Analog sensors act as a type of adjustable resistor. As the state of the sensor changes, the voltage reporting back to the robot changes as well. Think of a dimmer switch, the brightness of the lights in the room depends on the where the setting of the knob of slider is. As the knob is adjusted the resistance level adjusts proportionally and the light continuously changes to the output from the knob.
Unlike the binary (either/or) status of digital sensors, analog sensors consider all numbers within a specific, given range. When using an analog sensor the actionable trigger will typically be some range like, between 1.2 and 2.2 volts or greater than 0.5 volts.
REV Robotics offers one analog sensor, known as a Potentiometer (REV-31-1155). The Potentiometer can be used to sense or measure the angular position of an shaft.
Each Analog Port on the Control Hub (REV-31-1595) or Expansion Hub (REV-31-1153) has two channels for communication. However, a potentiometer can only be configured to channels 0 or 2; so it is not possible to connect two potentiometers on the same port.
Configuring the potentiometer is simple. In the active configuration select the port being utilized, in this case it is port 0, and choose "Analog Input."