German to English Tech/Engineering Electronics / Elect Eng

Explanation: Eddy current test instruments for detecting cracks and flaws in bolt heads and nuts etc.

"mit 1- oder 2-kanaligen Glockensensoren / Topfsensoren / Hutsensoren".

Sorry, it's not much to go on - no pictures. I can't get a lead on any of them and was wondering if they're internal terms.
Any thoughts would be much appreciated.