Watchdog Timer (External)

An external watchdog timer is preferred to an internal watchdog timer to assure that outputs go to the Off state fo the watchdog's logic is not properly exectued every scan. Same as an "internal" WDT except the WDT performance cannot be compromised by any failure in the system it is monitoring (e.g., no common mode fualt within the PES). As a result many WDTs provided with PESs are not suitable as safety WDTs.