Capacitive Proximity Sensor

Model	LJC18A3-H-Z/BX
Polarity	NPN
Voltage	DC 6-36V
Current	200mA
Dimensions	Rosca M18 x 61mm
Detection distance	up to 10mm
Switch type	Normally open
Brown cable	V+
Blue cable	V-
Black cable	Signal
Temperature	-25ºC to 70ºC
Cable length	180cm

The capacitive proximity sensors detects the presence of materials with a high dielectric constant, like the PCB or aluminium heat beds.

Contrary to the inductive proximity sensor, this one also detects non-ferric materials separated up to 10mm.

When using borosilicate glass in 3D printers, this distance decreases to 1mm due to the low dielectric constant of this type of glass. The measures are better in the center than in the corners of the glass in this case. With normal glass (or mirrors) the detection distance is greater and the device also correctly works in the corners.

These sensors are often used in 3D printers to automatically level the heat bed with the Z axis thus preventing poor printing results due to surface irregularities.

The Marlin firmware supports this functionality, indicated as Auto Bed Levelling in the Configuration.h file.