pressure sensors, and Freescale’s featured products and their applications. </li></ul></ul><ul><li>Outline </li></ul><ul><ul><li>Basic knowledge of pressure sensors </li></ul></ul><ul><ul><li>Design considerations for different levels of sensor integration </li></ul></ul><ul><ul><li>Interfacing pressure sensors to MCUs </li></ul></ul><ul><ul><li>Featured products and applications </li></ul></ul><ul><ul><li>Other design considerations </li></ul></ul><ul><li>Content </li></ul><ul><ul><li>14 pages </li></ul></ul><ul><li>Duration </li></ul><ul><ul><li>10 Minutes </li></ul></ul>
  3. 3. Pressure and Pressure Measurement <ul><li>Fluid pressure can be defined as the measure of force per-unit-area exerted by a fluid, acting perpendicularly to any surface it contacts. </li></ul><ul><li>Three categories of pressure measurements: </li></ul><ul><ul><li>Absolute pressure </li></ul></ul><ul><ul><li>Gage pressure </li></ul></ul><ul><ul><li>Differential pressure </li></ul></ul>
  4. 4. Static vs. Dynamic Pressure Systems Static Pressure Systems P abs = P + ( ρ x g x H) P abs : the absolute pressure at depth H. P: the external pressure at the top of liquid. ρ : the density of the fluid g: the acceleration due to gravity H: the depth at which the pressure is desired. A dynamic system with a fluid flowing through a pipe or duct
  5. 5. Pressure Sensors Basics
  6. 6. Basic Structure of Freescale’s Pressure Sensor
  7. 7. Fully Integrated Pressure Sensor Schematic
  8. 8. Design Considerations for Different Levels of Sensor Integration <ul><li>Priced higher than compensated / uncompensated device </li></ul><ul><li>No amplification needed </li></ul><ul><li>Direct interface to MPU </li></ul><ul><li>Signal conditioning, calibration of span and offset, temperature compensation included on-chip </li></ul>Integrated Pressure Sensors <ul><li>Lower sensitivity due to span compensation (compared to uncompensated) </li></ul><ul><li>Priced higher than uncompensated device </li></ul><ul><li>Requires signal conditioning / amplification of output signal </li></ul><ul><li>Reduced device-to-device variations in offset and span </li></ul><ul><li>Reduced temperature drift in offset and span </li></ul><ul><li>Reasonable input impedance </li></ul><ul><li>Low level output allows flexibility in signal conditioning </li></ul>Temperature Compensated & Calibrated <ul><li>Temperature compensation circuitry required </li></ul><ul><li>Requires signal conditioning / amplification of output signal </li></ul><ul><li>Relatively low input impedance (400 Ω typical) </li></ul><ul><li>High sensitivity </li></ul><ul><li>Lowest device cost </li></ul><ul><li>Low-Level output allows flexibility of signal conditioning </li></ul>Uncompensated Sensors Design Considerations Design Advantages Integration Level
  9. 9. MPXH Series <ul><li>Features </li></ul><ul><li>Pressure ranges up to 300 kP </li></ul><ul><li>Temperature compensated from -40ºC to +125ºC </li></ul><ul><li>Amplified analog output </li></ul><ul><li>Ideally suited for microcontroller interfacing </li></ul><ul><li>Small rugged polyphenylene-sulfide (PPS) surface mount package </li></ul><ul><li>High accuracy in the 0ºC to +85ºC range </li></ul><ul><li>Available with axial and side port </li></ul><ul><li>Typical Applications </li></ul><ul><li>Barometric absolute pressure (BAP) </li></ul><ul><li>Manifold absolute pressure (MAP) </li></ul><ul><li>Barometric and altimetric measurements </li></ul><ul><li>Industrial control </li></ul><ul><li>Water-level measurement for washing machines and dishwashers </li></ul>
  10. 10. MPXV and MPXA Series <ul><li>Features </li></ul><ul><li>• Pressure ranges up to 250 kPa </li></ul><ul><li>• Temperature compensated from -40ºC to +125ºC </li></ul><ul><li>• Amplified analog output </li></ul><ul><li>• Ideally suited for microcontroller interfacing </li></ul><ul><li>• Rugged PPS surface mount small outline package (SOP) </li></ul><ul><li>• Available with axial and side port </li></ul><ul><li>Typical Applications </li></ul><ul><li>• BAP </li></ul><ul><li>• MAP </li></ul><ul><li>• Process control </li></ul><ul><li>• Barometric and altimetric measurements </li></ul><ul><li>• Industrial control </li></ul><ul><li>• Water-level measurement for washing machines and dishwashers </li></ul>
  11. 11. Noise Considerations <ul><li>Two Types of noise in a piezo-resistive integrated pressure sensor </li></ul><ul><ul><li>Shot noise – the result of non-uniform flow of carriers across a junction and is independent of temperature </li></ul></ul><ul><ul><li>1/f noise – results from crystal defects and also due to wafer processing </li></ul></ul><ul><li>Noise can also come from external circuits </li></ul>Integrated Pressure Sensor with RC LP Filter to Filter Out Noise
  12. 12. Interfacing Pressure Sensors to MCUs
  13. 13. Implementing Auto-Zero Function <ul><li>A zero pressure reference condition must be known to exist in the system. </li></ul><ul><li>Auto-zero can be implemented easily when an integrated pressure sensor is interfaced to an MCU. </li></ul><ul><ul><li>Sample the sensor output when a known zero reference is applied to the sensor. Store current zero pressure offset as CZPO. </li></ul></ul><ul><ul><li>Sample the sensor output at the current applied pressure. Call this SP. </li></ul></ul><ul><ul><li>Subtract the stored offset correction, CZPO, from SP. The pressure being measured is simply calculated as: </li></ul></ul>P MEAS = (SP − CZPO)/S
  14. 14. Additional Resource <ul><li>For ordering the pressure sensors, please click the part list or </li></ul><ul><li>Call our sales hotline </li></ul><ul><li>For additional inquires contact our technical service hotline </li></ul><ul><li>For more product information go to </li></ul><ul><ul><li>http://www.freescale.com/webapp/sps/site/taxonomy.jsp?nodeId=01126990368716 </li></ul></ul>

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