Et '''fanggitters''' formål er, at forhindre [[sekundær emission]]selektroner udsendes fra anoden og nå frem til skærmgitteret.<ref name="NEET">{{cite book
 | title  = The Navy Electricity and Electronics Training Series, Module 06: Introduction to Electronic Emission, Tubes, and Power Supplies
 | publisher  = United States Navy
 | date  = 1998
 | location  = 
 | pages  = 13
 | language  = 
 | url  = https://books.google.com/books?id=xuL4CgAAQBAJ&pg=PT135&dq=Tetrode+%22secondary+emission%22+%22other+electrons%22
 | doi  = 
 | id  = 
 | isbn  = 132966776X
 }}{{Dødt link|date=oktober 2023 |bot=InternetArchiveBot |fix-attempted=yes }}</ref><ref name="Whitaker" /><ref name="Solymar">{{cite book
 | last1  = Solymar
 | first1 = Lazlo 
 | title  = Modern Physical Electronics
 | publisher = Springer Science and Business Media 
 | date   = 2012
 | location = 
 | pages  = 8
 | language = 
 | url    = https://books.google.com/books?id=FncrBgAAQBAJ&pg=PA8&dq=Tetrode+%22secondary+emission%22+%22other+electrons%22
 | doi    = 
 | id     = 
 | isbn   = 9401165076
 }}</ref> 
Sekundær emissionselektroner kan forårsage ustabilitet og [[parasitisk oscillation]] i elektronrør.
Fysik