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Automating Manufacturing Systems - Process Control and ...

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continuous sensors - 23.22<br />

These sensors are very common <strong>and</strong> have typical accuracies of 0.5%.<br />

23.2.5.2 - Venturi Valves<br />

When a flowing fluid or gas passes through a narrow pipe section (neck) the pressure<br />

drops. If there is no flow the pressure before <strong>and</strong> after the neck will be the same. The<br />

faster the fluid flow, the greater the pressure difference before <strong>and</strong> after the neck. This is<br />

known as a Venturi valve. Figure 23.23 shows a Venturi valve being used to measure a<br />

fluid flow rate. The fluid flow rate will be proportional to the pressure difference before<br />

<strong>and</strong> at the neck (or after the neck) of the valve.<br />

differential<br />

pressure<br />

transducer<br />

fluid flow<br />

Figure 23.23<br />

A Venturi Valve

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