Hi,
I'm looking to install 2 TMD's in a hot standby configuration. Both TMD's will run in parallel with each other.
An HMI will be attached to each PLC RS232 comm's port but only reading / writing to one via modbus etc
Each PLC will monitor the other PLC's watchdog output (is there one?) if the watchdog contact is active the comm's will be switched over via output relay or similar to the second PLC and vice versa.
This leaves me with a problem, the data in the first duty PLC will need to be constantly synchronised with the standby PLC so when the PLC's change over any timer values,output commands written from the HMI etc are the same.
I will probably need to use at least two extra TMD's as remote I/O in the field collecting data, reading inputs etc. this will also need to "switch" onto the standby PLC......
Is this possible? has it been done before?
?