1. Relay Input and Output in PLC
It is relay which directly relates to external equipments, either from external equipments input nor external equipments output.
More clear sees picture form of physical of from PLC ( Example PLC Keyence )
From above Picture :
for Relay Input PLC is : 000 , 001 , 002 , 003 , 004 , 005 , 006 , 007 , 008 , 009 , 010 , 011 , 012 , 013 , 014 , and 015.
and Output PLC is : 500 , 501 , 502 , 503 , 504 , 505 , 506 , and 507.
2. Internal Relay PLC
It is relay which there is no in physical of a PLC and existence of in Program Ladder PLC.
Name of differ from Internal Relay is Auxilliary Relay, Marker, Flag, Special Relay, etc.
Example Ladder PLC Program with Internal Relay :
From above Picture :
for Relay Input PLC is :
0000 in Ladder Program PLC and 000 in Input physical of PLC.
0001 in Ladder Program PLC and 000 in Input physical of PLC.
and Output PLC is :
0500 in Ladder Program PLC and 500 in Output physical of PLC.
0501 in Ladder Program PLC and 501 in Output physical of PLC.
For Internal Relay PLC is :
1 unit internal relay 1000 as output relay.
2 unit internal relay 1000 and 1100 as input relay.