View source for Research On Inductive Proximity Sensors

Inductive proximity sensors are circuits that maintain a oscillating magnetic fields while sensing the reluctance of the circuit through the voltage amplitude of the oscillation.
The magnetic fields induce eddy currents in proximate ferrous materials.
Since eddy currents create opposing magnetic fields, reluctance in the sensor circuit (which contains a coil) increases.[http://machinedesign.com/sensors/proximity-sensors-compared-inductive-capacitive-photoelectric-and-ultrasonic]

Inductive proximity sensors are sorted by sensing range, which depends on field strength and field frequency.
They come in normally-closed (NC) versions and normally-open (NO) versions with PNP or NPN switching.
NC, NO, PNP and NPN defines the wiring interface but is not relevant to the sensing itself.[https://sensortech.wordpress.com/2011/01/18/industrial-sensing-fundamentals-%E2%80%93-back-to-the-basics-npn-vs-pnp/]

= Summary of [[3D_Printer_Bed_Leveling#Assessment_Matrix]] Results on Inductive Sensing =
Sensor weighs ~45 grams and is most often placed near print head.
The added moving weight is regarded as the major drawback of that bed probe solution, as compared to the others.
Other factors that help comparison with other sensors:
*Non-invasive sensing
*Does not detect glass surface
*Does not detect through tip of tool head
*Works without adding motors
*Requires signal filtering (normally done by Schmitt trigger within ready-made sensor unit)
*Price/unit: $3
*Very easy to build bed probe from
*Repeatability is good
*Works with aluminum bed without glass (too low sensing range). Ferrous metal bed gives good enough sensing range for having glass bed above it.
*There are detailed instructions available
*Smartfriendz, Bq and Printrbot all use inductive sensing.
*Less sensitive to bed irregularities than capacitive sensing.


= Models =
== LJ12A3-4-Z/BX ==

=== Sourcing ===
Supplied by Folgertech [http://folgertech.com/products/lj12a3-4-z-bx-inductive-proximity-sensor-switch here].

=== Wiring ===
3 wire, NPN, NO

Needs to be supplied 6-36 V. This means we need to build a voltage divider to interface with RAMPS logic.
Some reports having gotten 6 V sensors to work by feeding them the Arduino's 5 V [http://forums.reprap.org/read.php?219,477467,477467], so we should try that first.