Hello

Can any body explan about watchdong time in detail... ??

Attached capture is step7 v5.5 encoder pn io properties.

Thank you.

Hello RetroK;

A PLC program operates on the principle of a scan, and a maximum scantime is associated with it as a safeguard: if the program execution takes more time than it is allowed, it probably means that it has entered an endless loop, so the CPU's OS will restart the processor, considering it is in a unrecoverable fault.

The timer that is used to validate the PLC scan is called a watchdog timer; it runs while the program scan is active, and it is reset at the end of every scan. It becomes active only if the scan exceeds the allowed time of the watchdog timer, and declares a major fault.

Watchdog timers can monitor any scan in a computerized system. In your specific case, the watchdog timer is checking whether the Profinet cycle time limits have been exceeded.

This is a procedure that originated with computer programs, well before pLCs were on the market as described in this atricle:

Watchdog timer - Wikipedia, the free encyclopedia

Hope this helps,

Daniel Chartier

Hello

watchdog timer is mainly used to monitor failure of your processor.

if you see your image in which for watchdog is monitoring scanning of  I/Os.

if I/O system as per configured in program is not scan or updated withing 50 nos of update cycles & each update cycle will be 2.00 ms i.e total 100.00 (watch dog timer) then CPU will assumes that there is some major fault & then it will restarts the processor as well as give diagnostic for same in buffer for failure reason.

you can read more info for watch dog timer on internet which is for micro-controller / processor same will be applicable in PLC also.