Homing signal

To determine the position, a reference is required between drive and machine. The reference point is made with a homing cycle, which evaluates the position of a homing signal.
To do this, analog encoders can have an additional track, which provides a homing mark. The absolution position determined with the homing mark (related to 1 revolution) is assigned to exactly one measurement step.
And so before an absolute reference is created or the last selected reference point is found again, the homing mark must be run over. In the least favorable case, this requires a turn of up to 360°.

Example: optical analog encoder with homing signal:

	1	Light source
	2	Collector
	3	Screen
	4	Glass element (signal encoder)
	Sensors
	5a	SIN/COS track
	5b	Homing signal

(Illustration from http://content.heidenhain.de/presentation/basics/de)