Inductive/Capacitive sensor - how it works

[nForce]

I have found this diagram (it's in german) but I think from pictograms you will understand what it means.
This diagram is for an inductive sensor, so what does it mean and how does it work? I have read about it, but this diagram I don't understand.

[SeanB]

From left to right is the sense coil and it's associated tuning capacitor. Then comes the oscillator that drives the tuned coil. Then the comparator that measures the amplitude of the oscillator signal, and finally the output stage that gives a signal that external units use.

Basically the oscillator uses a tuned circuit, and as ferrous material ( or basically any metal) gets brought close to the coil, which is in a ferrite cup so there is a large air gap on the one end used for sensing,  it has 2 effects on the oscillator. First is it changes the oscillator frequency, as it changes the magnetic circuit, and second it damps the oscillation as it extracts energy from the oscillator due to the loss in the metal. This is then detected by the comparator as a variation in either amplitude or frequency ( depends on the actual type) and this then is used to drive the power output stage. Output stage in industrial applications will be one of a variety. Either a NAMUR output dfor intrinsically safe sensor types, or a NPN or PNP type output stage, which either switches the output to ground or the supply rail respectively. Final type is AC only, and can be either 2 wire or 3 wire, 3 wire having a separate output line, and 2 wire relying on there being an actual relay coil, with a range of current between limits and also a range of AC supply voltages, so that when the sensing limit is reached operates the coil, with a small voltage drop when energised providing enough power to keep the sensor powered.