Wednesday, August 18, 2010

You Can Get a Watchdog with Your Power Supply?

Watchdog timers are common place in the world of computing and embedded systems. It’s the watchdog timer’s job to notice if a computing device, such as a microcontroller, has hung up or froze. If it has the watchdog timer performs a reset. The whole thing works by setting the watchdog timer for a specific count. Once the computing device starts operating the watchdog timer starts its counting. It is the computing device’s job to send a command to the watchdog timer to let it know it is still running (referred to as “kicking the dog” or “feeding the dog”). Once the watchdog gets that command it resets  and starts counting again.
Recently Agilent added watchdog timer functionality to its N6700 modular power system family of supplies. The N6700 watchdog functionality works similar to the description above with the “feed the dog” timer reset coming from the IO connection with the computer. A timer reset occurs whenever SCPI traffic from the computer occurs. If the watchdog timer does not receive a reset in the user’s specified count it goes into a protection mode and shuts its outputs off.
The whole idea of adding this functionality developed from customer feedback. The customer was running durability tests on multiple DUTs. The tests lasted for weeks or months at a time. During the tests it wasn’t uncommon for the computer to freeze or crash (damn you windows). During testing the supply outputs were cycled high and low. If the computer goes down while the supplies are on the high end and there was no one around to notice the DUTs would be destroyed. From there the tests had to be started from scratch with new DUTs, very costly. The moral of the story here is do not be afraid to tell your test and measurement company reps what capabilities you need because they do listen!

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