My workShop Dust Collection System needs a dust detector to monitor
the depth of sawdust in it's bin.

When the dust bin fills up, the large Wynn Env filter clogs up and must be
cleaned, along with the cleanout box, this is not a quick or simple job.

I have tried several types of dust detector (sound and IR devices) but, so
far, none has been reliable. 

Reading the articles on the web, the other folks seem to be happy with using a
garage door opener safety beam. as a detector.  The system uses a cyclone
particle separator with a 6" diameter transparent hose leading down to 
the dust bin.  The Safety Beam transmitter and receiver are placed on either 
side of this hose to see when the bin starts to overflow.