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Automating Manufacturing Systems - Process Control and ...

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continuous sensors - 23.29<br />

R t<br />

=<br />

R o e<br />

β⎛<br />

1 T -- – ----<br />

1 ⎞<br />

⎝ ⎠<br />

T o<br />

∴T<br />

where,<br />

βT<br />

= -------------------------------- o<br />

R<br />

T t<br />

o<br />

ln⎛-----<br />

⎞ + β<br />

⎝ ⎠<br />

R o<br />

R o<br />

, R t<br />

= resistances at reference <strong>and</strong> measured temps.<br />

T o<br />

, T = reference <strong>and</strong> actual temperatures<br />

β = constant for device<br />

Figure 23.29<br />

Thermistor Calculations<br />

Aside: The circuit below can be used to convert the resistance of the thermistor to a voltage<br />

using a Wheatstone bridge <strong>and</strong> an inverting amplifier.<br />

+V<br />

R1<br />

R3<br />

R5<br />

R2<br />

R4<br />

-<br />

+<br />

Vout<br />

Figure 23.30<br />

Thermistor Signal Conditioning Circuit<br />

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

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