12.5.8 Other sensors
Piezoelectric sensors are used for sensing force that can be produced by pressure,
weight, or acceleration. These devices have high sensitivity but are poor at
sensing low-level forces due to offset and drift caused by temperature variations.
Piezoelectric devices are normally packaged with a buffer amplifier and conditioning
as shown in Fig. 5.12b but extra gain stages may be needed before transmission.
Any extra conditioning necessary can be obtained from the manufacturers’
specifications.
Angular and distance measuring devices are digital in nature so that any
conditioning required is done at the controller; only the correct format is needed
for transmission.
Bimetallic sensors are temperature-sensing devices that can be used with a
mechanical linkage to operate a display directly such as in an oven thermometer
but are not accurate enough for linear control applications. Other bimetallic devices
operate switches (mercury in glass or mechanical contacts) as simple / ON/OFF
devices; such are used in thermostat applications normally without conditioning.
Taguchi, chemical, smoke detectors, and similar types of sensors all require
conditioning; the type and extent of the conditioning required depends on the
application and manufacturers’ specifications and will not be discussed here.