Logic Diagrams DOE-HDBK-1016/2-93 ENGINEERING LOGIC DIAGRAMS Rev. 0 Page 5 PR-05 Figure 3  Basic Logic Symbols Figure 4  Conventions for Depicting Multiple Inputs The AND gate has a common variation called a COINCIDENCE gate.  Logic gates are not limited to two inputs.  Theoretically, there is no limit to the number of inputs a gate can have. But,  as  the  number  of  inputs  increases,  the  symbol  must  be  altered  to  accommodate  the increased inputs.  There are two basic ways to show multiple inputs.  Figure 4 demonstrates both  methods,  using  an  OR  gate  as  an  example.    The  symbols  used  in  Figure  4  are  used extensively  in  computer  logic  diagrams.    Process  control  logic  diagrams  usually  use  the symbology shown in Figure 2.