Automating Manufacturing Systems - Process Control and ...

continuous sensors - 23.29
R t
=
R o
e
β 1 T -- 1
– ⎛ ⎞ ----
⎝
T o
⎠
∴T
βT
= -------------------------------- o
⎛
R
----- t
ln + β ⎞
T o
R o
⎝ ⎠
where,
R o
, R t
= resistances at reference and measured temps.
T o
, T = reference and actual temperatures
β = constant for device
Figure 23.29
Thermistor Calculations
Aside: The circuit below can be used to convert the resistance of the thermistor to a voltage
using a Wheatstone bridge and an inverting amplifier.
+V
R1
R3
R5
R2
R4
-
+
Vout
Figure 23.30
Thermistor Signal Conditioning Circuit