Automating Manufacturing Systems - Process Control and ...

continuous sensors - 23.30
Thermistors are small, inexpensive devices that are often made as beads, or metallized
surfaces. The devices respond quickly to temperature changes, and they have a
higher resistance, so junction effects are not an issue. Typical accuracies are 1%, but the
devices are not linear, have a limited temperature/resistance range and can be self heating.
23.2.6.4 - Other Sensors
IC sensors are becoming more popular. They output a digital reading and can have
accuracies better than 0.01%. But, they have limited temperature ranges, and require some
knowledge of interfacing methods for serial or parallel data.
Pyrometers are non-contact temperature measuring devices that use radiated heat.
These are normally used for high temperature applications, or for production lines where it
is not possible to mount other sensors to the material.
23.2.7 Light
23.2.7.1 - Light Dependant Resistors (LDR)
Light dependant resistors (LDRs) change from high resistance (>Mohms) in bright
light to low resistance (