Pressure Methods

1. Pressure Methods • Manometer • Elastic Transducers • Measuring Vacuum • Balancing Force on known area • Electrical Pressure Transducers

2. Manometers Manometers measure a pressure difference by balancing the weight of a fluid column between the two pressures of interest. Large pressure differences are measured with heavy fluids, such as mercury (e.g. 760 mm Hg = 1 atmosphere). Small pressure differences, such as those experienced in experimental wind tunnels or venturi flowmeters, are measured by lighter fluids such as water (27.7 inch H2O = 1 psi; 1 cm H2O = 98.1 Pa).

3. Liquid/Gas Pressure 1 atm = 760 torr = 101 kPa. AND Hg = 13.5951 g cm-3 • Where • p is unknown pressure • Po is Ambient pressure • is fluid density g is gravitational force h is fluid column

4. Manometers • http://www.chm.davidson.edu/vce/GASLAWS/Pressure.html

5. Pressure by Elastic Transducers • Bourdon • Bellows • Diaphragm

6. Pressure Measurement Pressure Measurement Bourdon gauge A Bourdon gauge uses a coiled tube, which, as it expands due to pressure increase causes a rotation of an arm connected to the tube. In 1849 the Bourdon tube pressure gauge was patented in France by Eugene Bourdon.

7. Pressure Measurement A second type of aneroid gauge uses the deflection of a flexible membrane that separates regions of different pressure. The amount of deflection is repeatable for known pressures so the pressure can be determined by using calibration. The deformation of a thin diaphragm is dependent on the difference in pressure between its two faces. Diaphragm The reference face can be open to atmosphere to measure gauge pressure, open to a second port to measure differential pressure, or can be sealed against a vacuum or other fixed reference pressure to measure absolute pressure. The deformation can be measured using mechanical, optical or capacitive techniques. Ceramic and metallic diaphragms are used.

8. Diaphragms

9. Bellows The bellows pressure sensor is made of a sealed chamber that has multiple ridges like the pleats of an accordion that are compressed slightly when the sensor is manufactured. When pressure is applied to the chamber, the chamber will try to expand and open the pleats. which uses a spring to oppose the movement of the bellows and provides a means to adjust the amount of travel the chamber will have when pressure is applied

10. Pressure Mapping • http://www.tekscan.com/medical.html

11. Pressure Measurement Piezoresistor For typical stress values in the MPa range the stress dependent voltage drop along the resistor Vr, can be considered to be linear. A piezoresistor aligned with the x-axis as shown in the figure may be described by: Where: Vr is Voltage across piezoresistor R0 is unstrained value of Piezoresistor I is applied current L, T are transverse and longitudinal coefficient xx, yy, and zz are tensile components

12. Pressure Measurement Strain Gauge 900 1800 2700 00

13. Pressure Measurement In a capacitance-type pressure sensor, a high-frequency, high-voltage oscillator is used to charge the sensing electrode elements. In a two-plate capacitor sensor design, the movement of the diaphragm between the plates is detected as an indication of the changes in process pressure. Capacitive

14. Pressure Measurement Potentiometer The potentiometric pressure sensor provides a simple method for obtaining an electronic output from a mechanical pressure gauge. The device consists of a precision potentiometer, whose wiper arm is mechanically linked to a Bourdon or bellows element. The movement of the wiper arm across the potentiometer converts the mechanically detected sensor deflection into a resistance measurement, using a Wheatstone bridge circuit

15. Pressure Measurement Resonant of wire The resonant-wire pressure transducer was introduced in the late 1970s. In this design (Figure 3-7), a wire is gripped by a static member at one end, and by the sensing diaphragm at the other. An oscillator circuit causes the wire to oscillate at its resonant frequency. A change in process pressure changes the wire tension, which in turn changes the resonant frequency of the wire. A digital counter circuit detects the shift. Because this change in frequency can be detected quite precisely, this type of transducer can be used for low differential pressure applications as well as to detect absolute and gauge pressures.

16. Applications • AUTOMOTIVE • MEDICAL DEVICES • ERGONOMICS • ROBOTICS

17. Automotive Measuring tire footprints and their distributed contact pressures under motion is no easy feat---but PPS has a solution.  Our industrial-grade sensors are proven to have the speed, resolution, and ruggedness for this demanding application.  Tire Tread Measurement PPS tire footprint sensors feature auxiliary analog inputs capable of reading position encoder or accelerometer data to correlate the type of motion with the tactile data.  And they can be configured to fit tread widths for nearly any size vehicle.

18. Automotive Dynamic Brake Pad Measurement System

19. Medical Devices Revolutionizing Early Detection of Breast Cancer http://www.pressureprofile.com/case-study-mti.php

20. Medical Devices The osteopathic approach to medicine

21. Medical Devices State-of-the-Art Foot Scanning