Sensor calibration is an adjustment performed on a sensor to make that sensor functions accurately. Calibration only needs to be carried out once unless the sensor's height, line's color intensity or background color has changed.

Infrared Sensor works similarly like an ultrasonic sensor, but it detects reflected light instead of sound.

Same as ultrasonic sensor, infrared sensor has a transmitter and a receiver. Transmitter emits infrared light onto a surface, and that infrared light will be reflected if it is directed at a white coloured surface; then receiver will pickup the signal from the reflected light.

On the contrary, if infrared is directed to a black coloured surface, it will be absorbed by the surface instead, and won’t get reflected. As a result, receiver won’t detect any reflected signal.