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Automating Manufacturing Systems - Process Control and ...

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continuous sensors - 23.32<br />

23.2.9 Others<br />

A number of other detectors/sensors are listed below,<br />

Combustion - gases such as CO2 can be an indicator of combustion<br />

Humidity - normally in gases<br />

Dew Point - to determine when condensation will form<br />

23.3 INPUT ISSUES<br />

Signals from transducers are typically too small to be read by a normal analog<br />

input card. Amplifiers are used to increase the magnitude of these signals. An example of<br />

a single ended signal amplifier is shown in Figure 23.32. The amplifier is in an inverting<br />

configuration, so the output will have an opposite sign from the input. Adjustments are<br />

provided for gain <strong>and</strong> offset adjustments.<br />

Note: op-amps are used in this section to implement the amplifiers because they are<br />

inexpensive, common, <strong>and</strong> well suited to simple design <strong>and</strong> construction projects.<br />

When purchasing a commercial signal conditioner, the circuitry will be more complex,<br />

<strong>and</strong> include other circuitry for other factors such as temperature compensation.<br />

www.PA<strong>Control</strong>.com

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