SUPPLY
The sensors are designed for industrial DC voltages (usually in the automation they use
24 volts), ac or universal (both)
OUTPUTS
If the electric output signal can be any value between certain limits, the sensor is analog. Typically, the controller receives the signal is digital and, therefore, uses an AD converter.
If it can be only two values, for example, 120mv and 5v, the sensor will be digital.
TYPES OF SENSORS
Depending on your application there are various families and types of sensors for use
POSITION
Compared with a reference, determine the physical location
Potentiometer (resistance)Ultrasonic (measures time by
acoustic waves)Encoders (angular motion)
Inductive (capture ferromagnetic materials by varying
the electromagnetic field)Capacitive (electrostatic field variation).
TEMPERATURE
The most common and cheapest is the thermocouple. But it is not accurate for temperatures below 1 ºC