Inductive Sensor

Introduction

Inductive sensors are used to sense the Z height on 3D printers. For Marlin with RAMPS - use one that has a 5V output, as opposed to 12V, as RAMPS cannot handle 12V without using additional components.

Part numbers look like LJ18A3-8-Z/BY-5V for the 2018 D3D with LCD screen - where we use the 8 mm distance sensing to facilitate the sensor not hitting the print bed.

• 5V is the critical part - 5V input - so can be powered from the RAMPS board directly
• LJ18 - the 18 refers to the diameter of the sensor in mm
• -8- refers to the distance of sensing
• Z/BY refers to normally open vs normally closed

Tom's Guide 1

• Mentions 12v sensor with voltage divider. Video description sources the 5V sensor

Tom's Guide 2

• Comparison - essentially, all distance sensing capacitive sensors are quite good.

Samples

• From Aliexpress -
• 3 Wire Polarity: NPN Detection
• Voltage: DC 5V
• Ouput Status: Normally Open
• Part number: LJ18A3-8-Z/BX
• See part numbers and what they mean at Aliexpress - [1]

The BX vs BY is NPN vs PNP Detection - appears wiring will be different

How to wire LJ18A3-8-Z/BX-5V vs Z/BY?

Notes

• For normally open, Z_MIN_ENDSTOP_INVERTING in configuration.h of Marlin should be set to false? See [2]
• NPN vs PNP - [3]
• See D3D BOM for sourcing.
• See D3D Height Controller for design