lect 13 pressure measurement

7/30/2019 Lect 13 Pressure Measurement

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Pressure Methods

Manometer

Elastic Transducers

Measuring Vacuum

Balancing Force on known area

Electrical Pressure Transducers


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Manometers

Manometers measure a pressure difference bybalancing 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

orventuri flowmeters, are measured by lighterfluids such as water (27.7 inch H2O = 1 psi; 1

cm H2O = 98.1 Pa).
http://www.efunda.com/formulae/fluids/venturi_flowmeter.cfmhttp://www.efunda.com/formulae/fluids/venturi_flowmeter.cfm


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Liquid/Gas Pressure

0PrGage essure p p p ghr= = - =V

Where

p is unknown pressure

Po is Ambient pressure

is fluid density

g is gravitational force

h is fluid column

1 atm = 760 torr = 101 kPa. AND Hg= 13.5951 g cm-3


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Manometers

http://www.chm.davidson.edu/vce/GASL

AWS/Pressure.html
http://www.chm.davidson.edu/vce/GASLAWS/Pressure.htmlhttp://www.chm.davidson.edu/vce/GASLAWS/Pressure.htmlhttp://www.chm.davidson.edu/vce/GASLAWS/Pressure.htmlhttp://www.chm.davidson.edu/vce/GASLAWS/Pressure.html


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Pressure by Elastic Transducers

Bourdon

Bellows

Diaphragm


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Pressure Measurement Pressure

Measurement

Bourdon gaugeA 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 Eu

gene Bourdon.
http://en.wikipedia.org/wiki/Rotationhttp://en.wikipedia.org/wiki/Francehttp://en.wikipedia.org/wiki/Eugene_Bourdonhttp://en.wikipedia.org/wiki/Eugene_Bourdonhttp://en.wikipedia.org/wiki/Eugene_Bourdonhttp://en.wikipedia.org/wiki/Francehttp://en.wikipedia.org/wiki/Rotation


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Pressure Measurement

DiaphragmA second type of aneroid gauge uses the deflection of aflexible 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.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 referencepressure to measure absolute pressure.

The deformation can be measured using

mechanical, optical or capacitive

techniques. Ceramic and metallic

diaphragms are used.
http://en.wikipedia.org/wiki/Deflectionhttp://en.wikipedia.org/wiki/Artificial_membranehttp://en.wikipedia.org/wiki/Artificial_membranehttp://en.wikipedia.org/wiki/Deflection


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Diaphragms


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Bellows

The bellows pressure sensor is madeof 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 toadjust the amount of travel the

chamber will have when pressure is

applied


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Pressure Mapping

http://www.tekscan.com/medical.html
http://www.tekscan.com/medical.htmlhttp://www.tekscan.com/medical.html


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PiezoresistorFor 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
http://en.wikipedia.org/wiki/Pascal_(unit)http://en.wikipedia.org/wiki/Pascal_(unit)


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Strain Gauge

00 900 1800

2700


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CapacitiveIn a capacitance-type

pressure sensor, a high-

frequency, high-voltage

oscillator is used to charge

the sensing electrodeelements. In a two-plate

capacitor sensor design, the

movement of the diaphragm

between the plates isdetected as an indication of

the changes in process

pressure.


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PotentiometerThe 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 ismechanically linked to a Bourdon or bellows element.

The movement of the wiper arm

across the potentiometer converts

the mechanically detected sensordeflection into a resistance

measurement, using a

Wheatstone bridge circuit


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The resonant-wire pressure transducer was introduced in the late1970s. 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 tooscillate at its resonant frequency. Achange in process pressure changesthe wire tension, which in turnchanges the resonant frequency ofthe wire. A digital counter circuit

detects the shift. Because this changein frequency can be detected quiteprecisely, this type of transducer canbe used for low differential pressureapplications as well as to detectabsolute and gauge pressures.

Resonant of wire


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Applications

AUTOMOTIVE

MEDICAL DEVICES

ERGONOMICSROBOTICS
http://pressureprofile.com/index-automotive.phphttp://pressureprofile.com/index-medical.phphttp://pressureprofile.com/index-ergonomics.phphttp://pressureprofile.com/products-robotouchhttp://pressureprofile.com/products-robotouchhttp://pressureprofile.com/index-ergonomics.phphttp://pressureprofile.com/index-medical.phphttp://pressureprofile.com/index-automotive.php


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Automotive

Measuring tire footprints and their distributed contactpressures 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.PPS tire footprint sensors feature

auxiliary analog inputs capable of

reading position encoder or

accelerometer data to correlate thetype of motion with the tactile

data. And they can be configured to fit

tread widths for nearly any size vehicle.

Tire Tread Measurement


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Automotive

Dynamic Brake Pad Measurement System


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Medical Devices

Revolutionizing Early Detection of Breast Cancer

http://www.pressureprofile.com/case-study-mti.php
http://www.pressureprofile.com/case-study-mti.phphttp://www.pressureprofile.com/case-study-mti.phphttp://www.pressureprofile.com/case-study-mti.phphttp://www.pressureprofile.com/case-study-mti.phphttp://www.pressureprofile.com/case-study-mti.phphttp://www.pressureprofile.com/case-study-mti.php


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Medical Devices

The osteopathic approach to medicine
http://www.pressureprofile.com/products-fingertps


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Medical Devices

State-of-the-Art Foot Scanning
http://www.esoles.com/

lect 13 pressure measurement

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