When printing, after a while sometimes even after some minutes my Vertex Delta K8800) performs by itself an unload filament command.
When unloaded and loaded the filament it proceeds printing for a while and then unloads the filament again.
This behavior is extremely annoying. I cannot finish most components because of this.
Maybe it was the filament detector.
After disconnnecting the printer works pretty well 
Next thing is to build a better filament detector.
Is there a schematic for the detector to download?
The detector is a regular switch.
I guess you can take these wires and connect you’re detector on it 
Thanks you. I let you (the forum) know how i solved this problem.
But this topic has low priority. The filament is long enough to last a while.