In a previous blog Flush or Non-Flush, Looks Can Be Deceiving, Jeff mentions the two common housing designs of inductive sensors, flush and non-flush. So what does this mean to you when you are applying an inductive or even a capacitive sensor?
Flush-style sensors actually have a shield that restricts the magnetic field so that it only radiates out of the face of the sensor. Flush-style, or shielded sensors, can be mounted flush in a metal bracket or even in your machine without the metal causing the sensor to false trigger. When mounting two shielded inductive proximity sensors next to each other, you should typically leave one diameter of the sensor between adjacent sensors. The shielded-style of sensor will typically have approximately one-half of the sensing distance that a non-shielded version will have. For example, a 12mm shielded inductive sensor will have a sensing distance 2mm whereas a non-shielded version will have a sensing distance of 4mm. Although shielded style sensors have a shorter sensing range they can be buried in a machine or a bracket that will offer protection against damage.

Non-flush, or unshielded sensors, do not have the shield around the end of the sensor so the field can radiate from the face to the sides of the sensor in a larger pattern. This style of sensor cannot be mounted flush in a metal bracket, as the metal will cause the sensor to actuate. When installing a non-shielded sensor in metal you should have one diameter from each edge of the sensor to the nearest metal flange. In other words, you need to have a pocket in the metal that is three times the diameter of the sensor wide and at least two times the sensing distance of the sensor deep with the sensor mounted in the middle.
For an excellent demonstration of shielded verses unshielded mounting of inductive sensors, check out this video!