Watchdog Timers Improve Safety and Reliability of Critical PLC-Controlled Systems

A Watchdog Timer can be added to PLC- or computer-controlled systems to improve safety and reliability. The separate, independent, timer is triggered at regular intervals by the control system.

When operating normally, the PLC continuously retriggers the timer. If a fault occurs in the logic hardware or software, the timer is not retriggered within the expected interval. The timer’s output can shut down critical systems or alert an operator before safety concerns arise.

An example of a Watchdog Timer in wide use is Regent Controls’ TM2222.

• Timer is independent of the PLC or computer. Hardware based. No software to program.
• Timer can be adjusted for any cycle rate or scan time. Fixed timing is also available.
• Models available for 120VAC and 24VDC control systems.