Pacific school of Engineering Sub: I.P.C Topic: Pressure measurement Guided by Piyush modi Mayani Chintak Sudani Dhrutik Bhikadiya Hardik Kotadiya Hardik Manavadariya Maulik

Content 1.Overview 2.Types of Measurement 3.U-tube Manometer 4.Bourdon Gauge 5.Diaphragm and Bellows Element 6.Strain Gauge 7.Piezoresistive Gauge 8.Quartz Gauge

Overview Pressure (P ) expresses the magnitude of normal force (F-N) per unit area (A-m 2 ) applied on a surface Units: Pa(= N/m 2), psi(=lbf/in 2 ), bar (=10 5 Pa=100 kPa), mbar (=100 Pa=1 hPa), atm (=101.3 kPa), mmHg (or Torr), inHg, etc. Where P abs : Absolute pressure P atm : Atmospheric pressure (standard is: kPa = psi=760 mmHg=29.92 inHg) P gage : Gage pressure

Types of Measurement Mechanical –U-tube manometer, Bourdon tube, Diaphragm and Bellows Mechanical pressure measurement devices are large and cumbersome. Not suited for automated control loops typical in industry. Electrical –Strain Gauge, Capacitive sensor, Potentiometric, Resonant Wire, Piezoelectric, Magnetic, Optical

U-tube Manometer Measures difference in pressure between two points in a pipe. Typical in laboratories. Principles: Hydrostatic Law ∆P=ρ g h

U-tube Manometer Mercury Water Manometer Air Water Manometer Applications : air pressure, pipe pressure, etc.

Bourdon Gauge Flexible element used as sensor. Pressure changes cause change in element position. Element connected to pointer to reference pressure.

Bourdon Gauge Principles: change in curvature of the tube is proportional to difference of pressure inside from that outside the tube Applications: tire pressure, pressure at the top or along the walls of tanks or vessels

Bourdon Gauge -The Bourdon gauge consists of a bent tube with an elliptic cross section closed at one end and connected at the other open end to the chamber in which the pressure is to be measured. -Pressure differences between the environment of the gauge and the interior cause forces to act on the two walls of the tube so that it is bent by an amount that depends on the pressure difference between the environment and the interior. -The bending is transformed by a lever to a pointer whose position can be calibrated. The importance of this type of gauge is that it is very robust and that it covers a range of pressure measurement from pressures higher than atmospheric pressure down to rough vacuum (about10 mbar). -The accuracy and reproducibility are relatively poor, so that it is not suitable for precision measurements, and its usefulness for vacuum measurements is limited.

Diaphragm and Bellows Element Similar concept to Bourdon type. Widely used because they require less space and can be made from materials that resist corrosion.

Diaphragm If each element is sealed with a known, fixed internal pressure, flex will depend on pressure change on outside. Stacking amplifies effect!

Strain Gauge Measures deflection of elastic diaphragm due to pressure difference across diaphragm. Widely used in industry. Used for small pressure ranges. Measurements tend to drift.

Strain Gauge Principles: ∆ P  ∆ Resistance  ∆ Voltage Applications: Sensors for internal combustion engines, automotive, research etc.

Piezoresistive Gauge Measures the charge developed across quartz crystal due to change in pressure. Charge decays rapidly making unsuitable for static pressure measurements. Sensors are very rugged. Pressure can be applied longitudinally or transversally. Used to measure dynamic pressure changes associated with explosions and pulsations.

Piezoresistive Gauge Principles: ∆Pressure = ∆Charge = ∆Resistance = ∆Voltage Applications: Very accurate for small pressure differentials e.g. Difference between indoor and outdoor pressure Digital Manometer

Piezoresistive Gauge -Similar to the diaphragm gauge the piezoresistive gauge consists of a small evacuated capsule closed with a thin silicon diaphragm at the side exposed to the space whose pressure is to be measured. -On one side of this diaphragm are placed thin film piezoresists produced by evaporation and which are connected to form a bridge circuit. -By deformation of the silicon diaphragm the bridge is put out of balance by an amount depending on the deformation. To avoid destruction of the silicon diaphragm by corrosive gases there exist models in which a small volume filled with special oil is placed between the silicon diaphragm and the vacuum space. -This volume is closed at the side of the vacuum space whose pressure is to be measured by a thin stainless-steel diaphragm. The special oil serves as an incompressible pressure transducer. -Depending on the gauge construction the pressure reading covers a range of 0.1 to 200 mbar or 1 to 2000 mbar. The pressure reading is independent of the kind of gas.

Quartz Gauge Principles: ∆ Pressure  ∆ Charge  ∆ Voltage Applications: measurements with high accuracy, good repeatability, high resolution. e g. Quartz Clock