detect solids levels in a box

[billycan]

I have a an enclosed box into which various sized packages are dropped through a chute at the top. i want to be able to determine the maximum height of the highest parcel in the box before allowing another parcel to be dropped which may jam the chute. the box is 60cmX60cmX60cm.
the idea is to generate a signal which could be used to display the height in cm or to compare with a pre-set set figure so that it can indicate whethert there is sufficient space to admit a new parcel.
I am trying to find suitable sensors, can anyone please help

 

[(*steve*)]

Have you considered an ultrasonic range sensor like an HC-SR04?

You might want to use several so you can detect the vertical rather than slant distance.

 

[shrtrnd]

I'd consider an optical break-the-light-beam type, with a light source and an optical sensor. You can use multiple
devices if you're trying to cover a large area, but I'd use one light source and photo-cell detector with a few
mirrors to direct the light beam across the entire top of the package box.

 

[Externet]

A video camera can do it.
Another method uses a string and a board that is periodically lowered and retrieved, checking at which point there is no tension on the string. It is used in silos.

 

[spaceman]

PLC 's do this function in just about every automated factory. Very old technology. Call a factory around your way and ask for the production supervisor. Ask him/her for some of their discarded equipment.