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Automating Manufacturing Systems - Process Control and ...

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continuous sensors - 23.21<br />

VDρ<br />

R = -----------<br />

u<br />

where,<br />

R<br />

=<br />

Reynolds number<br />

V =<br />

D =<br />

ρ =<br />

u =<br />

velocity<br />

pipe diameter<br />

fluid density<br />

viscosity<br />

23.2.5.1 - Pressure<br />

Figure 23.22 shows different two mechanisms for pressure measurement. The<br />

Bourdon tube uses a circular pressure tube. When the pressure inside is higher than the<br />

surrounding air pressure (14.7psi approx.) the tube will straighten. A position sensor, connected<br />

to the end of the tube, will be elongated when the pressure increases.<br />

pressure<br />

increase<br />

pressure<br />

increase<br />

position sensor<br />

position sensor<br />

pressure<br />

pressure<br />

a) Bourdon Tube<br />

b) Baffle<br />

Figure 23.22<br />

Pressure Transducers

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