FIRST: take advantage of your mentors expertise

[techhelpbb]

Originally Posted by de_

re sampling: I'd thought capturing power line transients might best be done with a custom analog over voltage or under voltage threshold circuit that thats trigger a counter that measures the length of the glitch and stops when the power returns to within normal bounds. The logger gets interrupted and it reads the count. Might need a little distributed PIC to do it. The threshold under voltage or over voltage threshold would be such that could or would cause corruption, hangs or reboots in the CRio and other critical devices. The logger would record a "device Bridge PS undervoltage for X ms" event.

Overvoltage detection would immediately identify situations where the bridge or camera were accidently powered with 12v, both of which happened to us this year. Also our Crio rebooted a number of times, cause never absolutely confirmed.

I completely agree.

That's what I already made a set of modules with op-amps that have a voltage reference, a voltage divider and a latch at the output (a latching voltage comparator).

You set them for the voltage you want to consider too high, or too low and when it hits that point the output sets and stays that way till you clear it.

You can feed that output into the cRIO, drive an LED with it, or connect it to something like a relay as a breaker.

The fancy version uses digital pots (R2R ladders) and is actually calibrated and self testing from a small hand held unit I made.

I originally created them because I kept getting told Team 11's robot mounted Jaguar electronic motor controls had power quality issues last year. So I finally got fed up and made something fast enough (and practical to use on a moving robot) to demonstrate the truth or falsehood of the statement. It wasn't true.

Obviously there is a time for the output to transition, so there is a response time, but it's *much* smaller than for a data logger, and approaches the sort of response time you get from an oscilloscope. Really I could actually do this with discrete transistors or on a wafer...but this is a kid's toy.

The reason I didn't set the circuit up to time the length of the glitch is that it's once again a quantization issue. Even if a small cheap PIC looks at the output of the voltage comparator if the glitch is fast enough it just disappears. With the latch you can force a really short glitch to show up...even if your time counter resolution is too low. So what if your counter misrepresents a 0.1uS glitch for something longer? It's still a glitch and it did not slip by.