I want to design a control logic circuit using relay logic. I want to have a bit as a marker as in PLC. Can I use a contactor for this function and then use auxiliary coils as a latch as in PLCs.
Figure 1. A latching relay circuit.
The familiar PLC latching circuit is based on traditional relay logic which came before the PLC.
Just remember that in a PLC the program is executed sequentially whereas in relay logic everything is happening in parallel. This can catch out the unwary when converting from one to the other. Note also that the relay will reset (unlatch) when power is cycled.