Capacitive sensors for level detection use a spherical field to detect the product bulk material or liquid e g.
Sensor to detect plastic only.
Plastic granulate sugar oil aqueous media directly or through a container wall.
Inductive sensors detect metal objects contactless and wear free.
Omron also have sensor to detect aluminum non iron then it would be three sensors and more logic to decide.
Inductive proximity sensors can only detect metal targets.
Prices are indicative only and may vary by country.
Typical applications are in the wood paper glass plastic food chemical and semiconductor browse capacitive linear position sensors datasheets for ifm electronic gmbh.
Unlike photoelectric sensors this allows a inductive proximity sensor to detect a metal object through opaque plastic.
Even though you cou.
You have to do some logic that both type of sensors are on then it is metal only capacitance sensor is on it is plastic or glass.
Or you want to distinguish diffeent types of plastic say pvc vs.
Google for omron or ifm proximity sensors learn and find something you want and purchase.
They do not detect non metal targets such as plastic wood paper and ceramic.
The rectangular housing plastic for inductive sensor by bernstein is a robust plastic case with a size of 27x10mm and 60x36mm.
Metals are conductive while plastics ceramics are not.
While infra red sensors have been in use for some time to enable fast sorting of two or three plastic streams for recycling the latest developments allow the rapid recognition and reliable separation of six different plastics at the same time using near infra red laser diodes and detectors this enables the practicable and cost effective recycling of mixed plastic waste streams.
Dr zia s tiny 2 5 mm by 2 5 mm sensor is able to be swirled through a liquid and detect concentration levels as low as two parts per billion using a test that takes less than 10 minutes.
The question is vague but here is my train of thoughts.
Still you could go for indirect methods like reflectivity infrared signature by black body radiation.
Balluff s patented hybrid capacitive technology sensor series detects water based conductive media through thick glass and plastic walls while compensating for moisture foam and material build up.