Tire Pressure Gauge

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Tire Pressure Gauge

Instrumentation andMetrologyBy:Mohit MaheshwariRoll no.49


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Pressure (SI unit pascal)

It is the force acted on a unit area

A force in the nature of thrust which

is distributed over the surfaceA force acting against within a

surface in a closed container

Measured in bar, torr, psi,atmosphere etc.

Classified into

Static- is uniform in all directions, so


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Terms related to Pressure

Absolute pressure is zeroreferenced against a perfect vacuum,so it is equal to gauge pressure plusatmospheric pressure.

Gauge pressure is zero referencedagainst ambient air pressure, so it is

equal to absolute pressure minusatmospheric pressure. Negative signsare usually omitted.

Differential pressure is the


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Pressure sensors

It acts as a transducer ; it generates asignal as a function of the pressureimposed.

These are manufactured frompiezoelectric substance like quartz.

Two types:Force Collector type-(such a

diaphragm, piston, bourdon tube, orbellows) to measure strain (or

deflection) due to applied force


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Application

Pressure sensing

Altitude sensing

Flow sensing

Level / Depth sensing

Leak Testing

Pitot tube

Sphygmomanometer

.


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Instruments classified

Low pressure (below 1 mm of Hg)-manometers and low pressure gauges

Pressure (above 1 mm of Hg to 1000atmosphere)- Bourdon tube andDiaphragm gauges

Low vacuum and ultra highvacuum(760 torr-10-4 torr)-Mcleod,thermal conductivity.

Varying pressure- Engine Indicatorand cathode ray oscilloscope.


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Tire pressure gauge

A tire-pressure gauge is a pressuregauge used to measure the pressureof tires on a vehicle

Environmental conditions canintroduce a 13% to 15% variability inpressure due to temperature (0 C to

40 C), and additional changes canresult due to altitude.

Built-in tire pressure sensors-Used to fill tire will low pressureautomatically. The problem with this


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Types of tire pressure gauges

Stick Gauges- small but not veryaccurate

Analog Gauges- Dial gauges areeasy to use from a distance,such as while inflatingthe tire.

Digital Pressure Gauge- fast andeasy to use

Tire Pressure Monitoring Systems-Some vehicles have automated


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Working principle

Tire pressure are mostly calculatedeither using

Bourdon Pressure Tube(Membrane typeManometer)

Diaphragm or

Bellows


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Bourdon Pressure Tube(membrane type)

Bourdon uses theprinciple that a flattenedtube tends to change to a

more circular cross-section when pressurized

A flattened thin-wall,

closed-end tube isconnected at the hollowend to a fixed pipecontaining the fluidpressure to be measured


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Mechanical Side of BourdonStationary parts:

A: Receiver block. This joins the inlet pipe tothe fixed end

of the Bourdon tube (1) and secures

the chassis plate (B).The two holes receive screws

that secure the case.

B: Chassis plate. The face card is attached to

this. It containsbearing holes for the axles.

C: Secondary chassis plate. It supports theouter ends of the axles.


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Diaphragm

A pile of pressure capsuleswith corrugated diaphragmsin an aneroid barograph.

A second type of aneroidgauge uses the deflection of aflexible membrane that

separates regions of differentpressure. The amount ofdeflection is repeatable forknown pressures so the

pressure can be determined


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Bellows

In gauges intended to sense smallpressures or pressure differences, orrequire that an absolute pressure bemeasured, the gear train and needlemay be driven by an enclosed andsealed bellows chamber, called an

aneroid, which means "withoutliquid".

This bellows configuration is used inaneroid barometers (barometers withan indicatin needle and dial card),


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Whats InsideThe parts of a typical pressure gaugelook like this:

Spring

Calibrated rodPiston

Polished inner surface of valve

Rubber seals and a pin


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How it works

The inside of the tube is polished smooth.The piston is made ofsoft rubber so it

seals nicely against the tube, and theinside of the tube is lubricated with alight oil to improve the seal. In thepicture below, you can see that the piston

is at one end of the tube and the stop is
http://auto.howstuffworks.com/question105.htmhttp://auto.howstuffworks.com/question105.htm


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. If you look in the opening, you willbe able to see a rubber seal and a

small fixed pin. The rubber sealpresses against the lip of the valvestem to prevent air from leakingduring the measurement, and the pin

depresses the valve pin in the valvestem to let air flow into the gauge.

The distance the piston travels is

relative to the pressure in the tire.


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There is a calibrated rodinside the

tube.The calibrated rod rides on top of the

piston, but the rod and the piston arenot connected and there is a fairlytight fit between the rod and the stop.

When the pressure is released, thepiston moves back to the left but the

rod stays in its maximum position to


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Thankyou

Tire Pressure Gauge

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