What will happen if we use same logic to programme two different types of PLC?
As far as I understand Anurag , PLCs are customized hardware . Processors changes and so does the logic processing . Ladder logic is the core that changes the the programming changes.
They have their own bus interface e.g: PROFINET/BUS of Siemens vs SCADA
Now because of IIoT there are TCP/IP interfaces .
Your process control logic is important it could be implemented with any PLC you used...
Basically, Logic is Logic.
If it is straight bit logic (N.O contacts, N.C contacts and outputs) most of the time it will transfer between any PLC. However, there are exceptions. Modicon logic doesn't scan the same way Allen Bradley does, so there are instances where the same logic will not work. One shots are very different between manufacture as well. Most of the instructions past bit logic e.g. timers, counters, shift registers, etc. are handled different by different manufactures. The concepts will remain the same but for instance, how a timer/ counter resets may be very different.
Theoritically a PLC program can be ported to any manufacturer's PLC as long as they all subscribe to IEC 61131-3. As Michael pointed out, processing time is always an issue. You will get different behaviour with different PLCs. In most of industrial processing applications that would be the case. Rule of thumb is not to mix equipment from different manufacturers. The money saved is not worth the down time. This goes for all automation equipment, including PLC.
I don't know but the Scan Time may vary between different vendors. Combinational Logic may be not affected, Sequential Logic I don't know, there are good answers up to address that.
Different PLC ( Siemens, Fanuc, etc.) have a different internal memory organization (registers, way to acces of them way, way to set/reset timmers and counters, etc.) so even when are using IEC 61131-3 appear some problems, as Godon pointed out.
Siemens, allen bradley, etc. all they use Ladder logic as a programming language that represents a program by a graphical diagram based on the circuit diagrams of relay logic hardware which which will be easy to be converted to every PLC standards.
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