Understanding Pressure Sensors Class 1: The Basics of Specifying Pressure Sensors April 7, 2014 Randy Frank

Agenda Pressure Sensor Technologies Types of Measurements Specifying Pressure Converting Pressure Pressure Ratings Example Measurements Other Issues Summary

Technologies for Measuring Pressure Bourdon tube Bellows pressure capsule Fiberoptic high (combustion) pressure Linear variable differential transformer (LVDT) Ceramic capacitive Stainless steel diaphragm / strain gauge Piezoelectric Microelectromechanical Systems (MEMS) Silicon capacitive Silicon piezoresistive

Silicon Piezoresistive Pressure Sensors Understanding Smart Sensors

Type of Pressure Measurements Gauge Absolute Differential P1 P1 P1 Vacuum http://www.allsensors.com/engineering-resources/white-papers/pressure-points Atmosphere P2 (a) (b) (c) Source: http://www.allsensors.com/engineering-resources/white-papers/pressure-points

Example Pressure Measurements http://www.allsensors.com/engineering-resources/white-papers/pressure-points

Gauge Pressure Example Blood pressure Disposable invasive blood pressure: http://www.meritsensor.com/

Specifying Pressure Pressure is measured in: Torr (mmHg) Inches of Hg Inches and feet of water KiloPascals (kPa) and Pascals PSI (pounds per square inch) Bar and millibars http://www.wrh.noaa.gov/slc/projects/wxcalc/formulas/pressureConversion.pdf

Converting Pressure http://www.wrh.noaa.gov/slc/projects/wxcalc/formulas/pressureConversion.pdf http://www.wrh.noaa.gov/slc/projects/wxcalc/formulas/pressureConversion.pdf

Online Pressure Calculators/Conversion http://www.allsensors.com/ http://www.unitconversion.org/unit_converter/pressure.html http://www.allsensors.com/

Span Understanding Smart Sensors

Effect of Temperature Offset Temperature Shift (0°C-70°C), Typical: ±0.1 mV Temperature Effect on Resistance (0°C-70°C), typical: 2800 ppm/°C Temperature Effect on Span (0°C-70°C), Typical: -1900 ppm/°C http://www.allsensors.com/products/BLVR-L01D#product_series For All Sensors BLVR-L01D

Proof Pressure The level of pressure at which a component, pipe, tube, hose or other fluid passage will not yield during application of internal pressure. http://www.engnetglobal.com/tips/glossary.aspx?word=PROOF+PRESSURE

Burst Pressure The maximum pressure that a pressure sensor (diaphragm and/or package) can withstand before failure.

Proof and Burst Pressure Example Standard Pressure Ranges for BLVR-L01D Operating Range Proof Pressure Burst Pressure ±1 inH2O 100 inH2O 300 inH2O http://www.allsensors.com/products/BLVR-L01D#product_series

Absolute Pressure Example An altimeter is an absolute pressure gauge (measurement) that shows height above sea level. The air pressure to height above sea level conversion is frequently performed using a look up table. For example, 10,000 feet above sea level is 10.1 psia (69.7 kPa). Pressure altitude (halt) can be calculated using the equation: halt = (1-(psta/1013.25)^0.190284)x145366.45 Where: halt is the height in feet and psta is the pressure in millibars (mb) or hectopascals (hPa) Look up table: http://www.engineeringtoolbox.com/air-altitude-pressure-d_462.html Equation: http://www.wrh.noaa.gov/slc/projects/wxcalc/formulas/pressureAltitude.pdf http://www.allsensors.com/engineering-resources/white-papers/pressure-points

Height of a Liquid Column For a standing liquid, the absolute pressure at a depth H in a liquid is defined as: Pabs = P + (ρ x g x H) Where: Pabs is the absolute pressure at depth H in kg/m-s2 (or Pa) P is the external pressure at the top of the liquid, typically atmospheric pressure for open systems ρ is the density of the fluid (for example, pure water is 1 g/cm3 at 4°C and salt water is 1.025 g/cm3) g is the acceleration due to gravity (g = 9.81 m/s2) (32.174 ft/s2)) and H is the depth in meters or feet

Using Pressure to Measure Flow: A Differential Pressure Example http://www.allsensors.com/engineering-resources/white-papers/pressure-points

Calculating Flow q = cd π/4 D22 [2(P1 - P2) / ρ(1 - d4) ]1/2 Where: q is the flow in m3/s cD is the discharge coefficient, the area ratio = A2 /A1 P1 and P2 are in N/m2 ρ is the fluid density in kg/m3 D2 is the orifice, venturi or nozzle inside diameter (in m) p1"> D1 is the upstream and downstream pipe diameter (in m) and d = D2 / D1 diameter ratio http://www.allsensors.com/engineering-resources/white-papers/pressure-points

Other Issues Packaging related Media compatibility

Pressure Sensor Connections All Sensors Kavlico PCB Piezotronics http://www.pcb.com/TM_Pressure.asp?gclid=COOo7bjFvbICFWXhQgodnz4ACg High Pressure Sensors Industrial Products http://www.kavlico.com/products/industrial/high_pressure.php Pressure connection Electrical connection

Media Compatibility All Sensors: This series is intended for use with non-corrosive, non-ionic working fluids such as air, dry gases and the like. A protective parylene coating is optionally available for moisture/harsh media protection. Kavlico: The stainless steel package configurations make them suitable for a broad range of media. AST: Whether measuring hydraulic pressure in a manifold or corrosive media such as sea water or hydrogen, the AST4000 pressure sensor provides a thick diaphragm to maintain long-term stability and use. http://www.astsensors.com/pressure_sensors_and_transducers/AST4000

Summary Pressure Sensor Technologies Measurements Specifying Converting Ratings Packaging Issues A successful application considers all of them

Topics Later This Week Tuesday - Sensor Compensation and Signal Conditioning for Piezoresistive Sensors Wednesday - Case Study: Developing a Smart Pressure Sensor Thursday - An Introduction to Intelligent Sensor Interfaces Friday - Sensors in Extreme Applications