Unusual Switch / sensor needed Very Small.

[thebuj]

If you have money to throw at it, you could use a machine vision camera.

You could detect for any missing parts, defects, misalignments...

Cognex makes a powerful one, it can detect missing pins in a connector.

 

[leeyock]

From what I see, maybe a contrast sensor or colour sensor might be useful, as there is a significant colouring difference between your netting and the bricks.

I have tried using the sensor to detect copper wires and the results were positive. You might want to have a look.

http://www.di-soric.com/en/Colour-Sensors-di-soric-30458.html

 

[JesperMP]

This is a classical problem with a simple solution. Make a lever-arm arrangement that is moved by the material, and sense on the arm rather than on the material itself.

For example if the web moves vertically downwards, then the lever-arm can be like a small pivoted see-saw with a bit of weight on one side, so that it will naturally rest in a horisontal position. When the web passes by it forces the see-saw to pivot down on the other side. When the web disappears, the see-saw falls back to its original position.
Then use a regular prox to sense on the see-saw.

If the web moves upwards, or horisontally, you have to change the position of the weight and maybe add an angle to the see-saw. But the principle is the same. You get the idea.
In this way you can create a lever-arm that is designed to activate on the particular kind of material, wether it be super-heavy bulk, or like in your case very light and flimsy.

 

[Aabeck]

Is the material of the netting conductive? If so ground out the netting and have a probe hanging down wired to the 0V of a ice cube relay, wire the other side to your MCR +24V power. When the probe grounds out the relay will trip and give you a dry contact to the PLC to know netting is there.

 

[osmanjdt]

although sensor can detect the movement but this make twice job for production